// parzival.llc/mark/derive.txt
//
// The mark on parzival.llc is a fixed figure whose bands are weighted by the
// current statement's sha256: band i takes byte i of the hash and varies its
// thickness within twelve per cent of nominal, as set out below. Outline,
// bands and gaps never change. The mark therefore shows when the statement
// has been re-issued; the hash in the record shows which statement it is.
//
// The die (die.json) is the fixed figure: one or more closed polygons per
// band, in a 1000-wide coordinate space. It carries no information from the
// hash. Only the vertical scale of each band about its own centre line is set
// by the hash. Gaps keep their x positions; the outline keeps its shape.
//
// Usage:  node derive.txt <sha256-hex> [die.json] > mark.svg
//         node derive.txt <sha256-hex> die.json --favicon > favicon.svg
//
// Output is canonical: fixed attribute order, one decimal place, LF line
// endings, no whitespace variation. Two runs on the same hash and the same
// die produce byte-identical files. Plain Node, no dependencies.

'use strict';
const fs = require('fs');

const MIN = 0.88;          // thinnest impression
const RANGE = 0.24;        // MIN + RANGE = 1.12, the thickest
const INK = '#262626';     // foreground, matches the site's text colour

function weight(byte) {
  // byte 0..255 -> factor 0.88..1.12, rounded so the output is stable
  return Math.round((MIN + RANGE * (byte / 255)) * 10000) / 10000;
}

function hashBytes(hex) {
  if (!/^[0-9a-f]{64}$/i.test(hex)) throw new Error('expected a 64-character sha256 hex string');
  const out = [];
  for (let i = 0; i < 64; i += 2) out.push(parseInt(hex.slice(i, i + 2), 16));
  return out;
}

function fmt(n) {
  // one decimal place, no trailing ".0", no "-0.0"
  const s = (Math.round(n * 10) / 10).toFixed(1).replace(/\.0$/, '');
  return s === '-0' ? '0' : s;
}

function bandPath(band, factor) {
  // scale each polygon's y about the band's centre line; x untouched
  const cy = band.centre_y;
  const parts = [];
  for (const poly of band.polygons) {
    const pts = poly.map(([x, y]) => [x, cy + (y - cy) * factor]);
    parts.push('M' + pts.map(([x, y]) => fmt(x) + ' ' + fmt(y)).join('L') + 'Z');
  }
  return parts.join('');
}

function render(hashHex, die, opts = {}) {
  const bytes = hashBytes(hashHex);
  const [vx, vy, vw, vh] = die.viewBox;
  const lines = [];
  lines.push('<svg xmlns="http://www.w3.org/2000/svg" viewBox="' + [vx, vy, vw, vh].map(fmt).join(' ') + '" role="img" aria-label="Parzival LLC">');
  lines.push('<title>Parzival LLC</title>');
  die.bands.forEach((band, i) => {
    const f = opts.favicon ? 1 : weight(bytes[i]);
    lines.push('<path fill="' + INK + '" fill-rule="evenodd" data-band="' + i + '" data-weight="' + f.toFixed(4) + '" d="' + bandPath(band, f) + '"/>');
  });
  lines.push('</svg>');
  return lines.join('\n') + '\n';
}

if (require.main === module) {
  const args = process.argv.slice(2);
  const hex = args[0];
  const diePath = args.find(a => a.endsWith('.json')) || 'die.json';
  const favicon = args.includes('--favicon');
  const die = JSON.parse(fs.readFileSync(diePath, 'utf8'));
  process.stdout.write(render(hex, die, { favicon }));
}

module.exports = { render, weight, hashBytes };