/*
Copyright 2020 Bruno Windels <bruno@windels.cloud>

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 {ObservableValue} from "../observable/ObservableValue";

class Timeout {
    constructor(elapsed, ms) {
        this._reject = null;
        this._handle = null;
        const timeoutValue = elapsed.get() + ms;
        this._waitHandle = elapsed.waitFor(t => t >= timeoutValue);
    }

    elapsed() {
        return this._waitHandle.promise;
    }

    abort() {
        // will reject with AbortError
        this._waitHandle.dispose();
    }
}

class Interval {
    constructor(elapsed, ms, callback) {
        this._start = elapsed.get();
        this._last = this._start;
        this._interval = ms;
        this._callback = callback;
        this._subscription = elapsed.subscribe(this._update.bind(this));
    }

    _update(elapsed) {
        const prevAmount = Math.floor((this._last - this._start) / this._interval);
        const newAmount = Math.floor((elapsed - this._start) / this._interval);
        const amountDiff = Math.max(0, newAmount - prevAmount);
        this._last = elapsed;

        for (let i = 0; i < amountDiff; ++i) {
            this._callback();
        }
    }

    dispose() {
        if (this._subscription) {
            this._subscription();
            this._subscription = null;
        }
    }
}

class TimeMeasure {
    constructor(elapsed) {
        this._elapsed = elapsed;
        this._start = elapsed.get();
    }

    measure() {
        return this._elapsed.get() - this._start;
    }
}

export class Clock {
    constructor(baseTimestamp = 0) {
        this._baseTimestamp = baseTimestamp;
        this._elapsed = new ObservableValue(0);
        // should be callable as a function as well as a method
        this.createMeasure = this.createMeasure.bind(this);
        this.createTimeout = this.createTimeout.bind(this);
        this.now = this.now.bind(this);
    }

    createMeasure() {
        return new TimeMeasure(this._elapsed);
    }

    createTimeout(ms) {
        return new Timeout(this._elapsed, ms);
    }

    createInterval(callback, ms) {
        return new Interval(this._elapsed, ms, callback);
    }

    now() {
        return this._baseTimestamp + this.elapsed;
    }

    elapse(ms) {
        this._elapsed.set(this._elapsed.get() + Math.max(0, ms));
    }

    get elapsed() {
        return this._elapsed.get();
    }
}

export function tests() {
    return {
        "test timeout": async assert => {
            const clock = new Clock();
            Promise.resolve().then(() => {
                clock.elapse(500);
                clock.elapse(500);
            }).catch(assert.fail);
            const timeout = clock.createTimeout(1000);
            const promise = timeout.elapsed();
            assert(promise instanceof Promise);
            await promise;
        },
        "test interval": assert => {
            const clock = new Clock();
            let counter = 0;
            const interval = clock.createInterval(() => counter += 1, 200);
            clock.elapse(150);
            assert.strictEqual(counter, 0);
            clock.elapse(500);
            assert.strictEqual(counter, 3);
            interval.dispose();
        }
    }
}
