package main

import (
	"fmt"
	"net/url"
	"os"
	"os/signal"
	"path/filepath"
	"strings"
	"syscall"
	"time"

	"rssd/config"
	"rssd/downloader"
	"rssd/poller"
	"rssd/state"
)

const (
	stateFile = "state.json"
)

func main() {
	fmt.Fprintf(os.Stderr, "rssd: starting\n")

	// Load configuration.
	cfgPath := os.Getenv("RSSD_CONFIG")
	if cfgPath == "" {
		cfgPath = "~/.config/rssd/config.yaml"
	}
	cfgPath = config.ExpandPath(cfgPath) // resolve ~ early for consistent path usage
	cfg, err := config.Load(cfgPath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "rssd: fatal: %v\n", err)
		os.Exit(1)
	}

	// Load state — store alongside the config file.
	stateDir := filepath.Dir(cfgPath)
	sm, err := state.NewManager(filepath.Join(stateDir, stateFile))
	if err != nil {
		fmt.Fprintf(os.Stderr, "rssd: fatal: %v\n", err)
		os.Exit(1)
	}
	if err := sm.Load(); err != nil {
		fmt.Fprintf(os.Stderr, "rssd: warning: could not load state (%v), starting fresh\n", err)
	}

	// Start download worker pool.
	jobs := make(chan downloader.DownloadJob)
	pool := downloader.NewPool(cfg.Settings.DownloadPoolSize, cfg.Settings.BackoffBase, sm)
	go pool.Run(jobs)

	// Re-enqueue any "pending" jobs from a previous run that were never picked up by workers.
	sm.ForEachJob(func(j *state.JobSnapshot) {
		if j.Status == state.StatusPending {
			fmt.Fprintf(os.Stderr, "rssd: re-enqueued pending job %s\n", j.EnclosureURL)
			jobs <- downloader.DownloadJob{
				FeedURL:      j.FeedURL,
				EnclosureURL: j.EnclosureURL,
				DestPath:     j.DestPath,
			}
		}
	})

	fmt.Fprintf(os.Stderr, "rssd: workers started, polling feeds\n")
	sigCh := make(chan os.Signal, 1)
	signal.Notify(sigCh, syscall.SIGTERM, syscall.SIGINT)

	fmt.Fprintf(os.Stderr, "rssd: %d feeds configured, polling started\n", len(cfg.Feeds))

	// Launch a poller goroutine per feed.
	for _, feed := range cfg.Feeds {
		go pollFeed(feed, sm, jobs, cfg)
	}

	// Periodically dispatch retrying jobs whose backoff has elapsed.
	retryTicker := time.NewTicker(1 * time.Minute)
	defer retryTicker.Stop()
	go func() {
		for range retryTicker.C {
			dispatchRetries(sm, jobs, cfg.Settings.MaxRetries)
		}
	}()

	// Wait for shutdown signal.
	sig := <-sigCh
	fmt.Fprintf(os.Stderr, "rssd: received %v, shutting down...\n", sig)

	// Close jobs channel to stop accepting new work. Workers will finish in-flight downloads
	// but we don't wait — just exit and let the next run handle any remaining state.
	close(jobs)

	// Save final state before exiting so no progress is lost.
	if err := sm.Save(); err != nil {
		fmt.Fprintf(os.Stderr, "rssd: error saving final state: %v\n", err)
	}
	fmt.Fprintf(os.Stderr, "rssd: stopped\n")
}

func pollFeed(feed config.Feed, sm *state.Manager, jobs chan<- downloader.DownloadJob, cfg *config.Config) {
	fetcher := poller.NewFetcher()
	interval := cfg.PollIntervalFor(feed)

	fmt.Fprintf(os.Stderr, "rssd: polling %s every %s\n", feed.URL, interval)

	// Poll immediately on startup.
	pollAndEnqueue(feed, sm, jobs, fetcher, cfg)

	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	for range ticker.C {
		pollAndEnqueue(feed, sm, jobs, fetcher, cfg)
	}
}

func pollAndEnqueue(feed config.Feed, sm *state.Manager, jobs chan<- downloader.DownloadJob, fetcher *poller.Fetcher, cfg *config.Config) {
	feedState := sm.FindFeedByURL(feed.URL)
	var lastModified, etag string
	if feedState != nil {
		lastModified = feedState.LastModified
		etag = feedState.ETag
	}

	result, err := fetcher.Poll(feed.URL, lastModified, etag)
	if err != nil {
		fmt.Fprintf(os.Stderr, "rssd: error polling %s: %v\n", feed.URL, err)
		return
	}
	if result.NotModified {
		fmt.Fprintf(os.Stderr, "rssd: %s unchanged (skipping)\n", feed.URL)
		return
	}

	fmt.Fprintf(os.Stderr, "rssd: %s polled — %d enclosures found\n", feed.URL, len(result.NewEnclosures))

	if len(result.NewEnclosures) == 0 {
		fmt.Fprintf(os.Stderr, "rssd: warning: %s has no enclosures in latest items\n", feed.URL)
	}

