package git

import (
	"errors"
	"fmt"
	"os/exec"
	"path/filepath"
	"strings"
)

var ErrPathTraversal = errors.New("repo path outside of configured root")

var repoRoot string

func SetRepoRoot(root string) {
	repoRoot = filepath.Clean(root)
}

// run executes a git command inside repoPath with strict safety guarantees:
//   - repoPath is validated to be under the configured repoRoot (path traversal guard)
//   - args are passed as discrete values — never via shell interpolation
//   - the process inherits only a minimal, fixed environment
func run(repoPath string, args ...string) ([]byte, error) {
	clean := filepath.Clean(repoPath)
	if repoRoot != "" {
		root := repoRoot + string(filepath.Separator)
		if !strings.HasPrefix(clean+string(filepath.Separator), root) && clean != repoRoot {
			return nil, ErrPathTraversal
		}
	}

	cmd := exec.Command("git", args...)
	cmd.Dir = clean
	cmd.Env = []string{
		"GIT_TERMINAL_PROMPT=0",
		"HOME=/tmp", // prevent .gitconfig side-effects
	}
	out, err := cmd.Output()
	if err != nil {
		if exitErr, ok := err.(*exec.ExitError); ok {
			return nil, fmt.Errorf("git %s: %w: %s", args[0], err, exitErr.Stderr)
		}
		return nil, fmt.Errorf("git %s: %w", args[0], err)
	}
	return out, nil
}

// IsEmpty returns true when the repo has no commits on any branch.
// Uses for-each-ref so it doesn't depend on HEAD pointing to a valid branch
// (bare repos created without --initial-branch default to master, but clients
// may push to main, leaving HEAD dangling).
func IsEmpty(repoPath string) bool {
	out, err := run(repoPath, "for-each-ref", "--count=1", "refs/heads/")
	if err != nil {
		return true
	}
	return len(strings.TrimSpace(string(out))) == 0
}

func Init(path string) error {
	cmd := exec.Command("git", "init", "--bare", path)
	cmd.Env = []string{"GIT_TERMINAL_PROMPT=0", "HOME=/tmp"}
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("git init --bare: %w: %s", err, out)
	}
	env := []string{"GIT_TERMINAL_PROMPT=0", "HOME=/tmp"}

	// Point HEAD at main so clients pushing 'main' don't leave a dangling HEAD.
	head := exec.Command("git", "-C", path, "symbolic-ref", "HEAD", "refs/heads/main")
	head.Env = env
	_ = head.Run()

	// Allow pushes over HTTP (git http-backend checks this config key).
	cfg := exec.Command("git", "-C", path, "config", "http.receivepack", "true")
	cfg.Env = env
	_ = cfg.Run()

	return nil
}

type Commit struct {
	Hash    string `json:"hash"`
	Author  string `json:"author"`
	Message string `json:"message"`
	Date    string `json:"date"`
}

func Log(repoPath, branch string, limit int) ([]Commit, error) {
	out, err := run(repoPath,
		"log", branch,
		"--format=%H\x1f%an\x1f%s\x1f%ci",
		fmt.Sprintf("--max-count=%d", limit),
	)
	if err != nil {
		return nil, err
	}

	raw := strings.TrimSpace(string(out))
	if raw == "" {
		return nil, nil
	}

	var commits []Commit
	for _, line := range strings.Split(raw, "\n") {
		parts := strings.SplitN(line, "\x1f", 4)
		if len(parts) != 4 {
			continue
		}
		commits = append(commits, Commit{
			Hash:    parts[0],
			Author:  parts[1],
			Message: parts[2],
			Date:    parts[3],
		})
	}
	return commits, nil
}

type TreeEntry struct {
	Mode string `json:"mode"`
	Type string `json:"type"`
	Hash string `json:"hash"`
	Name string `json:"name"`
}

func TreeLS(repoPath, ref, subPath string) ([]TreeEntry, error) {
	// Short-circuit for repos with no commits yet.
	if IsEmpty(repoPath) {
		return nil, nil
	}
	treeRef := ref
	if subPath != "" {
		treeRef = ref + ":" + subPath
	}
	out, err := run(repoPath, "ls-tree", treeRef)
	if err != nil {
		return nil, err
	}

	var entries []TreeEntry
	for _, line := range strings.Split(strings.TrimSpace(string(out)), "\n") {
		if line == "" {
			continue
		}
		// format: <mode> SP <type> SP <hash> TAB <name>
		tabIdx := strings.Index(line, "\t")
		if tabIdx < 0 {
			continue
		}
		name := line[tabIdx+1:]
		fields := strings.Fields(line[:tabIdx])
		if len(fields) != 3 {
			continue
		}
		entries = append(entries, TreeEntry{
			Mode: fields[0],
			Type: fields[1],
			Hash: fields[2],
			Name: name,
		})
	}
	return entries, nil
}

type Branch struct {
	Name string `json:"name"`
}

func Branches(repoPath string) ([]Branch, error) {
	if IsEmpty(repoPath) {
		return nil, nil
	}
	out, err := run(repoPath, "branch", "--format=%(refname:short)")
	if err != nil {
		return nil, err
	}
	var branches []Branch
	for _, line := range strings.Split(strings.TrimSpace(string(out)), "\n") {
		if line != "" {
			branches = append(branches, Branch{Name: line})
		}
	}
	return branches, nil
}

func BlobCat(repoPath, ref, filePath string) ([]byte, error) {
	return run(repoPath, "show", ref+":"+filePath)
}

// FileDiff represents a single changed file in a diff.
type FileDiff struct {
	Path      string `json:"path"`
	OldPath   string `json:"oldPath,omitempty"` // set on renames
	Additions int    `json:"additions"`
	Deletions int    `json:"deletions"`
	Patch     string `json:"patch"` // unified diff hunk(s) for this file
}

// Diff returns per-file diffs between two refs.
func Diff(repoPath, base, head string) ([]FileDiff, error) {
	out, err := run(repoPath,
		"diff", "--unified=5", "--no-color",
		"--diff-filter=ACDMRT", // exclude untracked
		base+".."+head,
	)
	if err != nil {
		return nil, err
	}
	return parseUnifiedDiff(string(out)), nil
}

// parseUnifiedDiff splits a multi-file unified diff into per-file FileDiff entries.
func parseUnifiedDiff(raw string) []FileDiff {
	var files []FileDiff
	var cur *FileDiff
	var patchLines []string

	commit := func() {
		if cur != nil {
			cur.Patch = strings.Join(patchLines, "\n")
			files = append(files, *cur)
		}
	}

	for _, line := range strings.Split(raw, "\n") {
		if strings.HasPrefix(line, "diff --git ") {
			commit()
			cur = &FileDiff{}
			patchLines = nil
			continue
		}
		if cur == nil {
			continue
		}
		switch {
		case strings.HasPrefix(line, "--- a/"):
			cur.OldPath = strings.TrimPrefix(line, "--- a/")
		case strings.HasPrefix(line, "+++ b/"):
			cur.Path = strings.TrimPrefix(line, "+++ b/")
		case strings.HasPrefix(line, "+") && !strings.HasPrefix(line, "+++"):
			cur.Additions++
			patchLines = append(patchLines, line)
		case strings.HasPrefix(line, "-") && !strings.HasPrefix(line, "---"):
			cur.Deletions++
			patchLines = append(patchLines, line)
		default:
			patchLines = append(patchLines, line)
		}
	}
	commit()
	return files
}