eternity/lib/main.go

package lib

import (
	"archive/tar"
	"bytes"
	"crypto/ed25519"
	"encoding/binary"
	"encoding/json"
	"errors"
	"io"
	"math/big"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"

	"github.com/Masterminds/semver"
	"github.com/cespare/xxhash/v2"
	"github.com/klauspost/compress/zstd"
)

// SpecialFiles is a struct that contains the special files that are not to be deleted or replaced
type SpecialFiles struct {
	NoDelete  []string
	NoReplace []string
}

// Metadata is a struct that contains the metadata of the package
type Metadata struct {
	Name            string
	Description     string
	LongDescription string
	Version         semver.Version
	Author          string
	License         string
	Architecture    string
	// The decompressed size may be larger than the int64 allocated for a compressed file
	DecompressedSize big.Int
	Dependencies     []string
	SpecialFiles     SpecialFiles
}

// Build is a struct that contains the build configuration of the package
type Build struct {
	Type         string
	Dependencies []string
	Steps        []string
	TargetRoot   string
	HooksFolder  PotentiallyNullString
	FilesFolder  PotentiallyNullString
}

// PotentiallyNullString is a struct that contains a string that may be null
type PotentiallyNullString struct {
	Value string
	Null  bool
}

// Config is a struct that contains the configuration of the package
type Config struct {
	Metadata Metadata
	Build    Build
}

// Log is a struct that contains the log information
type Log struct {
	Level   string
	Content string
	Prompt  bool
}

// Logger is a struct that contains the functions and properties of the logger
type Logger struct {
	LogFunc         func(Log) string
	PromptSupported bool
}

var ErrEternityJsonOpenError = errors.New("error opening eternity.json")
var ErrEternityJsonReadError = errors.New("error reading eternity.json")
var ErrEternityJsonParseError = errors.New("error parsing eternity.json")
var ErrEternityJsonMapError = errors.New("error mapping eternity.json")

// interfaceToStringSlice converts an interface slice to a string slice
func interfaceToStringSlice(interfaceSlice []interface{}, interfaceName string) ([]string, error) {
	// Yes, it's meant to be empty and not nil: JSON arrays are empty, not nil
	//goland:noinspection GoPreferNilSlice
	stringSlice := []string{}
	for _, interfaceValue := range interfaceSlice {
		stringValue, ok := interfaceValue.(string)
		if !ok {
			return nil, errors.New(interfaceName + " are not strings")
		}
		stringSlice = append(stringSlice, stringValue)
	}

	return stringSlice, nil
}

// ParseConfig parses the eternity.json file
func ParseConfig(path string, logger *Logger) (Config, error, error) {
	// Open eternity.json
	logger.LogFunc(Log{
		Level:   "INFO",
		Content: "Parsing eternity.json",
		Prompt:  false,
	})
	file, err := os.Open(path)
	if err != nil {
		return Config{}, err, ErrEternityJsonOpenError
	}

	// Convert the file to a byte buffer
	var fileBytes bytes.Buffer
	_, err = io.Copy(&fileBytes, file)
	if err != nil {
		return Config{}, err, ErrEternityJsonReadError
	}

	// Parse the file as JSON
	var config map[string]interface{}
	err = json.Unmarshal(fileBytes.Bytes(), &config)
	if err != nil {
		return Config{}, err, ErrEternityJsonParseError
	}

	// Map SpecialFiles
	var parsedSpecialFiles SpecialFiles
	specialFiles, ok := config["specialFiles"].(map[string]interface{})
	if !ok {
		return Config{}, errors.New("specialFiles is not an object"), ErrEternityJsonMapError
	}
	noDelete, ok := specialFiles["noDelete"].([]interface{})
	if !ok {
		return Config{}, errors.New("noDelete is not an array"), ErrEternityJsonMapError
	}
	parsedSpecialFiles.NoDelete, err = interfaceToStringSlice(noDelete, "noDelete")
	if err != nil {
		return Config{}, err, ErrEternityJsonMapError
	}
	noReplace, ok := specialFiles["noReplace"].([]interface{})
	if !ok {
		return Config{}, errors.New("noReplace is not an array"), ErrEternityJsonMapError
	}
	parsedSpecialFiles.NoReplace, err = interfaceToStringSlice(noReplace, "noReplace")
	if err != nil {
		return Config{}, err, ErrEternityJsonMapError
	}

