package core

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

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
	}

	if err := runGit(a.ReposDir, "clone", "-q", "--config", "push.default=upstream", "--recursive", uri, destination); err != nil {
		return 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 runGit(filepath.Join(a.ReposDir, castle), "status")
}

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

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(string) error {
	return errors.New("unlink is not implemented in Go yet")
}

func (a *App) Track(string, string) error {
	return errors.New("track is not implemented in Go yet")
}

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) 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 runGit(dir string, args ...string) error {
	cmd := exec.Command("git", args...)
	cmd.Dir = dir
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.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
}

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/")

	if strings.HasPrefix(candidate, "file://") {
		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
}