From d60493e1b1cc70b7df7bfbab1b6d93affc512a9f Mon Sep 17 00:00:00 2001
From: "Alexander \"Arav\" Andreev" <me@arav.su>
Date: Mon, 30 Oct 2023 02:18:41 +0400
Subject: [PATCH] I think it's time to init a repo already. xD

---
 .gitignore                                    |   1 +
 Makefile                                      |  32 ++
 build/PKGBUILD                                |  26 ++
 cmd/mccl/commands/command.go                  |   5 +
 cmd/mccl/commands/install_command.go          | 325 ++++++++++++++++++
 cmd/mccl/commands/list_command.go             |  33 ++
 cmd/mccl/commands/run_command.go              | 163 +++++++++
 cmd/mccl/main.go                              | 232 +++++++++++++
 go.mod                                        |   5 +
 go.sum                                        |   2 +
 internal/assets/assets.go                     | 124 +++++++
 internal/manifest/argument.go                 |  60 ++++
 internal/manifest/argument_test.go            |  16 +
 internal/manifest/library.go                  | 136 ++++++++
 internal/manifest/manifest.go                 | 200 +++++++++++
 internal/manifest/rule.go                     | 122 +++++++
 internal/manifest/rule_test.go                |  49 +++
 internal/mccl_profile/profile.go              |  47 +++
 internal/version_manifest/version_manifest.go |  74 ++++
 pkg/retriever/retriever.go                    |  81 +++++
 pkg/util/locatejavahome_unix.go               |   8 +
 pkg/util/locatejavahome_windows.go            |  68 ++++
 pkg/util/osversion_unix.go                    |  26 ++
 pkg/util/osversion_windows.go                 |  29 ++
 pkg/util/util.go                              | 145 ++++++++
 25 files changed, 2009 insertions(+)
 create mode 100644 .gitignore
 create mode 100755 Makefile
 create mode 100644 build/PKGBUILD
 create mode 100755 cmd/mccl/commands/command.go
 create mode 100755 cmd/mccl/commands/install_command.go
 create mode 100755 cmd/mccl/commands/list_command.go
 create mode 100755 cmd/mccl/commands/run_command.go
 create mode 100755 cmd/mccl/main.go
 create mode 100755 go.mod
 create mode 100755 go.sum
 create mode 100755 internal/assets/assets.go
 create mode 100755 internal/manifest/argument.go
 create mode 100755 internal/manifest/argument_test.go
 create mode 100755 internal/manifest/library.go
 create mode 100755 internal/manifest/manifest.go
 create mode 100755 internal/manifest/rule.go
 create mode 100755 internal/manifest/rule_test.go
 create mode 100644 internal/mccl_profile/profile.go
 create mode 100755 internal/version_manifest/version_manifest.go
 create mode 100755 pkg/retriever/retriever.go
 create mode 100644 pkg/util/locatejavahome_unix.go
 create mode 100644 pkg/util/locatejavahome_windows.go
 create mode 100644 pkg/util/osversion_unix.go
 create mode 100644 pkg/util/osversion_windows.go
 create mode 100755 pkg/util/util.go

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..6dd29b7
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+bin/
\ No newline at end of file
diff --git a/Makefile b/Makefile
new file mode 100755
index 0000000..a05159f
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,32 @@
+TARGET=mccl
+
+ifeq ($(shell go env GOOS),windows)
+	EXEC_NAME=${TARGET}.exe
+else
+	EXEC_NAME=${TARGET}
+endif
+DESTDIR:=
+PREFIX:=/usr/local
+
+VERSION=0.1.0
+
+FLAGS:=-buildmode=pie -modcacherw -mod=readonly -trimpath
+LDFLAGS:= -ldflags "-s -w -X main.programVersion=${VERSION}"
+
+.PHONY: ${TARGET} install uninstall clean
+
+${TARGET}:
+ifeq ($(shell go env GOOS),windows)
+	go build -o bin/$@.exe ${LDFLAGS} ${FLAGS} cmd/$@/main.go
+else
+	go build -o bin/$@ ${LDFLAGS} ${FLAGS} cmd/$@/main.go
+endif
+
+install:
+	install -Dm 0755 bin/${EXEC_NAME} ${DESTDIR}${PREFIX}/bin/${EXEC_NAME}
+
+uninstall:
+	rm ${DESTDIR}${PREFIX}/bin/${EXEC_NAME}
+
+clean:
+	rm -f bin/*
\ No newline at end of file
diff --git a/build/PKGBUILD b/build/PKGBUILD
new file mode 100644
index 0000000..521539f
--- /dev/null
+++ b/build/PKGBUILD
@@ -0,0 +1,26 @@
+# Maintainer: Alexander "Arav" Andreev <me@arav.su>
+pkgname=mccl
+pkgver=0.1.0
+pkgrel=1
+pkgdesc="Console Minecraft launcher"
+arch=('i686' 'x86_64' 'arm' 'armv6h' 'armv7h' 'aarch64')
+url="https://git.arav.su/Arav/mccl"
+license=('GPL3')
+makedepends=('go>=1.17')
+source=("${pkgver}.tar.gz::https://git.arav.su/Arav/mccl/archive/v${pkgver}.tar.gz")
+md5sums=('SKIP')
+
+build() {
+    cd "$srcdir/$pkgname"
+    export GOPATH="$srcdir"/gopath
+    export CGO_CPPFLAGS="${CPPFLAGS}"
+    export CGO_CFLAGS="${CFLAGS}"
+    export CGO_CXXFLAGS="${CXXFLAGS}"
+    export CGO_LDFLAGS="${LDFLAGS}"
+    make VERSION=$pkgver DESTDIR="$pkgdir" PREFIX="/usr"
+}
+
+package() {
+    cd "$srcdir/$pkgname"
+    make DESTDIR="$pkgdir" PREFIX="/usr" install
+}
diff --git a/cmd/mccl/commands/command.go b/cmd/mccl/commands/command.go
new file mode 100755
index 0000000..fa17d32
--- /dev/null
+++ b/cmd/mccl/commands/command.go
@@ -0,0 +1,5 @@
+package commands
+
+type Command interface {
+	Run() error
+}
diff --git a/cmd/mccl/commands/install_command.go b/cmd/mccl/commands/install_command.go
new file mode 100755
index 0000000..67d1bc9
--- /dev/null
+++ b/cmd/mccl/commands/install_command.go
@@ -0,0 +1,325 @@
+package commands
+
+import (
+	"archive/zip"
+	"errors"
+	"fmt"
+	"io"
+	"mccl/internal/assets"
+	"mccl/internal/manifest"
+	"mccl/internal/version_manifest"
+	"mccl/pkg/retriever"
+	"mccl/pkg/util"
+	"os"
+	"path"
+	"runtime"
+	"strings"
+	"time"
+)
+
+type InstallCommand struct {
+	Id      string
+	DestDir string
+}
+
+func NewInstallCommand(id, destDir string) *InstallCommand {
+	return &InstallCommand{Id: id, DestDir: destDir}
+}
+
+func (ic *InstallCommand) Run() error {
+	if ic.Id == "" {
+		return errors.New("an empty Minecraft version was provided")
+	}
+	if ic.DestDir == "" {
+		return errors.New("an empty path was provided")
+	}
+	return ic.install_vanilla_client()
+}
+
+func (ic *InstallCommand) install_vanilla_client() error {
+	var err error
+	var data []byte
+
+	if ic.DestDir == "." {
+		execPath, _ := os.Executable()
+		ic.DestDir = path.Dir(execPath)
+	}
+
+	if _, err := os.Stat(ic.DestDir); err != nil {
+		if err := os.Mkdir(ic.DestDir, 0777); err != nil {
+			return err
+		}
+	}
+
+	fmt.Print("Retrieving a version_manifest_v2.json... ")
+	data, err = util.GetFromUrl(version_manifest.VersionManifestUrl, "", "", -1)
+	if err != nil {
+		return err
+	}
+
+	versionManifest, err := version_manifest.New(data)
+	if err != nil {
+		return err
+	}
+	fmt.Println("Done")
+
+	var version version_manifest.Version
+	if ic.Id == "release" || ic.Id == "latest-release" {
+		version, err = versionManifest.GetLatest(version_manifest.VersionTypeRelease)
+		if err != nil {
+			return err
+		}
+	} else if ic.Id == "snapshot" || ic.Id == "latest-snapshot" {
+		version, err = versionManifest.GetLatest(version_manifest.VersionTypeSnapshot)
+		if err != nil {
+			return err
+		}
+	} else {
+		version, err = versionManifest.Get(ic.Id)
+		if err != nil {
+			return err
+		}
+	}
+	fmt.Printf("Version %s (%s) was chosen.\n", version.Id, version.Type)
+
+	fmt.Print("Retrieving a manifest file... ")
+	manifestPath := path.Join(ic.DestDir, "versions", version.Id, version.Id+".json")
+	data, err = util.LoadOrDownloadFile(manifestPath, version.Url, version.Sha1, "sha1", -1)
+	if err != nil {
+		return err
+	}
+
+	manifst, err := manifest.New(data)
+	if err != nil {
+		return err
+	}
+	fmt.Println("Done")
+
+	if !util.IsFileExist(manifestPath) {
+		fmt.Print("Writing a manifest file to ", manifestPath, " ... ")
+		if err := util.WriteFile(manifestPath, data); err != nil {
+			return err
+		}
+		fmt.Println("Done")
+	} else {
+		fmt.Println(manifestPath, "does exist. Skipping")
+	}
+
+	clientPath := path.Join(ic.DestDir, "versions", manifst.Id, manifst.Id+".jar")
+	if !util.IsFileExist(clientPath) {
+		fmt.Print("Retrieving and writing a client to ", clientPath, " ... ")
+		data, err = util.LoadOrDownloadFile(clientPath, manifst.Downloads["client"].Url,
+			manifst.Downloads["client"].Sha1, "sha1", manifst.Downloads["client"].Size)
+		if err != nil {
+			return err
+		}
+		if err := util.WriteFile(clientPath, data); err != nil {
+			return err
+		}
+		fmt.Println("Done")
+	} else {
+		fmt.Println(clientPath, "does exist. Skipping")
+	}
+
+	fmt.Printf("Retrieving an asset index %s.json... ", manifst.AssetIndex.Id)
+	assetIndexPath := path.Join(ic.DestDir, "assets", "indexes", manifst.AssetIndex.Id+".json")
+
+	data, err = util.LoadOrDownloadFile(assetIndexPath, manifst.AssetIndex.Url,
+		manifst.AssetIndex.Sha1, "sha1", manifst.AssetIndex.Size)
+	if err != nil {
+		return err
+	}
+
+	asts, err := assets.New(data)
+	if err != nil {
+		return err
+	}
+	fmt.Println("Done")
+
+	if !util.IsFileExist(assetIndexPath) {
+		fmt.Printf("Writing an asset index %s to %s...", manifst.AssetIndex.Id, assetIndexPath)
+		if err := util.WriteFile(assetIndexPath, data); err != nil {
+			return err
+		}
+		fmt.Println("Done")
+	} else {
+		fmt.Printf("%s does exist. Skip writing\n", assetIndexPath)
+	}
+
+	fmt.Print("Retrieving assets...")