	// Declare the parsedMetadata object
	var parsedMetadata Metadata

	// Append parsedSpecialFiles to parsedMetadata
	parsedMetadata.SpecialFiles = parsedSpecialFiles

	// Map the metadata
	parsedMetadata.Name, ok = config["name"].(string)
	if !ok {
		return Config{}, errors.New("name is not a string"), ErrEternityJsonMapError
	}
	parsedMetadata.Description, ok = config["desc"].(string)
	if !ok {
		return Config{}, errors.New("description is not a string"), ErrEternityJsonMapError
	}
	parsedMetadata.LongDescription, ok = config["longDesc"].(string)
	if !ok {
		return Config{}, errors.New("longDesc is not a string"), ErrEternityJsonMapError
	}
	versionString, ok := config["version"].(string)
	if !ok {
		return Config{}, errors.New("version is not a string"), ErrEternityJsonMapError
	}
	versionPointer, err := semver.NewVersion(versionString)
	if err != nil {
		return Config{}, err, ErrEternityJsonMapError
	}
	parsedMetadata.Version = *versionPointer
	parsedMetadata.Author, ok = config["author"].(string)
	if !ok {
		return Config{}, errors.New("author is not a string"), ErrEternityJsonMapError
	}
	parsedMetadata.License, ok = config["license"].(string)
	if !ok {
		return Config{}, errors.New("license is not a string"), ErrEternityJsonMapError
	}
	parsedMetadata.Architecture, ok = config["arch"].(string)
	if !ok {
		return Config{}, errors.New("arch is not a string"), ErrEternityJsonMapError
	}
	dependencies, ok := config["deps"].([]interface{})
	if !ok {
		return Config{}, errors.New("deps is not an array"), ErrEternityJsonMapError
	}
	parsedMetadata.Dependencies, err = interfaceToStringSlice(dependencies, "dependencies")
	if err != nil {
		return Config{}, err, ErrEternityJsonMapError
	}

	// Map build
	var parsedBuild Build
	build, ok := config["build"].(map[string]interface{})
	if !ok {
		return Config{}, errors.New("build is not an object"), ErrEternityJsonMapError
	}
	parsedBuild.Type, ok = build["type"].(string)
	if !ok {
		return Config{}, errors.New("type is not a string"), ErrEternityJsonMapError
	}
	buildDependencies, ok := build["deps"].([]interface{})
	if !ok {
		return Config{}, errors.New("deps is not an array"), ErrEternityJsonMapError
	}
	parsedBuild.Dependencies, err = interfaceToStringSlice(buildDependencies, "deps")
	if err != nil {
		return Config{}, err, ErrEternityJsonMapError
	}
	steps, ok := build["steps"].([]interface{})
	if !ok {
		return Config{}, errors.New("steps is not an array"), ErrEternityJsonMapError
	}
	parsedBuild.Steps, err = interfaceToStringSlice(steps, "steps")
	if err != nil {
		return Config{}, err, ErrEternityJsonMapError
	}
	parsedBuild.TargetRoot, ok = build["root"].(string)
	if !ok {
		return Config{}, errors.New("root is not a string"), ErrEternityJsonMapError
	}
	hooksFolder, ok := build["hooks"].(string)
	if !ok {
		parsedBuild.HooksFolder = PotentiallyNullString{Null: true}
	} else {
		parsedBuild.HooksFolder = PotentiallyNullString{Null: false, Value: hooksFolder}
	}
	filesFolder, ok := build["files"].(string)
	if !ok {
		parsedBuild.FilesFolder = PotentiallyNullString{Null: true}
	} else {
		parsedBuild.FilesFolder = PotentiallyNullString{Null: false, Value: filesFolder}
	}

	// Create the final Config object
	parsedConfig := Config{
		Metadata: parsedMetadata,
		Build:    parsedBuild,
	}

	// Return the final Config object
	return parsedConfig, nil, nil
}

var ErrBuildEPKTemporaryDirectoryError = errors.New("error creating temporary directory")
var ErrBuildEPKCreateHooksError = errors.New("error creating hooks directory")
var ErrBuildEPKCopyHooksError = errors.New("error copying hooks")
var ErrBuildEPKChrootError = errors.New("chroot builds are not supported yet")
var ErrBuildEPKUnrestrictedError = errors.New("unrestricted builds are not supported yet")
var ErrBuildEPKBuildShError = errors.New("error creating build.sh")
var ErrBuildEPKWritingBuildShError = errors.New("error writing to build.sh")
var ErrBuildEPKTargetRootError = errors.New("error creating target root")
var ErrBuildEPKExecutingBuildShError = errors.New("error executing build.sh")
var ErrBuildEPKCountingFilesError = errors.New("error counting files")
var ErrBuildEPKBadBuildType = errors.New("bad build type")

