package core

import (
	"errors"
	"fmt"
	"io"
	"io/fs"
	"os"
	"os/exec"
	"path/filepath"
	"sort"
	"strings"

	git "github.com/go-git/go-git/v5"
)

type App struct {
	HomeDir  string
	ReposDir string
	Stdout   io.Writer
	Stderr   io.Writer
	Verbose  bool
	Force    bool
}

func New(stdout io.Writer, stderr io.Writer) (*App, error) {
	home, err := os.UserHomeDir()
	if err != nil {
		return nil, fmt.Errorf("resolve home directory: %w", err)
	}

	return &App{
		HomeDir:  home,
		ReposDir: filepath.Join(home, ".homesick", "repos"),
		Stdout:   stdout,
		Stderr:   stderr,
	}, nil
}

func (a *App) Version(version string) error {
	_, err := fmt.Fprintln(a.Stdout, version)
	return err
}

func (a *App) ShowPath(castle string) error {
	_, err := fmt.Fprintln(a.Stdout, filepath.Join(a.ReposDir, castle))
	return err
}

func (a *App) Clone(uri string, destination string) error {
	if uri == "" {
		return errors.New("clone requires URI")
	}

	if destination == "" {
		destination = deriveDestination(uri)
	}
	if destination == "" {
		return fmt.Errorf("unable to derive destination from uri %q", uri)
	}

	if err := os.MkdirAll(a.ReposDir, 0o755); err != nil {
		return fmt.Errorf("create repos directory: %w", err)
	}

	destinationPath := filepath.Join(a.ReposDir, destination)

	if fi, err := os.Stat(uri); err == nil && fi.IsDir() {
		if err := os.Symlink(uri, destinationPath); err != nil {
			return fmt.Errorf("symlink local castle: %w", err)
		}
		return nil
	}

	_, err := git.PlainClone(destinationPath, false, &git.CloneOptions{
		URL:               uri,
		RecurseSubmodules: git.DefaultSubmoduleRecursionDepth,
	})
	if err != nil {
		return fmt.Errorf("clone %q into %q failed: %w", uri, destinationPath, err)
	}

	return nil
}

func (a *App) List() error {
	if err := os.MkdirAll(a.ReposDir, 0o755); err != nil {
		return err
	}

	var castles []string
	err := filepath.WalkDir(a.ReposDir, func(path string, d fs.DirEntry, walkErr error) error {
		if walkErr != nil {
			return walkErr
		}
		if !d.IsDir() || d.Name() != ".git" {
			return nil
		}

		castleRoot := filepath.Dir(path)
		rel, err := filepath.Rel(a.ReposDir, castleRoot)
		if err != nil {
			return err
		}
		castles = append(castles, rel)
		return filepath.SkipDir
	})
	if err != nil {
		return err
	}

	sort.Strings(castles)
	for _, castle := range castles {
		castleRoot := filepath.Join(a.ReposDir, castle)
		remote, remoteErr := gitOutput(castleRoot, "config", "remote.origin.url")
		if remoteErr != nil {
			remote = ""
		}
		_, writeErr := fmt.Fprintf(a.Stdout, "%s %s\n", castle, strings.TrimSpace(remote))
		if writeErr != nil {
			return writeErr
		}
	}

	return nil
}

func (a *App) Status(castle string) error {
	return runGitWithIO(filepath.Join(a.ReposDir, castle), a.Stdout, a.Stderr, "status")
}

func (a *App) Diff(castle string) error {
	return runGitWithIO(filepath.Join(a.ReposDir, castle), a.Stdout, a.Stderr, "diff")
}

func (a *App) Pull(castle string) error {
	if strings.TrimSpace(castle) == "" {
		castle = "dotfiles"
	}
	return runGitWithIO(filepath.Join(a.ReposDir, castle), a.Stdout, a.Stderr, "pull")
}

func (a *App) Push(castle string) error {
	if strings.TrimSpace(castle) == "" {
		castle = "dotfiles"
	}
	return runGitWithIO(filepath.Join(a.ReposDir, castle), a.Stdout, a.Stderr, "push")
}

func (a *App) Commit(castle string, message string) error {
	if strings.TrimSpace(castle) == "" {
		castle = "dotfiles"
	}

	trimmedMessage := strings.TrimSpace(message)
	if trimmedMessage == "" {
		return errors.New("commit requires message")
	}

	castledir := filepath.Join(a.ReposDir, castle)
	if err := runGitWithIO(castledir, a.Stdout, a.Stderr, "add", "--all"); err != nil {
		return err
	}

	return runGitWithIO(castledir, a.Stdout, a.Stderr, "commit", "-m", trimmedMessage)
}

func (a *App) Destroy(castle string) error {
	if strings.TrimSpace(castle) == "" {
		castle = "dotfiles"
	}

	castleRoot := filepath.Join(a.ReposDir, castle)
	castleInfo, err := os.Lstat(castleRoot)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return fmt.Errorf("castle %q not found", castle)
		}
		return err
	}

