//SEE https://github.com/mourner/flatqueue

export default class FlatQueue {

    constructor() {
        this.ids = [];
        this.values = [];
        this.length = 0;
    }

    clear() {
        this.length = 0;
    }

    push(id, value) {
        let pos = this.length++;

        while (pos > 0) {
            let parent = ((pos + 1) >>> 1) - 1;
            let parentValue = this.values[parent];
            if (value >= parentValue) break;
            this.ids[pos] = this.ids[parent];
            this.values[pos] = parentValue;
            pos = parent;
        }

        this.ids[pos] = id;
        this.values[pos] = value;
    }

    pop() {
        if (this.length === 0) return undefined;

        let top = this.ids[0];
        this.length--;

        if (this.length > 0) {
            let id = this.ids[0] = this.ids[this.length];
            let value = this.values[0] = this.values[this.length];
            let halfLength = this.length >> 1;
            let pos = 0;

            while (pos < halfLength) {
                let left = (pos << 1) + 1;
                let right = left + 1;
                let bestIndex = this.ids[left];
                let bestValue = this.values[left];
                let rightValue = this.values[right];

                if (right < this.length && rightValue < bestValue) {
                    left = right;
                    bestIndex = this.ids[right];
                    bestValue = rightValue;
                }
                if (bestValue >= value) break;

                this.ids[pos] = bestIndex;
                this.values[pos] = bestValue;
                pos = left;
            }

            this.ids[pos] = id;
            this.values[pos] = value;
        }

        return top;
    }

    peek() {
        if (this.length === 0) return undefined;
        return this.ids[0];
    }

    peekValue() {
        if (this.length === 0) return undefined;
        return this.values[0];
    }

    shrink() {
        this.ids.length = this.values.length = this.length;
    }
}