package main

import (
	"bytes"
	"compress/zlib"
	"crypto/sha1"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

func main() {
	if len(os.Args) < 2 {
		fmt.Fprintf(os.Stderr, "usage: mygit <command> [<args>...]\n")
		os.Exit(1)
	}

	switch command := os.Args[1]; command {
	case "init":
		for _, dir := range []string{".git", ".git/objects", ".git/refs"} {
			if err := os.MkdirAll(dir, 0755); err != nil {
				fmt.Fprintf(os.Stderr, "Error creating directory: %s\n", err)
			}
		}

		headFileContents := []byte("ref: refs/heads/main\n")
		if err := os.WriteFile(".git/HEAD", headFileContents, 0644); err != nil {
			fmt.Fprintf(os.Stderr, "Error writing file: %s\n", err)
		}

		fmt.Println("Initialized git directory")

	case "cat-file":
		object := os.Args[3]
		filePath := fmt.Sprintf(".git/objects/%s/%s", object[:2], object[2:])
		file, err := os.Open(filePath)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Error opening file: %s\n", err)
			os.Exit(1)
		}
		defer file.Close()

		r, err := zlib.NewReader(file)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Error creating zlib reader: %s\n", err)
			os.Exit(1)
		}
		defer r.Close()

		w, err := io.ReadAll(r)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Error reading zlib data: %s\n", err)
			os.Exit(1)
		}

		parts := bytes.Split(w, []byte("\x00"))
		if len(parts) < 2 {
			fmt.Fprintf(os.Stderr, "Invalid zlib data\n")
			os.Exit(1)
		}

		fmt.Print(string(parts[1]))

	case "hash-object":
		object := os.Args[3]
		file, err := os.ReadFile(object)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Error reading file: %s\n", err)
			os.Exit(1)
		}
		stats, err := os.Stat(object)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Error getting file stats: %s\n", err)
			os.Exit(1)
		}
		content := string(file)
		contentAndHeader := fmt.Sprintf("blob %d\x00%s", stats.Size(), content)
		sha := sha1.Sum([]byte(contentAndHeader))
		hash := fmt.Sprintf("%x", sha)
		blobName := []rune(hash)
		blobPath := ".git/objects/"

		for i, v := range blobName {
			blobPath += string(v)
			if i == 1 {
				blobPath += "/"
			}
		}

		var buffer bytes.Buffer
		z := zlib.NewWriter(&buffer)
		z.Write([]byte(contentAndHeader))
		z.Close()

		if err := os.MkdirAll(filepath.Dir(blobPath), os.ModePerm); err != nil {
			fmt.Fprintf(os.Stderr, "Error creating directory: %s\n", err)
			os.Exit(1)
		}

		f, err := os.Create(blobPath)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Error creating file: %s\n", err)
			os.Exit(1)
		}
		defer f.Close()

		if _, err := f.Write(buffer.Bytes()); err != nil {
			fmt.Fprintf(os.Stderr, "Error writing to file: %s\n", err)
			os.Exit(1)
		}

		fmt.Print(hash)

	case "ls-tree":
		fileNames := []string{}
		files, err := os.ReadDir(".")
		if err != nil {
			fmt.Fprintf(os.Stderr, "Unknown error %s\n", err)
			os.Exit(1)
		}

		for _, file := range files {
			if file.Name() != ".git" {
				fileNames = append(fileNames, file.Name())
			}
		}

		sort.Strings(fileNames)
		fmt.Println(strings.Join(fileNames, "\n"))

	default:
		fmt.Fprintf(os.Stderr, "Unknown command %s\n", command)
		os.Exit(1)
	}
}