// BuildEPK builds the EPK package into a build directory
func BuildEPK(projectDir string, inMemory bool, buildConfig Build, logger *Logger) (big.Int, string, error, error) {
	var tempDir string

	switch buildConfig.Type {
	case "chroot":
		return *big.NewInt(0), "", nil, ErrBuildEPKChrootError
	case "unrestricted":
		return *big.NewInt(0), "", nil, ErrBuildEPKUnrestrictedError
	case "host":
		// Set up the temp dir
		var err error
		if inMemory {
			// Builds in /tmp. This means that the program must fit in RAM. Luckily, most programs do.
			// If you're building a large program, you might want to consider using a disk build.
			tempDir, err = os.MkdirTemp("/tmp", "eternity-build-")
		} else {
			// Builds on disk. This is slower but if your program can't fit in RAM, you're out of luck.
			// If your program can fit in RAM, you might want to consider using an in-memory build.
			tempDir, err = os.MkdirTemp(projectDir, "eternity-build-")
		}
		if err != nil {
			return *big.NewInt(0), tempDir, err, ErrBuildEPKTemporaryDirectoryError
		}

		// Copy the hooks folder
		if buildConfig.HooksFolder.Null != true {
			hooksDir := filepath.Join(projectDir, buildConfig.HooksFolder.Value)
			targetHooksDir := filepath.Join(tempDir, buildConfig.HooksFolder.Value)
			logger.LogFunc(Log{
				Level: "INFO", Content: "Copying hooks from " + hooksDir + " to " + targetHooksDir, Prompt: false,
			})

			err = os.MkdirAll(targetHooksDir, 0755)
			if err != nil {
				return *big.NewInt(0), tempDir, err, ErrBuildEPKCreateHooksError
			}

			err = os.CopyFS(targetHooksDir, os.DirFS(hooksDir))
			if err != nil {
				return *big.NewInt(0), tempDir, err, ErrBuildEPKCopyHooksError
			}
		}

		// Generate the shell script
		logger.LogFunc(Log{
			Level: "INFO", Content: "Generating shell script", Prompt: false,
		})

		// Create the shell script
		shellScript := "#!/bin/sh\n"
		for _, step := range buildConfig.Steps {
			shellScript += step + "\n"
		}

		file, err := os.OpenFile(tempDir+"/build.sh", os.O_CREATE|os.O_RDWR, 0755)
		if err != nil {
			return *big.NewInt(0), tempDir, err, ErrBuildEPKBuildShError
		}

		_, err = file.WriteString(shellScript)
		if err != nil {
			return *big.NewInt(0), tempDir, err, ErrBuildEPKWritingBuildShError
		}

		// Set up the target root
		targetRoot := filepath.Join(tempDir, buildConfig.TargetRoot)
		err = os.MkdirAll(targetRoot, 0755)
		if err != nil {
			return *big.NewInt(0), tempDir, err, ErrBuildEPKTargetRootError
		}

		// Execute the shell script in BWrap
		logger.LogFunc(Log{
			Level: "INFO", Content: "Starting up container environment (replicating host files)", Prompt: false,
		})

		// Allow me to explain why it's in BWrap. It's very difficult to cut off internet access without root, so I just
		// copy-pasted most of the host files into the container, then disabled networking. This also allows us to use
		// fakeroot and minimises the blast radius of a malicious package (hopefully) by not allowing the home directory
		// or any files owned by root to be viewed or modified (too bad if you've got sensitive data in /var or /etc :P)
		arguments := []string{
			"--unshare-net",
			"--bind", "/bin", "/bin",
			"--bind", "/lib", "/lib",
			"--bind", "/lib64", "/lib64",
			"--bind", "/usr", "/usr",
			"--bind", "/etc", "/etc",
			"--bind", "/var", "/var",
			"--bind", "/sys", "/sys",
			"--bind", "/opt", "/opt",
			"--bind", targetRoot, filepath.Join("/", buildConfig.TargetRoot),
			"--bind", tempDir, "/eternity",
			"--dev", "/dev",
			"--tmpfs", "/run",
			"--tmpfs", "/tmp",
			"--proc", "/proc",
			"/usr/bin/fakeroot-tcp", "--",
			"/bin/sh", "/eternity/build.sh",
		}