+
+	assetsDir := path.Join(ic.DestDir, "assets", "objects")
+	ar := retriever.New()
+	defer ar.Close()
+
+	assetsCount := len(asts.Objects)
+	var assetItems []retriever.Retrievable
+
+	for _, v := range asts.Objects {
+		assetItems = append(assetItems, v)
+	}
+
+	go func() {
+		if err := ar.Run(assetItems, assets.RetrieveAsset, assetsDir); err != nil {
+			fmt.Println("\n", err)
+			os.Exit(1)
+		}
+	}()
+
+	for written, cnt := 0, 0; cnt < assetsCount; {
+		if len(ar.GetErrorChan()) > 0 {
+			return <-ar.GetErrorChan()
+		}
+
+		if cnt < assetsCount {
+			written += <-ar.GetDoneChan()
+		}
+		cnt++
+
+		fmt.Printf("\rRetrieving assets... %d/%d (%d/%d)", written, manifst.AssetIndex.TotalSize, cnt, assetsCount)
+	}
+	fmt.Printf("\nRetrieving assets... Done\n")
+
+	if manifst.Logging.Client.Argument != "" {
+		logConfPath := path.Join(ic.DestDir, "assets", "log_configs", manifst.Logging.Client.File.Id)
+		if !util.IsFileExist(logConfPath) {
+			fmt.Printf("Retrieving and writing %s...", logConfPath)
+			data, err = util.LoadOrDownloadFile(logConfPath, manifst.Logging.Client.File.Url,
+				manifst.Logging.Client.File.Sha1, "sha1", manifst.Logging.Client.File.Size)
+			if err != nil {
+				return err
+			}
+			if err := util.WriteFile(logConfPath, data); err != nil {
+				return err
+			}
+			fmt.Println("Done")
+		} else {
+			fmt.Printf("%s does exist. Skip writing\n", logConfPath)
+		}
+	}
+
+	fmt.Print("Retrieving libraries...")
+
+	librariesDir := path.Join(ic.DestDir, "libraries")
+	lr := retriever.New()
+	defer lr.Close()
+
+	var libraryItems []retriever.Retrievable
+	var totalLibrariesSize int64 = 0
+
+	for _, lib := range manifst.Libraries {
+		if lib.CheckRules() {
+			files := lib.ToFile()
+
+			for _, f := range files {
+				totalLibrariesSize += f.Size
+				libraryItems = append(libraryItems, f)
+			}
+		}
+	}
+
+	go func() {
+		if err := lr.Run(libraryItems, manifest.RetrieveLibrary, librariesDir); err != nil {
+			fmt.Println("\n", err)
+			os.Exit(1)
+		}
+	}()
+
+	librariesCount := len(libraryItems)
+
+	for written, cnt := 0, 0; cnt < librariesCount; {
+		if len(lr.GetErrorChan()) > 0 {
+			return <-lr.GetErrorChan()
+		}
+
+		if cnt < librariesCount {
+			written += <-lr.GetDoneChan()
+		}
+		cnt++
+
+		fmt.Printf("\rRetrieving libraries... %d/%d (%d/%d)",
+			written, totalLibrariesSize, cnt, librariesCount)
+	}
+
+	fmt.Printf("\nRetrieving libraries... Done\n")
+
+	releaseTime, err := time.Parse(time.RFC3339, manifst.ReleaseTime)
+	if err != nil {
+		releaseTime, err = time.Parse("2006-01-02T15:04:05Z0700", manifst.ReleaseTime)
+		if err != nil {
+			return err
+		}
+	}
+
+	firstVerWithNoExtract, _ := time.Parse(time.DateOnly, "2017-10-25")
+	if releaseTime.Before(firstVerWithNoExtract) {
+		nativesDir := path.Join(ic.DestDir, "versions", manifst.Id, "natives")
+
+		if err := os.MkdirAll(nativesDir, 0777); err != nil {
+			return err
+		}
+
+		fmt.Printf("Extracting native libraries to %s ... ", nativesDir)
+		for _, lib := range libraryItems {
+			l := lib.(util.File)
+
+			if !strings.Contains(l.GetName(), "natives") {
+				continue
+			}
+
+			zipFile, err := zip.OpenReader(path.Join(librariesDir, l.Path))
+			if err != nil {
+				return err
+			}
+			defer zipFile.Close()
+
+			for _, f := range zipFile.File {
+				if strings.HasPrefix(f.Name, "META-INF/") {
+					continue
+				}
+
+				if strings.Contains(f.Name, "64") && runtime.GOARCH != "amd64" {
+					continue
+				}
+
+				switch runtime.GOARCH {
+				case "386":
+					if strings.Contains(f.Name, "64") {
+						continue
+					}
+				case "amd64":
+					if !strings.Contains(f.Name, "64") {
+						continue
+					}
+				}
+
+				if util.IsFileExist(path.Join(nativesDir, f.Name)) {
+					continue
+				}
+
+				frc, err := f.Open()
+				if err != nil {
+					return err
+				}
+				defer frc.Close()
+
+				out, err := os.OpenFile(path.Join(nativesDir, f.Name), os.O_CREATE|os.O_RDWR, 0666)
+				if err != nil {
+					return err
+				}
+				defer out.Close()
+
+				written, err := io.Copy(out, frc)
+				if err != nil {
+					return fmt.Errorf("failed to extract file %s: %s", f.Name, err)
+				} else if written != int64(f.UncompressedSize64) {
+					return fmt.Errorf("failed to extract file %s: size is %d, but %d was written",
+						f.Name, f.UncompressedSize64, written)
+				}
+			}
+		}
+		fmt.Println("Done")
+	}
+
+	return nil
+}
diff --git a/cmd/mccl/commands/list_command.go b/cmd/mccl/commands/list_command.go
new file mode 100755
index 0000000..4c25545
--- /dev/null
+++ b/cmd/mccl/commands/list_command.go
@@ -0,0 +1,33 @@
+package commands
+
+import (
+	"fmt"
+	"os"
+	"path"
+)
+
+type ListCommand struct {
+	GameDir string
+}
+
+func NewListCommand(gameDir string) *ListCommand {
+	return &ListCommand{GameDir: gameDir}
+}
+
+func (lc *ListCommand) Run() error {
+	versionsDir := path.Join(lc.GameDir, "versions")
+	if _, err := os.Stat(versionsDir); err != nil {
+		return fmt.Errorf("versions directory wasn't found inside %s", lc.GameDir)
+	}
+	entries, err := os.ReadDir(path.Join(lc.GameDir, "versions"))
+	if err != nil {
+		return err
+	}
+	fmt.Println("There are following versions installed:")
+	for _, entry := range entries {
+		if entry.IsDir() {
+			fmt.Println(entry.Name())
+		}
+	}
+	return nil
+}
diff --git a/cmd/mccl/commands/run_command.go b/cmd/mccl/commands/run_command.go
new file mode 100755
index 0000000..0191bec
--- /dev/null
+++ b/cmd/mccl/commands/run_command.go
@@ -0,0 +1,163 @@
+package commands
+
+import (
+	"errors"
+	"fmt"
+	"mccl/internal/manifest"
+	mcclprofile "mccl/internal/mccl_profile"
+	"mccl/pkg/util"
+	"os"
+	"os/exec"
+	"path"
+	"regexp"
+	"strings"
+)
+
+type RunCommand struct {
