bemusic/bemuse

import { Speedcore } from '../speedcore'
import { uniq, map } from '../util/lodash'
import { BMSChart } from '../bms/chart'
import { SpeedSegment } from '../speedcore/segment'

const precedence = { bpm: 1, stop: 2 }

/**
 * A Timing represents the timing information of a musical score.
 * A Timing object provides facilities to synchronize between
 * metric time (seconds) and musical time (beats).
 *
 * A Timing are created from a series of actions:
 *
 * - BPM changes.
 * - STOP action.
 */
export class Timing {
  _speedcore: Speedcore<TimingSegment>
  _eventBeats: number[]
  /**
   * Constructs a Timing with an initial BPM and specified actions.
   *
   * Generally, you would use `Timing.fromBMSChart` to create an instance
   * from a BMSChart, but the constructor may also be used in other situations
   * unrelated to the BMS file format. (e.g. bmson package)
   */
  constructor(initialBPM: number, actions: TimingAction[]) {
    const state = { bpm: initialBPM, beat: 0, seconds: 0 }
    const segments: TimingSegment[] = []
    segments.push({
      t: 0,
      x: 0,
      dx: state.bpm / 60,
      bpm: state.bpm,
      inclusive: true,
    })
    actions = actions.slice()
    actions.sort(function (a, b) {
      return a.beat - b.beat || precedence[a.type] - precedence[b.type]
    })
    actions.forEach(function (action) {
      const beat = action.beat
      let seconds = state.seconds + ((beat - state.beat) * 60) / state.bpm
      switch (action.type) {
        case 'bpm':
          state.bpm = action.bpm
          segments.push({
            t: seconds,
            x: beat,
            dx: state.bpm / 60,
            bpm: state.bpm,
            inclusive: true,
          })
          break
        case 'stop':
          segments.push({
            t: seconds,
            x: beat,
            dx: 0,
            bpm: state.bpm,
            inclusive: true,
          })
          seconds += ((action.stopBeats || 0) * 60) / state.bpm
          segments.push({
            t: seconds,
            x: beat,
            dx: state.bpm / 60,
            bpm: state.bpm,
            inclusive: false,
          })
          break
        default:
          throw new Error('Unrecognized segment object!')
      }
      state.beat = beat
      state.seconds = seconds
    })
    this._speedcore = new Speedcore(segments)
    this._eventBeats = uniq(map(actions, (action) => action.beat))
  }

  /**
   * Convert the given beat into seconds.
   * @param {number} beat
   */
  beatToSeconds(beat: number) {
    return this._speedcore.t(beat)
  }

  /**
   * Convert the given second into beats.
   * @param {number} seconds
   */
  secondsToBeat(seconds: number) {
    return this._speedcore.x(seconds)
  }

  /**
   * Returns the BPM at the specified beat.
   * @param {number} beat
   */
  bpmAtBeat(beat: number) {
    return this._speedcore.segmentAtX(beat).bpm
  }

  /**
   * Returns an array representing the beats where there are events.
   */
  getEventBeats() {
    return this._eventBeats
  }

  /**
   * Creates a Timing instance from a BMSChart.
   * @param {BMSChart} chart
   */
  static fromBMSChart(chart: BMSChart) {
    void BMSChart
    const actions: TimingAction[] = []
    chart.objects.all().forEach(function (object) {
      let bpm
      const beat = chart.measureToBeat(object.measure, object.fraction)
      if (object.channel === '03') {
        bpm = parseInt(object.value, 16)
        actions.push({ type: 'bpm', beat: beat, bpm: bpm })
      } else if (object.channel === '08') {
        bpm = +chart.headers.get('bpm' + object.value)!
        if (!isNaN(bpm)) actions.push({ type: 'bpm', beat: beat, bpm: bpm })
      } else if (object.channel === '09') {
        const stopBeats = +chart.headers.get('stop' + object.value)! / 48
        actions.push({ type: 'stop', beat: beat, stopBeats: stopBeats })
      }
    })
    return new Timing(+chart.headers.get('bpm')! || 60, actions)
  }
}

export type TimingAction = BPMTimingAction | StopTimingAction
export interface BaseTimingAction {
  /** where this action occurs */
  beat: number
}
export interface BPMTimingAction extends BaseTimingAction {
  type: 'bpm'
  /** BPM to change to */
  bpm: number
}
export interface StopTimingAction extends BaseTimingAction {
  type: 'stop'
  /** number of beats to stop */
  stopBeats: number
}

interface TimingSegment extends SpeedSegment {
  bpm: number
}