musicbrainz-source.lua

---------------------------
-- Source initialization --
---------------------------

source = {
  id = "grl-musicbrainz",
  name = "MusicBrainz",
  description = "A plugin for fetching music metadata",
  supported_keys = {
    "title",
    "artist",
    "album",
    "duration",
    "mb-artist-id",
    "mb-release-id",
    "mb-release-date"
  },
  supported_media = { "audio" },
  resolve_keys = {
    ["type"] = "audio",
    required = {
   	  "mb-recording-id"
    }
  },
  tags = { 'music', 'net:internet', 'net:plaintext' },
}

------------------
-- Source utils --
------------------

MUSICBRAINZ_BASE = "http://musicbrainz.org/ws/2/"
MUSICBRAINZ_LOOKUP_ARTIST = MUSICBRAINZ_BASE .. "artist/%s"
MUSICBRAINZ_LOOKUP_RECORDING = MUSICBRAINZ_BASE .. "recording/%s?inc=artists+releases"
MUSICBRAINZ_LOOKUP_RELEASE = MUSICBRAINZ_BASE .. "release/%s"

media_table = {}
---------------------------------
-- Handlers of Grilo functions --
---------------------------------

function grl_source_resolve(media, options, callback)
  local media = grl.get_media_keys()

  if not media or
      not media.mb_recording_id or
      #media.mb_recording_id == 0 then
    grl.callback()
    return
  end

  media_table['mb_recording_id'] = media.mb_recording_id
  media_table['mb_artist_id'] = media.mb_artist_id
  media_table['mb_release_id'] = media.mb_release_id

  musicbrainz_execute_resolve()
end

---------------
-- Utilities --
---------------

function musicbrainz_execute_resolve()

  --[[Resolve recording related keys first as it can provide artist and release
  related metadata if it were requested]]
  rec_id = media_table['mb_recording_id']
  if rec_id then
    recording_url = string.format (MUSICBRAINZ_LOOKUP_RECORDING, rec_id)
    debug_str = string.format ("Resolving metadata for recording ID: %s", rec_id)
    grl.debug(debug_str)
    grl.fetch(recording_url, fetch_recording_cb)
  end

	-- TODO: add metadata resolution for mb_artist_id and mb_release_id

end

--[[These functions append fetched values to the table 'media_table' which is then returned to grl.callback]]
function fetch_recording_cb(results)
  recording = get_recording(results)

  if not recording then
    grl.callback()
  else
    if recording.title then
      media_table['title'] = recording.title.xml
    end

    if recording.artist-credit and
        recording.artist-credit.name-credit and
        recording.artist-credit.name-credit.artist then
      artist = recording.artist-credit.name-credit.artist
      media_table['artist'] = artist.name.xml
      media_table['mb-artist-id'] = artist.id.xml
    end

    if recording.release-list and
        #recording.release-list ~= 0 then
      local release = nil
      for index, rel in pairs(recording.release-list) do
        if rel.artist-credit and rel.artist-credit.name-credit and
            rel.artist-credit.name-credit.artist and
            rel.artist-credit.name-credit.artist.id.xml == media_table['mb-artist-id'] then
          release = rel
        end
      end

      --if no release with given artist-id then consider only the first result
      if release == nil then
        release = recording.release-list[1]
      end

      media_table['album'] = release.title.xml
      media_table['mb-release-id'] = release.id.xml
    end

    --[[TODO: media_table needs to be updated by other resolve functions as well
    before its finally sent to grl.callback]]
    grl.callback(media_table)
  end
end

function get_recording(results)
  if not results then return nil end
  local results_table = grl.lua.xml.string_to_table(results)
  if not results_table then return nil end

  if results_table.metadata and
      results_table.metadata.recording then
    return results_table.metadata.recording
  end

  return nil
end