const Scan = {
    videoInputDevice: [],
    videoElement: document.getElementById("video"),
    // 获取到的媒体设备
    gotDevices(deviceInfos) {
        let that = this;
        for (let i = 0; i !== deviceInfos.length; ++i) {
            let deviceInfo = deviceInfos[i];
            if (deviceInfo.kind === 'audioinput') {
                // 音频设备
            } else if (deviceInfo.kind === 'videoinput') {
                // 视频设备
                that.videoInputDevice.push(deviceInfo);
            } else {
                // 其他设备
                console.log('Found one other kind of source/device: ', deviceInfo);
            }
        }
    },
    getStream() {
        let that = this;
        if (window.stream) {
            window.stream.getTracks().forEach((track) => {
                track.stop();
            });
        }

        let constraints = {
            // 包含audio 可声明音频设备调用
            // 声明视频设备调用
            // video: true
            video: {
                deviceId: {
                    // [1].deviceId 表示后置摄像头,默认开启的是前置摄像头
                    exact: that.videoInputDevice[1].deviceId
                }
            }
        };

        // 视频设备初始化
        navigator.mediaDevices.getUserMedia(constraints).then(that.gotStream.bind(that)).catch(that.handleError.bind(that));
        that.captureToCanvas();
        that.decode();
    },

    handleError(error) {
        console.log('Error: ', error);
    },

    gotStream(stream) {
        let that = this;
        window.stream = stream; // make stream available to console
        that.videoElement.srcObject = stream;
    },

    init() {
        let that = this;
        // API参考
        // https://developer.mozilla.org/zh-CN/docs/Web/API/MediaDevices/enumerateDevices
        // 先获取设备列表，方便调用后置摄像头
        let devices = navigator.mediaDevices.enumerateDevices().then(that.gotDevices.bind(that));
        
        document.querySelector('#scan').addEventListener('click', () => {
            devices.then(that.getStream.bind(that)).catch(that.handleError.bind(that));
        });
    }
};
Scan.init();