package api

import (
	"context"
	"encoding/json"
	"net/http"
	"strconv"

	"github.com/jackc/pgx/v5/pgtype"

	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
	syncpkg "git.fabledsword.com/bvandeusen/minstrel/internal/sync"
)

// SyncBatchLimit caps the number of change rows returned per call.
// Clients that need more loop with the returned cursor.
const SyncBatchLimit = 1000

// syncResponse is the wire shape returned by GET /api/library/sync.
// upserts and deletes are separated by entity type so clients can apply
// them to typed local tables. cursor is the largest library_changes.id
// the server returned in this batch — clients pass it back as `since`
// next time.
type syncResponse struct {
	Cursor  int64                        `json:"cursor"`
	Upserts map[string][]json.RawMessage `json:"upserts"`
	Deletes map[string][]string          `json:"deletes"`
}

// handleLibrarySync returns batched upserts + deletes since the supplied
// cursor. Cursor is the last `library_changes.id` the client has seen.
// Empty / zero / invalid cursor means "give me everything" (initial sync).
//
// Responses:
//   - 204 No Content — no changes since cursor
//   - 200 OK         — JSON syncResponse with upserts, deletes, new cursor
//   - 410 Gone       — cursor older than oldest log row; client must reset
//   - 401 / 500      — standard envelope errors
func (h *handlers) handleLibrarySync(w http.ResponseWriter, r *http.Request) {
	user, ok := requireUser(w, r)
	if !ok {
		return
	}
	ctx := r.Context()

	since, err := strconv.ParseInt(r.URL.Query().Get("since"), 10, 64)
	if err != nil || since < 0 {
		since = 0
	}

	q := dbq.New(h.pool)

	// 410 path: if the requested cursor is older than the oldest row,
	// tell the client to reset. (No compaction job in this slice; the
	// path exists for future compaction support.)
	if since > 0 {
		minCursor, err := q.GetMinLibraryChangeCursor(ctx)
		if err != nil {
			writeErrWithLog(w, h.logger, "library_sync: GetMinLibraryChangeCursor", err)
			return
		}
		if minCursor > 0 && since+1 < minCursor {
			writeErr(w, &apierror.Error{
				Status:  http.StatusGone,
				Code:    "cursor_too_old",
				Message: "reset client cursor to 0 and resync",
			})
			return
		}
	}

	changes, err := q.GetLibraryChangesSince(ctx, dbq.GetLibraryChangesSinceParams{
		ID:    since,
		Limit: SyncBatchLimit,
	})
	if err != nil {
		writeErrWithLog(w, h.logger, "library_sync: GetLibraryChangesSince", err)
		return
	}

	if len(changes) == 0 {
		w.WriteHeader(http.StatusNoContent)
		return
	}

	// Group ids by entity type so we can fetch upsert payloads in batches.
	upsertIDs := map[syncpkg.EntityType][]string{}
	deleteIDs := map[syncpkg.EntityType][]string{}
	var maxID int64
	for _, c := range changes {
		et := syncpkg.EntityType(c.EntityType)
		if c.ID > maxID {
			maxID = c.ID
		}
		if c.Op == string(syncpkg.OpUpsert) {
			upsertIDs[et] = append(upsertIDs[et], c.EntityID)
		} else {
			deleteIDs[et] = append(deleteIDs[et], c.EntityID)
		}
	}

	upserts, err := h.hydrateUpserts(ctx, q, user.ID, upsertIDs)
	if err != nil {
		writeErrWithLog(w, h.logger, "library_sync: hydrateUpserts", err)
		return
	}

	// Format deletes — convert EntityType keys to strings for JSON.
	deletes := make(map[string][]string, len(deleteIDs))
	for et, ids := range deleteIDs {
		deletes[string(et)] = ids
	}

	writeJSON(w, http.StatusOK, syncResponse{
		Cursor:  maxID,
		Upserts: upserts,
		Deletes: deletes,
	})
}