	// Save updated feed metadata for next conditional request.
	sm.UpsertFeed(feed.URL, result.LastModified, result.ETag)

	// Enqueue new enclosures (filtered by start_date).
	startDate := feed.PublishedAt()
	for _, encInfo := range result.NewEnclosures {
		// Skip items older than the configured start date.
		if !startDate.IsZero() && (!encInfo.PublishedAt.IsZero() && encInfo.PublishedAt.Before(startDate)) {
			fmt.Fprintf(os.Stderr, "rssd: skipping %s (published %s, before start_date %s)\n",
				encInfo.URL,
				encInfo.PublishedAt.Format("2006-01-02"),
				feed.StartDate)
			continue
		}

		destPath := computeDestPath(feed.OutputDir, encInfo)
		if sm.AddJob(feed.URL, encInfo.URL, destPath, cfg.Settings.MaxRetries) {
			fmt.Fprintf(os.Stderr, "rssd: enqueued %s -> %s\n", encInfo.URL, destPath)
			jobs <- downloader.DownloadJob{
				FeedURL:      feed.URL,
				EnclosureURL: encInfo.URL,
				DestPath:     destPath,
			}
		} else {
			job := sm.FindJobByURL(encInfo.URL)
			if job != nil {
				fmt.Fprintf(os.Stderr, "rssd: skipping %s (already %s)\n", encInfo.URL, job.Status)
			} else {
				fmt.Fprintf(os.Stderr, "rssd: skipping duplicate %s\n", encInfo.URL)
			}
		}
	}

	if err := sm.Save(); err != nil {
		fmt.Fprintf(os.Stderr, "rssd: error saving state: %v\n", err)
	}
}

// dispatchRetries scans all jobs in state and re-enqueues those whose backoff has elapsed.
func dispatchRetries(sm *state.Manager, jobs chan<- downloader.DownloadJob, maxRetries int) {
	// Collect snapshots (lock released before any callback invocation).
	var ready []downloader.DownloadJob
	var failed []string

	sm.ForEachJob(func(snap *state.JobSnapshot) {
		if snap.Status != state.StatusRetrying {
			return
		}

		if snap.AttemptCount >= maxRetries {
			// Permanently failed — use UpdateJob to mutate the live state.
			sm.UpdateJob(snap.EnclosureURL, func(j *state.Job) {
				j.Status = state.StatusFailed
			})
			failed = append(failed, fmt.Sprintf("%s (after %d attempts: %s)",
				snap.EnclosureURL, snap.AttemptCount, snap.Error))
			return
		}

		if snap.NextAttemptAt == nil || time.Now().After(*snap.NextAttemptAt) {
			// Re-enqueue — use UpdateJob to mutate the live state.
			sm.UpdateJob(snap.EnclosureURL, func(j *state.Job) {
				j.Status = state.StatusPending
				j.NextAttemptAt = nil
			})
			ready = append(ready, downloader.DownloadJob{
				FeedURL:      snap.FeedURL,
				EnclosureURL: snap.EnclosureURL,
				DestPath:     snap.DestPath,
			})
		}
	})

	if len(failed) > 0 {
		for _, msg := range failed {
			fmt.Fprintf(os.Stderr, "rssd: %s permanently failed\n", msg)
		}
	}

	// Send to channel and persist state (lock released).
	for _, job := range ready {
		jobs <- job
	}

	if err := sm.Save(); err != nil {
		fmt.Fprintf(os.Stderr, "rssd: error saving state (retry dispatch): %v\n", err)
	}
}

// sanitizeFilename replaces characters that are invalid or problematic in filenames.
func sanitizeFilename(s string) string {
	replacer := strings.NewReplacer(
		"/", "_", "\\", "_", ":", "_", "<", "_", ">", "_", "|", "_", "\"", "_", "?", "_", "*", "_",
	)
	s = replacer.Replace(s)
	for strings.Contains(s, "__") {
		s = strings.ReplaceAll(s, "__", "_")
	}
	return strings.TrimSpace(s)
}

// computeDestPath constructs the local file path from an enclosure URL and output directory.
// The filename is prefixed with YYYYMMDD - for chronological sorting when dates are available.
func computeDestPath(outputDir string, encInfo poller.EnclosureInfo) string {
	baseName := sanitizeFilename(encInfo.Title)
	if baseName == "" {
		// Fallback to enclosure URL basename if title is empty or invalid.
		parsed, err := url.Parse(encInfo.URL)
		if err != nil || parsed.Path == "" || parsed.Path == "/" {
			return filepath.Join(outputDir, strings.ReplaceAll(encInfo.URL, "/", "_"))
		}
		baseName = sanitizeFilename(filepath.Base(parsed.Path))
		if baseName == "." || baseName == "" {
			baseName = "unknown"
		}
	}

	// Prepend date prefix for chronological sorting if available.
	if !encInfo.PublishedAt.IsZero() {
		datePrefix := encInfo.PublishedAt.Format("2006-01-02")
		return filepath.Join(outputDir, fmt.Sprintf("%s - %s", datePrefix, baseName))
	}

	return filepath.Join(outputDir, baseName)
}