parchment/cpkg.go

package main

import (
	"encoding/binary"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
)

type fileData struct {
	name    string
	content []byte
}

type cpkg struct {
	packageName string
	files       []fileData
}

func NewCpkg(packageName string) *cpkg {
	return &cpkg{
		packageName: packageName,
		files:       make([]fileData, 0),
	}
}

func (c *cpkg) AddFile(fsys fs.FS, path string) error {
	file, err := fs.ReadFile(fsys, path)
	if err != nil {
		return err
	}
	c.files = append(c.files, fileData{name: path, content: file})
	return nil
}

// cpkg file header format:
// 1 byte: filename length
// n bytes: filename
// 4 bytes: file size (uint32)
func (c *cpkg) createCpkgFileHeader(file fileData) []byte {
	headerBytes := make([]byte, 0)
	headerBytes = append(headerBytes, byte(len(file.name)))
	headerBytes = append(headerBytes, []byte(file.name)...)

	// file size (uint32 - 4 bytes)
	fileSizeBytes := make([]byte, 4)
	binary.LittleEndian.PutUint32(fileSizeBytes, uint32(len(file.content)))
	headerBytes = append(headerBytes, fileSizeBytes...)

	return headerBytes
}

// cpkg header format:
// 4 bytes: magic number "Cpkg"
// 2 bytes: version
// 4 bytes: file count
func (c *cpkg) createCpkgHeader() []byte {
	headerBytes := make([]byte, 0)
	headerBytes = append(headerBytes, []byte("Cpkg")...)

	// version (uint16 - 2 bytes)
	versionBytes := make([]byte, 2)
	binary.LittleEndian.PutUint16(versionBytes, 1)
	headerBytes = append(headerBytes, versionBytes...)

	// file count (uint32 - 4 bytes)
	fileCountBytes := make([]byte, 4)
	binary.LittleEndian.PutUint32(fileCountBytes, uint32(len(c.files)))
	headerBytes = append(headerBytes, fileCountBytes...)

	return headerBytes
}

func (c *cpkg) Create() (bool, error) {
	file, err := os.Create(c.packageName + ".cpkg")
	if err != nil {
		return false, err
	}
	defer file.Close()

	// Write main header
	header := c.createCpkgHeader()
	n, err := file.Write(header)
	if err != nil {
		return false, fmt.Errorf("failed to write header: %w", err)
	}
	if n != len(header) {
		return false, fmt.Errorf("incomplete header write: wrote %d of %d bytes", n, len(header))
	}

	// Write each file
	for i, fileData := range c.files {
		// Write file header
		fileHeader := c.createCpkgFileHeader(fileData)
		n, err := file.Write(fileHeader)
		if err != nil {
			return false, fmt.Errorf("failed to write header for file %d (%s): %w", i, fileData.name, err)
		}
		if n != len(fileHeader) {
			return false, fmt.Errorf("incomplete header write for file %d (%s): wrote %d of %d bytes", i, fileData.name, n, len(fileHeader))
		}

		// Write file content
		n, err = file.Write(fileData.content)
		if err != nil {
			return false, fmt.Errorf("failed to write content for file %d (%s): %w", i, fileData.name, err)
		}
		if n != len(fileData.content) {
			return false, fmt.Errorf("incomplete content write for file %d (%s): wrote %d of %d bytes", i, fileData.name, n, len(fileData.content))
		}

	}

	return true, nil
}

func (c *cpkg) Unpack(fsys fs.FS) error {
	file, err := os.Open(c.packageName + ".cpkg")
	if err != nil {
		return err
	}
	defer file.Close()

	// Read main header (10 bytes)
	header := make([]byte, 10)
	_, err = file.Read(header)
	if err != nil {
		return fmt.Errorf("failed to read header: %w", err)
	}

	// Verify magic number
	magicNumber := string(header[:4])
	if magicNumber != "Cpkg" {
		return fmt.Errorf("invalid cpkg file: wrong magic number")
	}

	// Verify version
	version := binary.LittleEndian.Uint16(header[4:6])
	if version != 1 {
		return fmt.Errorf("unsupported cpkg file version: %d", version)
	}

	// Read file count
	fileCount := binary.LittleEndian.Uint32(header[6:10])

	// Clear existing files array
	c.files = make([]fileData, 0, fileCount)

	// Read each file sequentially
	for i := 0; i < int(fileCount); i++ {
		// Read filename length (1 byte)
		fileNameLengthBuf := make([]byte, 1)
		n, err := file.Read(fileNameLengthBuf)
		if err != nil {
			return fmt.Errorf("failed to read filename length for file %d: %w", i, err)
		}
		if n != 1 {
			return fmt.Errorf("incomplete read of filename length for file %d: got %d bytes, expected 1", i, n)
		}
		fileNameLength := fileNameLengthBuf[0]

		// Read filename
		fileNameBuf := make([]byte, fileNameLength)
		n, err = file.Read(fileNameBuf)
		if err != nil {
			return fmt.Errorf("failed to read filename for file %d: %w", i, err)
		}
		if n != int(fileNameLength) {
			return fmt.Errorf("incomplete read of filename for file %d: got %d bytes, expected %d", i, n, fileNameLength)
		}
		fileName := string(fileNameBuf)

		// Read file size (4 bytes)
		fileSizeBuf := make([]byte, 4)
		n, err = file.Read(fileSizeBuf)
		if err != nil {
			return fmt.Errorf("failed to read file size for file %d: %w", i, err)
		}
		if n != 4 {
			return fmt.Errorf("incomplete read of file size for file %d: got %d bytes, expected 4", i, n)
		}
		fileSize := binary.LittleEndian.Uint32(fileSizeBuf)

		// Read file content
		fileContent := make([]byte, fileSize)
		n, err = file.Read(fileContent)
		if err != nil {
			return fmt.Errorf("failed to read content for file %d (%s): %w", i, fileName, err)
		}
		if n != int(fileSize) {
			return fmt.Errorf("incomplete read of content for file %d (%s): got %d bytes, expected %d", i, fileName, n, fileSize)
		}

		c.files = append(c.files, fileData{name: fileName, content: fileContent})
	}

	// Write files to filesystem in subdirectory with the package name
	err = os.MkdirAll(c.packageName, 0755)
	if err != nil {
		return fmt.Errorf("failed to create output directory: %w", err)
	}

	for _, fileData := range c.files {
		outputPath := filepath.Join(c.packageName, fileData.name)

		// Create parent directories if they don't exist
		parentDir := filepath.Dir(outputPath)
		err = os.MkdirAll(parentDir, 0755)
		if err != nil {
			return fmt.Errorf("failed to create directory for file %s: %w", fileData.name, err)
		}

		err = os.WriteFile(outputPath, fileData.content, 0644)
		if err != nil {
			return fmt.Errorf("failed to write file %s: %w", fileData.name, err)
		}
	}

	return nil
}