		if buildConfig.FilesFolder.Null != true {
			arguments = arguments[:len(arguments)-4]
			arguments = append(
				arguments, "--bind", filepath.Join(projectDir, buildConfig.FilesFolder.Value), filepath.Join("/", buildConfig.FilesFolder.Value),
				"/usr/bin/fakeroot-tcp", "--",
				"/bin/sh", "/eternity/build.sh",
			)
		}

		err = exec.Command("bwrap", arguments...).Run()
		if err != nil {
			return *big.NewInt(0), tempDir, err, ErrBuildEPKExecutingBuildShError
		}

		// Hopefully, the build was successful. Let's give the user a file and size count.
		var fileCount int
		var sizeCount big.Int
		// We start at -1 because the root directory is not counted
		dirCount := -1
		err = filepath.Walk(targetRoot, func(path string, info os.FileInfo, err error) error {
			if info.IsDir() {
				dirCount++
			} else {
				fileCount++
			}
			// Both directories and files need to have their sizes counted
			sizeCount.Add(&sizeCount, big.NewInt(info.Size()))
			return nil
		})
		if err != nil {
			return *big.NewInt(0), tempDir, err, ErrBuildEPKCountingFilesError
		}

		logger.LogFunc(Log{
			Level: "INFO",
			Content: "Build successful. " + strconv.Itoa(fileCount) + " files and " + strconv.Itoa(dirCount) +
				" directories created," + " totalling " + sizeCount.String() + " bytes.",
			Prompt: false,
		})

		return sizeCount, tempDir, nil, nil
	default:
		return *big.NewInt(0), "", errors.New(buildConfig.Type), ErrBuildEPKBadBuildType
	}
}

// CreateTar creates a tar archive from a directory
func CreateTar(targetDir string, output io.Writer) error {
	tarWriter := tar.NewWriter(output)
	err := filepath.Walk(targetDir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}

		if !info.Mode().IsRegular() {
			return nil
		}

		header, err := tar.FileInfoHeader(info, path)
		if err != nil {
			return err
		}

		header.Name = strings.TrimPrefix(strings.Replace(path, targetDir, "", -1), string(filepath.Separator))

		err = tarWriter.WriteHeader(header)
		if err != nil {
			return err
		}

		file, err := os.Open(path)
		if err != nil {
			return err
		}

		_, err = io.Copy(tarWriter, file)
		if err != nil {
			return err
		}

		err = file.Close()
		if err != nil {
			return err
		}

		return nil
	})

	if err != nil {
		return err
	} else {
		err = tarWriter.Close()
		if err != nil {
			return err
		} else {
			return nil
		}
	}
}

// These errors are in the wrong order due to this function being rewritten.
// Oh well, not like it matters.

// ConstPackageEPKMagicNumber is the magic number for an EPK file: "epk" in ASCII / UTF-8
var ConstPackageEPKMagicNumber = []byte{0x65, 0x70, 0x6B}

// ConstPackageEPKBigEndian is the letter "b" in ASCII / UTF-8
var ConstPackageEPKBigEndian = []byte{0x62}

// ConstPackageEPKLittleEndian is the letter "l" in ASCII / UTF-8
var ConstPackageEPKLittleEndian = []byte{0x6C}

// ConstPackageEPKInitialByteOffset is the initial byte offset for an EPK file until we arrive at the signature. 12 = 3 + 1 + 8: 3 for the magic number, 1 for the endian, and 8 for the tar offset
var ConstPackageEPKInitialByteOffset int64 = 12

// ConstPackageEPKSignatureLength is the length of the signature
var ConstPackageEPKSignatureLength int64 = 64

// ConstPackageEPKPublicKeyLength is the length of the public key
var ConstPackageEPKPublicKeyLength int64 = 32

// ConstPackageEPKMetadataOffset is the offset of the metadata in the EPK file
var ConstPackageEPKMetadataOffset = 108

// All these errors are out of order once I rewrote this to stream instead of using a buffer.
// Oh well, not like it matters.

