package git

import (
	"bytes"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
)

// Repo wraps a bare directory that is a Git repository.
type Repo struct {
	root string
	// mu serialises whole operations (a background sync racing a user
	// save would otherwise corrupt index/merge state).
	mu sync.Mutex
	// sshCommand is exported to git as GIT_SSH_COMMAND when set, so
	// remotes can be reached with a dedicated key and known_hosts file
	// even though the server runs without a home directory.
	sshCommand string
}

// Open returns a Repo for an existing directory, initialising Git if needed.
func Open(root string) (*Repo, error) {
	r := &Repo{root: root}
	if err := r.initIfNeeded(); err != nil {
		return nil, err
	}
	return r, nil
}

func (r *Repo) initIfNeeded() error {
	out, _ := r.run("rev-parse", "--is-inside-work-tree")
	if strings.TrimSpace(out) == "true" {
		return nil
	}
	_, err := r.run("init")
	return err
}

// Commit writes data to path and creates a Git commit authored by author.
func (r *Repo) Commit(path, content, message, author, email string) error {
	r.mu.Lock()
	defer r.mu.Unlock()
	full := filepath.Join(r.root, path)
	if err := writeFile(full, content); err != nil {
		return err
	}
	if _, err := r.run("add", path); err != nil {
		return err
	}
	_, err := r.run(
		"-c", fmt.Sprintf("user.name=%s", author),
		"-c", fmt.Sprintf("user.email=%s", email),
		"commit", "-m", message,
	)
	return err
}

// Log returns the commit history for a file, including added/removed line counts.
func (r *Repo) Log(path string) ([]LogEntry, error) {
	r.mu.Lock()
	defer r.mu.Unlock()
	out, err := r.run("log", "--format=COMMIT|%H|%an|%ae|%ai|%s", "--numstat", "--", path)
	if err != nil {
		return nil, err
	}
	var entries []LogEntry
	var current *LogEntry
	for _, line := range strings.Split(strings.TrimSpace(out), "\n") {
		if strings.HasPrefix(line, "COMMIT|") {
			if current != nil {
				entries = append(entries, *current)
			}
			parts := strings.SplitN(strings.TrimPrefix(line, "COMMIT|"), "|", 5)
			if len(parts) == 5 {
				current = &LogEntry{
					Hash:    parts[0],
					Author:  parts[1],
					Email:   parts[2],
					Date:    parts[3],
					Subject: parts[4],
				}
			}
		} else if current != nil && strings.Contains(line, "\t") {
			// numstat line: "added\tremoved\tfilename"
			fields := strings.SplitN(line, "\t", 3)
			if len(fields) == 3 {
				added, _ := strconv.Atoi(fields[0])
				removed, _ := strconv.Atoi(fields[1])
				current.Added += added
				current.Removed += removed
			}
		}
	}
	if current != nil {
		entries = append(entries, *current)
	}
	return entries, nil
}

// Diff returns the unified diff between two commits for a file.
func (r *Repo) Diff(path, fromHash, toHash string) (string, error) {
	r.mu.Lock()
	defer r.mu.Unlock()
	out, err := r.run("diff", fromHash, toHash, "--", path)
	return out, err
}

// Show returns the file content at a specific commit.
func (r *Repo) Show(hash, path string) (string, error) {
	r.mu.Lock()
	defer r.mu.Unlock()
	return r.run("show", fmt.Sprintf("%s:%s", hash, path))
}

// HasUncommitted returns true if the working tree contains untracked or
// modified files that have not yet been committed.
func (r *Repo) HasUncommitted() bool {
	r.mu.Lock()
	defer r.mu.Unlock()
	out, err := r.run("status", "--porcelain")
	return err == nil && strings.TrimSpace(out) != ""
}

// CommitAll stages every file in the repo root and creates a commit.
func (r *Repo) CommitAll(message, author, email string) error {
	r.mu.Lock()
	defer r.mu.Unlock()
	if _, err := r.run("add", "-A"); err != nil {
		return err
	}
	_, err := r.run(
		"-c", fmt.Sprintf("user.name=%s", author),
		"-c", fmt.Sprintf("user.email=%s", email),
		"commit", "-m", message,
	)
	return err
}

// Move renames a file from oldPath to newPath and creates a Git commit.
func (r *Repo) Move(oldPath, newPath, message, author, email string) error {
	r.mu.Lock()
	defer r.mu.Unlock()
	if _, err := r.run("mv", oldPath, newPath); err != nil {
		return err
	}
	_, err := r.run(
		"-c", fmt.Sprintf("user.name=%s", author),
		"-c", fmt.Sprintf("user.email=%s", email),
		"commit", "-m", message,
	)
	return err
}

type LogEntry struct {
	Hash    string
	Author  string
	Email   string
	Date    string
	Subject string
	Added   int
	Removed int
}

func writeFile(path, content string) error {
	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
		return err
	}
	return os.WriteFile(path, []byte(content), 0644)
}

func (r *Repo) run(args ...string) (string, error) {
	cmd := exec.Command("git", append([]string{"-C", r.root}, args...)...)
	cmd.Env = append(os.Environ(), "GIT_TERMINAL_PROMPT=0")
	if r.sshCommand != "" {
		cmd.Env = append(cmd.Env, "GIT_SSH_COMMAND="+r.sshCommand)
	}
	var stdout, stderr bytes.Buffer
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr
	if err := cmd.Run(); err != nil {
		return "", fmt.Errorf("git %v: %w — %s", args, err, stderr.String())
	}
	return stdout.String(), nil
}