/**
 * Geometry for the ornament kit, as pure functions so every page draws the
 * same shapes and tests can pin them down. Randomness is seeded, so a star
 * path looks the same on every build.
 */

export const colors = {
  sky: "#0E1522",
  midnight: "#131C2B",
  lines: "#26344A",
  linesStrong: "#3A4C66",
  starlight: "#F4F2ED",
  text: "#ECE9E2",
  soft: "#C8D3D8",
  muted: "#9FB3BD",
  teal: "#14A39A",
  tealBright: "#2BC2B7",
  gold: "#C9A24A",
  goldBright: "#D8B35A",
  violetOnDark: "#9A70F5",
  /** Light mode only. */
  violet: "#6A2FE0",
  goldDeep: "#8A6516",
  tealDeep: "#0A726B",
} as const;

/** A small, fast seeded generator (mulberry32). */
export function seeded(seed: number): () => number {
  let a = seed >>> 0;
  return () => {
    a = (a + 0x6d2b79f5) >>> 0;
    let t = a;
    t = Math.imul(t ^ (t >>> 15), t | 1);
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}

/** A string to a seed, so components can be seeded by a name. */
export function seedOf(text: string): number {
  let h = 2166136261;
  for (let i = 0; i < text.length; i++) h = Math.imul(h ^ text.charCodeAt(i), 16777619);
  return h >>> 0;
}

const r1 = (n: number) => Math.round(n * 10) / 10;

/**
 * The thin four-point star used everywhere: points of a polygon centered on
 * (cx, cy) with outer radius r. The waist stays at 16% so it never reads as a
 * cross.
 */
export function starPoints(cx: number, cy: number, r: number): string {
  const w = r * 0.16;
  const pts: [number, number][] = [
    [cx, cy - r],
    [cx + w, cy - w],
    [cx + r, cy],
    [cx + w, cy + w],
    [cx, cy + r],
    [cx - w, cy + w],
    [cx - r, cy],
    [cx - w, cy - w],
  ];
  return pts.map(([x, y]) => `${r1(x)},${r1(y)}`).join(" ");
}

export type StarPathMark = { kind: "dot"; x: number; y: number; r: number } | { kind: "star"; x: number; y: number; r: number; gold: boolean };

export interface StarPath {
  /** Dotted segments between marks, stopping short of each. */
  links: { x1: number; y1: number; x2: number; y2: number }[];
  marks: StarPathMark[];
}

export const strengths = { calm: 0.1, standard: 0.22, wild: 0.42 } as const;

/**
 * Greg's star path: a straight line replaced by evenly spread stars, each
 * nudged off the line, joined by dotted segments. About a third of the points
 * are small violet stars, the rest Starlight dots. Ends stay on the line.
 */
export function starPath(o: {
  x1: number;
  x2: number;
  y: number;
  steps: number;
  seed: number;
  strength?: keyof typeof strengths;
  /** Put a large gold star at the middle point. */
  centerStar?: boolean;
  /** Leave the end points off, when a gold line or star already marks them. */
  openEnds?: boolean;
  gap?: number;
  dot?: number;
  star?: number;
}): StarPath {
  const rand = seeded(o.seed);
  const step = (o.x2 - o.x1) / o.steps;
  const nudge = strengths[o.strength ?? "standard"] * Math.abs(step);
  const gap = o.gap ?? 4;
  const points = Array.from({ length: o.steps + 1 }, (_, i) => {
    const ends = i === 0 || i === o.steps;
    return { x: o.x1 + step * i, y: ends ? o.y : o.y + (rand() * 2 - 1) * nudge };
  });
  const mid = Math.round(o.steps / 2);
  const marks: StarPathMark[] = points.map((p, i) => {
    if (o.centerStar && i === mid) return { kind: "star", x: r1(p.x), y: r1(p.y), r: (o.star ?? 4) * 3, gold: true };
    // Every third point, offset by the seed, is a small star.
    const isStar = (i + (o.seed % 3)) % 3 === 1;
    return isStar ? { kind: "star", x: r1(p.x), y: r1(p.y), r: o.star ?? 4, gold: false } : { kind: "dot", x: r1(p.x), y: r1(p.y), r: o.dot ?? 1.5 };
  });
  const links = points.slice(1).map((b, i) => {
    const a = points[i]!;
    const dx = b.x - a.x;
    const dy = b.y - a.y;
    const len = Math.hypot(dx, dy) || 1;
    const ux = dx / len;
    const uy = dy / len;
    const ga = gap + (marks[i]!.kind === "star" ? marks[i]!.r * 0.5 : 0);
    const gb = gap + (marks[i + 1]!.kind === "star" ? marks[i + 1]!.r * 0.5 : 0);
    return { x1: r1(a.x + ux * ga), y1: r1(a.y + uy * ga), x2: r1(b.x - ux * gb), y2: r1(b.y - uy * gb) };
  });
  const drop = (i: number) => o.openEnds && (i === 0 || i === points.length - 1);
  return { links, marks: marks.filter((_, i) => !drop(i)) };
}

/** Tick marks for a scale: a long tick every `major`, short ones between. */
export function ticks(width: number, count: number, major = 5): { x: number; long: boolean }[] {
  const step = width / count;
  return Array.from({ length: count + 1 }, (_, i) => ({ x: r1(0.5 + step * i), long: i % major === 0 }));
}

/** Ticks around a circle, for tick rings on step numbers and medallions. */
export function ringTicks(size: number, count = 48, major = 4): { x1: number; y1: number; x2: number; y2: number; long: boolean }[] {
  const c = size / 2;
  const outer = c - 1;
  return Array.from({ length: count }, (_, i) => {
    const a = (i / count) * Math.PI * 2;
    const long = i % major === 0;
    const inner = outer - (long ? size * 0.066 : size * 0.033);
    const f = (n: number) => Math.round(n * 100) / 100;
    return { x1: f(c + Math.cos(a) * outer), y1: f(c + Math.sin(a) * outer), x2: f(c + Math.cos(a) * inner), y2: f(c + Math.sin(a) * inner), long };
  });
}

/**
 * Constellation dust: sparse specks for a page background as CSS
 * radial-gradients, about one in five gold. Static by design.
 */
export function dust(count: number, seed: number): string {
  const rand = seeded(seed);
  const specks: string[] = [];
  for (let i = 0; i < count; i++) {
    const size = [1, 1, 1.2, 1.6][Math.floor(rand() * 4)];
    const alpha = [0.25, 0.35, 0.6][Math.floor(rand() * 3)];
    const gold = rand() < 0.2;
    const color = gold ? `rgba(216,179,90,${alpha})` : `rgba(236,233,226,${alpha})`;
    specks.push(`radial-gradient(${size}px ${size}px at ${r1(rand() * 100)}% ${r1(rand() * 100)}%, ${color}, transparent)`);
  }
  return specks.join(", ");
}