	// Only attempt unlinking managed home files for regular castle directories.
	if castleInfo.Mode()&os.ModeSymlink == 0 {
		castleHome := filepath.Join(castleRoot, "home")
		if info, statErr := os.Stat(castleHome); statErr == nil && info.IsDir() {
			if unlinkErr := a.UnlinkCastle(castle); unlinkErr != nil {
				return unlinkErr
			}
		}
	}

	return os.RemoveAll(castleRoot)
}

func (a *App) Open(castle string) error {
	if strings.TrimSpace(castle) == "" {
		castle = "dotfiles"
	}

	editor := strings.TrimSpace(os.Getenv("EDITOR"))
	if editor == "" {
		return errors.New("the $EDITOR environment variable must be set to use this command")
	}

	castleHome := filepath.Join(a.ReposDir, castle, "home")
	if info, err := os.Stat(castleHome); err != nil || !info.IsDir() {
		return fmt.Errorf("could not open %s, expected %s to exist and contain dotfiles", castle, castleHome)
	}

	castleRoot := filepath.Join(a.ReposDir, castle)
	cmd := exec.Command("sh", "-c", editor+" .")
	cmd.Dir = castleRoot
	cmd.Stdout = a.Stdout
	cmd.Stderr = a.Stderr
	if err := cmd.Run(); err != nil {
		return fmt.Errorf("open failed: %w", err)
	}

	return nil
}

func (a *App) Exec(castle string, command []string) error {
	commandString := strings.TrimSpace(strings.Join(command, " "))
	if commandString == "" {
		return errors.New("exec requires COMMAND")
	}

	castleRoot := filepath.Join(a.ReposDir, castle)
	if _, err := os.Stat(castleRoot); err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return fmt.Errorf("castle %q not found", castle)
		}
		return err
	}

	cmd := exec.Command("sh", "-c", commandString)
	cmd.Dir = castleRoot
	cmd.Stdout = a.Stdout
	cmd.Stderr = a.Stderr
	if err := cmd.Run(); err != nil {
		return fmt.Errorf("exec failed: %w", err)
	}

	return nil
}

func (a *App) ExecAll(command []string) error {
	commandString := strings.TrimSpace(strings.Join(command, " "))
	if commandString == "" {
		return errors.New("exec_all requires COMMAND")
	}

	if _, err := os.Stat(a.ReposDir); err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil
		}
		return err
	}

	var castles []string
	err := filepath.WalkDir(a.ReposDir, func(path string, d fs.DirEntry, walkErr error) error {
		if walkErr != nil {
			return walkErr
		}
		if !d.IsDir() || d.Name() != ".git" {
			return nil
		}

		castleRoot := filepath.Dir(path)
		rel, err := filepath.Rel(a.ReposDir, castleRoot)
		if err != nil {
			return err
		}
		castles = append(castles, rel)
		return filepath.SkipDir
	})
	if err != nil {
		return err
	}

	sort.Strings(castles)
	for _, castle := range castles {
		if err := a.Exec(castle, []string{commandString}); err != nil {
			return fmt.Errorf("exec_all failed for %q: %w", castle, err)
		}
	}

	return nil
}

func (a *App) Generate(castlePath string) error {
	trimmed := strings.TrimSpace(castlePath)
	if trimmed == "" {
		return errors.New("generate requires PATH")
	}

	absCastle, err := filepath.Abs(trimmed)
	if err != nil {
		return err
	}

	if err := os.MkdirAll(absCastle, 0o755); err != nil {
		return err
	}

	if err := runGitWithIO(absCastle, a.Stdout, a.Stderr, "init"); err != nil {
		return err
	}

	githubUser := ""
	if out, cfgErr := gitOutput(absCastle, "config", "github.user"); cfgErr == nil {
		githubUser = strings.TrimSpace(out)
	}

	if githubUser != "" {
		repoName := filepath.Base(absCastle)
		url := fmt.Sprintf("git@github.com:%s/%s.git", githubUser, repoName)
		if err := runGitWithIO(absCastle, a.Stdout, a.Stderr, "remote", "add", "origin", url); err != nil {
			return err
		}
	}