+	Id         string
+	GameDir    string
+	Username   string
+	AuthUuid   string
+	JavaXmx    string
+	UseProfile bool
+}
+
+func NewRunCommand(id, gameDir, user, uuid, jxmx string, useProfile bool) *RunCommand {
+	return &RunCommand{Id: id, GameDir: gameDir, Username: user, AuthUuid: uuid, JavaXmx: jxmx, UseProfile: useProfile}
+}
+
+func (rc *RunCommand) Run() error {
+	if rc.Id == "" {
+		return errors.New("an empty Minecraft version was provided")
+	}
+	if err := os.Chdir(rc.GameDir); err != nil {
+		return err
+	}
+	if rc.UseProfile {
+		if util.IsFileExist(path.Join(rc.GameDir, mcclprofile.ProfileFileName)) {
+			p, err := mcclprofile.Load(rc.GameDir)
+			if err != nil {
+				return err
+			}
+			rc.Username = p.Username
+			rc.AuthUuid = p.Uuid
+			rc.JavaXmx = p.JavaXmx
+		} else {
+			p := mcclprofile.Profile{
+				Username: rc.Username,
+				Uuid:     rc.AuthUuid,
+				JavaXmx:  rc.JavaXmx}
+			if err := p.Store(rc.GameDir); err != nil {
+				return err
+			}
+		}
+	}
+	return rc.run_client()
+}
+
+func (rc *RunCommand) run_client() error {
+	manifestPath := path.Join(rc.GameDir, "versions", rc.Id, rc.Id+".json")
+
+	data, err := util.ReadFile(manifestPath)
+	if err != nil {
+		return err
+	}
+
+	manifst, err := manifest.New(data)
+	if err != nil {
+		return err
+	}
+
+	if manifst.InheritsFrom != "" {
+		manifestPath := path.Join(rc.GameDir, "versions", manifst.InheritsFrom, manifst.InheritsFrom+".json")
+
+		data, err := util.ReadFile(manifestPath)
+		if err != nil {
+			return err
+		}
+
+		inherit, err := manifest.New(data)
+		if err != nil {
+			return err
+		}
+
+		if err := manifst.InheritFrom(inherit); err != nil {
+			return err
+		}
+	}
+
+	p := make(map[string]string)
+
+	p["auth_player_name"] = rc.Username
+	p["version_name"] = manifst.Id
+	p["game_directory"] = rc.GameDir
+	p["assets_root"] = "assets"
+	p["game_assets"] = p["assets_root"]
+	p["assets_index_name"] = manifst.AssetIndex.Id
+	p["auth_uuid"] = rc.AuthUuid
+	p["auth_access_token"] = "null"
+	p["auth_session"] = p["auth_access_token"]
+	p["clientid"] = manifst.Id
+	p["auth_xuid"] = "null"
+	p["user_type"] = "legacy"
+	p["version_type"] = manifst.Type
+	p["natives_directory"] = path.Join("", "versions", manifst.Id, "natives")
+	p["launcher_name"] = "mccl"
+	p["launcher_version"] = "0.1.0"
+	p["classpath"] = manifst.BuildClasspath("", "versions")
+	if manifst.Logging.Client.File.Id != "" {
+		p["logging_path"] = path.Join("assets", "log_configs", manifst.Logging.Client.File.Id)
+	}
+
+	if strings.Contains(manifst.Id, "forge") {
+		p["library_directory"] = "libraries"
+		p["classpath_separator"] = util.PathSeparator()
+	}
+
+	cl := manifst.BuildCommandLine(p)
+
+	if rc.JavaXmx != "" {
+		ok, err := regexp.MatchString("^\\d+(K|k|M|m|G|g|T|t)$", rc.JavaXmx)
+		if ok && err == nil {
+			rc.JavaXmx = "-Xmx" + rc.JavaXmx
+			tcl := []string{}
+			tcl = append(tcl, rc.JavaXmx)
+			cl = append(tcl, cl...)
+		} else if err != nil || !ok {
+			if err != nil {
+				fmt.Printf("An error occured while parsing Java -Xmx parameter: %s. Game's default will be used. ", err)
+			} else {
+				fmt.Printf("Mismatch occured while parsing Java -Xmx parameter. Game's default will be used. ")
+			}
+			fmt.Printf("Right form is <number>Kk|Mm|Gg|Tt, e.g. 4G.")
+		}
+	}
+
+	javaHome, err := util.LocateJavaHome(manifst.JavaVersion.Component, manifst.JavaVersion.MajorVersion)
+	if err != nil {
+		return err
+	}
+
+	cmd := exec.Command(path.Join(javaHome, "bin", "java"), cl...)
+	// stdout, err := cmd.StdoutPipe()
+	// cmd.Stderr = cmd.Stdout
+	// if err != nil {
+	// 	return err
+	// }
+	// defer stdout.Close()
+
+	// scanner := bufio.NewScanner(stdout)
+	// go func() {
+	// 	for scanner.Scan() {
+	// 		fmt.Println(scanner.Text())
+	// 	}
+	// }()
+
+	fmt.Printf("Minecraft version %s is started with usename %s and player's UUID %s.\n",
+		manifst.Id, rc.Username, rc.AuthUuid)
+	if err := cmd.Run(); err != nil && (err.Error() != "exec: already started") {
+		return err
+	}
+
+	return nil
+}
diff --git a/cmd/mccl/main.go b/cmd/mccl/main.go
new file mode 100755
index 0000000..ddd911a
--- /dev/null
+++ b/cmd/mccl/main.go
@@ -0,0 +1,232 @@
+package main
+
+import (
+	"fmt"
+	"mccl/cmd/mccl/commands"
+	mcclprofile "mccl/internal/mccl_profile"
+	"os"
+)
+
+var programVersion string
+
+func main() {
+	args, err := parseArguments(os.Args[1:])
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		usage()
+		os.Exit(1)
+	}
+
+	if args.ShowVersion {
+		version()
+	}
+
+	if args.ShowHelp {
+		usage()
+	}
+
+	if args.ShowHelp || args.ShowVersion {
+		os.Exit(0)
+	}
+
+	if len(os.Args) < 2 {
+		usage()
+		os.Exit(0)
+	}
+
+	var cmd commands.Command
+
+	switch args.Command {
+	case "install":
+		fallthrough
+	case "i":
+		cmd = commands.NewInstallCommand(args.GameVersion, args.Directory)
+	case "run":
+		fallthrough
+	case "r":
+		cmd = commands.NewRunCommand(args.GameVersion, args.Directory,
+			args.Username, args.Uuid, args.JavaXmx, args.UseProfile)
+	case "list":
+		fallthrough
+	case "l":
+		cmd = commands.NewListCommand(args.Directory)
+	default:
+		usage()
+		os.Exit(0)
+	}
+
+	exitCode := 0
+
+	if err := cmd.Run(); err != nil {
+		fmt.Println(err)
+		exitCode = 1
+	}
+
+	if args.DemandPressEnter {
+		fmt.Fprint(os.Stderr, "Press the enter key to continue...")
+		fmt.Scanln()
+	}
+
+	os.Exit(exitCode)
+}
+
+func version() {
+	fmt.Fprintf(os.Stderr, "mccl ver. %s\nCopyright (c)  2023  Alexander \"Arav\" Andreev <me@arav.su>\n", programVersion)
+	fmt.Fprintln(os.Stderr, "License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.")
+}
+
+func usage() {
+	fmt.Fprintln(os.Stderr, "Usage: mccl [<common options>]... command arguments... [options]...")
