package api

import (
	"errors"
	"net/http"
	"time"

	"github.com/jackc/pgx/v5"

	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
	"git.fabledsword.com/bvandeusen/minstrel/internal/auth"
	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
	"git.fabledsword.com/bvandeusen/minstrel/internal/playlists"
)

// foryouRefreshResp is the wire shape for POST
// /api/playlists/system/for-you/refresh. track_ids is the playlist's
// tracks in playlist position order — the frontend enqueues this
// list directly to start playback without a second roundtrip.
//
// playlist_id is null + track_ids empty when the build succeeded but
// the user's library yielded no eligible candidates (degenerate
// empty-library case).
type foryouRefreshResp struct {
	PlaylistID *string  `json:"playlist_id"`
	TrackCount int32    `json:"track_count"`
	TrackIDs   []string `json:"track_ids"`
}

// handleForYouRefresh re-runs BuildSystemPlaylists synchronously for
// the calling user and returns their freshly-built For-You playlist.
// Used by the home Playlists row's For-You tile play button: click
// triggers refresh, the response carries the track IDs, the
// frontend enqueues + auto-plays.
//
// Authenticated user only — each user refreshes only their own
// For-You.
func (h *handlers) handleForYouRefresh(w http.ResponseWriter, r *http.Request) {
	user, ok := auth.UserFromContext(r.Context())
	if !ok {
		writeErr(w, apierror.Unauthorized("auth_required", ""))
		return
	}
	if err := playlists.BuildSystemPlaylists(r.Context(), h.pool, h.logger, user.ID, time.Now(), h.dataDir); err != nil {
		h.logger.Error("for-you refresh: build failed",
			"user_id", uuidToString(user.ID), "err", err)
		writeErr(w, apierror.InternalMsg("build failed", err))
		return
	}

	q := dbq.New(h.pool)
	sysVariant := "for_you"
	pl, err := q.GetSystemPlaylistByVariantForUser(r.Context(),
		dbq.GetSystemPlaylistByVariantForUserParams{
			UserID:        user.ID,
			SystemVariant: &sysVariant,
		})
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			// Build succeeded but no For-You row — empty library.
			writeJSON(w, http.StatusOK, foryouRefreshResp{
				PlaylistID: nil,
				TrackCount: 0,
				TrackIDs:   []string{},
			})
			return
		}
		h.logger.Error("for-you refresh: lookup failed",
			"user_id", uuidToString(user.ID), "err", err)
		writeErr(w, apierror.InternalMsg("lookup failed", err))
		return
	}

	// Fetch tracks in playlist position order so the frontend can
	// enqueue them directly.
	rows, err := q.ListPlaylistTracks(r.Context(), pl.ID)
	if err != nil {
		h.logger.Error("for-you refresh: list tracks failed",
			"playlist_id", uuidToString(pl.ID), "err", err)
		writeErr(w, apierror.InternalMsg("list tracks failed", err))
		return
	}
	trackIDs := make([]string, 0, len(rows))
	for _, row := range rows {
		// Skip rows where the track was removed from the library
		// (LiveTrackID won't be Valid). The snapshot row still
		// exists in playlist_tracks, but there's nothing to enqueue.
		if !row.LiveTrackID.Valid {
			continue
		}
		trackIDs = append(trackIDs, uuidToString(row.LiveTrackID))
	}

	idStr := uuidToString(pl.ID)
	writeJSON(w, http.StatusOK, foryouRefreshResp{
		PlaylistID: &idStr,
		TrackCount: pl.TrackCount,
		TrackIDs:   trackIDs,
	})
}