ep-133-project-export/src/lib/exporters/ableton/midi.ts

import type { AblMidiEvent } from '../../transformers/ableton';

export type AbletonMidiControllerTargets = Record<string, { '@Id': number }>;

type AutomationPoint = {
  time: number;
  value: number;
};

const CHANNEL_PRESSURE_TARGET = 129;
const SENTINEL_TIME = -63072000;

export function decodeChannelPressure(event: AblMidiEvent) {
  if (
    event.data.length !== 4 ||
    event.data[0] !== 0xd0 ||
    event.data[1] > 127 ||
    event.data[2] !== 0xff ||
    event.data[3] !== 0
  ) {
    return undefined;
  }

  return event.data[1];
}

function floatEvents(points: AutomationPoint[]) {
  return points.map((point, index) => ({
    '@Id': index,
    '@Time': point.time,
    '@Value': point.value,
  }));
}

export function buildMidiClipEnvelopes(
  events: AblMidiEvent[],
  controllerTargets: AbletonMidiControllerTargets,
) {
  const target = controllerTargets[`ControllerTargets.${CHANNEL_PRESSURE_TARGET}`]?.['@Id'];
  if (target === undefined) {
    return [];
  }

  const points: AutomationPoint[] = [{ time: SENTINEL_TIME, value: 0 }];
  let previousValue = 0;
  let eventCount = 0;

  events.forEach((event) => {
    const value = decodeChannelPressure(event);
    if (value === undefined) {
      return;
    }

    const time = event.position / 96;
    points.push({ time, value: previousValue });
    points.push({ time, value });
    previousValue = value;
    eventCount++;
  });

  if (eventCount === 0) {
    return [];
  }

  return [
    {
      '@Id': 0,
      EnvelopeTarget: { PointeeId: { '@Value': target } },
      Automation: {
        Events: { FloatEvent: floatEvents(points) },
        AutomationTransformViewState: {
          IsTransformPending: { '@Value': 'false' },
          TimeAndValueTransforms: {},
        },
      },
      LoopSlot: { Value: {} },
      ScrollerTimePreserver: {
        LeftTime: { '@Value': 0 },
        RightTime: { '@Value': 0 },
      },
    },
  ];
}