// hydrateUpserts loads the current row payloads for each upserted id,
// keyed by entity type (string form). Returns json.RawMessage values so
// each entity's full sqlc row shape passes through unchanged.
//
// Per-user entities (likes, playlists, playlist_tracks) are scoped to
// userID — the change log is global but each user only sees rows that
// concern them.
func (h *handlers) hydrateUpserts(
	ctx context.Context,
	q *dbq.Queries,
	userID pgtype.UUID,
	ids map[syncpkg.EntityType][]string,
) (map[string][]json.RawMessage, error) {
	out := map[string][]json.RawMessage{}

	if rows := ids[syncpkg.EntityArtist]; len(rows) > 0 {
		uuids := stringsToUUIDs(rows)
		artists, err := q.GetArtistsByIDs(ctx, uuids)
		if err != nil {
			return nil, err
		}
		for _, a := range artists {
			b, _ := json.Marshal(a)
			out["artist"] = append(out["artist"], b)
		}
	}
	if rows := ids[syncpkg.EntityAlbum]; len(rows) > 0 {
		uuids := stringsToUUIDs(rows)
		albums, err := q.GetAlbumsByIDs(ctx, uuids)
		if err != nil {
			return nil, err
		}
		for _, a := range albums {
			b, _ := json.Marshal(a)
			out["album"] = append(out["album"], b)
		}
	}
	if rows := ids[syncpkg.EntityTrack]; len(rows) > 0 {
		uuids := stringsToUUIDs(rows)
		tracks, err := q.GetTracksByIDs(ctx, uuids)
		if err != nil {
			return nil, err
		}
		for _, t := range tracks {
			b, _ := json.Marshal(t)
			out["track"] = append(out["track"], b)
		}
	}

	userIDStr := syncpkg.FormatUUID(userID)

	if rows := ids[syncpkg.EntityLikeTrack]; len(rows) > 0 {
		out["like_track"] = scopedLikeRows(rows, userIDStr, "track_id")
	}
	if rows := ids[syncpkg.EntityLikeAlbum]; len(rows) > 0 {
		out["like_album"] = scopedLikeRows(rows, userIDStr, "album_id")
	}
	if rows := ids[syncpkg.EntityLikeArtist]; len(rows) > 0 {
		out["like_artist"] = scopedLikeRows(rows, userIDStr, "artist_id")
	}

	if rows := ids[syncpkg.EntityPlaylist]; len(rows) > 0 {
		uuids := stringsToUUIDs(rows)
		playlists, err := q.GetPlaylistsByIDs(ctx, uuids)
		if err != nil {
			return nil, err
		}
		for _, p := range playlists {
			// Filter: only return playlists owned by this user OR public ones
			if syncpkg.FormatUUID(p.UserID) != userIDStr && !p.IsPublic {
				continue
			}
			b, _ := json.Marshal(p)
			out["playlist"] = append(out["playlist"], b)
		}
	}
	if rows := ids[syncpkg.EntityPlaylistTrack]; len(rows) > 0 {
		// playlist_track ids are "<playlist>:<track>" — we don't know
		// playlist ownership here without a JOIN. Pass through; client
		// reconciles against its locally-cached playlists.
		var msgs []json.RawMessage
		for _, id := range rows {
			parts := splitOnce(id, ":")
			if len(parts) != 2 {
				continue
			}
			b, _ := json.Marshal(map[string]string{
				"playlist_id": parts[0],
				"track_id":    parts[1],
			})
			msgs = append(msgs, b)
		}
		out["playlist_track"] = msgs
	}
	return out, nil
}

// scopedLikeRows filters composite-key like rows to those owned by userID
// and emits {user_id, <entityKey>} JSON shapes. entityKey is "track_id",
// "album_id", or "artist_id" depending on the like table.
func scopedLikeRows(rows []string, userIDStr, entityKey string) []json.RawMessage {
	var msgs []json.RawMessage
	for _, id := range rows {
		parts := splitOnce(id, ":")
		if len(parts) != 2 || parts[0] != userIDStr {
			continue
		}
		b, _ := json.Marshal(map[string]string{
			"user_id":  parts[0],
			entityKey:  parts[1],
		})
		msgs = append(msgs, b)
	}
	return msgs
}

// stringsToUUIDs parses each string as a pgtype.UUID. Invalid entries
// are skipped silently — they can't have come from a valid scan/mutation.
func stringsToUUIDs(strs []string) []pgtype.UUID {
	out := make([]pgtype.UUID, 0, len(strs))
	for _, s := range strs {
		u, ok := parseUUID(s)
		if !ok {
			continue
		}
		out = append(out, u)
	}
	return out
}

// splitOnce returns [before, after] split at the first occurrence of sep,
// or [s] if sep doesn't appear. Used for composite-key parsing.
func splitOnce(s, sep string) []string {
	for i := 0; i+len(sep) <= len(s); i++ {
		if s[i:i+len(sep)] == sep {
			return []string{s[:i], s[i+len(sep):]}
		}
	}
	return []string{s}
}