var ErrPackageEPKFailedToWriteHash = errors.New("error writing hash to EPK file")
var ErrPackageEPKFailedToSeek = errors.New("error seeking in EPK file")
var ErrPackageEPKCreateDistDirError = errors.New("error creating dist directory")
var ErrPackageEPKMoveToDistError = errors.New("error moving to dist directory")
var ErrPackageEPKTarError = errors.New("error creating tar")
var ErrPackageEPKJSONMarshal = errors.New("error marshalling JSON")
var ErrPackageEPKCreateCompressionWriterError = errors.New("error creating ZStandard writer")
var ErrPackageEPKCompressCloseError = errors.New("error closing EPK ZStandard writer")
var ErrPackageEPKCannotOpenFile = errors.New("error opening EPK file for writing")
var ErrPackageEPKCannotWriteFile = errors.New("error writing to EPK file")
var ErrPackageEPKCannotCloseFile = errors.New("error closing EPK file")

// PackageEPK packages the EPK work directory into an EPK file
func PackageEPK(metaData Metadata, build Build, tempDir string, output string, privateKey ed25519.PrivateKey, logger *Logger) (error, error) {
	// Create the EPK
	logger.LogFunc(Log{
		Level: "INFO", Content: "Packaging EPK", Prompt: false,
	})

	// Ok. Let's construct targetDir, then hooksDir
	targetDir := filepath.Join(tempDir, build.TargetRoot)
	distDir := tempDir + "/dist"

	err := os.MkdirAll(distDir, 0755)
	if err != nil {
		return err, ErrPackageEPKCreateDistDirError
	}

	err = os.Rename(targetDir, distDir+"/root")
	if err != nil {
		return err, ErrPackageEPKMoveToDistError
	}

	if build.HooksFolder.Null != true {
		hooksDir := filepath.Join(tempDir, build.HooksFolder.Value)
		err = os.Rename(hooksDir, distDir+"/hooks")
		if err != nil {
			return err, ErrPackageEPKMoveToDistError
		}
	}

	// Map the metadata to a JSON string
	logger.LogFunc(Log{
		Level: "INFO", Content: "Calculating package metadata", Prompt: false,
	})

	dataTemplate := map[string]interface{}{
		"name":     metaData.Name,
		"author":   metaData.Author,
		"version":  metaData.Version.String(),
		"desc":     metaData.Description,
		"longDesc": metaData.LongDescription,
		"license":  metaData.License,
		"arch":     metaData.Architecture,
		"deps":     metaData.Dependencies,
		"specialFiles": map[string][]string{
			"noDelete":  metaData.SpecialFiles.NoDelete,
			"noReplace": metaData.SpecialFiles.NoReplace,
		},
		"size": metaData.DecompressedSize.String(),
	}

	// Make the data template into a JSON string
	dataTemplateBytes, err := json.Marshal(dataTemplate)
	if err != nil {
		return err, ErrPackageEPKJSONMarshal
	}

	// Calculate the offsets
	logger.LogFunc(Log{
		Level: "INFO", Content: "Calculating binary offsets", Prompt: false,
	})

	// Calculate the length of the data template
	var dataTemplateLength int64
	for range dataTemplateBytes {
		dataTemplateLength++
	}

	// Calculate the tar offset
	var tarOffset int64
	tarOffset = int64(ConstPackageEPKMetadataOffset) + dataTemplateLength

	logger.LogFunc(Log{
		Level: "INFO", Content: "Calculating binary properties", Prompt: false,
	})

	// We need to determine the endianness of the architecture so that it's optimal for the target system
	// We assume little-endian by default because most architectures are little-endian (why would you use big-endian?)
	littleEndian := true
	switch metaData.Architecture {
	case "ppc64":
		littleEndian = false
	case "ppc":
		littleEndian = false
	case "mips64":
		littleEndian = false
	case "mips":
		littleEndian = false
	case "s390":
		littleEndian = false
	case "s390x":
		littleEndian = false
	case "sparc64":
		littleEndian = false
	case "sparc":
		littleEndian = false
	default:
		littleEndian = true
	}

	// Create the byte arrays for the tar offset
	tarOffsetBytes := make([]byte, 8)

	// Write as much as we can to the file
	logger.LogFunc(Log{
		Level: "INFO", Content: "Writing to file", Prompt: false,
	})

	// Open the file buffer
	file, err := os.OpenFile(output, os.O_CREATE|os.O_RDWR|os.O_TRUNC, 0644)
	if err != nil {
		return err, ErrPackageEPKCannotOpenFile
	}

