const DEFAULT_AUDIO_STREAM_END_SILENCE_MS = 500;

const GOOGLE_REALTIME_BROWSER_SESSION_TTL_MS = 30 * 60 * 1000;

const GOOGLE_REALTIME_BROWSER_NEW_SESSION_TTL_MS = 60 * 1000;

const MULAW_LINEAR_SAMPLES = new Int16Array(256);

for (let i = 0; i < MULAW_LINEAR_SAMPLES.length; i += 1) {

MULAW_LINEAR_SAMPLES[i] = decodeMulawSample(i);

}

type GoogleRealtimeSensitivity = "low" | "high";

type GoogleRealtimeThinkingLevel = "minimal" | "low" | "medium" | "high";

function buildGoogleLiveConnectConfig(config: GoogleRealtimeLiveConfig): LiveConnectConfig {

const functionDeclarations = buildFunctionDeclarations(config.tools);

const realtimeInputConfig = buildRealtimeInputConfig(config);

const thinkingConfig = buildThinkingConfig(config);

return {

responseModalities: ["AUDIO" as Modality],

...(typeof config.temperature === "number" && config.temperature > 0

},

systemInstruction: config.instructions,

...(functionDeclarations.length > 0 ? { tools: [{ functionDeclarations }] } : {}),

...(buildRealtimeInputConfig(config)

? { realtimeInputConfig: buildRealtimeInputConfig(config) }

: {}),

...(realtimeInputConfig ? { realtimeInputConfig } : {}),

inputAudioTranscription: {},

outputAudioTranscription: {},

...(typeof config.enableAffectiveDialog === "boolean"

? { enableAffectiveDialog: config.enableAffectiveDialog }

: {}),

...(buildThinkingConfig(config) ? { thinkingConfig: buildThinkingConfig(config) } : {}),

...(thinkingConfig ? { thinkingConfig } : {}),

};

}

this.audioStreamEnded = false;

}

const pcm = this.toInputPcm(audio);

const pcm16k = resamplePcm(

pcm,

this.audioFormat.sampleRateHz,

GOOGLE_REALTIME_INPUT_SAMPLE_RATE,

);

const pcm16k = this.toGoogleInputPcm16k(audio);

this.session.sendRealtimeInput({

audio: {

data: pcm16k.toString("base64"),

return this.audioFormat.encoding === "pcm16" ? audio : mulawToPcm(audio);

}

private toGoogleInputPcm16k(audio: Buffer): Buffer {

if (

this.audioFormat.encoding === "g711_ulaw" &&

this.audioFormat.sampleRateHz === 8_000 &&

GOOGLE_REALTIME_INPUT_SAMPLE_RATE === 16_000

) {

return convertMulaw8kToPcm16k(audio);

}

return resamplePcm(

this.toInputPcm(audio),

this.audioFormat.sampleRateHz,

GOOGLE_REALTIME_INPUT_SAMPLE_RATE,

);

}

private toOutputAudio(pcm: Buffer, sampleRate: number): Buffer {

return this.audioFormat.encoding === "pcm16"

? resamplePcm(pcm, sampleRate, this.audioFormat.sampleRateHz)

}

}

function convertMulaw8kToPcm16k(muLaw: Buffer): Buffer {

if (muLaw.length === 0) {

return Buffer.alloc(0);

}

const pcm = Buffer.alloc(muLaw.length * 4);

for (let i = 0; i < muLaw.length; i += 1) {

const current = MULAW_LINEAR_SAMPLES[muLaw[i] ?? 0] ?? 0;

const next = MULAW_LINEAR_SAMPLES[muLaw[i + 1] ?? muLaw[i] ?? 0] ?? current;

pcm.writeInt16LE(current, i * 4);

pcm.writeInt16LE(Math.round((current + next) / 2), i * 4 + 2);

}

return pcm;

}

function decodeMulawSample(value: number): number {

const muLaw = ~value & 0xff;

const sign = muLaw & 0x80;

const exponent = (muLaw >> 4) & 0x07;

const mantissa = muLaw & 0x0f;

let sample = ((mantissa << 3) + 132) << exponent;

sample -= 132;

return sign ? -sample : sample;

}

async function createGoogleRealtimeBrowserSession(

req: RealtimeVoiceBrowserSessionCreateRequest,

): Promise<RealtimeVoiceBrowserSession> {