audio-ui/lib/audio/effects/selection.ts

/**
 * Utilities for applying effects to audio selections
 */

import type { Selection } from '@/types/selection';
import { getAudioContext } from '../context';

/**
 * Extract a region from an audio buffer
 */
export function extractRegion(
  buffer: AudioBuffer,
  startTime: number,
  endTime: number
): AudioBuffer {
  const audioContext = getAudioContext();
  const sampleRate = buffer.sampleRate;
  const numberOfChannels = buffer.numberOfChannels;

  const startSample = Math.floor(startTime * sampleRate);
  const endSample = Math.floor(endTime * sampleRate);
  const length = endSample - startSample;

  const regionBuffer = audioContext.createBuffer(
    numberOfChannels,
    length,
    sampleRate
  );

  for (let channel = 0; channel < numberOfChannels; channel++) {
    const sourceData = buffer.getChannelData(channel);
    const targetData = regionBuffer.getChannelData(channel);

    for (let i = 0; i < length; i++) {
      targetData[i] = sourceData[startSample + i];
    }
  }

  return regionBuffer;
}

/**
 * Replace a region in an audio buffer with processed audio
 */
export function replaceRegion(
  originalBuffer: AudioBuffer,
  processedRegion: AudioBuffer,
  startTime: number
): AudioBuffer {
  const audioContext = getAudioContext();
  const sampleRate = originalBuffer.sampleRate;
  const numberOfChannels = originalBuffer.numberOfChannels;

  // Create new buffer with same length as original
  const newBuffer = audioContext.createBuffer(
    numberOfChannels,
    originalBuffer.length,
    sampleRate
  );

  const startSample = Math.floor(startTime * sampleRate);

  for (let channel = 0; channel < numberOfChannels; channel++) {
    const originalData = originalBuffer.getChannelData(channel);
    const processedData = processedRegion.getChannelData(channel);
    const newData = newBuffer.getChannelData(channel);

    // Copy everything from original
    for (let i = 0; i < originalBuffer.length; i++) {
      newData[i] = originalData[i];
    }

    // Replace the selected region with processed data
    for (let i = 0; i < processedRegion.length; i++) {
      if (startSample + i < newBuffer.length) {
        newData[startSample + i] = processedData[i];
      }
    }
  }

  return newBuffer;
}

/**
 * Apply an effect function to a selection, or entire buffer if no selection
 */
export function applyEffectToSelection(
  buffer: AudioBuffer,
  selection: Selection | null,
  effectFn: (buffer: AudioBuffer) => AudioBuffer
): AudioBuffer {
  if (!selection || selection.start === selection.end) {
    // No selection, apply to entire buffer
    return effectFn(buffer);
  }

  // Extract the selected region
  const region = extractRegion(buffer, selection.start, selection.end);

  // Apply effect to the region
  const processedRegion = effectFn(region);

  // Replace the region in the original buffer
  return replaceRegion(buffer, processedRegion, selection.start);
}

/**
 * Apply an async effect function to a selection, or entire buffer if no selection
 */
export async function applyAsyncEffectToSelection(
  buffer: AudioBuffer,
  selection: Selection | null,
  effectFn: (buffer: AudioBuffer) => Promise<AudioBuffer>
): Promise<AudioBuffer> {
  if (!selection || selection.start === selection.end) {
    // No selection, apply to entire buffer
    return await effectFn(buffer);
  }

  // Extract the selected region
  const region = extractRegion(buffer, selection.start, selection.end);

  // Apply effect to the region
  const processedRegion = await effectFn(region);

  // Replace the region in the original buffer
  return replaceRegion(buffer, processedRegion, selection.start);
}