package scanner

import (
	"context"
	"fmt"
	"maps"
	"slices"
	"sync/atomic"
	"time"

	ppl "github.com/google/go-pipeline/pkg/pipeline"
	"github.com/navidrome/navidrome/consts"
	"github.com/navidrome/navidrome/core/playlists"
	"github.com/navidrome/navidrome/log"
	"github.com/navidrome/navidrome/model"
	"github.com/navidrome/navidrome/utils/run"
	"github.com/navidrome/navidrome/utils/slice"
)

type scannerImpl struct {
	ds  model.DataStore
	pls playlists.Playlists
}

// scanState holds the state of an in-progress scan, to be passed to the various phases
type scanState struct {
	progress          chan<- *ProgressInfo
	fullScan          bool
	changesDetected   atomic.Bool
	libraries         model.Libraries  // Store libraries list for consistency across phases
	targets           map[int][]string // Optional: map[libraryID][]folderPaths for selective scans
	totalLibraryCount int              // Total number of libraries (unfiltered), for cross-library move detection
	failedLibs        map[int]bool     // Libraries that could not be scanned in this run
}

func (s *scanState) sendProgress(info *ProgressInfo) {
	if s.progress != nil {
		s.progress <- info
	}
}

func (s *scanState) isSelectiveScan() bool {
	return len(s.targets) > 0
}

func (s *scanState) sendWarning(msg string) {
	s.sendProgress(&ProgressInfo{Warning: msg})
}

func (s *scanState) markFailed(libID int) {
	if s.failedLibs == nil {
		s.failedLibs = map[int]bool{}
	}
	s.failedLibs[libID] = true
}

func (s *scanState) sendError(err error) {
	s.sendProgress(&ProgressInfo{Error: err.Error()})
}

func (s *scannerImpl) scanFolders(ctx context.Context, fullScan bool, targets []model.ScanTarget, progress chan<- *ProgressInfo) {
	startTime := time.Now()

	state := scanState{
		progress:        progress,
		fullScan:        fullScan,
		changesDetected: atomic.Bool{},
	}

	// Set changesDetected to true for full scans to ensure all maintenance operations run
	if fullScan {
		state.changesDetected.Store(true)
	}

	// Get libraries and optionally filter by targets
	allLibs, err := s.ds.Library().GetAll(ctx)
	if err != nil {
		state.sendWarning(fmt.Sprintf("getting libraries: %s", err))
		return
	}
	state.totalLibraryCount = len(allLibs)

	if len(targets) > 0 {
		// Selective scan: filter libraries and build targets map
		state.targets = make(map[int][]string)

		libPaths := slice.ToMap(allLibs, func(lib model.Library) (int, string) {
			return lib.ID, lib.Path
		})

		for _, target := range targets {
			folderPath := model.LibraryRelativePath(libPaths[target.LibraryID], target.FolderPath)
			if folderPath == "" {
				folderPath = "."
			}
			state.targets[target.LibraryID] = append(state.targets[target.LibraryID], folderPath)
		}

		// Filter libraries to only those in targets
		state.libraries = slice.Filter(allLibs, func(lib model.Library) bool {
			return len(state.targets[lib.ID]) > 0
		})

		log.Info(ctx, "Scanner: Starting selective scan", "fullScan", state.fullScan, "numLibraries", len(state.libraries), "numTargets", len(targets))
	} else {
		// Full library scan
		state.libraries = allLibs
		log.Info(ctx, "Scanner: Starting scan", "fullScan", state.fullScan, "numLibraries", len(state.libraries))
	}

	// Store scan type and start time
	scanType := "quick"
	if state.fullScan {
		scanType = "full"
	}
	if state.isSelectiveScan() {
		scanType += "-selective"
	}
	_ = s.ds.Property().Put(ctx, consts.LastScanTypeKey, scanType)
	_ = s.ds.Property().Put(ctx, consts.LastScanStartTimeKey, startTime.Format(time.RFC3339))

	// if there was a full scan in progress, force a full scan
	if !state.fullScan {
		for _, lib := range state.libraries {
			// A pending PID rescan already restarts in full through its own job
			if lib.NeedsPIDRescan() {
				continue
			}
			if lib.FullScanInProgress {
				log.Info(ctx, "Scanner: Interrupted full scan detected", "lib", lib.Name)
				state.fullScan = true
				if state.isSelectiveScan() {
					_ = s.ds.Property().Put(ctx, consts.LastScanTypeKey, "full-selective")
				} else {
					_ = s.ds.Property().Put(ctx, consts.LastScanTypeKey, "full")
				}
				break
			}
		}
	}

	// Prepare libraries for scanning (initialize LastScanStartedAt if needed)
	err = s.prepareLibrariesForScan(ctx, &state)
	if err != nil {
		log.Error(ctx, "Scanner: Error preparing libraries for scan", err)
		state.sendError(err)
		return
	}

	err = run.Sequentially(
		// Phase 1: Scan all libraries and import new/updated files
		runPhase[*folderEntry](ctx, 1, createPhaseFolders(ctx, &state, s.ds)),