	return os.MkdirAll(filepath.Join(absCastle, "home"), 0o755)
}

func (a *App) Link(castle string) error {
	if strings.TrimSpace(castle) == "" {
		castle = "dotfiles"
	}
	return a.LinkCastle(castle)
}

func (a *App) LinkCastle(castle string) error {
	castleHome := filepath.Join(a.ReposDir, castle, "home")
	info, err := os.Stat(castleHome)
	if err != nil || !info.IsDir() {
		return fmt.Errorf("could not symlink %s, expected %s to exist and contain dotfiles", castle, castleHome)
	}

	subdirs, err := readSubdirs(filepath.Join(a.ReposDir, castle, ".homesick_subdir"))
	if err != nil {
		return err
	}

	if err := a.linkEach(castleHome, castleHome, subdirs); err != nil {
		return err
	}

	for _, subdir := range subdirs {
		base := filepath.Join(castleHome, subdir)
		if _, err := os.Stat(base); err != nil {
			if errors.Is(err, os.ErrNotExist) {
				continue
			}
			return err
		}

		if err := a.linkEach(castleHome, base, subdirs); err != nil {
			return err
		}
	}

	return nil
}

func (a *App) Unlink(castle string) error {
	if strings.TrimSpace(castle) == "" {
		castle = "dotfiles"
	}
	return a.UnlinkCastle(castle)
}

func (a *App) UnlinkCastle(castle string) error {
	castleHome := filepath.Join(a.ReposDir, castle, "home")
	info, err := os.Stat(castleHome)
	if err != nil || !info.IsDir() {
		return fmt.Errorf("could not symlink %s, expected %s to exist and contain dotfiles", castle, castleHome)
	}

	subdirs, err := readSubdirs(filepath.Join(a.ReposDir, castle, ".homesick_subdir"))
	if err != nil {
		return err
	}

	if err := a.unlinkEach(castleHome, castleHome, subdirs); err != nil {
		return err
	}

	for _, subdir := range subdirs {
		base := filepath.Join(castleHome, subdir)
		if _, err := os.Stat(base); err != nil {
			if errors.Is(err, os.ErrNotExist) {
				continue
			}
			return err
		}

		if err := a.unlinkEach(castleHome, base, subdirs); err != nil {
			return err
		}
	}

	return nil
}

func (a *App) Track(filePath string, castle string) error {
	return a.TrackPath(filePath, castle)
}

func (a *App) TrackPath(filePath string, castle string) error {
	if strings.TrimSpace(castle) == "" {
		castle = "dotfiles"
	}

	trimmedFile := strings.TrimSpace(filePath)
	if trimmedFile == "" {
		return errors.New("track requires FILE")
	}

	castleRoot := filepath.Join(a.ReposDir, castle)
	castleHome := filepath.Join(castleRoot, "home")
	info, err := os.Stat(castleHome)
	if err != nil || !info.IsDir() {
		return fmt.Errorf("could not track %s, expected %s to exist and contain dotfiles", castle, castleHome)
	}

	absolutePath, err := filepath.Abs(strings.TrimRight(trimmedFile, string(filepath.Separator)))
	if err != nil {
		return err
	}
	if _, err := os.Lstat(absolutePath); err != nil {
		return err
	}

	relativeDir, err := filepath.Rel(a.HomeDir, filepath.Dir(absolutePath))
	if err != nil {
		return err
	}
	if relativeDir == ".." || strings.HasPrefix(relativeDir, ".."+string(filepath.Separator)) {
		return fmt.Errorf("track requires file under %s", a.HomeDir)
	}

	castleTargetDir := filepath.Join(castleHome, relativeDir)
	if relativeDir == "." {
		castleTargetDir = castleHome
	}
	if err := os.MkdirAll(castleTargetDir, 0o755); err != nil {
		return err
	}

	trackedPath := filepath.Join(castleTargetDir, filepath.Base(absolutePath))
	if _, err := os.Lstat(trackedPath); err == nil {
		return fmt.Errorf("%s already exists", trackedPath)
	} else if !errors.Is(err, os.ErrNotExist) {
		return err
	}

	if err := os.Rename(absolutePath, trackedPath); err != nil {
		return err
	}

	subdirChanged := false
	if relativeDir != "." {
		subdirPath := filepath.Join(castleRoot, ".homesick_subdir")
		subdirChanged, err = appendUniqueSubdir(subdirPath, relativeDir)
		if err != nil {
			return err
		}
	}

