rrweb/src/replay/machine.ts

import { createMachine, interpret, assign, StateMachine } from '@xstate/fsm';
import {
  playerConfig,
  eventWithTime,
  actionWithDelay,
  ReplayerEvents,
  EventType,
  Emitter,
  IncrementalSource,
} from '../types';
import { Timer, addDelay } from './timer';
import { needCastInSyncMode } from '../utils';

export type PlayerContext = {
  events: eventWithTime[];
  timer: Timer;
  timeOffset: number;
  baselineTime: number;
  lastPlayedEvent: eventWithTime | null;
};
export type PlayerEvent =
  | {
      type: 'PLAY';
      payload: {
        timeOffset: number;
      };
    }
  | {
      type: 'CAST_EVENT';
      payload: {
        event: eventWithTime;
      };
    }
  | { type: 'PAUSE' }
  | { type: 'TO_LIVE'; payload: { baselineTime?: number } }
  | {
      type: 'ADD_EVENT';
      payload: {
        event: eventWithTime;
      };
    }
  | {
      type: 'END';
    };
export type PlayerState =
  | {
      value: 'playing';
      context: PlayerContext;
    }
  | {
      value: 'paused';
      context: PlayerContext;
    }
  | {
      value: 'live';
      context: PlayerContext;
    };

/**
 * If the array have multiple meta and fullsnapshot events,
 * return the events from last meta to the end.
 */
export function discardPriorSnapshots(
  events: eventWithTime[],
  baselineTime: number,
): eventWithTime[] {
  for (let idx = events.length - 1; idx >= 0; idx--) {
    const event = events[idx];
    if (event.type === EventType.Meta) {
      if (event.timestamp <= baselineTime) {
        return events.slice(idx);
      }
    }
  }
  return events;
}

type PlayerAssets = {
  emitter: Emitter;
  getCastFn(event: eventWithTime, isSync: boolean): () => void;
};
export function createPlayerService(
  context: PlayerContext,
  { getCastFn, emitter }: PlayerAssets,
) {
  const playerMachine = createMachine<PlayerContext, PlayerEvent, PlayerState>(
    {
      id: 'player',
      context,
      initial: 'paused',
      states: {
        playing: {
          on: {
            PAUSE: {
              target: 'paused',
              actions: ['pause'],
            },
            CAST_EVENT: {
              target: 'playing',
              actions: 'castEvent',
            },
            END: {
              target: 'paused',
              actions: ['resetLastPlayedEvent', 'pause'],
            },
            ADD_EVENT: {
              target: 'playing',
              actions: ['addEvent'],
            },
          },
        },
        paused: {
          on: {
            PLAY: {
              target: 'playing',
              actions: ['recordTimeOffset', 'play'],
            },
            CAST_EVENT: {
              target: 'paused',
              actions: 'castEvent',
            },
            TO_LIVE: {
              target: 'live',
              actions: ['startLive'],
            },
            ADD_EVENT: {
              target: 'paused',
              actions: ['addEvent'],
            },
          },
        },
        live: {
          on: {
            ADD_EVENT: {
              target: 'live',
              actions: ['addEvent'],
            },
            CAST_EVENT: {
              target: 'live',
              actions: ['castEvent'],
            },
          },
        },
      },
    },
    {
      actions: {
        castEvent: assign({
          lastPlayedEvent: (ctx, event) => {
            if (event.type === 'CAST_EVENT') {
              return event.payload.event;
            }
            return ctx.lastPlayedEvent;
          },
        }),
        recordTimeOffset: assign((ctx, event) => {
          let timeOffset = ctx.timeOffset;
          if ('payload' in event && 'timeOffset' in event.payload) {
            timeOffset = event.payload.timeOffset;
          }
          return {
            ...ctx,
            timeOffset,
            baselineTime: ctx.events[0].timestamp + timeOffset,
          };
        }),
        play(ctx) {
          const { timer, events, baselineTime, lastPlayedEvent } = ctx;
          timer.clear();
          for (const event of events) {
            // TODO: improve this API
            addDelay(event, baselineTime);
          }
          const neededEvents = discardPriorSnapshots(events, baselineTime);

