// Package killist maintains a persistent list of track titles that should
// be automatically skipped during playback — a direct port of the Delphi
// KillList / KillFile feature.
package killist

import (
	"bufio"
	"os"
	"path/filepath"
	"strings"
	"sync"
)

// KillList is a thread-safe set of track titles to skip.
type KillList struct {
	mu       sync.RWMutex
	titles   map[string]struct{}
	filepath string
}

// Load reads the kill list from disk (creates an empty list if the file
// does not exist yet).
func Load(path string) (*KillList, error) {
	kl := &KillList{
		titles:   make(map[string]struct{}),
		filepath: path,
	}

	f, err := os.Open(path)
	if os.IsNotExist(err) {
		return kl, nil
	}
	if err != nil {
		return nil, err
	}
	defer f.Close()

	sc := bufio.NewScanner(f)
	for sc.Scan() {
		line := strings.TrimSpace(sc.Text())
		if line != "" {
			kl.titles[line] = struct{}{}
		}
	}
	return kl, sc.Err()
}

// Contains reports whether the given title is on the kill list.
func (kl *KillList) Contains(title string) bool {
	kl.mu.RLock()
	defer kl.mu.RUnlock()
	_, ok := kl.titles[title]
	return ok
}

// Add appends a title and persists the list.
func (kl *KillList) Add(title string) error {
	kl.mu.Lock()
	defer kl.mu.Unlock()
	kl.titles[title] = struct{}{}
	return kl.save()
}

// Remove removes a title and persists the list.
func (kl *KillList) Remove(title string) error {
	kl.mu.Lock()
	defer kl.mu.Unlock()
	delete(kl.titles, title)
	return kl.save()
}

// List returns all titles currently on the kill list.
func (kl *KillList) List() []string {
	kl.mu.RLock()
	defer kl.mu.RUnlock()
	out := make([]string, 0, len(kl.titles))
	for t := range kl.titles {
		out = append(out, t)
	}
	return out
}

// save writes the kill list atomically: it writes to a temp file in the same
// directory, flushes, closes, then renames over the target. This ensures the
// existing file is never truncated on a partial write or flush error.
func (kl *KillList) save() error {
	dir := filepath.Dir(kl.filepath)
	tmp, err := os.CreateTemp(dir, ".killist-*.tmp")
	if err != nil {
		return err
	}
	tmpName := tmp.Name()

	w := bufio.NewWriter(tmp)
	for t := range kl.titles {
		if _, err := w.WriteString(t + "\n"); err != nil {
			tmp.Close()
			os.Remove(tmpName)
			return err
		}
	}
	if err := w.Flush(); err != nil {
		tmp.Close()
		os.Remove(tmpName)
		return err
	}
	if err := tmp.Close(); err != nil {
		os.Remove(tmpName)
		return err
	}
	return os.Rename(tmpName, kl.filepath)
}