+	fmt.Fprintln(os.Stderr, "Common options:\n"+
+		"  -h,--help     show help\n"+
+		"  -v,--version  show version\n"+
+		"  --demand-press-enter\n"+
+		"                ask to press the enter key before closing\n"+
+		"Commands:\n"+
+		"  \033[1minstall|i\033[0m version directory\n"+
+		"    Install any vanilla version (for mod loaders use theirs installers)\n"+
+		"  \033[1mrun|r\033[0m version directory [-u username] [-U UUID] [-java-Xmx memory] [--profile]\n"+
+		"    Run vanilla, forge, fabric, quilt, the others aren't tested\n"+
+		"  \033[1mlist|l\033[0m directory\n"+
+		"    List all installed versions in directory\n"+
+		"Explanation of arguments and options for commands:\n"+
+		"    version    minecraft's version \n"+
+		"    directory  a path to where Minecraft will be installed\n"+
+		"    -u,--username username\n"+
+		"               player's username (Anonymous by default)\n"+
+		"    -U,--uuid UUID\n"+
+		"               player's account UUID (all zeroes by default)\n"+
+		"    --java-Xmx memory\n"+
+		"               java's -Xmx param, e.g. 4G\n"+
+		"    --profile\n"+
+		"               load/save username, UUID, and -Xmx from/to a file.\n"+
+		"               Once saved, you can ommit -u,-U and --java-Xmx,\n"+
+		"               since they are stored in", mcclprofile.ProfileFileName)
+}
+
+type arguments struct {
+	ShowVersion      bool
+	ShowHelp         bool
+	DemandPressEnter bool
+
+	Command     string
+	GameVersion string
+	Directory   string
+	Username    string
+	Uuid        string
+	JavaXmx     string
+
+	UseProfile bool
+}
+
+type errNoOptArg struct {
+	ArgName string
+}
+
+func (e errNoOptArg) Error() string {
+	return fmt.Sprintf("%s option demands an argument, but it wasn't provided", e.ArgName)
+}
+
+func parseArguments(args []string) (parsed arguments, err error) {
+	parsed.Username = "Anonymous"
+	parsed.Directory = "."
+	parsed.Uuid = "00000000-0000-0000-0000-000000000000"
+	for i := 0; i < len(args); i++ {
+		if len(args[i]) > 2 && args[i][0] == '-' && args[i][1] == '-' {
+			switch args[i][2:] {
+			case "version":
+				parsed.ShowVersion = true
+			case "help":
+				parsed.ShowHelp = true
+			case "demand-press-enter":
+				parsed.DemandPressEnter = true
+			case "username":
+				if len(args) == i+1 || args[i+1][0] == '-' {
+					err = errNoOptArg{ArgName: args[i]}
+					return
+				}
+				parsed.Username = args[i+1]
+				i++
+			case "uuid":
+				if len(args) == i+1 || args[i+1][0] == '-' {
+					err = errNoOptArg{ArgName: args[i]}
+					return
+				}
+				parsed.Uuid = args[i+1]
+				i++
+			case "java-Xmx":
+				if len(args) == i+1 || args[i+1][0] == '-' {
+					err = errNoOptArg{ArgName: args[i]}
+					return
+				}
+				parsed.JavaXmx = args[i+1]
+				i++
+			case "profile":
+				parsed.UseProfile = true
+			default:
+				err = fmt.Errorf("an unknown option %s was provided", args[i])
+				return
+			}
+		} else if args[i][0] == '-' && len(args[i]) > 1 {
+			for _, option := range args[i][1:] {
+				switch option {
+				case 'v':
+					parsed.ShowVersion = true
+				case 'h':
+					parsed.ShowHelp = true
+				case 'u':
+					if len(args) == i+1 || args[i+1][0] == '-' {
+						err = errNoOptArg{ArgName: args[i]}
+						return
+					}
+					parsed.Username = args[i+1]
+					i++
+				case 'U':
+					if len(args) == i+1 || args[i+1][0] == '-' {
+						err = errNoOptArg{ArgName: args[i]}
+						return
+					}
+					parsed.Uuid = args[i+1]
+					i++
+				default:
+					err = fmt.Errorf("an unknown option %c was provided", option)
+					return
+				}
+			}
+		} else {
+			if parsed.Command != "" {
+				err = fmt.Errorf("only one command should present")
+				return
+			}
+			switch parsed.Command = args[i]; parsed.Command {
+			case "i":
+				fallthrough
+			case "install":
+				fallthrough
+			case "r":
+				fallthrough
+			case "run":
+				if len(args) <= i+3 || args[i+1][0] == '-' || args[i+2][0] == '-' {
+					err = fmt.Errorf("not enough arguments was provided")
+					return
+				}
+				parsed.GameVersion = args[i+1]
+				parsed.Directory = args[i+2]
+				i += 2
+			case "l":
+				fallthrough
+			case "list":
+				if len(args) <= i+2 || args[i+1][0] == '-' {
+					err = fmt.Errorf("not enough arguments was provided")
+					return
+				}
+				parsed.Directory = args[i+1]
+				i++
+			default:
+				err = fmt.Errorf("an unknown command %s was provided", parsed.Command)
+				return
+			}
+		}
+	}
+	return
+}
diff --git a/go.mod b/go.mod
new file mode 100755
index 0000000..e1c1581
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,5 @@
+module mccl
+
+go 1.17
+
+require golang.org/x/sys v0.13.0
diff --git a/go.sum b/go.sum
new file mode 100755
index 0000000..d4673ec
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+golang.org/x/sys v0.13.0 h1:Af8nKPmuFypiUBjVoU9V20FiaFXOcuZI21p0ycVYYGE=
+golang.org/x/sys v0.13.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
diff --git a/internal/assets/assets.go b/internal/assets/assets.go
new file mode 100755
index 0000000..a231705
--- /dev/null
+++ b/internal/assets/assets.go
@@ -0,0 +1,124 @@
+package assets
+
+import (
+	"crypto/sha1"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"mccl/pkg/retriever"
+	"net/http"
+	"os"
+	"path"
+)
+
+// assetDownloadUrl is a base URL for an asset to be retrieved from, first %s
+// is a directory which name is first two characters of a hash that goes
+// under the second %s.
+const assetDownloadUrl = "https://resources.download.minecraft.net/%s/%s"
+
+// Asset represents a single asset file, that is some resource like a texture,
+// or a sound, and so on.
+type Asset struct {
+	Hash string `json:"hash"`
+	Size int64  `json:"size"`
+}
+
+// url forms a full URL to an asset.
+func (a *Asset) url() string {
+	return fmt.Sprintf(assetDownloadUrl, a.Hash[:2], a.Hash)
+}
+
+// path forms a relative path to an asset.
+func (a *Asset) path() string {
+	return path.Join(a.Hash[:2], a.Hash)
+}
+
+// Retrieve is a method of a Retrievable interface that is used to download
+// an asset from Mojang's server. It performs the checks for a valid size
+// and hash. Returns a slice of bytes an asset consists of or an error
+// if something gone wrong.
+func (a Asset) Retrieve() ([]byte, error) {
+	resp, err := http.Get(a.url())
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("failed to download a file. Status code is %d", resp.StatusCode)
+	} else if resp.ContentLength != a.Size {
+		return nil, fmt.Errorf("response size mismatch. %d != %d", resp.ContentLength, a.Size)
+	}
+
+	buf, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	if l := len(buf); l != int(a.Size) {
+		return nil, fmt.Errorf("file size mismatch. %d != %d", l, a.Size)
+	}
+
+	h := sha1.New()
+	if _, err := h.Write(buf); err != nil {
+		return nil, err
+	}
+
+	if hex.EncodeToString(h.Sum(nil)) != a.Hash {
+		return nil, errors.New("hash mismatch")
+	}
+
+	return buf, nil
+}
+
+// Assets represents an asset index file.
+type Assets struct {
+	Objects map[string]Asset `json:"objects"`
+}
+
+// New returns a new Assets that is being unmarshaled from a JSON data.
+func New(data []byte) (*Assets, error) {
+	a := &Assets{}
+	if err := json.Unmarshal(data, a); err != nil {
+		return nil, err
+	}
+	return a, nil
+}
+
+// RetrieveAsset is a special retriever.WorkerFunc function that is used to
+// check for an existency of an asset, and, if not, to retrieve it and write
+// it to an actual file.
+func RetrieveAsset(item retriever.Retrievable, basePath string) (int, error) {
+	asset := item.(Asset)
+
+	p := path.Join(basePath, asset.path())
+	if s, err := os.Stat(p); err == nil && s.Size() == asset.Size {
+		return int(s.Size()), nil
+	}
+
+	data, err := item.Retrieve()
+	if err != nil {
+		return 0, err
+	}
+
+	if err := os.MkdirAll(path.Dir(p), 0777); err != nil {
+		return 0, err
+	}
+
+	tf, err := os.Create(p)
+	if err != nil {
+		return 0, err
+	}
+	defer tf.Close()
+
+	written, err := tf.Write(data)
+	if err != nil {
+		return 0, err
+	} else if written != len(data) {
+		return 0, fmt.Errorf("written bytes length mismatch. %d != %d", written, len(data))
+	}
+
+	return written, nil
+}
diff --git a/internal/manifest/argument.go b/internal/manifest/argument.go
new file mode 100755
index 0000000..ff5416e
--- /dev/null
+++ b/internal/manifest/argument.go
@@ -0,0 +1,60 @@
+package manifest
+
+import (
+	"bytes"
+	"encoding/json"
+)
+
+// Argument is a special struct that was made to handle a mixed-typed array
+// of arguments in a manifest.