          const actions = new Array<actionWithDelay>();
          for (const event of neededEvents) {
            let lastPlayedTimestamp = lastPlayedEvent?.timestamp;
            if (
              lastPlayedEvent?.type === EventType.IncrementalSnapshot &&
              lastPlayedEvent.data.source === IncrementalSource.MouseMove
            ) {
              lastPlayedTimestamp =
                lastPlayedEvent.timestamp +
                lastPlayedEvent.data.positions[0]?.timeOffset;
            }
            if (
              lastPlayedTimestamp &&
              lastPlayedTimestamp < baselineTime &&
              (event.timestamp <= lastPlayedTimestamp ||
                event === lastPlayedEvent)
            ) {
              continue;
            }
            const isSync = event.timestamp < baselineTime;
            if (isSync && !needCastInSyncMode(event)) {
              continue;
            }
            const castFn = getCastFn(event, isSync);
            if (isSync) {
              castFn();
            } else {
              actions.push({
                doAction: () => {
                  castFn();
                  emitter.emit(ReplayerEvents.EventCast, event);
                },
                delay: event.delay!,
              });
            }
          }
          emitter.emit(ReplayerEvents.Flush);
          timer.addActions(actions);
          timer.start();
        },
        pause(ctx) {
          ctx.timer.clear();
        },
        resetLastPlayedEvent: assign((ctx) => {
          return {
            ...ctx,
            lastPlayedEvent: null,
          };
        }),
        startLive: assign({
          baselineTime: (ctx, event) => {
            ctx.timer.toggleLiveMode(true);
            ctx.timer.start();
            if (event.type === 'TO_LIVE' && event.payload.baselineTime) {
              return event.payload.baselineTime;
            }
            return Date.now();
          },
        }),
        addEvent: assign((ctx, machineEvent) => {
          const { baselineTime, timer, events } = ctx;
          if (machineEvent.type === 'ADD_EVENT') {
            const { event } = machineEvent.payload;
            addDelay(event, baselineTime);
            events.push(event);
            const isSync = event.timestamp < baselineTime;
            const castFn = getCastFn(event, isSync);
            if (isSync) {
              castFn();
            } else {
              timer.addAction({
                doAction: () => {
                  castFn();
                  emitter.emit(ReplayerEvents.EventCast, event);
                },
                delay: event.delay!,
              });
              if (!timer.isActive()) {
                timer.start();
              }
            }
          }
          return { ...ctx, events };
        }),
      },
    },
  );
  return interpret(playerMachine);
}

export type SpeedContext = {
  normalSpeed: playerConfig['speed'];
  timer: Timer;
};

export type SpeedEvent =
  | {
      type: 'FAST_FORWARD';
      payload: { speed: playerConfig['speed'] };
    }
  | {
      type: 'BACK_TO_NORMAL';
    }
  | {
      type: 'SET_SPEED';
      payload: { speed: playerConfig['speed'] };
    };

export type SpeedState =
  | {
      value: 'normal';
      context: SpeedContext;
    }
  | {
      value: 'skipping';
      context: SpeedContext;
    };

export function createSpeedService(context: SpeedContext) {
  const speedMachine = createMachine<SpeedContext, SpeedEvent, SpeedState>(
    {
      id: 'speed',
      context,
      initial: 'normal',
      states: {
        normal: {
          on: {
            FAST_FORWARD: {
              target: 'skipping',
              actions: ['recordSpeed', 'setSpeed'],
            },
            SET_SPEED: {
              target: 'normal',
              actions: ['setSpeed'],
            },
          },
        },
        skipping: {
          on: {
            BACK_TO_NORMAL: {
              target: 'normal',
              actions: ['restoreSpeed'],
            },
            SET_SPEED: {
              target: 'normal',
              actions: ['setSpeed'],
            },
          },
        },
      },
    },
    {
      actions: {
        setSpeed: (ctx, event) => {
          if ('payload' in event) {
            ctx.timer.setSpeed(event.payload.speed);
          }
        },
        recordSpeed: assign({
          normalSpeed: (ctx) => ctx.timer.speed,
        }),
        restoreSpeed: (ctx) => {
          ctx.timer.setSpeed(ctx.normalSpeed);
        },
      },
    },
  );

  return interpret(speedMachine);
}

export type PlayerMachineState = StateMachine.State<
  PlayerContext,
  PlayerEvent,
  PlayerState
>;

export type SpeedMachineState = StateMachine.State<
  SpeedContext,
  SpeedEvent,
  SpeedState
>;