		// Phase 2: Process missing files, checking for moves
		runPhase[*missingTracks](ctx, 2, createPhaseMissingTracks(ctx, &state, s.ds)),

		// Phases 3 and 4 can be run in parallel
		run.Parallel(
			// Phase 3: Refresh all new/changed albums and update artists
			runPhase[*model.Album](ctx, 3, createPhaseRefreshAlbums(ctx, &state, s.ds)),

			// Phase 4: Import/update playlists
			runPhase[*model.Folder](ctx, 4, createPhasePlaylists(ctx, &state, s.ds, s.pls)),
		),

		// Final Steps (cannot be parallelized):

		// Run GC if there were any changes (Remove dangling tracks, empty albums and artists, and orphan annotations)
		s.runGC(ctx, &state),

		// Queue artwork for entities that never resolved (after GC, so nothing dangling is queued)
		s.runEnqueueMissingArtwork(ctx, &state),

		// Refresh artist and tags stats
		s.runRefreshStats(ctx, &state),

		// Update last_scan_completed_at for all libraries
		s.runUpdateLibraries(ctx, &state),
	)
	if err != nil {
		log.Error(ctx, "Scanner: Finished with error", "duration", time.Since(startTime), err)
		_ = s.ds.Property().Put(ctx, consts.LastScanErrorKey, err.Error())
		state.sendError(err)
		return
	}

	_ = s.ds.Property().Put(ctx, consts.LastScanErrorKey, "")

	if state.changesDetected.Load() {
		state.sendProgress(&ProgressInfo{ChangesDetected: true})
	}

	if state.isSelectiveScan() {
		log.Info(ctx, "Scanner: Finished scanning selected folders", "duration", time.Since(startTime), "numTargets", len(targets))
	} else {
		log.Info(ctx, "Scanner: Finished scanning all libraries", "duration", time.Since(startTime))
	}
}

// prepareLibrariesForScan initializes the scan for all libraries in the state.
// It calls ScanBegin for libraries that haven't started scanning yet (LastScanStartedAt is zero),
// reloads them to get the updated state, and filters out any libraries that fail to initialize.
func (s *scannerImpl) prepareLibrariesForScan(ctx context.Context, state *scanState) error {
	var successfulLibs []model.Library

	for _, lib := range state.libraries {
		// A library with a changed PID config restarts its scan: resuming would skip the folders that
		// the interrupted scan already processed with the old config
		pidRescan := lib.NeedsPIDRescan()
		if lib.LastScanStartedAt.IsZero() || pidRescan {
			// This is a new scan - mark it as started
			err := s.ds.WithTxRetry(ctx, func(ctx context.Context, tx model.DataStore) error {
				return tx.Library().ScanBegin(ctx, lib.ID, state.fullScan || pidRescan)
			}, "scanner: begin library scan")
			if err != nil {
				log.Error(ctx, "Scanner: Error marking scan start", "lib", lib.Name, err)
				state.sendWarning(err.Error())
				continue
			}

			// Reload library to get updated state (timestamps, etc.)
			reloadedLib, err := s.ds.Library().Get(ctx, lib.ID)
			if err != nil {
				log.Error(ctx, "Scanner: Error reloading library", "lib", lib.Name, err)
				state.sendWarning(err.Error())
				continue
			}
			lib = *reloadedLib
		} else {
			// This is a resumed scan
			log.Debug(ctx, "Scanner: Resuming previous scan", "lib", lib.Name,
				"lastScanStartedAt", lib.LastScanStartedAt, "fullScan", lib.FullScanInProgress)
		}

		successfulLibs = append(successfulLibs, lib)
	}

	if len(successfulLibs) == 0 {
		return fmt.Errorf("no libraries available for scanning")
	}

	// Update state with only successfully initialized libraries
	state.libraries = successfulLibs
	return nil
}

func (s *scannerImpl) runGC(ctx context.Context, state *scanState) func() error {
	return func() error {
		state.sendProgress(&ProgressInfo{ForceUpdate: true})
		return s.ds.WithTxRetry(ctx, func(ctx context.Context, tx model.DataStore) error {
			if state.changesDetected.Load() {
				start := time.Now()

				// For selective scans, extract library IDs to scope GC operations
				var libraryIDs []int
				if state.isSelectiveScan() {
					libraryIDs = slices.Collect(maps.Keys(state.targets))
					log.Debug(ctx, "Scanner: Running selective GC", "libraryIDs", libraryIDs)
				}

				if err := tx.GC(ctx, libraryIDs...); err != nil {
					return fmt.Errorf("running GC: %w", err)
				}
				log.Debug(ctx, "Scanner: GC completed", "elapsed", time.Since(start))
			} else {
				log.Debug(ctx, "Scanner: No changes detected, skipping GC")
			}
			return nil
		}, "scanner: GC")
	}
}

