const test=require("node:test");
const assert=require("assert");

class Fib {
    constructor(limit) {
        this.limit=limit;
        this.count=0;
        this.val=0;
        this.next_val=1;
    }
    
    [Symbol.iterator]() {
        return new FibIterator(this);
    }
}

class FibIterator {
    constructor(fib) {
        this.fib=fib;
    }
                     
    next() {
        if (this.fib.count <= this.fib.limit) {
            let tmp = this.fib.val;
            this.fib.val = this.fib.next_val;
            this.fib.next_val = tmp+this.fib.next_val;
            this.fib.count++;
            return {done:false, value:tmp};
        } else {
            return {done:true};
        }
    }
}

test("Fib(6)", (t)=> {
    let results = [];
    for (let f of new Fib(6)) { results.push(f); }
    assert.deepStrictEqual(results,[0,1,1,2,3,5,8]);
});

test("Fib(42)", (t)=> {
    let result = -1;
    for (let f of new Fib(42)) { result = f; }
    assert.strictEqual(result,267914296);
});

test("Fib(2) destructure", (t)=> {
    let [a,b,c] = new Fib(6);
    assert.deepStrictEqual([a,b,c],[0,1,1]);
});

test("Fib(6) spread", (t)=> {
    assert.deepStrictEqual([...new Fib(6)], [0,1,1,2,3,5,8]);
});