	// Write the magic number
	_, err = file.Write(ConstPackageEPKMagicNumber)
	if err != nil {
		return err, ErrPackageEPKCannotWriteFile
	}

	// Write the endianness and correct the offsets based on the endianness
	// I know it's wasteful to convert an int64 to an uint64, but binary doesn't support int64 with custom Endian-ness
	// and file.Seek doesn't
	// support uint64.
	if littleEndian {
		binary.LittleEndian.PutUint64(tarOffsetBytes, uint64(tarOffset))
		_, err = file.Write(ConstPackageEPKLittleEndian)
	} else {
		binary.BigEndian.PutUint64(tarOffsetBytes, uint64(tarOffset))
		_, err = file.Write(ConstPackageEPKBigEndian)
	}
	if err != nil {
		return err, ErrPackageEPKCannotWriteFile
	}

	_, err = file.Write(tarOffsetBytes)
	if err != nil {
		return err, ErrPackageEPKCannotWriteFile
	}
	_, err = file.WriteAt(dataTemplateBytes, int64(ConstPackageEPKMetadataOffset))
	if err != nil {
		return err, ErrPackageEPKCannotWriteFile
	}

	// Create the tar archive
	logger.LogFunc(Log{
		Level: "INFO", Content: "Creating tar", Prompt: false,
	})

	// Move the file pointer to the tar offset so that we can write the tar archive
	seek, err := file.Seek(tarOffset, io.SeekStart)
	if err != nil {
		return err, ErrPackageEPKFailedToSeek
	}
	if seek != tarOffset {
		return err, ErrPackageEPKFailedToSeek
	}

	// Create the hash writer
	xxHash := xxhash.New()
	_, err = xxHash.Write(dataTemplateBytes)
	if err != nil {
		return err, nil
	}

	// Create a multi-writer so we can write to the file and the hash at the same time
	multiWriter := io.MultiWriter(file, xxHash)

	// Create the ZStandard writer
	writer, err := zstd.NewWriter(multiWriter, zstd.WithEncoderLevel(zstd.SpeedDefault))
	if err != nil {
		return err, ErrPackageEPKCreateCompressionWriterError
	}

	// We start writing the tar archive
	err = CreateTar(distDir, writer)
	if err != nil {
		return err, ErrPackageEPKTarError
	}

	// Close the ZStandard writer
	err = writer.Close()
	if err != nil {
		return err, ErrPackageEPKCompressCloseError
	}

	// Great, let's sign the EPK
	logger.LogFunc(Log{
		Level: "INFO", Content: "Signing EPK", Prompt: false,
	})

	// Sign the hash
	signature := ed25519.Sign(privateKey, xxHash.Sum(nil))
	publicKey := privateKey.Public().(ed25519.PublicKey)

	// Write the signature and public key to the file
	// Reverse the pointer back to the start of the file so our offsets are correct
	_, err = file.Seek(0, io.SeekStart)
	if err != nil {
		return err, ErrPackageEPKFailedToSeek
	}

	// Write the signature
	_, err = file.WriteAt(signature, ConstPackageEPKInitialByteOffset)
	if err != nil {
		return err, ErrPackageEPKCannotWriteFile
	}

	// Write the public key
	_, err = file.WriteAt(publicKey, ConstPackageEPKInitialByteOffset+ConstPackageEPKSignatureLength)
	if err != nil {
		return err, ErrPackageEPKCannotWriteFile
	}

	// Close the file
	err = file.Close()
	if err != nil {
		return err, ErrPackageEPKCannotCloseFile
	}

	return nil, nil
}

// ConstGenerateRepositoryRepoDataOffset is the offset of the repository data in the repository.json file: it is 3 (magic) + 64 (the signature) + 32 (the public key) = 99
var ConstGenerateRepositoryRepoDataOffset int64 = 99

