package main

import (
	"bufio"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"runtime"
	"strings"

	lua "github.com/yuin/gopher-lua"
)

const (
	configFileName = "config.lua"
	filesDirName   = "files"
)

type packageConfig struct {
	targets map[string]string
}

func main() {
	if len(os.Args) < 2 {
		usage()
		os.Exit(1)
	}

	args := os.Args[1:]

	var err error
	switch args[0] {
	case "apply":
		err = applyCmd(args[1:])
	case "add":
		err = addCmd(args[1:])
	case "help", "-h", "--help":
		usage()
		return
	default:
		err = fmt.Errorf("unknown command %q", args[0])
	}

	if err != nil {
		fmt.Fprintln(os.Stderr, "sigil:", err)
		os.Exit(1)
	}
}

func usage() {
	fmt.Println("sigil: minimal dotfile symlink manager")
	fmt.Println("usage:")
	fmt.Println("  sigil apply [--prune]")
	fmt.Println("  sigil add <path>")
}

func applyCmd(args []string) error {
	prune := false
	for _, arg := range args {
		if arg == "--prune" {
			prune = true
			continue
		}
		return fmt.Errorf("unknown flag %q", arg)
	}

	repo, err := repoPath()
	if err != nil {
		return err
	}

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

	var stales []string

	for _, entry := range entries {
		if !entry.IsDir() || strings.HasPrefix(entry.Name(), ".") {
			continue
		}

		pkgDir := filepath.Join(repo, entry.Name())
		configPath := filepath.Join(pkgDir, configFileName)
		if _, err := os.Stat(configPath); err != nil {
			if errors.Is(err, os.ErrNotExist) {
				continue
			}
			return err
		}

		cfg, err := loadConfig(configPath)
		if err != nil {
			return fmt.Errorf("%s: %w", entry.Name(), err)
		}

		targetRoot, err := selectTarget(cfg.targets)
		if err != nil {
			return fmt.Errorf("%s: %w", entry.Name(), err)
		}

		filesDir := filepath.Join(pkgDir, filesDirName)
		if _, err := os.Stat(filesDir); err != nil {
			if errors.Is(err, os.ErrNotExist) {
				continue
			}
			return err
		}

		if err := applyPackage(filesDir, targetRoot); err != nil {
			return fmt.Errorf("%s: %w", entry.Name(), err)
		}

		stale, err := findStaleLinks(filesDir, targetRoot)
		if err != nil {
			return fmt.Errorf("%s: %w", entry.Name(), err)
		}
		stales = append(stales, stale...)
	}

	if len(stales) == 0 {
		return nil
	}

	if prune {
		return removeLinks(stales)
	}

	ok, err := promptYesNo("Found stale links. Prune them?", false)
	if err != nil {
		return err
	}
	if ok {
		return removeLinks(stales)
	}

	return nil
}

func addCmd(args []string) error {
	if len(args) < 1 {
		return errors.New("missing path")
	}

	argPath := args[0]
	if !filepath.IsAbs(argPath) {
		if cwd, err := os.Getwd(); err == nil {
			argPath = filepath.Join(cwd, argPath)
		}
	}

	absPath, err := filepath.Abs(argPath)
	if err != nil {
		return err
	}

	info, err := os.Lstat(absPath)
	if err != nil {
		return err
	}
	if info.Mode()&os.ModeSymlink != 0 {
		return fmt.Errorf("%s is a symlink; refusing to add", absPath)
	}

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

	defaultTarget := absPath
	if !info.IsDir() {
		defaultTarget = filepath.Dir(absPath)
	}

	defaultPkg := filepath.Base(defaultTarget)
	if info.IsDir() {
		defaultPkg = filepath.Base(absPath)
	}

	reader := bufio.NewReader(os.Stdin)
	pkgName := promptWithDefault(reader, "Package name", defaultPkg)
	if pkgName == "" {
		return errors.New("package name cannot be empty")
	}

	targetRootInput := promptWithDefault(reader, "Target path", defaultTarget)
	targetRoot, err := filepath.Abs(expandHome(targetRootInput))
	if err != nil {
		return err
	}

