// The sums the contrast check runs on, tested away from a browser.
//
// The check itself needs a page to look at, but the arithmetic underneath it doesn't —
// and the arithmetic is the part that decides whether a real fault is reported or
// waved through. Faded text used to be filed as "not checked" rather than measured;
// this is the compositing that replaced that.
const test = require("node:test");
const { describe } = require("node:test");
const assert = require("node:assert");
const LayoutAudit = require("./uiAudit");

const WHITE = { r: 255, g: 255, b: 255, a: 1 };
const BLACK = { r: 0, g: 0, b: 0, a: 1 };
const PAGE = { r: 28, g: 28, b: 28, a: 1 };      // the felt page behind everything
const PUCK = { r: 44, g: 44, b: 44, a: 1 };      // a seat's own background

describe("the ratio itself", () => {
    test("black on white is the full 21:1, either way round", () => {
        assert.ok(Math.abs(LayoutAudit.contrastRatio(BLACK, WHITE) - 21) < 0.01);
        assert.ok(Math.abs(LayoutAudit.contrastRatio(WHITE, BLACK) - 21) < 0.01);
    });

    test("a colour against itself is 1:1", () => {
        assert.ok(Math.abs(LayoutAudit.contrastRatio(PUCK, PUCK) - 1) < 0.001);
    });
});

describe("text on a box that is being faded", () => {
    // opacity on a box fades the box and its text together onto whatever is behind
    // it — so a dimmed seat is not grey text on a dark puck, it is a faded puck and
    // faded text both landing on the page.
    const fade = alpha => ({ alpha, behind: PAGE });

    test("at full strength nothing is composited", () => {
        const painted = LayoutAudit.asPainted(WHITE, PUCK, { alpha: 1, behind: PAGE });
        assert.deepEqual(painted.fg, WHITE);
        assert.deepEqual(painted.bg, PUCK);
    });

    test("fading moves both the text and its background, not just the text", () => {
        const painted = LayoutAudit.asPainted(WHITE, PUCK, fade(0.7));
        assert.ok(painted.fg.r < WHITE.r, "the text dims");
        assert.ok(painted.bg.r < PUCK.r, "and so does what it sits on");
        assert.ok(painted.bg.r > PAGE.r, "but not all the way to the page");
    });

    test("which is what stops a fade being reported as a fault it isn't", () => {
        // Dimming light text on a dark puck over a dark page costs contrast, but far
        // less than measuring the faded text against the *unfaded* puck would claim.
        const honest = LayoutAudit.asPainted(WHITE, PUCK, fade(0.7));
        const wrong = { fg: LayoutAudit.over({ ...WHITE, a: 0.7 }, PUCK), bg: PUCK };
        assert.ok(LayoutAudit.contrastRatio(honest.fg, honest.bg) >
            LayoutAudit.contrastRatio(wrong.fg, wrong.bg));
    });

    test("a fade all the way out lands everything on the page behind", () => {
        const painted = LayoutAudit.asPainted(WHITE, PUCK, fade(0));
        assert.deepEqual(painted.fg, PAGE);
        assert.deepEqual(painted.bg, PAGE);
    });

    test("with nothing known to be behind it, the fade is left alone", () => {
        // Better to measure the unfaded pair than to invent a backdrop.
        const painted = LayoutAudit.asPainted(WHITE, PUCK, { alpha: 0.5, behind: null });
        assert.deepEqual(painted.fg, WHITE);
        assert.deepEqual(painted.bg, PUCK);
    });
});

describe("a fade makes small grey text worse, which is the fault it went looking for", () => {
    // Deliberately not asserting a particular CSS colour here: the page's own greys are
    // measured in the browser, against the real gradients, where they live. What this
    // pins is the direction — that dimming a box costs its text contrast, which is why
    // filing faded text as "not checked" hid faults rather than avoiding false ones.
    test("the same grey scores lower once its box is dimmed", () => {
        const grey = LayoutAudit.parseColour("rgb(138, 138, 138)");
        const solid = LayoutAudit.asPainted(grey, PUCK, { alpha: 1, behind: PAGE });
        const dimmed = LayoutAudit.asPainted(grey, PUCK, { alpha: 0.7, behind: PAGE });
        assert.ok(LayoutAudit.contrastRatio(dimmed.fg, dimmed.bg) <
            LayoutAudit.contrastRatio(solid.fg, solid.bg));
    });

    test("and a lighter grey scores higher at the same fade", () => {
        const at = colour => {
            const painted = LayoutAudit.asPainted(LayoutAudit.parseColour(colour), PUCK, { alpha: 0.7, behind: PAGE });
            return LayoutAudit.contrastRatio(painted.fg, painted.bg);
        };
        assert.ok(at("rgb(174, 174, 174)") > at("rgb(138, 138, 138)"));
    });
});

describe("reading a colour off the page", () => {
    test("rgb and rgba both come back as numbers", () => {
        assert.deepEqual(LayoutAudit.parseColour("rgb(1, 2, 3)"), { r: 1, g: 2, b: 3, a: 1 });
        assert.deepEqual(LayoutAudit.parseColour("rgba(1, 2, 3, 0.5)"), { r: 1, g: 2, b: 3, a: 0.5 });
    });

    test("a gradient gives up every stop, because text could be over any of them", () => {
        const stops = LayoutAudit.gradientStops("linear-gradient(rgb(203, 170, 240), rgb(169, 127, 214))");
        assert.equal(stops.length, 2);
        assert.deepEqual(stops[0], { r: 203, g: 170, b: 240, a: 1 });
        assert.deepEqual(stops[1], { r: 169, g: 127, b: 214, a: 1 });
    });

    test("no background image, no stops", () => {
        assert.deepEqual(LayoutAudit.gradientStops("none"), []);
    });
});