+//
+// An argument in a manifest could be:
+//   - a single string
+//   - an object consists of rules array field and a value field that could be
+//     a single string or an array of strings.
+type Argument struct {
+	Rules []Rule   `json:"rules"`
+	Value []string `json:"value"`
+}
+
+// CheckRules returns true if all rules passed and a feature set in a rule if
+// applicable, a FeatureUnknown otherwise.
+func (a Argument) CheckRules() (ok bool, feature Feature) {
+	feature = FeatureUnknown
+	for _, r := range a.Rules {
+		ok, feature = r.Check()
+		if !ok {
+			return false, feature
+		}
+	}
+	return true, feature
+}
+
+// UnmarshalJSON had to be implemented because of mixed-typed nature of an
+// arguments array in a manifest.
+func (a *Argument) UnmarshalJSON(data []byte) error {
+	if data[0] == '"' {
+		a.Value = append(a.Value, string(data[1:len(data)-1]))
+	} else if data[0] == '{' && bytes.Contains(data, []byte("value\": \"")) {
+		singleValArg := struct {
+			Rules []Rule `json:"rules"`
+			Value string `json:"value"`
+		}{}
+		if err := json.Unmarshal(data, &singleValArg); err != nil {
+			return err
+		}
+		a.Rules = singleValArg.Rules
+		a.Value = append(a.Value, singleValArg.Value)
+	} else if data[0] == '{' {
+		multiValArg := struct {
+			Rules []Rule   `json:"rules"`
+			Value []string `json:"value"`
+		}{}
+		if err := json.Unmarshal(data, &multiValArg); err != nil {
+			return err
+		}
+		a.Rules = multiValArg.Rules
+		a.Value = multiValArg.Value
+	}
+	return nil
+}
diff --git a/internal/manifest/argument_test.go b/internal/manifest/argument_test.go
new file mode 100755
index 0000000..9cd97cc
--- /dev/null
+++ b/internal/manifest/argument_test.go
@@ -0,0 +1,16 @@
+package manifest
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestArgument(t *testing.T) {
+	s := []byte("{\"rules\": [{ \"action\": \"allow\", \"os\": { \"name\": \"osx\" } }], \"value\":[\"-XstartOnFirstThread\"]}")
+	a := Argument{}
+	if err := json.Unmarshal(s, &a); err != nil {
+		t.Fatal(err)
+	}
+	ok, f := a.CheckRules()
+	t.Log(a, ok, f)
+}
diff --git a/internal/manifest/library.go b/internal/manifest/library.go
new file mode 100755
index 0000000..d6b326a
--- /dev/null
+++ b/internal/manifest/library.go
@@ -0,0 +1,136 @@
+package manifest
+
+import (
+	"fmt"
+	"mccl/pkg/retriever"
+	"mccl/pkg/util"
+	"os"
+	"path"
+	"runtime"
+	"strings"
+)
+
+type Library struct {
+	Downloads struct {
+		Artifact    util.File            `json:"artifact"`
+		Classifiers map[string]util.File `json:"classifiers"`
+	} `json:"downloads"`
+	Name  string `json:"name"`
+	Url   string `json:"url"`
+	Rules []Rule `json:"rules"`
+}
+
+func (l *Library) Path() string {
+	if l.Downloads.Artifact.Path != "" {
+		return l.Downloads.Artifact.Path
+	}
+
+	return l.pathFromName()
+}
+
+func (l *Library) ToFile() []util.File {
+	var f []util.File
+	if l.Downloads.Artifact.Url != "" {
+		f = append(f, l.Downloads.Artifact)
+	} else if l.Url != "" {
+		lf := util.File{
+			Id:   l.Name,
+			Url:  path.Join(l.Url, l.pathFromName()),
+			Size: -1,
+			Path: l.pathFromName(),
+		}
+		f = append(f, lf)
+	}
+
+	if natives := l.Natives(); natives != nil {
+		f = append(f, *natives)
+	}
+
+	return f
+}
+
+func (l *Library) pathFromName() string {
+	parts := strings.Split(l.Name, ":")
+	parts = append(strings.Split(parts[0], "."), parts[1:]...)
+	pth := path.Join(parts...)
+	jarName := strings.Join([]string{parts[len(parts)-2], parts[len(parts)-1]}, "-") + ".jar"
+	return path.Join(pth, jarName)
+}
+
+func RetrieveLibrary(item retriever.Retrievable, destDir string) (int, error) {
+	l := item.(util.File)
+	p := path.Join(destDir, l.Path)
+
+	if s, err := os.Stat(p); err == nil && s.Size() == l.Size {
+		return int(l.Size), nil
+	}
+
+	data, err := item.Retrieve()
+	if err != nil {
+		return 0, err
+	}
+
+	if err := os.MkdirAll(path.Dir(p), 0777); err != nil {
+		return 0, err
+	}
+
+	tf, err := os.Create(p)
+	if err != nil {
+		return 0, err
+	}
+	defer tf.Close()
+
+	written, err := tf.Write(data)
+	if err != nil {
+		return 0, err
+	} else if written != len(data) {
+		return 0, fmt.Errorf("written bytes length mismatch. %d != %d", written, len(data))
+	}
+
+	return written, nil
+}
+
+func (l *Library) CheckRules() bool {
+	if strings.Contains(l.Name, "natives") {
+		nat := strings.SplitAfter(l.Name, ":")[3]
+		nats := strings.Split(nat, "-")
+
+		archR := Rule{Action: ActionAllow}
+		if len(nats) == 3 {
+			archR.Os.Arch = nats[2]
+			l.Rules = append(l.Rules, archR)
+		}
+	}
+
+	for _, r := range l.Rules {
+		if ok, _ := r.Check(); !ok {
+			return false
+		}
+	}
+
+	return true
+}
+
+func (l *Library) Natives() *util.File {
+	if !l.CheckRules() {
+		return nil
+	}
+
+	var nativeOs string
+	switch v := runtime.GOOS; v {
+	case "windows":
+		fallthrough
+	case "linux":
+		nativeOs = "natives-" + v
+	case "darwin":
+		nativeOs = "natives-macos"
+	}
+
+	if len(l.Downloads.Classifiers) > 0 {
+		if v, ok := l.Downloads.Classifiers[nativeOs]; ok {
+			return &v
+		}
+	}
+
+	return nil
+}
diff --git a/internal/manifest/manifest.go b/internal/manifest/manifest.go
new file mode 100755
index 0000000..90a7169
--- /dev/null
+++ b/internal/manifest/manifest.go
@@ -0,0 +1,200 @@
+package manifest
+
+import (
+	"encoding/json"
+	"fmt"
+	"mccl/pkg/util"
+	"path"
+	"strings"
+)
+
+type Manifest struct {
+	InheritsFrom string `json:"inheritsFrom"`
+	Arguments    struct {
+		Game []Argument `json:"game"`
+		Jvm  []Argument `json:"jvm"`
+	} `json:"arguments"`
+	AssetIndex struct {
+		util.File
+		TotalSize int `json:"totalSize"`
+	} `json:"assetIndex"`
+	Assets          string               `json:"assets"`
+	ComplianceLevel int                  `json:"complianceLevel"`
+	Downloads       map[string]util.File `json:"downloads"`
+	Id              string               `json:"id"`
+	JavaVersion     struct {
+		Component    string `json:"component"`
+		MajorVersion int    `json:"majorVersion"`
+	} `json:"javaVersion"`
+	Libraries []Library `json:"libraries"`
+	Logging   struct {
+		Client struct {
+			Argument string    `json:"argument"`
+			File     util.File `json:"file"`
+			Type     string    `json:"type"`
+		} `json:"client"`
+	} `json:"logging"`
+	MainClass              string `json:"mainClass"`
+	MinecraftArguments     string `json:"minecraftArguments"`
+	MinimumLauncherVersion int    `json:"minimumLauncherVersion"`
+	ReleaseTime            string `json:"releaseTime"`
+	Time                   string `json:"time"`
+	Type                   string `json:"type"`
+}
+
+// New returns a new Manifest for a specific Minecraft version.
+func New(data []byte) (*Manifest, error) {
+	m := &Manifest{}
+	if err := json.Unmarshal(data, m); err != nil {
+		return nil, err
+	}
+
+	return m, nil
+}
+
+func (m *Manifest) BuildCommandLine(properties map[string]string) (arguments []string) {
+	if m.MinecraftArguments != "" {
+		arguments = append(arguments, fmt.Sprintf("-Djava.library.path=%s", properties["natives_directory"]))
+		arguments = append(arguments, "-cp")
+		arguments = append(arguments, properties["classpath"])
+		arguments = append(arguments, m.MainClass)
+		args := strings.Split(m.MinecraftArguments, " ")
+		for _, arg := range args {
+			if strings.HasPrefix(arg, "${") {
+				propName := arg[2 : len(arg)-1]
+				arg = properties[propName]
+			}
+			arguments = append(arguments, arg)
+		}
+		return arguments
+	}
+
+	var allArgs []Argument
+
+	allArgs = append(allArgs, m.Arguments.Jvm...)
