r3bl-ts-utils/src/timer-utils/timer-reducer.ts

The `r3bl-ts-utils` package is a set of useful TypeScript functions and classes that can be used in Node.js and browser environments. They are inspired by Kotlin stdlib, and Rust to write code as expressions rather than statements, colorized text, powerfu

/*
 * Copyright (c) 2022 R3BL LLC. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

import { State, TimerErrors } from "./externals"
import { TimerInternal } from "./internals"

interface StartAction {
  type: "start"
  startTime: number
}

interface StopAction {
  type: "stop"
  stopTime: number
}

export type Actions = StartAction | StopAction

type ReducerFnType = (timer: TimerInternal, currentState?: State, action?: Actions) => State

/**
 * @throws TimerErrors
 */
export const reducerFn: ReducerFnType = (
  timer: TimerInternal,
  currentState?: State,
  action?: Actions
): State => {
  if (!currentState)
    return {
      runtimeStatus: "created_not_started",
      startTime: 0,
      stopTime: 0,
    }

  const { runtimeStatus } = currentState
  const {
    CantStart_AlreadyStopped,
    CantStart_AlreadyRunning,
    CantStop_AlreadyStopped,
    CantStop_NotStarted,
  } = TimerErrors

  if (action)
    switch (action.type) {
      case "start":
        if (runtimeStatus === "created_not_started") return startFn(timer, currentState, action)
        if (runtimeStatus === "stopped") throw CantStart_AlreadyStopped
        if (runtimeStatus === "running") throw CantStart_AlreadyRunning
        break
      case "stop":
        if (runtimeStatus === "created_not_started") throw CantStop_NotStarted
        if (runtimeStatus === "stopped") throw CantStop_AlreadyStopped
        if (runtimeStatus === "running") return stopFn(timer, currentState, action)
        break
    }

  return currentState
}

function stopFn(timer: TimerInternal, currentState: State, action: StopAction): State {
  timer.actuallyStop()
  return { ...currentState, runtimeStatus: "stopped", stopTime: action.stopTime }
}

function startFn(timer: TimerInternal, currentState: State, action: StartAction): State {
  timer.actuallyStart()
  return {
    ...currentState,
    runtimeStatus: "running",
    startTime: action.startTime,
  }
}