// Arrays. The compiler gives only `a[i]`, `a[i] = x` and `a.length`, which can
// also be written. Every method here is built on those
//
// Not as the spec says:
// - A method takes one value where the spec takes any number (`push(x)`,
//   `unshift(x)`, `concat(other)`), because more need rest params
// - A callback gets the element and its index, not the array too
// - Holes are not skipped: a callback sees undefined for a hole

// `Array(n)` and `new Array(n)` make an array of `n` holes
function Array(n) {
    const a = [];
    if (n !== undefined) a.length = n;
    return a;
}

Array.prototype = {
    // ── Change the array ──
    push(x) {
        this[this.length] = x;
        return this.length;
    },
    pop() {
        if (this.length === 0) return undefined;
        const x = this[this.length - 1];
        this.length = this.length - 1;
        return x;
    },
    shift() {
        if (this.length === 0) return undefined;
        const x = this[0];
        for (let i = 1; i < this.length; i++) this[i - 1] = this[i];
        this.length = this.length - 1;
        return x;
    },
    unshift(x) {
        for (let i = this.length; i > 0; i--) this[i] = this[i - 1];
        this[0] = x;
        return this.length;
    },
    reverse() {
        for (let i = 0, j = this.length - 1; i < j; i++, j--) {
            const x = this[i];
            this[i] = this[j];
            this[j] = x;
        }
        return this;
    },
    fill(x, start, end) {
        const len = this.length;
        const s = relativeIndex(start === undefined ? 0 : start, len);
        const e = relativeIndex(end === undefined ? len : end, len);
        for (let i = s; i < e; i++) this[i] = x;
        return this;
    },

    // ── Read ──
    at(i) {
        if (i < 0) i += this.length;
        return this[i];
    },
    indexOf(x, from) {
        for (let i = from === undefined ? 0 : relativeIndex(from, this.length); i < this.length; i++) {
            if (this[i] === x) return i;
        }
        return -1;
    },
    lastIndexOf(x) {
        for (let i = this.length - 1; i >= 0; i--) {
            if (this[i] === x) return i;
        }
        return -1;
    },
    includes(x) {
        return this.indexOf(x) !== -1;
    },
    join(sep) {
        const s = sep === undefined ? "," : sep;
        let out = "";
        for (let i = 0; i < this.length; i++) {
            if (i > 0) out = out + s;
            const x = this[i];
            if (x !== undefined && x !== null) out = out + String(x);
        }
        return out;
    },
    toString() {
        return this.join(",");
    },

    // ── Make a new array ──
    slice(start, end) {
        const len = this.length;
        const s = relativeIndex(start === undefined ? 0 : start, len);
        const e = relativeIndex(end === undefined ? len : end, len);
        const out = [];
        for (let i = s; i < e; i++) out[i - s] = this[i];
        return out;
    },
    concat(other) {
        const out = this.slice();
        for (let i = 0; i < other.length; i++) out[out.length] = other[i];
        return out;
    },

    // ── With a callback ──
    forEach(f) {
        for (let i = 0; i < this.length; i++) f(this[i], i);
    },
    map(f) {
        const out = [];
        for (let i = 0; i < this.length; i++) out[i] = f(this[i], i);
        return out;
    },
    filter(f) {
        const out = [];
        for (let i = 0; i < this.length; i++) {
            if (f(this[i], i)) out[out.length] = this[i];
        }
        return out;
    },
    reduce(f, init) {
        let acc = init;
        for (let i = 0; i < this.length; i++) acc = f(acc, this[i], i);
        return acc;
    },
    find(f) {
        for (let i = 0; i < this.length; i++) {
            if (f(this[i], i)) return this[i];
        }
        return undefined;
    },
    findIndex(f) {
        for (let i = 0; i < this.length; i++) {
            if (f(this[i], i)) return i;
        }
        return -1;
    },
    some(f) {
        for (let i = 0; i < this.length; i++) {
            if (f(this[i], i)) return true;
        }
        return false;
    },
    every(f) {
        for (let i = 0; i < this.length; i++) {
            if (!f(this[i], i)) return false;
        }
        return true;
    },
};

__link_proto_array(Array.prototype);