garden.ts

/**
 * Generative garden for the for-funsies board.
 *
 * At build time the site produces a deterministic "constellation" that
 * accumulates as the repository does: every commit adds a star, every build
 * adds a growth ring, and the whole field is seeded from the repository's own
 * history (commit hashes, authors, dates) plus the ledger's contributor list.
 * Two consecutive builds are never identical because main only moves when a
 * new commit lands — so the build count, the latest hash, and the star field
 * all change together.
 *
 * This module is pure and dependency-free (node: builtins only). It is used
 * by scripts/build_site.js at build time and is never shipped to the browser,
 * so it holds no DOM references and poses no XSS surface.
 */

import { createHash } from "node:crypto";

export interface CommitInfo {
  hash: string;
  author: string;
  date: string;
}

export interface GardenSnapshot {
  /** Number of commits in the repository — the build counter. */
  build: number;
  /** Short hash of the most recent commit. */
  latestHash: string;
  /** ISO date of the most recent commit. */
  latestDate: string;
  /** De-duplicated contributor handles from the ledger. */
  contributors: string[];
  /** Commit history, newest first, capped for a bounded field. */
  commits: CommitInfo[];
}

/** Deterministic 32-bit hash of a string (FNV-1a). */
function hash32(input: string): number {
  let h = 2166136261;
  for (let i = 0; i < input.length; i++) {
    h ^= input.charCodeAt(i);
    h = Math.imul(h, 16777619);
  }
  return h >>> 0;
}

/** Convert a 32-bit hash into a number in [0, 1). */
function unit(hashValue: number): number {
  return (hashValue >>> 0) / 4294967296;
}

/** A small deterministic PRNG so sequences are reproducible per build. */
function mulberry32(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 soft, deterministic accent palette tuned for the site's light/dark themes. */
function hueFor(author: string): number {
  return Math.floor(unit(hash32(`author:${author}`)) * 360);
}

function escapeXml(value: string): string {
  return value
    .replace(/&/g, "&amp;")
    .replace(/</g, "&lt;")
    .replace(/>/g, "&gt;")
    .replace(/"/g, "&quot;")
    .replace(/'/g, "&#39;");
}

/**
 * Render the generative constellation as an inline SVG string.
 *
 * Layout is stable per commit: each commit's star sits at a position derived
 * solely from its own hash, so as new commits land the existing stars stay put
 * and the field *grows* rather than reshuffling. This gives the "accumulates
 * over time" quality the brief asks for.
 */
export function renderGarden(snap: GardenSnapshot): string {
  const W = 800;
  const H = 360;
  const CX = W / 2;
  const CY = H / 2;

  // Seed the ambient field from the latest commit so its density/ambient
  // colours drift with every build.
  const rng = mulberry32(hash32(`garden:${snap.latestHash}:${snap.build}`));

  // Concentric growth rings: one per build, capped so the field stays readable.
  const ringCount = Math.min(snap.build, 24);
  let rings = "";
  for (let r = 1; r <= ringCount; r++) {
    const radius = 18 + r * 6.5;
    const opacity = 0.05 + (r / ringCount) * 0.12;
    rings += `<circle cx="${CX}" cy="${CY}" r="${radius.toFixed(1)}" fill="none" stroke="currentColor" stroke-opacity="${opacity.toFixed(3)}" stroke-width="1"/>`;
  }

  // One star per commit, position fixed by the commit's own hash.
  const maxStars = Math.min(snap.commits.length, 160);
  let stars = "";
  for (let i = 0; i < maxStars; i++) {
    const c = snap.commits[i];
    if (!c) continue;
    const angle = unit(hash32(`angle:${c.hash}`)) * Math.PI * 2;
    const radius = 26 + unit(hash32(`radius:${c.hash}`)) * 120;
    const x = CX + Math.cos(angle) * radius;
    const y = CY + Math.sin(angle) * radius * 0.72;
    const hue = hueFor(c.author);
    const size = 1.3 + unit(hash32(`size:${c.hash}`)) * 2.4;
    const age = snap.build > 0 ? i / Math.max(snap.build, 1) : 0.5;

    // Connect every star back to the core so the constellation reads as a web.
    stars += `<line x1="${CX}" y1="${CY}" x2="${x.toFixed(1)}" y2="${y.toFixed(1)}" stroke="hsl(${hue} 70% 55%)" stroke-opacity="${(0.08 + age * 0.12).toFixed(3)}" stroke-width="0.8"/>`;
    stars += `<circle cx="${x.toFixed(1)}" cy="${y.toFixed(1)}" r="${size.toFixed(2)}" fill="hsl(${hue} 80% ${45 + age * 25}%)" fill-opacity="${(0.55 + age * 0.4).toFixed(3)}"/>`;
  }

  // Ambient sprinkle — deterministic but seeded from history, so it shifts.
  let ambient = "";
  for (let i = 0; i < 40; i++) {
    const x = rng() * W;
    const y = rng() * H;
    const r = 0.4 + rng() * 0.9;
    const o = 0.12 + rng() * 0.3;
    ambient += `<circle cx="${x.toFixed(1)}" cy="${y.toFixed(1)}" r="${r.toFixed(2)}" fill="currentColor" fill-opacity="${o.toFixed(3)}"/>`;
  }

  // The core: colour and pulse derive from the latest commit.
  const coreHue = hueFor(snap.latestHash);
  const pulse = snap.build % 60;

  // Caption — build count, repo age, contributor count. All real repo data.
  const contributorCount = snap.contributors.length;
  const latest = snap.latestDate.slice(0, 10);
  const caption = `build ${snap.build} · ${snap.commits.length} commits · ${contributorCount} ${
    contributorCount === 1 ? "contributor" : "contributors"
  } · latest ${latest}`;

  return `<svg xmlns="http://www.w3.org/2000/svg" width="${W}" height="${H}" viewBox="0 0 ${W} ${H}" role="img" aria-label="${escapeXml(caption)}">
  <rect width="${W}" height="${H}" fill="none"/>
  <text x="${CX}" y="${H - 14}" text-anchor="middle" font-family="ui-monospace,'SF Mono',Menlo,Consolas,monospace" font-size="11" fill="currentColor" fill-opacity="0.55">${escapeXml(caption)}</text>
  ${ambient}
  ${rings}
  ${stars}
  <circle cx="${CX}" cy="${CY}" r="9" fill="hsl(${coreHue} 85% 55%)" fill-opacity="0.9"/>
  <circle cx="${CX}" cy="${CY}" r="${(9 + (pulse % 5)).toFixed(1)}" fill="none" stroke="hsl(${coreHue} 85% 60%)" stroke-opacity="0.35" stroke-width="1.5"/>
</svg>`;
}

/** Build a snapshot from raw git + ledger inputs. Pure, no I/O. */
export function buildSnapshot(commits: CommitInfo[], contributors: string[]): GardenSnapshot {
  const latest = commits[0];
  return {
    build: Math.max(commits.length, 1),
    latestHash: latest?.hash ?? "none",
    latestDate: latest?.date ?? "",
    contributors,
    commits,
  };
}