	pkgDir := filepath.Join(repo, pkgName)
	if _, err := os.Stat(pkgDir); err == nil {
		return fmt.Errorf("package %q already exists", pkgName)
	} else if !errors.Is(err, os.ErrNotExist) {
		return err
	}

	filesDir := filepath.Join(pkgDir, filesDirName)
	if err := os.MkdirAll(filesDir, 0o755); err != nil {
		return err
	}

	configPath := filepath.Join(pkgDir, configFileName)
	if err := writeConfig(configPath, targetRoot); err != nil {
		return err
	}

	if info.IsDir() {
		if err := moveDirContents(absPath, filesDir); err != nil {
			return err
		}
	} else {
		rel, err := filepath.Rel(targetRoot, absPath)
		if err != nil {
			return err
		}
		if strings.HasPrefix(rel, "..") {
			return fmt.Errorf("path %s is outside target %s", absPath, targetRoot)
		}

		destPath := filepath.Join(filesDir, rel)
		if err := os.MkdirAll(filepath.Dir(destPath), 0o755); err != nil {
			return err
		}
		if err := os.Rename(absPath, destPath); err != nil {
			return err
		}
	}

	return applyPackage(filesDir, targetRoot)
}

func applyPackage(filesDir, targetRoot string) error {
	if err := ensureDir(targetRoot); err != nil {
		return err
	}

	return filepath.WalkDir(filesDir, func(path string, entry fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if path == filesDir {
			return nil
		}

		rel, err := filepath.Rel(filesDir, path)
		if err != nil {
			return err
		}
		targetPath := filepath.Join(targetRoot, rel)

		if entry.IsDir() {
			return ensureDir(targetPath)
		}

		srcAbs, err := filepath.Abs(path)
		if err != nil {
			return err
		}
		return linkFile(srcAbs, targetPath)
	})
}

func linkFile(src, dst string) error {
	if err := os.MkdirAll(filepath.Dir(dst), 0o755); err != nil {
		return err
	}

	if info, err := os.Lstat(dst); err == nil {
		if info.Mode()&os.ModeSymlink != 0 {
			current, err := os.Readlink(dst)
			if err != nil {
				return err
			}
			if current == src {
				return nil
			}
			return fmt.Errorf("conflict at %s (points to %s)", dst, current)
		}
		return fmt.Errorf("conflict at %s (exists and is not a symlink)", dst)
	} else if !errors.Is(err, os.ErrNotExist) {
		return err
	}

	return os.Symlink(src, dst)
}

func ensureDir(path string) error {
	info, err := os.Lstat(path)
	if err == nil {
		if info.IsDir() {
			return nil
		}
		return fmt.Errorf("%s exists and is not a directory", path)
	}
	if !errors.Is(err, os.ErrNotExist) {
		return err
	}
	return os.MkdirAll(path, 0o755)
}

func loadConfig(path string) (*packageConfig, error) {
	L := lua.NewState()
	defer L.Close()
	L.OpenLibs()

	if err := L.DoFile(path); err != nil {
		return nil, err
	}
	if L.GetTop() == 0 {
		return nil, errors.New("config.lua must return a table")
	}

	value := L.Get(-1)
	tbl, ok := value.(*lua.LTable)
	if !ok {
		return nil, errors.New("config.lua must return a table")
	}

	targetVal := tbl.RawGetString("target")
	targetTbl, ok := targetVal.(*lua.LTable)
	if !ok {
		return nil, errors.New("config.target must be a table")
	}

	targets := make(map[string]string)
	targetTbl.ForEach(func(k, v lua.LValue) {
		ks, ok1 := k.(lua.LString)
		vs, ok2 := v.(lua.LString)
		if ok1 && ok2 {
			targets[string(ks)] = expandHome(string(vs))
		}
	})

	if len(targets) == 0 {
		return nil, errors.New("config.target is empty")
	}

	return &packageConfig{targets: targets}, nil
}

func selectTarget(targets map[string]string) (string, error) {
	osKey := runtime.GOOS
	if osKey == "darwin" {
		osKey = "macos"
	}
	if target, ok := targets[osKey]; ok {
		return expandHome(target), nil
	}
	if target, ok := targets["default"]; ok {
		return expandHome(target), nil
	}
	return "", fmt.Errorf("missing target for %s and default", osKey)
}