+
+	if m.Logging.Client.Argument != "" {
+		logConf := strings.Split(m.Logging.Client.Argument, "${")[0]
+		logConf += properties["logging_path"]
+		allArgs = append(allArgs, Argument{Value: []string{logConf}})
+	}
+
+	allArgs = append(allArgs, Argument{Value: []string{m.MainClass}})
+	allArgs = append(allArgs, m.Arguments.Game...)
+
+	for _, arg := range allArgs {
+		ok, feature := arg.CheckRules()
+		if !ok {
+			continue
+		} else if feature != FeatureUnknown {
+			if _, ok := properties[feature.String()]; !ok {
+				continue
+			}
+		}
+
+		for _, v := range arg.Value {
+			if strings.Contains(v, "${library_directory}") {
+				v = strings.ReplaceAll(v, "${library_directory}", properties["library_directory"])
+				v = strings.ReplaceAll(v, "${classpath_separator}", properties["classpath_separator"])
+			} else if i := strings.Index(v, "${"); i != -1 {
+				j := strings.Index(v, "}")
+				propName := v[i+2 : j]
+				switch propName {
+				case "version_name":
+					if strings.Contains(m.Id, "forge") {
+						v = strings.ReplaceAll(v, "${version_name}", m.InheritsFrom)
+					} else {
+						v = strings.ReplaceAll(v, "${version_name}", m.Id)
+					}
+
+				case "assets_index_name":
+					v = m.Assets
+				case "version_type":
+					v = m.Type
+				default:
+					v = strings.Replace(v, v[i:j+1], properties[propName], 1)
+				}
+			}
+			arguments = append(arguments, v)
+		}
+	}
+
+	return arguments
+}
+
+func (m *Manifest) BuildClasspath(baseDir, clientPath string) string {
+	var sb []string = make([]string, 0, len(m.Libraries))
+	for _, lib := range m.Libraries {
+		if lib.CheckRules() {
+			sb = append(sb, path.Join(baseDir, "libraries", lib.Path()))
+			if natives := lib.Natives(); natives != nil {
+				sb = append(sb, path.Join(baseDir, "libraries", natives.Path))
+			}
+		}
+	}
+
+	if m.InheritsFrom != "" {
+		sb = append(sb, path.Join(clientPath, m.InheritsFrom, m.InheritsFrom+".jar"))
+	} else {
+		sb = append(sb, path.Join(clientPath, m.Id, m.Id+".jar"))
+	}
+
+	return strings.Join(sb, util.PathSeparator())
+}
+
+func (m *Manifest) InheritFrom(parent *Manifest) error {
+	if parent == nil {
+		return nil
+	}
+
+	m.Arguments.Game = append(parent.Arguments.Game, m.Arguments.Game...)
+	m.Arguments.Jvm = append(parent.Arguments.Jvm, m.Arguments.Jvm...)
+
+	if m.AssetIndex.TotalSize == 0 {
+		m.AssetIndex.File = parent.AssetIndex.File
+		m.AssetIndex.TotalSize = parent.AssetIndex.TotalSize
+	}
+
+	if m.Assets == "" {
+		m.Assets = parent.Assets
+	}
+
+	if m.ComplianceLevel == 0 {
+		m.ComplianceLevel = parent.ComplianceLevel
+	}
+
+	if m.Downloads == nil {
+		m.Downloads = make(map[string]util.File)
+	}
+
+	for k, v := range parent.Downloads {
+		m.Downloads[k] = v
+	}
+
+	if m.Id == "" {
+		m.Id = parent.Id
+	}
+
+	if m.JavaVersion.Component != "" {
+		m.JavaVersion.Component = parent.JavaVersion.Component
+		m.JavaVersion.MajorVersion = parent.JavaVersion.MajorVersion
+	}
+
+	m.Libraries = append(m.Libraries, parent.Libraries...)
+
+	if m.Logging.Client.Argument == "" {
+		m.Logging.Client.Argument = parent.Logging.Client.Argument
+		m.Logging.Client.Type = parent.Logging.Client.Type
+		m.Logging.Client.File = parent.Logging.Client.File
+	}
+
+	if m.MainClass == "" {
+		m.MainClass = parent.MainClass
+	}
+
+	if m.MinecraftArguments == "" {
+		m.MinecraftArguments = parent.MinecraftArguments
+	}
+
+	return nil
+}
diff --git a/internal/manifest/rule.go b/internal/manifest/rule.go
new file mode 100755
index 0000000..87f463f
--- /dev/null
+++ b/internal/manifest/rule.go
@@ -0,0 +1,122 @@
+package manifest
+
+import (
+	"mccl/pkg/util"
+	"regexp"
+	"runtime"
+)
+
+type Feature int
+
+const (
+	FeatureIsDemoUser Feature = iota
+	FeatureHasCustomResolution
+	FeatureHasQuickPlaysSupport
+	FeatureIsQuickPlaySingleplayer
+	FeatureIsQuickPlayMultiplayer
+	FeatureIsQuickPlayRealms
+	FeatureUnknown
+)
+
+func (f Feature) String() string {
+	switch f {
+	case FeatureIsDemoUser:
+		return "is_demo_user"
+	case FeatureHasCustomResolution:
+		return "has_custom_resolution"
+	case FeatureHasQuickPlaysSupport:
+		return "has_quick_plays_support"
+	case FeatureIsQuickPlayMultiplayer:
+		return "is_quick_play_multiplayer"
+	case FeatureIsQuickPlayRealms:
+		return "is_quick_play_realms"
+	case FeatureIsQuickPlaySingleplayer:
+		return "is_quick_play_singleplayer"
+	default:
+		return ""
+	}
+}
+
+type Action string
+
+const (
+	ActionAllow    Action = "allow"
+	ActionDisallow Action = "disallow"
+	ActionUnknown  Action = ""
+)
+
+type Rule struct {
+	Action Action `json:"action"`
+	Os     struct {
+		Name    string `json:"name"`
+		Arch    string `json:"arch"`
+		Version string `json:"version"`
+	} `json:"os"`
+	Features struct {
+		IsDemoUser              bool `json:"is_demo_user"`
+		HasCustomResolution     bool `json:"has_custom_resolution"`
+		HasQuickPlaysSupport    bool `json:"has_quick_plays_support"`
+		IsQuickPlaySingleplayer bool `json:"is_quick_play_singleplayer"`
+		IsQuickPlayMultiplayer  bool `json:"is_quick_play_multiplayer"`
+		IsQuickPlayRealms       bool `json:"is_quick_play_realms"`
+	} `json:"features"`
+}
+
+func (r *Rule) GetFeature() Feature {
+	switch {
+	case r.Features.IsDemoUser:
+		return FeatureIsDemoUser
+	case r.Features.HasCustomResolution:
+		return FeatureHasCustomResolution
+	case r.Features.HasQuickPlaysSupport:
+		return FeatureHasQuickPlaysSupport
+	case r.Features.IsQuickPlayMultiplayer:
+		return FeatureIsQuickPlayMultiplayer
+	case r.Features.IsQuickPlaySingleplayer:
+		return FeatureIsQuickPlaySingleplayer
+	case r.Features.IsQuickPlayRealms:
+		return FeatureIsQuickPlayRealms
+	default:
+		return FeatureUnknown
+	}
+}
+
+func (r *Rule) Check() (bool, Feature) {
+	feature := r.GetFeature()
+
+	osArchOk := true
+	switch r.Os.Arch {
+	case "x86":
+		osArchOk = r.Action == ActionAllow && runtime.GOARCH == "386"
+	case "x86_64":
+		osArchOk = r.Action == ActionAllow && runtime.GOARCH == "amd64"
+	case "arm64":
+		osArchOk = r.Action == ActionAllow && runtime.GOARCH == "arm64"
+	}
+
+	osName := runtime.GOOS
+	if osName == "darwin" {
+		osName = "osx"
+	}
+
+	osNameOk := true
+	if r.Os.Name != "" {
+		if r.Action == ActionAllow {
+			osNameOk = r.Os.Name == osName
+		} else {
+			osNameOk = r.Os.Name != osName
+		}
+	}
+
+	osVersionOk := true
+	if r.Os.Name == osName && r.Os.Version != "" {
+		ver, err := util.OSVersion()
+		if err != nil {
+			return false, feature
+		}
+		ok, _ := regexp.MatchString(r.Os.Version, ver)
+		osVersionOk = ok && r.Action == ActionAllow
+	}
+
+	return osArchOk && osNameOk && osVersionOk, feature
+}
diff --git a/internal/manifest/rule_test.go b/internal/manifest/rule_test.go
new file mode 100755
index 0000000..fd99d21
--- /dev/null
+++ b/internal/manifest/rule_test.go
@@ -0,0 +1,49 @@
+package manifest
+
+import (
+	"runtime"
+	"testing"
+)
+
+func TestRuleOsName(t *testing.T) {
+	macos := Rule{Action: ActionAllow}
+	macos.Os.Name = "osx"
+
+	if ok, _ := macos.Check(); runtime.GOOS != "darwin" && ok {
+		t.Fatal("Rule.Os.Name == 'osx', but is true on ", runtime.GOOS)
+	}
+
