feat: integrate authored nightdrive soundtrack

src/audio/soundtrack-transport.ts

@@ -0,0 +1,53 @@
+import type { AudioJourneyState } from '@/audio/types';
+
+export const SOUNDTRACK_SAMPLE_RATE = 48_000;
+export const MUSIC_BPM = 86;
+export const MUSIC_BAR_SECONDS = 4 * 60 / MUSIC_BPM;
+export const MAIN_PHRASE_BARS = 8;
+
+export const INTRO_IN_END_SAMPLE = 267_907;
+export const INTRO_FIRST_PASS_END_SAMPLE = 1_339_535;
+export const INTRO_LOOP_START_SAMPLE = INTRO_FIRST_PASS_END_SAMPLE;
+export const INTRO_LOOP_END_SAMPLE = 2_411_163;
+export const INTRO_OUT_START_SAMPLE = INTRO_LOOP_END_SAMPLE;
+export const INTRO_OUT_END_SAMPLE = 2_679_070;
+export const INTRO_RUNTIME_END_SAMPLE = 2_691_070;
+
+export const INTRO_IN_END_SECONDS = INTRO_IN_END_SAMPLE / SOUNDTRACK_SAMPLE_RATE;
+export const INTRO_FIRST_PASS_END_SECONDS = INTRO_FIRST_PASS_END_SAMPLE / SOUNDTRACK_SAMPLE_RATE;
+export const INTRO_LOOP_START_SECONDS = INTRO_LOOP_START_SAMPLE / SOUNDTRACK_SAMPLE_RATE;
+export const INTRO_LOOP_END_SECONDS = INTRO_LOOP_END_SAMPLE / SOUNDTRACK_SAMPLE_RATE;
+export const INTRO_OUT_START_SECONDS = INTRO_OUT_START_SAMPLE / SOUNDTRACK_SAMPLE_RATE;
+export const INTRO_OUT_END_SECONDS = INTRO_OUT_END_SAMPLE / SOUNDTRACK_SAMPLE_RATE;
+export const INTRO_RUNTIME_END_SECONDS = INTRO_RUNTIME_END_SAMPLE / SOUNDTRACK_SAMPLE_RATE;
+
+export type InitialPlayback =
+  | { readonly kind: 'intro' }
+  | { readonly kind: 'main'; readonly offsetSeconds: number };
+
+export function resolveInitialPlayback(state: AudioJourneyState): InitialPlayback {
+  return state.atStart
+    ? { kind: 'intro' }
+    : { kind: 'main', offsetSeconds: mainPhraseOffsetSeconds(state.entryPhrase) };
+}
+
+export function mainPhraseOffsetSeconds(entryPhrase: number): number {
+  const finitePhrase = Number.isFinite(entryPhrase) ? Math.trunc(entryPhrase) : 0;
+  const phrase = Math.min(7, Math.max(0, finitePhrase));
+  const targetSamples = Math.round(
+    phrase * MAIN_PHRASE_BARS * MUSIC_BAR_SECONDS * SOUNDTRACK_SAMPLE_RATE,
+  );
+  return targetSamples / SOUNDTRACK_SAMPLE_RATE;
+}
+
+export function nextSafeBarTime(
+  now: number,
+  anchorTime: number,
+  minimumLeadSeconds: number,
+): number {
+  const earliest = Math.max(anchorTime, now + Math.max(0, minimumLeadSeconds));
+  const elapsedBars = (earliest - anchorTime) / MUSIC_BAR_SECONDS;
+  const oneSampleInBars = 1 / SOUNDTRACK_SAMPLE_RATE / MUSIC_BAR_SECONDS;
+  const nextBar = Math.ceil(elapsedBars - oneSampleInBars);
+  return anchorTime + nextBar * MUSIC_BAR_SECONDS;
+}