package api

import (
	"net/http"
	"strings"

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

// maxReplayGainIDs caps one lookup. A player asks for the tracks around the
// one it is about to play, never a whole library.
const maxReplayGainIDs = 200

// replayGainResp is the wire shape for GET /api/tracks/replay-gain. Tracks
// with no gain known are absent from items: no adjustment.
type replayGainResp struct {
	Items map[string]library.ReplayGain `json:"items"`
}

// handleGetReplayGain implements GET /api/tracks/replay-gain?ids=a,b,c (M464
// #4997): ReplayGain 2.0 values (dB to -18 LUFS, linear peaks) for each track,
// and for its album when the whole album is measured.
//
// A lookup rather than fields on TrackRef. Tracks reach the player through
// about fifteen surfaces in two wire shapes (TrackRef and playlist entries),
// and only the player uses the gain. One call from the player, made for the
// tracks it is about to play, cannot be forgotten by a surface added later,
// and costs nothing on the pages that never play anything. Android takes the
// same values from the sync feed instead, so they are there offline.
func (h *handlers) handleGetReplayGain(w http.ResponseWriter, r *http.Request) {
	raw := strings.TrimSpace(r.URL.Query().Get("ids"))
	if raw == "" {
		writeJSON(w, http.StatusOK, replayGainResp{Items: map[string]library.ReplayGain{}})
		return
	}
	parts := strings.Split(raw, ",")
	if len(parts) > maxReplayGainIDs {
		writeErr(w, apierror.BadRequest("too_many_ids", "at most 200 ids per request"))
		return
	}
	ids := stringsToUUIDs(parts)
	gains, err := library.ReplayGainForTracks(r.Context(), dbq.New(h.pool), ids)
	if err != nil {
		writeErrWithLog(w, h.logger, "replay gain: lookup", apierror.InternalMsg("lookup failed", err))
		return
	}
	items := make(map[string]library.ReplayGain, len(gains))
	for id, g := range gains {
		items[uuidToString(id)] = g
	}
	writeJSON(w, http.StatusOK, replayGainResp{Items: items})
}