+	linux := Rule{Action: ActionAllow}
+	linux.Os.Name = "linux"
+
+	if ok, _ := linux.Check(); runtime.GOOS != "linux" && ok {
+		t.Fatalf("Rule.Os.Name == '%s', but is true on %s\n", linux.Os.Name, runtime.GOOS)
+	}
+
+	windows := Rule{Action: ActionAllow}
+	windows.Os.Name = "windows"
+
+	if ok, _ := windows.Check(); runtime.GOOS != "windows" && ok {
+		t.Fatalf("Rule.Os.Name == '%s', but is true on %s\n", windows.Os.Name, runtime.GOOS)
+	}
+
+	x86 := Rule{Action: ActionAllow}
+	x86.Os.Arch = "x86"
+
+	if ok, _ := x86.Check(); runtime.GOARCH != "386" && ok {
+		t.Fatalf("Rule.Os.Arch == '%s', but is true on %s\n", windows.Os.Arch, runtime.GOOS)
+	}
+
+	emptyAllow := Rule{Action: ActionAllow}
+
+	if ok, _ := emptyAllow.Check(); !ok {
+		t.Fatalf("An empty allow rule must return true\n")
+	}
+
+	disOsx := Rule{Action: ActionDisallow}
+	disOsx.Os.Name = "osx"
+
+	if ok, _ := disOsx.Check(); runtime.GOOS != "darwin" && !ok {
+		t.Fatalf("A disallow rule for OSX must return false, and true for other OSes\n")
+	}
+}
diff --git a/internal/mccl_profile/profile.go b/internal/mccl_profile/profile.go
new file mode 100644
index 0000000..2b70e7f
--- /dev/null
+++ b/internal/mccl_profile/profile.go
@@ -0,0 +1,47 @@
+package mcclprofile
+
+import (
+	"encoding/json"
+	"os"
+	"path"
+)
+
+const ProfileFileName = "mccl_profile.json"
+
+type Profile struct {
+	Username string `json:"username"`
+	Uuid     string `json:"uuid"`
+	JavaXmx  string `json:"java-Xmx"`
+}
+
+func (p *Profile) Store(rootDir string) error {
+	pf, err := os.OpenFile(path.Join(rootDir, ProfileFileName), os.O_CREATE|os.O_RDWR, 0666)
+	if err != nil {
+		return err
+	}
+	defer pf.Close()
+
+	je := json.NewEncoder(pf)
+	je.SetIndent("", "\t")
+	if err := je.Encode(p); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func Load(rootDir string) (*Profile, error) {
+	p := &Profile{}
+	pf, err := os.Open(path.Join(rootDir, ProfileFileName))
+	if err != nil {
+		return nil, err
+	}
+	defer pf.Close()
+
+	jd := json.NewDecoder(pf)
+	if err := jd.Decode(p); err != nil {
+		return nil, err
+	}
+
+	return p, nil
+}
diff --git a/internal/version_manifest/version_manifest.go b/internal/version_manifest/version_manifest.go
new file mode 100755
index 0000000..038dccf
--- /dev/null
+++ b/internal/version_manifest/version_manifest.go
@@ -0,0 +1,74 @@
+package version_manifest
+
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+)
+
+// VersionManifestUrl is a URL to a version manifest JSON file of version 2.
+const VersionManifestUrl = "https://launchermeta.mojang.com/mc/game/version_manifest_v2.json"
+
+// VersionType is telling if it is a stable release or an intermedialry snapshot.
+type VersionType string
+
+const (
+	// VersionTypeSnapshot is an unstable intermediary version of a game.
+	VersionTypeSnapshot VersionType = "snapshot"
+	// VersionTypeRelease is a stable release version of a game.
+	VersionTypeRelease VersionType = "release"
+)
+
+// Version holds an information about a particular version.
+type Version struct {
+	Id          string      `json:"id"`
+	Type        VersionType `json:"type"`
+	Url         string      `json:"url"`
+	Time        time.Time   `json:"time"`
+	ReleaseTime time.Time   `json:"releaseTime"`
+	Sha1        string      `json:"sha1"`
+}
+
+// VersionManifest holds an array of all game versions, also a latest metadata
+// that holds the latest release and snapshot.
+type VersionManifest struct {
+	Latest struct {
+		Release  string `json:"release"`
+		Snapshot string `json:"snapshot"`
+	} `json:"latest"`
+	Versions []Version `json:"versions"`
+}
+
+// New returns a new VersionManifest that holds info on every
+// known Minecraft version.
+func New(data []byte) (*VersionManifest, error) {
+	vm := &VersionManifest{}
+	if err := json.Unmarshal(data, vm); err != nil {
+		return nil, err
+	}
+	return vm, nil
+}
+
+// GetLatest returns a latest release or snapshot depending on a type provided.
+func (vm *VersionManifest) GetLatest(typ VersionType) (Version, error) {
+	var version string
+	switch typ {
+	case VersionTypeSnapshot:
+		version = vm.Latest.Snapshot
+	case VersionTypeRelease:
+		version = vm.Latest.Release
+	default:
+		return Version{}, fmt.Errorf("version type %s doesn't exist", typ)
+	}
+	return vm.Get(version)
+}
+
+// Get returns a specific version of Minecraft.
+func (vm *VersionManifest) Get(version string) (Version, error) {
+	for _, v := range vm.Versions {
+		if v.Id == version {
+			return v, nil
+		}
+	}
+	return Version{}, fmt.Errorf("version %s not found", version)
+}
diff --git a/pkg/retriever/retriever.go b/pkg/retriever/retriever.go
new file mode 100755
index 0000000..6d62b5d
--- /dev/null
+++ b/pkg/retriever/retriever.go
@@ -0,0 +1,81 @@
+package retriever
+
+import (
+	"fmt"
+	"runtime"
+	"sync"
+)
+
+// Retrievable must be implemented by any type used with Retriever.
+type Retrievable interface {
+	// Retrieve is used just to retrieve some data from somewhere (usually from
+	// network) and return a slice of bytes or nil and an error. If you need to
+	// write the data retrieved use a WorkerFunc where you can call this method.
+	Retrieve() ([]byte, error)
+}
+
+// Retriever allows to retrieve a bunch of files in parallel taking care of
+// errors and a done channel that returns an amount of bytes written.
+type Retriever struct {
+	retrieveErrors chan error
+	retrieveDone   chan int
+}
+
+// New returns a new Retriever with a base path set.
+func New() *Retriever {
+	return &Retriever{
+		retrieveErrors: make(chan error, 1),
+		retrieveDone:   make(chan int)}
+}
+
+// GetErrorChan returns an error channel.
+//
+// An error channel holds just one error and hangs after that. So it is considered
+// as a "soft panic".
+func (r *Retriever) GetErrorChan() chan error {
+	return r.retrieveErrors
+}
+
+// GetDoneChan returns a channel that is used to track a progress. Its value
+// is an amount of bytes written for an item.
+func (r *Retriever) GetDoneChan() chan int {
+	return r.retrieveDone
+}
+
+// WorkerFunc accepts a Retrievable item and a basePath where an item should be
+// placed to. And it returns how much was written and an error if something
+// went wrong.
+type WorkerFunc func(item Retrievable, basePath string) (int, error)
+
+// Run runs in parallel a number of CPU threads * 2 WorkerFunc functions.
+// If an error occured it stops and returns that error.
+func (r *Retriever) Run(items []Retrievable, worker WorkerFunc, basePath string) error {
+	var workersGroup sync.WaitGroup
+	retrieveLimiter := make(chan struct{}, runtime.NumCPU()*2)
+	for _, item := range items {
+		if len(r.retrieveErrors) > 0 {
+			workersGroup.Wait()
+			return <-r.retrieveErrors
+		}
+		retrieveLimiter <- struct{}{}
+		workersGroup.Add(1)
+		go func(item Retrievable) {
+			bytesLen, err := worker(item, basePath)
+			workersGroup.Done()
+			<-retrieveLimiter
+			if err != nil {
+				r.retrieveErrors <- fmt.Errorf("failed to retrieve: %s", err)
+				return
+			}
+			r.retrieveDone <- bytesLen
+		}(item)
+	}
+	workersGroup.Wait()
+	return nil
+}
+
+// Close the channels.