// ConstGenerateRepositoryEPKMagicNumber is the magic number for an EPK repository: "eon" in ASCII / UTF-8, for obvious reasons
var ConstGenerateRepositoryEPKMagicNumber = []byte{0x65, 0x6F, 0x6E}

var ErrGenerateRepositoryStatError = errors.New("error stating file or directory")
var ErrGenerateRepositoryNotDirectory = errors.New("not a directory")
var ErrGenerateRepositoryRepositoryNameContainsSlash = errors.New("repository name contains a slash")
var ErrGenerateRepositoryFailedToWalk = errors.New("error walking directory")
var ErrGenerateRepositoryCannotUnmarshalJSON = errors.New("error unmarshalling JSON")
var ErrGenerateRepositoryCannotMarshalJSON = errors.New("error marshalling JSON")
var ErrGenerateRepositoryCannotOpenFile = errors.New("error opening file for writing")
var ErrGenerateRepositoryCannotWriteFile = errors.New("error writing to file")
var ErrGenerateRepositoryCannotCloseFile = errors.New("error closing file")

func GenerateRepository(directory string, privateKey ed25519.PrivateKey, logger *Logger) (error, error) {
	// First, we need to see if the directory exists
	logger.LogFunc(Log{
		Level: "INFO", Content: "Generating repository", Prompt: false,
	})

	info, err := os.Stat(directory)
	if err != nil {
		return err, ErrGenerateRepositoryStatError
	}

	if !info.IsDir() {
		return nil, ErrGenerateRepositoryNotDirectory
	}

	// Create the EPK map
	epkMap := make(map[string]interface{})

	// See if the repository.json file exists
	_, err = os.Stat(directory + "/repository.erf")
	if err != nil {
		if !errors.Is(err, os.ErrNotExist) {
			return err, ErrGenerateRepositoryStatError
		} else {
			if logger.PromptSupported {
				// Ask the user for the name of the repository
				repoName := logger.LogFunc(Log{
					Level: "PROMPT", Content: "Enter the name of the repository", Prompt: true,
				})

				// Check the repository name does not contain any slashes
				if strings.Contains(repoName, "/") {
					return nil, ErrGenerateRepositoryRepositoryNameContainsSlash
				}

				// Ask the user for the description of the repository
				repoDesc := logger.LogFunc(Log{
					Level: "PROMPT", Content: "Enter a short description of the repository", Prompt: true,
				})

				// Ask the user for the author of the repository
				repoAuthor := logger.LogFunc(Log{
					Level: "PROMPT",
					Content: "Enter your preferred author name. This must be the same as the author name used in " +
						"eternity.json and associated with your keypair, otherwise it will cause issues with EPK" +
						" verification and your repository will be rejected by Eon and cannot be trusted.",
					Prompt: true,
				})

				// Now append the metadata to the EPK map
				epkMap["name"] = repoName
				epkMap["desc"] = repoDesc
				epkMap["author"] = repoAuthor
			} else {
				logger.LogFunc(Log{
					Level: "FATAL",
					Content: "Please fill in the author, name, and description of the repository in repository.json. " +
						"Your author name must be the same as the author name used in eternity.json and associated with " +
						"your keypair, otherwise it will cause issues with EPK verification and your repository will be " +
						"rejected by Eon and cannot be trusted.",
					Prompt: false,
				})
			}
		}
	} else {
		// Since it does exist, we can extract the name and description from it
		file, err := os.ReadFile(directory + "/repository.erf")
		if err != nil {
			return err, ErrGenerateRepositoryCannotOpenFile
		}

		// Unmarshal the JSON
		var oldRepositoryMap map[string]interface{}

		err = json.Unmarshal(file[ConstGenerateRepositoryRepoDataOffset:], &oldRepositoryMap)
		if err != nil {
			return err, ErrGenerateRepositoryCannotUnmarshalJSON
		}

		// Copy the author, name, and description to the EPK map
		epkMap["name"] = oldRepositoryMap["name"]
		epkMap["desc"] = oldRepositoryMap["desc"]
		epkMap["author"] = oldRepositoryMap["author"]
	}

	// Add a list of packages to the EPK map
	epkMap["packages"] = make([]map[string]interface{}, 0)

	// Now, walk the directory
	err = filepath.Walk(directory, func(path string, info os.FileInfo, err error) error {
		// If error is not nil, return it
		if err != nil {
			return err
		}

		// Ignore directories
		if info.IsDir() {
			return nil
		}

		// Ok. We need to check if the file actually is an EPK file
		file, err := os.Open(path)
		if err != nil {
			return err
		}

		// Read the first 3 bytes
		magicNumber := make([]byte, 3)
		_, err = file.Read(magicNumber)
		if err != nil {
			return err
		}

		// Check if the magic number is correct
		if !bytes.Equal(magicNumber, ConstPackageEPKMagicNumber) {
			// It isn't an EPK file, so we can ignore it
			return nil
		}