	if err := a.linkPath(trackedPath, absolutePath); err != nil {
		return err
	}

	repo, err := git.PlainOpen(castleRoot)
	if err != nil {
		return err
	}
	worktree, err := repo.Worktree()
	if err != nil {
		return err
	}

	trackedRelativePath := filepath.Join("home", relativeDir, filepath.Base(absolutePath))
	if relativeDir == "." {
		trackedRelativePath = filepath.Join("home", filepath.Base(absolutePath))
	}
	if _, err := worktree.Add(filepath.ToSlash(filepath.Clean(trackedRelativePath))); err != nil {
		return err
	}

	if subdirChanged {
		if _, err := worktree.Add(".homesick_subdir"); err != nil {
			return err
		}
	}

	return nil
}

func appendUniqueSubdir(path string, subdir string) (bool, error) {
	existing, err := readSubdirs(path)
	if err != nil {
		return false, err
	}

	cleanSubdir := filepath.Clean(subdir)
	for _, line := range existing {
		if filepath.Clean(line) == cleanSubdir {
			return false, nil
		}
	}

	file, err := os.OpenFile(path, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o644)
	if err != nil {
		return false, err
	}
	defer file.Close()

	if _, err := file.WriteString(cleanSubdir + "\n"); err != nil {
		return false, err
	}

	return true, nil
}

func (a *App) linkEach(castleHome string, baseDir string, subdirs []string) error {
	entries, err := os.ReadDir(baseDir)
	if err != nil {
		return err
	}

	for _, entry := range entries {
		name := entry.Name()
		if name == "." || name == ".." {
			continue
		}

		source := filepath.Join(baseDir, name)
		ignore, err := matchesIgnoredDir(castleHome, source, subdirs)
		if err != nil {
			return err
		}
		if ignore {
			continue
		}

		relDir, err := filepath.Rel(castleHome, baseDir)
		if err != nil {
			return err
		}

		destination := filepath.Join(a.HomeDir, relDir, name)
		if relDir == "." {
			destination = filepath.Join(a.HomeDir, name)
		}

		if err := a.linkPath(source, destination); err != nil {
			return err
		}
	}

	return nil
}

func (a *App) unlinkEach(castleHome string, baseDir string, subdirs []string) error {
	entries, err := os.ReadDir(baseDir)
	if err != nil {
		return err
	}

	for _, entry := range entries {
		name := entry.Name()
		if name == "." || name == ".." {
			continue
		}

		source := filepath.Join(baseDir, name)
		ignore, err := matchesIgnoredDir(castleHome, source, subdirs)
		if err != nil {
			return err
		}
		if ignore {
			continue
		}

		relDir, err := filepath.Rel(castleHome, baseDir)
		if err != nil {
			return err
		}

		destination := filepath.Join(a.HomeDir, relDir, name)
		if relDir == "." {
			destination = filepath.Join(a.HomeDir, name)
		}

		if err := unlinkPath(destination); err != nil {
			return err
		}
	}

	return nil
}

func unlinkPath(destination string) error {
	info, err := os.Lstat(destination)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil
		}
		return err
	}

	if info.Mode()&os.ModeSymlink == 0 {
		return nil
	}

	return os.Remove(destination)
}

func (a *App) linkPath(source string, destination string) error {
	absSource, err := filepath.Abs(source)
	if err != nil {
		return err
	}

	if err := os.MkdirAll(filepath.Dir(destination), 0o755); err != nil {
		return err
	}

	info, err := os.Lstat(destination)
	if err == nil {
		if info.Mode()&os.ModeSymlink != 0 {
			target, readErr := os.Readlink(destination)
			if readErr == nil && target == absSource {
				return nil
			}
		}

		if !a.Force {
			return fmt.Errorf("%s exists", destination)
		}

		if rmErr := os.RemoveAll(destination); rmErr != nil {
			return rmErr
		}
	} else if !errors.Is(err, os.ErrNotExist) {
		return err
	}

	if err := os.Symlink(absSource, destination); err != nil {
		return err
	}

	return nil
}

func readSubdirs(path string) ([]string, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return []string{}, nil
		}
		return nil, err
	}

	lines := strings.Split(string(data), "\n")
	result := make([]string, 0, len(lines))
	for _, line := range lines {
		trimmed := strings.TrimSpace(line)
		if trimmed == "" {
			continue
		}
		result = append(result, filepath.Clean(trimmed))
	}

	return result, nil
}

func matchesIgnoredDir(castleHome string, candidate string, subdirs []string) (bool, error) {
	absCandidate, err := filepath.Abs(candidate)
	if err != nil {
		return false, err
	}

	ignoreSet := map[string]struct{}{}
	for _, subdir := range subdirs {
		clean := filepath.Clean(subdir)
		for clean != "." && clean != string(filepath.Separator) {
			ignoreSet[filepath.Join(castleHome, clean)] = struct{}{}
			next := filepath.Dir(clean)
			if next == clean {
				break
			}
			clean = next
		}
	}