+func (r *Retriever) Close() {
+	close(r.retrieveDone)
+	close(r.retrieveErrors)
+}
diff --git a/pkg/util/locatejavahome_unix.go b/pkg/util/locatejavahome_unix.go
new file mode 100644
index 0000000..8adff7d
--- /dev/null
+++ b/pkg/util/locatejavahome_unix.go
@@ -0,0 +1,8 @@
+package util
+
+func LocateJavaHome(component string, majorVersion int) (string, error) {
+	if component == "jre-legacy" {
+		return "/usr/lib/jvm/java-8-openjdk/jre", nil
+	}
+	return "/usr/lib/jvm/default", nil
+}
diff --git a/pkg/util/locatejavahome_windows.go b/pkg/util/locatejavahome_windows.go
new file mode 100644
index 0000000..ce49c7b
--- /dev/null
+++ b/pkg/util/locatejavahome_windows.go
@@ -0,0 +1,68 @@
+package util
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	"golang.org/x/sys/windows/registry"
+)
+
+const legacyJavaRegPath = "SOFTWARE\\JavaSoft\\Java Runtime Environment"
+const jdkRegPath = "SOFTWARE\\JavaSoft\\JDK"
+
+func LocateJavaHome(component string, majorVersion int) (string, error) {
+	if component == "jre-legacy" {
+		jre, err := registry.OpenKey(registry.LOCAL_MACHINE, legacyJavaRegPath, registry.QUERY_VALUE)
+		if err != nil {
+			return "", err
+		}
+		curVer, _, err := jre.GetStringValue("CurrentVersion")
+		if err != nil {
+			return "", nil
+		}
+		mVer, err := strconv.ParseInt(strings.Split(curVer, ".")[1], 10, 64)
+		if err != nil {
+			return "", nil
+		}
+		if mVer < int64(majorVersion) {
+			return "", fmt.Errorf("installed JRE version %s is older than allowed 1.%d", curVer, majorVersion)
+		}
+		jre, err = registry.OpenKey(registry.LOCAL_MACHINE, fmt.Sprintf("%s\\%s", legacyJavaRegPath, curVer), registry.QUERY_VALUE)
+		if err != nil {
+			return "", err
+		}
+		javaHome, _, err := jre.GetStringValue("JavaHome")
+		if err != nil {
+			return "", err
+		}
+		return javaHome, nil
+	} else {
+		jdk, err := registry.OpenKey(registry.LOCAL_MACHINE, jdkRegPath, registry.QUERY_VALUE)
+		if err != nil {
+			return "", err
+		}
+		curVer, _, err := jdk.GetStringValue("CurrentVersion")
+		if err != nil {
+			return "", nil
+		}
+		mVer, err := strconv.ParseInt(strings.Split(curVer, ".")[0], 10, 64)
+		if err != nil {
+			return "", nil
+		}
+		if mVer < int64(majorVersion) {
+			return "", fmt.Errorf("installed JDK version %d is older than allowed %d", mVer, majorVersion)
+		}
+		jdk, err = registry.OpenKey(registry.LOCAL_MACHINE, fmt.Sprintf("%s\\%s", jdkRegPath, curVer), registry.QUERY_VALUE)
+		if err != nil {
+			return "", err
+		}
+		javaHome, _, err := jdk.GetStringValue("JavaHome")
+		if err != nil {
+			return "", err
+		}
+		return javaHome, nil
+	}
+
+	return "", nil
+}
diff --git a/pkg/util/osversion_unix.go b/pkg/util/osversion_unix.go
new file mode 100644
index 0000000..2b05121
--- /dev/null
+++ b/pkg/util/osversion_unix.go
@@ -0,0 +1,26 @@
+package util
+
+import (
+	"errors"
+	"os"
+	"runtime"
+	"strings"
+)
+
+func OSVersion() (string, error) {
+	switch osName := runtime.GOOS; osName {
+	case "linux":
+		// Implemented just in case for future. Guess if it will ever be needed
+		// then a kernel version will be used to compare against.
+		osRelease, err := os.ReadFile("/proc/sys/kernel/osrelease")
+		if err != nil {
+			return "", err
+		}
+		kVer := strings.Split(string(osRelease), "-")
+		if len(kVer) >= 1 {
+			return kVer[0], nil
+		}
+		return "", errors.New("malformed osrelease")
+	}
+	return "", errors.New("unknown OS")
+}
diff --git a/pkg/util/osversion_windows.go b/pkg/util/osversion_windows.go
new file mode 100644
index 0000000..2d70960
--- /dev/null
+++ b/pkg/util/osversion_windows.go
@@ -0,0 +1,29 @@
+package util
+
+import (
+	"errors"
+	"fmt"
+	"runtime"
+
+	"golang.org/x/sys/windows/registry"
+)
+
+func OSVersion() (string, error) {
+	switch osName := runtime.GOOS; osName {
+	case "windows":
+		verKey, err := registry.OpenKey(registry.LOCAL_MACHINE, "Software\\Microsoft\\Windows NT\\CurrentVersion", registry.QUERY_VALUE)
+		if err != nil {
+			return "", err
+		}
+		major, _, err := verKey.GetIntegerValue("CurrentMajorVersionNumber")
+		if err != nil {
+			return "", err
+		}
+		minor, _, err := verKey.GetIntegerValue("CurrentMinorVersionNumber")
+		if err != nil {
+			return "", err
+		}
+		return fmt.Sprintf("%d.%d", major, minor), nil
+	}
+	return "", errors.New("unknown OS")
+}
diff --git a/pkg/util/util.go b/pkg/util/util.go
new file mode 100755
index 0000000..79c3aa0
--- /dev/null
+++ b/pkg/util/util.go
@@ -0,0 +1,145 @@
+package util
+
+import (
+	"crypto/md5"
+	"crypto/sha1"
+	"encoding/base64"
+	"encoding/hex"
+	"fmt"
+	"hash"
+	"io"
+	"net/http"
+	"os"
+	"path"
+	"runtime"
+	"strings"
+)
+
+type File struct {
+	Id   string `json:"id"`
+	Sha1 string `json:"sha1"`
+	Size int64  `json:"size"`
+	Url  string `json:"url"`
+	Path string `json:"path"`
+}
+
+func (f File) Retrieve() ([]byte, error) {
+	return GetFromUrl(f.Url, f.Sha1, "sha1", f.Size)
+}
+
+func (f *File) GetName() string {
+	if f.Id == "" {
+		return f.Path
+	}
+	return f.Id
+}
+
+func GetFromUrl(url string, hash, hashType string, fSize int64) ([]byte, error) {
+	resp, err := http.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("status code returned is %d", resp.StatusCode)
+	}
+	if fSize != -1 && resp.ContentLength != -1 && resp.ContentLength != fSize {
+		return nil, fmt.Errorf("response size mismatch. %d != %d", resp.ContentLength, fSize)
+	}
+
+	data, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	if fSize != -1 && len(data) != int(fSize) {
+		return nil, fmt.Errorf("body size mismatch. %d != %d", len(data), fSize)
+	}
+
+	if hash != "" {
+		if err := CheckHash(data, hash, hashType); err != nil {
+			return nil, err
+		}
+	}
+
+	return data, nil
+}
+
+func IsFileExist(path string) bool {
+	_, err := os.Stat(path)
+	return err == nil
+}
+
+func WriteFile(fPath string, data []byte) error {
+	if err := os.MkdirAll(path.Dir(fPath), 0777); err != nil {
+		return err
+	}
+	if err := os.WriteFile(fPath, data, 0666); err != nil {
+		return err
+	}
+	return nil
+}
+
+func ReadFile(fPath string) ([]byte, error) {
+	if !IsFileExist(fPath) {
+		return nil, fmt.Errorf("File %s not found", fPath)
+	}
+
+	data, err := os.ReadFile(fPath)
+	if err != nil {
+		return nil, err
+	}
+
+	return data, nil
+}
+
+// LoadOrDownloadFile will check if file exists and correct, will download it otherwise.
+func LoadOrDownloadFile(fPath, url string, hash, hashType string, fSize int64) ([]byte, error) {
+	if IsFileExist(fPath) {
+		data, err := os.ReadFile(fPath)
+		if err != nil {
+			return nil, err
+		}
+		if hash != "" {
+			if err := CheckHash(data, hash, hashType); err != nil {
+				return nil, err
+			}
+		}
+		return data, nil
+	}
+
+	return GetFromUrl(url, hash, hashType, fSize)
+}
+
+func CheckHash(data []byte, fHash, hashType string) error {
+	var hasher hash.Hash
+
+	switch hashType {
+	case "sha1":
+		hasher = sha1.New()
+	case "md5":
+		hasher = md5.New()
+	default:
+		return fmt.Errorf("unsupported hash type %s", hashType)
+	}
+
+	if _, err := hasher.Write(data); err != nil {
+		return err
+	}
+	resultedHash := hasher.Sum(nil)
+
+	if (strings.Contains(fHash, "=") && base64.StdEncoding.EncodeToString(resultedHash) == fHash) ||
+		hex.EncodeToString(resultedHash) == fHash {
+		return nil
+	}
+
+	return fmt.Errorf("hash mismatch: %s != %s", hex.EncodeToString(resultedHash), fHash)
+}
+
+func PathSeparator() string {
+	if runtime.GOOS == "windows" {
+		return ";"
+	}
+	return ":"
+}