// The digital rain's arithmetic: columns, how they start and step, the glyph
// drawn, and the fade colour. The random source is passed in, so each case is
// exact. Run by `npm test`.
import assert from "node:assert/strict";
import { test } from "node:test";
import {
  CELL,
  GLYPHS,
  columnsFor,
  fadeColorOf,
  glyphFor,
  rainAllowed,
  startDrops,
  stepDrops,
} from "../src/shell/rain.ts";

const always = (n) => () => n;

test("the app's reduce setting stops the rain whatever the OS says", () => {
  assert.equal(rainAllowed("reduce", false), false);
  assert.equal(rainAllowed("reduce", true), false);
});

test("the app's allow setting runs the rain even on a reduce-motion OS", () => {
  assert.equal(rainAllowed("allow", true), true);
  assert.equal(rainAllowed("allow", false), true);
});

test("with no app setting the rain follows the OS", () => {
  assert.equal(rainAllowed(undefined, false), true);
  assert.equal(rainAllowed(undefined, true), false);
  assert.equal(rainAllowed("", true), false);
});

test("a canvas gets one column per cell, rounded up, and at least one", () => {
  assert.equal(columnsFor(CELL * 10), 10);
  assert.equal(columnsFor(CELL * 10 + 1), 11);
  assert.equal(columnsFor(0), 1);
});

test("columns start above the top, spread over 40 cells", () => {
  assert.deepEqual(
    startDrops(3, always(0)).map((row) => row === 0),
    [true, true, true],
  );
  assert.deepEqual(startDrops(2, always(0.5)), [-20, -20]);
  for (const row of startDrops(200, Math.random)) {
    assert.ok(row <= 0 && row >= -40, String(row));
  }
});

test("a step moves every column down one row", () => {
  assert.deepEqual(stepDrops([-3, 0, 5], 10_000, always(0)), [-2, 1, 6]);
});

test("a column past the bottom restarts only on a high enough roll", () => {
  const past = [Math.ceil(100 / CELL) + 1];
  assert.deepEqual(stepDrops(past, 100, always(0.99)), [1]);
  assert.deepEqual(stepDrops(past, 100, always(0.5)), [past[0] + 1]);
});

test("a column still on the canvas never restarts", () => {
  assert.deepEqual(stepDrops([2], 100, always(0.99)), [3]);
});

test("a step does not change the array it was given", () => {
  const drops = [1, 2];
  stepDrops(drops, 100, always(0.99));
  assert.deepEqual(drops, [1, 2]);
});

test("the glyph comes from the set, first and last at the ends of the roll", () => {
  assert.equal(glyphFor(always(0)), GLYPHS[0]);
  assert.equal(glyphFor(always(0.999999)), GLYPHS[GLYPHS.length - 1]);
});

test("the fade colour keeps the background's channels at a low alpha", () => {
  assert.equal(fadeColorOf("rgb(30, 30, 46)"), "rgba(30, 30, 46, 0.09)");
  assert.equal(fadeColorOf("rgb(239,241,245)"), "rgba(239, 241, 245, 0.09)");
  assert.equal(fadeColorOf("rgba(1, 2, 3, 0.5)"), "rgba(1, 2, 3, 0.09)");
});

test("a colour with no channels fades from the default background", () => {
  assert.equal(fadeColorOf("transparent"), "rgba(30, 30, 46, 0.09)");
  assert.equal(fadeColorOf(""), "rgba(30, 30, 46, 0.09)");
});