package main

import (
	"compress/gzip"
	"context"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"
)

const (
	playlistFilename = "playlist.m3u"
	epgFilename      = "epg.xml.gz"
)

type RefreshConfig struct {
	TargetURL         string
	PublicURL         string // base URL of this relay; "/epg" appended for url-tvg rewrite
	EPGURLs           []string
	PreferPlaylistEPG bool
	CacheDir          string
	Interval          time.Duration
}

func (c RefreshConfig) epgEnabled() bool {
	return len(c.EPGURLs) > 0 || c.PreferPlaylistEPG
}

// Refresher periodically refreshes the cached playlist and EPG. HTTP handlers
// read the cached files; the worker runs single-threaded and writes them
// atomically via os.Rename, so no synchronization is needed between the two.
type Refresher struct {
	cfg    RefreshConfig
	client *http.Client

	readyCh chan struct{}
	once    sync.Once
}

func NewRefresher(cfg RefreshConfig, client *http.Client) *Refresher {
	return &Refresher{
		cfg:     cfg,
		client:  client,
		readyCh: make(chan struct{}),
	}
}

// Run blocks until ctx is cancelled. It performs an immediate refresh on entry
// (so the cache is warm as quickly as possible), then ticks at cfg.Interval.
func (r *Refresher) Run(ctx context.Context) {
	if err := r.refresh(ctx); err != nil {
		slog.Warn("initial refresh failed", "err", err)
	} else {
		r.markReady()
	}

	t := time.NewTicker(r.cfg.Interval)
	defer t.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-t.C:
			if err := r.refresh(ctx); err != nil {
				slog.Warn("refresh failed", "err", err)
				continue
			}
			r.markReady()
		}
	}
}

// Ready reports whether at least one refresh has succeeded. Handlers use this
// to return 503 cleanly during the warm-up window.
func (r *Refresher) Ready() bool {
	select {
	case <-r.readyCh:
		return true
	default:
		return false
	}
}

func (r *Refresher) markReady() {
	r.once.Do(func() { close(r.readyCh) })
}

func (r *Refresher) refresh(ctx context.Context) error {
	if err := os.MkdirAll(r.cfg.CacheDir, 0o755); err != nil {
		return fmt.Errorf("cache dir: %w", err)
	}

	var epgPublicURL string
	if r.cfg.epgEnabled() {
		epgPublicURL = strings.TrimRight(r.cfg.PublicURL, "/") + "/epg"
	}

	tvgIDs, playlistEPG, err := r.refreshPlaylist(ctx, epgPublicURL)
	if err != nil {
		return fmt.Errorf("playlist: %w", err)
	}
	slog.Info("playlist refreshed",
		"tvg_ids", len(tvgIDs),
		"playlist_has_epg", playlistEPG != "",
	)

	if !r.cfg.epgEnabled() {
		return nil
	}

	epgURLs := r.cfg.EPGURLs
	if r.cfg.PreferPlaylistEPG && playlistEPG != "" {
		epgURLs = []string{playlistEPG}
	}
	if len(epgURLs) == 0 {
		slog.Warn("EPG enabled but no usable source URLs",
			"prefer_playlist_epg", r.cfg.PreferPlaylistEPG,
			"configured_urls", len(r.cfg.EPGURLs),
		)
		return nil
	}

	sourcePaths, err := r.fetchEPGSources(ctx, epgURLs)
	defer func() {
		for _, p := range sourcePaths {
			_ = os.Remove(p)
		}
	}()
	if err != nil {
		return err
	}

	return r.persistMergedEPG(sourcePaths, buildIDMap(tvgIDs))
}

func (r *Refresher) refreshPlaylist(ctx context.Context, epgURL string) (tvgIDs []string, playlistEPG string, err error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, r.cfg.TargetURL, nil)
	if err != nil {
		return nil, "", err
	}
	resp, err := r.client.Do(req)
	if err != nil {
		return nil, "", err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, "", fmt.Errorf("upstream status %s", resp.Status)
	}

	tmp := filepath.Join(r.cfg.CacheDir, playlistFilename+".tmp")
	f, err := os.Create(tmp)
	if err != nil {
		return nil, "", err
	}
	cleanup := func() {
		_ = f.Close()
		_ = os.Remove(tmp)
	}

	tvgIDs, playlistEPG, err = processPlaylist(resp.Body, f, epgURL)
	if err != nil {
		cleanup()
		return nil, "", err
	}
	if err := f.Sync(); err != nil {
		cleanup()
		return nil, "", err
	}
	if err := f.Close(); err != nil {
		_ = os.Remove(tmp)
		return nil, "", err
	}
	if err := os.Rename(tmp, filepath.Join(r.cfg.CacheDir, playlistFilename)); err != nil {
		_ = os.Remove(tmp)
		return nil, "", err
	}
	return tvgIDs, playlistEPG, nil
}

func (r *Refresher) fetchEPGSources(ctx context.Context, urls []string) (paths []string, err error) {
	for i, url := range urls {
		path := filepath.Join(r.cfg.CacheDir, fmt.Sprintf("epg-src-%d.xml.tmp", i))
		if ferr := fetchEPGSource(ctx, r.client, url, path); ferr != nil {
			slog.Warn("epg source fetch failed", "url", url, "err", ferr)
			_ = os.Remove(path)
			continue
		}
		paths = append(paths, path)
	}
	if len(paths) == 0 {
		return nil, errors.New("no EPG sources fetched successfully")
	}
	return paths, nil
}

func (r *Refresher) persistMergedEPG(sourcePaths []string, idMap map[string]string) error {
	sources := make([]io.ReadSeeker, 0, len(sourcePaths))
	closers := make([]io.Closer, 0, len(sourcePaths))
	defer func() {
		for _, c := range closers {
			_ = c.Close()
		}
	}()
	for _, p := range sourcePaths {
		f, err := os.Open(p)
		if err != nil {
			return err
		}
		sources = append(sources, f)
		closers = append(closers, f)
	}

	tmp := filepath.Join(r.cfg.CacheDir, epgFilename+".tmp")
	f, err := os.Create(tmp)
	if err != nil {
		return err
	}
	cleanup := func() {
		_ = f.Close()
		_ = os.Remove(tmp)
	}

	gw := gzip.NewWriter(f)
	if mergeErr := mergeEPG(sources, idMap, gw); mergeErr != nil {
		_ = gw.Close()
		cleanup()
		return mergeErr
	}
	if err := gw.Close(); err != nil {
		cleanup()
		return err
	}
	if err := f.Sync(); err != nil {
		cleanup()
		return err
	}
	if err := f.Close(); err != nil {
		_ = os.Remove(tmp)
		return err
	}
	return os.Rename(tmp, filepath.Join(r.cfg.CacheDir, epgFilename))
}