exports.handler = async function(context, event, callback) {
    const response = new Twilio.Response();
    response.appendHeader('Access-Control-Allow-Origin', '*');  // CORS対策

    // パラメータのチェック
    const IDENTITY = event.identity || '';  // ユーザID
    if (IDENTITY === '') callback(new Error(`Parameter 'identity' was not set.`));

    const roomName = event.room || '';  // ルーム名
    if (roomName === '') callback(new Error(`Parameter 'room' was not set.`));

    const attendeesCount = event.attendees || 0;    // 会議に招待した人数
    if (attendeesCount === 0) callback(new Error(`Parameter 'attendees' was not set.`));

    const ACCOUNT_SID = 'AC'; // TwilioのAccountSid
    const API_KEY = ''; // Twilio VideoのAPI Key
    const API_SECRET = ''; // Twilio VideoのAPI Secret

    const RECORDING = false;    // 録画
    const ROOM_TYPE = attendeesCount > 4 ? 'group' : 'group-small'; // Roomタイプ
    const MAX_PARTICIPANTS = attendeesCount > 4 ? 50 : 4; // 最大参加者数（Group Roomは50名まで）

    // Roomを生成
    const client = require('twilio')(API_KEY, API_SECRET, {accountSid: ACCOUNT_SID});
    await client.video.rooms.list({
        uniqueName: roomName,
    })
    .then(rooms => {
        console.log('rooms.length: ', rooms.length);
        if (rooms.length === 0) {
            // 開催中のRoomがないので生成
            return client.video.rooms.create({
                maxParticipants: MAX_PARTICIPANTS,
                recordParticipantsOnConnect: RECORDING,
                type: ROOM_TYPE,
                uniqueName: roomName,
                mediaRegion: 'jp1',
            });
        } else {
            return null;
        }
    })
    .then(room => {
        if (room) {
            console.log(`Room created. ${room.sid}`);
        } else {
            console.log(`Room was exist.`);
        }
    })
    .catch(error => {
        callback(new Error(`Room create error: ${error}`));
    });

    // アクセストークンの作成
    const AccessToken = Twilio.jwt.AccessToken;
    const VideoGrant = AccessToken.VideoGrant;

    const videoGrant = new VideoGrant({
        room: roomName
    });

    const accessToken = new AccessToken(
        ACCOUNT_SID,
        API_KEY,
        API_SECRET
    );

    accessToken.addGrant(videoGrant);
    accessToken.identity = IDENTITY;

    response.appendHeader('Content-Type', 'application/json');
    response.setBody({
        token: accessToken.toJwt()
    });
    callback(null, response);
};