		// We need to create a hash of the file
		xxHash := xxhash.New()
		_, err = io.Copy(xxHash, file)
		if err != nil {
			return err
		}

		// Extract the metadata. First, we get the endian-ness
		var littleEndian bool
		endian := make([]byte, 1)
		_, err = file.ReadAt(endian, 3)
		if err != nil {
			return err
		}
		if bytes.Equal(endian, ConstPackageEPKLittleEndian) {
			littleEndian = true
		} else if bytes.Equal(endian, ConstPackageEPKBigEndian) {
			littleEndian = false
		} else {
			return errors.New("invalid endianness")
		}

		// Now we get the tar offset
		var tarOffset int64
		tarOffsetBytes := make([]byte, 8)
		_, err = file.ReadAt(tarOffsetBytes, 4)
		if err != nil {
			return err
		}

		// Now we convert the tar offset to an int64
		if littleEndian {
			tarOffset = int64(binary.LittleEndian.Uint64(tarOffsetBytes))
		} else {
			tarOffset = int64(binary.BigEndian.Uint64(tarOffsetBytes))
		}

		// Now we can read in the metadata
		metadataBytes := make([]byte, tarOffset-int64(ConstPackageEPKMetadataOffset))
		_, err = file.ReadAt(metadataBytes, int64(ConstPackageEPKMetadataOffset))
		if err != nil {
			return err
		}

		// Now we can unmarshal the metadata
		var metadata map[string]interface{}
		err = json.Unmarshal(metadataBytes, &metadata)
		if err != nil {
			return err
		}

		// Now we have the hash, we need to add it to our data template
		dataTemplate := make(map[string]interface{})
		dataTemplate["hash"] = xxHash.Sum64()

		// Now we add some basic metadata
		dataTemplate["name"] = metadata["name"]
		dataTemplate["author"] = metadata["author"]
		dataTemplate["version"] = metadata["version"]
		dataTemplate["size"] = metadata["size"]
		dataTemplate["arch"] = metadata["arch"]
		dataTemplate["desc"] = metadata["desc"]
		dataTemplate["deps"] = metadata["deps"]

		// We add the path to the EPK file, relative to the directory
		relativePath, err := filepath.Rel(directory, path)
		if err != nil {
			return err
		}

		dataTemplate["path"] = relativePath

		// Append it to a list in the EPK map
		epkMap["packages"] = append(epkMap["packages"].([]map[string]interface{}), dataTemplate)

		return nil
	})

	// This error message is a bit vague, but meh.
	if err != nil {
		return err, ErrGenerateRepositoryFailedToWalk
	}

	// Great, now we need to marshal the EPK map and write it to a file
	epkMapBytes, err := json.Marshal(epkMap)
	if err != nil {
		return err, ErrGenerateRepositoryCannotMarshalJSON
	}

	// Write the EPK map to a file
	file, err := os.OpenFile(directory+"/repository.erf", os.O_CREATE|os.O_RDWR|os.O_TRUNC, 0644)
	if err != nil {
		return err, ErrGenerateRepositoryCannotOpenFile
	}

	// Sign the epk map
	xxHash := xxhash.New()
	_, err = xxHash.Write(epkMapBytes)
	if err != nil {
		return err, nil
	}

	signature := ed25519.Sign(privateKey, xxHash.Sum(nil))
	publicKey := privateKey.Public().(ed25519.PublicKey)

	// Write magic number
	_, err = file.Write(ConstGenerateRepositoryEPKMagicNumber)
	if err != nil {
		return err, ErrGenerateRepositoryCannotWriteFile
	}

	// Write signature
	_, err = file.WriteAt(signature, 3)
	if err != nil {
		return err, ErrGenerateRepositoryCannotWriteFile
	}

	// Write public key
	_, err = file.WriteAt(publicKey, 67)
	if err != nil {
		return err, ErrGenerateRepositoryCannotWriteFile
	}

	// Write the EPK map to the file
	_, err = file.WriteAt(epkMapBytes, ConstGenerateRepositoryRepoDataOffset)
	if err != nil {
		return err, ErrGenerateRepositoryCannotWriteFile
	}

	// Close the file
	err = file.Close()
	if err != nil {
		return err, ErrGenerateRepositoryCannotCloseFile
	}

	return nil, nil
}