import { describe, expect, it } from "@suaveplan/testing/runner";
import { PseudoRandomError } from "../errors/pseudo-random-error.js";
import { Sfc32Rng } from "./sfc32.js";

describe("Sfc32Rng", () => {
    it("is deterministic", { timeout: 5000 }, () => {
        const a = new Sfc32Rng("abc");
        const b = new Sfc32Rng("abc");
        for (let i = 0; i < 100; i += 1) {
            expect(a.nextUint32()).toBe(b.nextUint32());
        }
    });

    it("produces uint32 in range", { timeout: 5000 }, () => {
        const r = new Sfc32Rng(1);
        for (let i = 0; i < 1000; i += 1) {
            const v = r.nextUint32();
            expect(v).toBeGreaterThanOrEqual(0);
            expect(v).toBeLessThan(2 ** 32);
        }
    });

    it("skip === repeated nextUint32", { timeout: 5000 }, () => {
        const a = new Sfc32Rng(2);
        const b = new Sfc32Rng(2);
        a.skip(50);
        for (let i = 0; i < 50; i += 1) b.nextUint32();
        expect(a.nextUint32()).toBe(b.nextUint32());
    });

    it("at doesn't mutate self", { timeout: 5000 }, () => {
        const a = new Sfc32Rng(3);
        const ahead = a.at(10);
        expect(a.position).toBe(0);
        expect(ahead.position).toBe(10);
    });

    it("checkpoint/restore round-trip", { timeout: 5000 }, () => {
        const r = new Sfc32Rng(4);
        r.skip(7);
        const cp = r.checkpoint();
        const exp = [r.nextUint32(), r.nextUint32()];
        r.restore(cp);
        expect([r.nextUint32(), r.nextUint32()]).toEqual(exp);
    });

    it("restore rejects foreign algorithm", { timeout: 5000 }, () => {
        const r = new Sfc32Rng(5);
        expect(() =>
            r.restore({ algorithm: "mulberry32", state: [0], counter: 0 })
        ).toThrow(PseudoRandomError);
    });

    it("restore rejects bad state length or non-finite words", {
        timeout: 5000,
    }, () => {
        const r = new Sfc32Rng(6);
        expect(() =>
            r.restore({ algorithm: "sfc32", state: [1, 2], counter: 0 })
        ).toThrow(PseudoRandomError);
        expect(() =>
            r.restore({
                algorithm: "sfc32",
                state: [1, 2, 3, Number.NaN],
                counter: 0,
            })
        ).toThrow(PseudoRandomError);
    });

    it("rejects invalid skip/at", { timeout: 5000 }, () => {
        const r = new Sfc32Rng(7);
        expect(() => r.skip(-1)).toThrow(PseudoRandomError);
        expect(() => r.at(-1)).toThrow(PseudoRandomError);
    });

    it("fork yields distinct stream", { timeout: 5000 }, () => {
        const parent = new Sfc32Rng(8);
        const child = parent.fork("x");
        const a = [parent.nextUint32(), parent.nextUint32()];
        const b = [child.nextUint32(), child.nextUint32()];
        expect(a).not.toEqual(b);
    });

    it("nextFloat is in [0,1)", { timeout: 5000 }, () => {
        const r = new Sfc32Rng(9);
        for (let i = 0; i < 200; i += 1) {
            const f = r.nextFloat();
            expect(f).toBeGreaterThanOrEqual(0);
            expect(f).toBeLessThan(1);
        }
    });
});