func repoPath() (string, error) {
	if override := os.Getenv("SIGIL_REPO"); override != "" {
		return filepath.Abs(expandHome(override))
	}
	return filepath.Abs(expandHome("~/.dotfiles"))
}

func expandHome(path string) string {
	if path == "~" {
		home, err := os.UserHomeDir()
		if err != nil {
			return path
		}
		return home
	}
	if strings.HasPrefix(path, "~/") {
		home, err := os.UserHomeDir()
		if err != nil {
			return path
		}
		return filepath.Join(home, path[2:])
	}
	return path
}

func compressHome(path string) string {
	home, err := os.UserHomeDir()
	if err != nil {
		return path
	}
	clean := filepath.Clean(path)
	homeClean := filepath.Clean(home)
	if clean == homeClean {
		return "~"
	}
	if strings.HasPrefix(clean, homeClean+string(os.PathSeparator)) {
		rel := strings.TrimPrefix(clean, homeClean+string(os.PathSeparator))
		return filepath.Join("~", rel)
	}
	return path
}

func writeConfig(path, targetRoot string) error {
	osKey := "linux"
	if runtime.GOOS == "darwin" {
		osKey = "macos"
	}

	prettyTarget := compressHome(targetRoot)
	content := fmt.Sprintf("return {\n\ttarget = {\n\t\t%s = %q,\n\t\tdefault = %q,\n\t},\n}\n", osKey, prettyTarget, prettyTarget)
	return os.WriteFile(path, []byte(content), 0o644)
}

func promptWithDefault(reader *bufio.Reader, label, def string) string {
	if def != "" {
		fmt.Printf("%s [%s]: ", label, def)
	} else {
		fmt.Printf("%s: ", label)
	}

	text, _ := reader.ReadString('\n')
	text = strings.TrimSpace(text)
	if text == "" {
		return def
	}
	return text
}

func promptYesNo(message string, def bool) (bool, error) {
	reader := bufio.NewReader(os.Stdin)
	defLabel := "y/N"
	if def {
		defLabel = "Y/n"
	}
	fmt.Printf("%s [%s]: ", message, defLabel)
	text, err := reader.ReadString('\n')
	if err != nil {
		return false, err
	}
	text = strings.TrimSpace(strings.ToLower(text))
	if text == "" {
		return def, nil
	}
	return text == "y" || text == "yes", nil
}

func moveDirContents(srcDir, destDir string) error {
	entries, err := os.ReadDir(srcDir)
	if err != nil {
		return err
	}

	for _, entry := range entries {
		srcPath := filepath.Join(srcDir, entry.Name())
		destPath := filepath.Join(destDir, entry.Name())

		if _, err := os.Stat(destPath); err == nil {
			return fmt.Errorf("destination already exists: %s", destPath)
		} else if !errors.Is(err, os.ErrNotExist) {
			return err
		}

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

	return nil
}

func findStaleLinks(filesDir, targetRoot string) ([]string, error) {
	filesAbs, err := filepath.Abs(filesDir)
	if err != nil {
		return nil, err
	}

	var stale []string
	walkErr := filepath.WalkDir(targetRoot, func(path string, entry fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if entry.IsDir() {
			return nil
		}
		info, err := entry.Info()
		if err != nil {
			return err
		}
		if info.Mode()&os.ModeSymlink == 0 {
			return nil
		}

		src, err := os.Readlink(path)
		if err != nil {
			return err
		}
		if !filepath.IsAbs(src) {
			src = filepath.Join(filepath.Dir(path), src)
		}
		src = filepath.Clean(src)

		if !strings.HasPrefix(src, filesAbs+string(os.PathSeparator)) && src != filesAbs {
			return nil
		}

		if _, err := os.Stat(src); errors.Is(err, os.ErrNotExist) {
			stale = append(stale, path)
		}
		return nil
	})

	if walkErr != nil {
		return nil, walkErr
	}

	return stale, nil
}

func removeLinks(paths []string) error {
	for _, path := range paths {
		if err := os.Remove(path); err != nil {
			return err
		}
	}
	return nil
}