// runEnqueueMissingArtwork is the safety net for entities phase 1 never enqueued.
func (s *scannerImpl) runEnqueueMissingArtwork(ctx context.Context, state *scanState) func() error {
	return func() error {
		if !state.changesDetected.Load() {
			log.Debug(ctx, "Scanner: No changes detected, skipping artwork enqueue")
			return nil
		}
		start := time.Now()
		var total int64
		for _, kind := range []model.Kind{model.KindAlbumArtwork, model.KindArtistArtwork} {
			var n int64
			err := s.ds.WithTxRetry(ctx, func(ctx context.Context, tx model.DataStore) error {
				var err error
				n, err = tx.ArtworkQueue().EnqueueAllMissing(ctx, kind, model.ArtworkPriorityScan)
				return err
			}, "scanner: enqueue missing artwork")
			if err != nil {
				log.Error(ctx, "Scanner: Error enqueueing missing artwork", "kind", kind, err)
				return fmt.Errorf("enqueueing missing artwork: %w", err)
			}
			total += n
		}
		log.Debug(ctx, "Scanner: Enqueued missing artwork", "items", total, "elapsed", time.Since(start))
		return nil
	}
}

func (s *scannerImpl) runRefreshStats(ctx context.Context, state *scanState) func() error {
	return func() error {
		if !state.changesDetected.Load() {
			log.Debug(ctx, "Scanner: No changes detected, skipping refreshing stats")
			return nil
		}
		start := time.Now()
		stats, err := s.ds.Artist().RefreshStats(ctx, state.fullScan)
		if err != nil {
			log.Error(ctx, "Scanner: Error refreshing artists stats", err)
			return fmt.Errorf("refreshing artists stats: %w", err)
		}
		log.Debug(ctx, "Scanner: Refreshed artist stats", "stats", stats, "elapsed", time.Since(start))

		start = time.Now()
		err = s.ds.WithTxRetry(ctx, func(ctx context.Context, tx model.DataStore) error {
			return tx.Tag().UpdateCounts(ctx)
		}, "scanner: update tag counts")
		if err != nil {
			log.Error(ctx, "Scanner: Error updating tag counts", err)
			return fmt.Errorf("updating tag counts: %w", err)
		}
		log.Debug(ctx, "Scanner: Updated tag counts", "elapsed", time.Since(start))
		return nil
	}
}

func (s *scannerImpl) runUpdateLibraries(ctx context.Context, state *scanState) func() error {
	return func() error {
		start := time.Now()
		return s.ds.WithTxRetry(ctx, func(ctx context.Context, tx model.DataStore) error {
			for _, lib := range state.libraries {
				if err := tx.Library().ScanEnd(ctx, lib.ID); err != nil {
					return fmt.Errorf("updating last scan completed for %s: %w", lib.Name, err)
				}
				// A selective scan covers only part of the library, so the rest may still use the old PID
				// config. A library that could not be scanned did not apply it either.
				if !state.isSelectiveScan() && !state.failedLibs[lib.ID] {
					if err := tx.Library().SetScannedPID(ctx, lib.ID, lib.EffectivePID()); err != nil {
						return fmt.Errorf("updating PID conf for %s: %w", lib.Name, err)
					}
				}
				if state.changesDetected.Load() {
					log.Debug(ctx, "Scanner: Refreshing library stats", "lib", lib.Name)
					if err := tx.Library().RefreshStats(ctx, lib.ID); err != nil {
						return fmt.Errorf("refreshing library stats for %s: %w", lib.Name, err)
					}
				} else {
					log.Debug(ctx, "Scanner: No changes detected, skipping library stats refresh", "lib", lib.Name)
				}
			}
			log.Debug(ctx, "Scanner: Updated libraries after scan", "elapsed", time.Since(start), "numLibraries", len(state.libraries))
			return nil
		}, "scanner: update libraries")
	}
}

type phase[T any] interface {
	producer() ppl.Producer[T]
	stages() []ppl.Stage[T]
	finalize(error) error
	description() string
}

func runPhase[T any](ctx context.Context, phaseNum int, phase phase[T]) func() error {
	return func() error {
		log.Debug(ctx, fmt.Sprintf("Scanner: Starting phase %d: %s", phaseNum, phase.description()))
		start := time.Now()

		producer := phase.producer()
		stages := phase.stages()

		// Prepend a counter stage to the phase's pipeline
		counter, countStageFn := countTasks[T]()
		stages = append([]ppl.Stage[T]{ppl.NewStage(countStageFn, ppl.Name("count tasks"))}, stages...)

		var err error
		if log.IsGreaterOrEqualTo(log.LevelDebug) {
			var m *ppl.Metrics
			m, err = ppl.Measure(producer, stages...)
			log.Info(ctx, "Scanner: "+m.String(), err)
		} else {
			err = ppl.Do(producer, stages...)
		}

		err = phase.finalize(err)

		if err != nil {
			log.Error(ctx, fmt.Sprintf("Scanner: Error processing libraries in phase %d", phaseNum), "elapsed", time.Since(start), err)
		} else {
			log.Debug(ctx, fmt.Sprintf("Scanner: Finished phase %d", phaseNum), "elapsed", time.Since(start), "totalTasks", counter.Load())
		}

		return err
	}
}

func countTasks[T any]() (*atomic.Int64, func(T) (T, error)) {
	counter := atomic.Int64{}
	return &counter, func(in T) (T, error) {
		counter.Add(1)
		return in, nil
	}
}

var _ scanner = (*scannerImpl)(nil)