# src/Recorder.js

    import InlineWorker from 'inline-worker';

    class Recorder {
        constructor(source, cfg) {
          this.config = { bufferLen: 4096, numChannels: 2,
             mimeType: 'audio/webm'
          };

          this.recording = false;

          this.callbacks = {
              getBuffer: [],
              exportWAV: []
          };
            Object.assign(this.config, cfg);
            this.context = source.context;
            this.node = (this.context.createScriptProcessor ||
            this.context.createJavaScriptNode).call(this.context,
                this.config.bufferLen, this.config.numChannels, this.config.numChannels);

            this.node.onaudioprocess = (e) => {
                if (!this.recording) return;

                var buffer = [];
                for (var channel = 0; channel < this.config.numChannels; channel++) {
                    buffer.push(e.inputBuffer.getChannelData(channel));
                }
                this.worker.postMessage({
                    command: 'record',
                    buffer: buffer
                });
            };

            source.connect(this.node);
            this.node.connect(this.context.destination);    //this should not be necessary

            let self = {};
            this.worker = new InlineWorker(function () {
                let recLength = 0,
                    recBuffers = [],
                    sampleRate,
                    numChannels;

                this.onmessage = function (e) {
                    switch (e.data.command) {
                        case 'init':
                            init(e.data.config);
                            break;
                        case 'record':
                            record(e.data.buffer);
                            break;
                        case 'exportWAV':
                            exportWAV(e.data.type);
                            break;
                        case 'getBuffer':
                            getBuffer();
                            break;
                        case 'clear':
                            clear();
                            break;
                    }
                };

                function init(config) {
                    sampleRate = config.sampleRate;
                    numChannels = config.numChannels;
                    initBuffers();
                }

                function record(inputBuffer) {
                    for (var channel = 0; channel < numChannels; channel++) {
                        recBuffers[channel].push(inputBuffer[channel]);
                    }
                    recLength += inputBuffer[0].length;
                }

                function exportWAV(type) {
                    let buffers = [];
                    for (let channel = 0; channel < numChannels; channel++) {
                        buffers.push(mergeBuffers(recBuffers[channel], recLength));
                    }
                    let interleaved;
                    if (numChannels === 2) {
                        interleaved = interleave(buffers[0], buffers[1]);
                    } else {
                        interleaved = buffers[0];
                    }
                    let dataview = encodeWAV(interleaved);
                    let audioBlob = new Blob([dataview], {type: type});

                    this.postMessage({command: 'exportWAV', data: audioBlob});
                }

                function getBuffer() {
                    let buffers = [];
                    for (let channel = 0; channel < numChannels; channel++) {
                        buffers.push(mergeBuffers(recBuffers[channel], recLength));
                    }
                    this.postMessage({command: 'getBuffer', data: buffers});
                }

                function clear() {
                    recLength = 0;
                    recBuffers = [];
                    initBuffers();
                }

                function initBuffers() {
                    for (let channel = 0; channel < numChannels; channel++) {
                        recBuffers[channel] = [];
                    }
                }

                function mergeBuffers(recBuffers, recLength) {
                    let result = new Float32Array(recLength);
                    let offset = 0;
                    for (let i = 0; i < recBuffers.length; i++) {
                        result.set(recBuffers[i], offset);
                        offset += recBuffers[i].length;
                    }
                    return result;
                }

                function interleave(inputL, inputR) {
                    let length = inputL.length + inputR.length;
                    let result = new Float32Array(length);

                    let index = 0,
                        inputIndex = 0;

                    while (index < length) {
                        result[index++] = inputL[inputIndex];
                        result[index++] = inputR[inputIndex];
                        inputIndex++;
                    }
                    return result;
                }

                function floatTo16BitPCM(output, offset, input) {
                    for (let i = 0; i < input.length; i++, offset += 2) {
                        let s = Math.max(-1, Math.min(1, input[i]));
                        output.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7FFF, true);
                    }
                }

                function writeString(view, offset, string) {
                    for (let i = 0; i < string.length; i++) {
                        view.setUint8(offset + i, string.charCodeAt(i));
                    }
                }

                function encodeWAV(samples) {
                    let buffer = new ArrayBuffer(44 + samples.length * 2);
                    let view = new DataView(buffer);

                    /* RIFF identifier */
                    writeString(view, 0, 'RIFF');
                    /* RIFF chunk length */
                    view.setUint32(4, 36 + samples.length * 2, true);
                    /* RIFF type */
                    writeString(view, 8, 'WAVE');
                    /* format chunk identifier */
                    writeString(view, 12, 'fmt ');
                    /* format chunk length */
                    view.setUint32(16, 16, true);
                    /* sample format (raw) */
                    view.setUint16(20, 1, true);
                    /* channel count */
                    view.setUint16(22, numChannels, true);
                    /* sample rate */
                    view.setUint32(24, sampleRate, true);
                    /* byte rate (sample rate * block align) */
                    view.setUint32(28, sampleRate * 4, true);
                    /* block align (channel count * bytes per sample) */
                    view.setUint16(32, numChannels * 2, true);
                    /* bits per sample */
                    view.setUint16(34, 16, true);
                    /* data chunk identifier */
                    writeString(view, 36, 'data');
                    /* data chunk length */
                    view.setUint32(40, samples.length * 2, true);

                    floatTo16BitPCM(view, 44, samples);

                    return view;
                }
            }, self);

            this.worker.postMessage({
                command: 'init',
                config: {
                    sampleRate: this.context.sampleRate,
                    numChannels: this.config.numChannels
                }
            });

            this.worker.onmessage = (e) => {
                let cb = this.callbacks[e.data.command].pop();
                if (typeof cb == 'function') {
                    cb(e.data.data);
                }
            };
        }

        record() {
            this.recording = true;
        }

        stop() {
            this.recording = false;
        }

        clear() {
            this.worker.postMessage({command: 'clear'});
        }

        getBuffer(cb) {
            cb = cb || this.config.callback;
            if (!cb) throw new Error('Callback not set');

            this.callbacks.getBuffer.push(cb);

            this.worker.postMessage({command: 'getBuffer'});
        }

        exportWAV(cb, mimeType) {
            mimeType = mimeType || this.config.mimeType;
            cb = cb || this.config.callback;
            if (!cb) throw new Error('Callback not set');

            this.callbacks.exportWAV.push(cb);

            this.worker.postMessage({
                command: 'exportWAV',
                type: mimeType
            });
        }

        static
        forceDownload(blob, filename) {
            let url = (window.URL || window.webkitURL).createObjectURL(blob);
            let link = window.document.createElement('a');
            link.href = url;
            link.download = filename || 'output.wav';
            let click = document.createEvent("Event");
            click.initEvent("click", true, true);
            link.dispatchEvent(click);
        }
    }

    export default Recorder;