	_, ok := ignoreSet[absCandidate]
	return ok, nil
}

func runGitWithIO(dir string, stdout io.Writer, stderr io.Writer, args ...string) error {
	cmd := exec.Command("git", args...)
	cmd.Dir = dir
	cmd.Stdout = stdout
	cmd.Stderr = stderr
	if err := cmd.Run(); err != nil {
		return fmt.Errorf("git %s failed: %w", strings.Join(args, " "), err)
	}
	return nil
}

func gitOutput(dir string, args ...string) (string, error) {
	cmd := exec.Command("git", args...)
	cmd.Dir = dir
	out, err := cmd.Output()
	if err != nil {
		return "", err
	}
	return string(out), nil
}

// Rc runs the rc hooks for the given castle. It looks for executable files
// inside <castle>/.homesick.d and runs them in sorted (lexicographic) order
// with the castle root as the working directory, forwarding stdout and stderr
// to the App writers.
//
// If a .homesickrc file exists in the castle root and no parity.rb wrapper
// already exists in .homesick.d, a Ruby wrapper script named parity.rb is
// written there before execution so that it sorts first.
func (a *App) Rc(castle string) error {
	castleRoot := filepath.Join(a.ReposDir, castle)
	if _, err := os.Stat(castleRoot); err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return fmt.Errorf("castle %q not found", castle)
		}
		return err
	}

	homesickD := filepath.Join(castleRoot, ".homesick.d")
	homesickRc := filepath.Join(castleRoot, ".homesickrc")

	// If .homesickrc exists, ensure .homesick.d/parity.rb wrapper is created
	// (but do not overwrite an existing parity.rb).
	if _, err := os.Stat(homesickRc); err == nil {
		wrapperPath := filepath.Join(homesickD, "parity.rb")
		if _, err := os.Stat(wrapperPath); errors.Is(err, os.ErrNotExist) {
			if mkErr := os.MkdirAll(homesickD, 0o755); mkErr != nil {
				return fmt.Errorf("create .homesick.d: %w", mkErr)
			}
			wrapperContent := "#!/usr/bin/env ruby\n" +
				"# parity.rb — generated wrapper for legacy .homesickrc\n" +
				"# Evaluates .homesickrc in the context of the castle root.\n" +
				"rc_file = File.join(__dir__, '..', '.homesickrc')\n" +
				"eval(File.read(rc_file), binding, rc_file) if File.exist?(rc_file)\n"
			if writeErr := os.WriteFile(wrapperPath, []byte(wrapperContent), 0o755); writeErr != nil {
				return fmt.Errorf("write parity.rb: %w", writeErr)
			}
		}
	}

	if _, err := os.Stat(homesickD); err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil
		}
		return err
	}

	entries, err := os.ReadDir(homesickD)
	if err != nil {
		return err
	}

	// ReadDir returns entries in sorted order already.
	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		info, infoErr := entry.Info()
		if infoErr != nil {
			return infoErr
		}
		if info.Mode()&0o111 == 0 {
			// Not executable — skip.
			continue
		}
		scriptPath := filepath.Join(homesickD, entry.Name())
		cmd := exec.Command(scriptPath)
		cmd.Dir = castleRoot
		cmd.Stdout = a.Stdout
		cmd.Stderr = a.Stderr
		if runErr := cmd.Run(); runErr != nil {
			return fmt.Errorf("rc script %q failed: %w", entry.Name(), runErr)
		}
	}
	return nil
}

func deriveDestination(uri string) string {
	candidate := strings.TrimSpace(uri)
	candidate = strings.TrimPrefix(candidate, "https://github.com/")
	candidate = strings.TrimPrefix(candidate, "http://github.com/")
	candidate = strings.TrimPrefix(candidate, "git://github.com/")

	candidate = strings.TrimPrefix(candidate, "file://")

	candidate = strings.TrimSuffix(candidate, ".git")
	candidate = strings.TrimSuffix(candidate, "/")
	if candidate == "" {
		return ""
	}

	parts := strings.Split(candidate, "/")
	last := parts[len(parts)-1]
	if strings.Contains(last, ":") {
		a := strings.Split(last, ":")
		last = a[len(a)-1]
	}
	return last
}