import { DIRS, hexagon, key, opposite, random } from './core.js';
import { FLOWER_LEVEL, flowerTrackEmphasis } from './flower-study.js';

// Each grammar reserves real port pairs before the unused ports are completed.
// The seed moves gates and folds within that grammar; it never draws random rails.
export const ROUTE_FAMILIES = [
  { id: 'petals', name: '花瓣', description: '叶瓣回到花心，再沿另一片叶瓣离场。' },
  { id: 'orbits', name: '环绕', description: '同心环接入开放的径向通道，逐圈展开。' },
  { id: 'spiral', name: '螺旋', description: '连续深入的螺旋接回出盘通道。' },
  { id: 'switchback', name: '回折', description: '长通道在相邻分区折返，局部闸口改变顺序。' },
  { id: 'weave', name: '编织', description: '连续交替转向的带状路线跨过盘面。' },
  { id: 'crossing', name: '双叶跨区', description: '两片回环在中央交织，共用远端开放出口。' },
];

const mod = (value, base = 6) => (value % base + base) % base;
const rotate = ([q, r], turns) => {
  for (let i = 0; i < mod(turns); i++) [q, r] = [-r || 0, q + r || 0];
  return [q, r];
};
const direction = (a, b) => DIRS.findIndex(([q, r]) => b[0] - a[0] === q && b[1] - a[1] === r);
const step = ([q, r], d) => [q + DIRS[d][0], r + DIRS[d][1]];
const pairKey = (q, r, a, b) => `${q},${r}:${Math.min(a, b)},${Math.max(a, b)}`;

function ring(radius, [q, r] = [0, 0]) {
  const result = [];
  let at = [q, r + radius];
  for (let d = 0; d < 6; d++) for (let i = 0; i < radius; i++) {
    result.push(at);
    at = step(at, (d + 5) % 6);
  }
  return result;
}

function draft(radius) {
  const cells = hexagon(radius).map(cell => ({ ...cell, tracks: Array(6).fill(null) }));
  const board = new Map(cells.map(cell => [key(cell.q, cell.r), cell]));
  const featuredPorts = new Set();
  function pair(at, a, b) {
    const cell = board.get(key(...at));
    if (!cell || a < 0 || b < 0 || a === b) throw new Error(`Invalid route pair at ${at}: ${a},${b}`);
    if ((cell.tracks[a] !== null && cell.tracks[a] !== b) || (cell.tracks[b] !== null && cell.tracks[b] !== a)) {
      throw new Error(`Route grammar overlaps a port at ${at}: ${a},${b}`);
    }
    cell.tracks[a] = b; cell.tracks[b] = a;
    featuredPorts.add(`${at}:${a}`); featuredPorts.add(`${at}:${b}`);
  }
  function replace(at, pairs) {
    const cell = board.get(key(...at));
    for (const port of pairs.flat()) {
      const partner = cell.tracks[port];
      if (partner !== null) cell.tracks[partner] = null;
      cell.tracks[port] = null;
    }
    for (const [a, b] of pairs) pair(at, a, b);
  }
  function path(points, entry, exit) {
    for (let i = 0; i < points.length; i++) {
      pair(points[i], i ? direction(points[i], points[i - 1]) : entry,
        i + 1 < points.length ? direction(points[i], points[i + 1]) : exit);
    }
  }
  function loop(points) {
    for (let i = 0; i < points.length; i++) pair(points[i], direction(points[i], points[mod(i - 1, points.length)]), direction(points[i], points[(i + 1) % points.length]));
  }
  function ray(at, dir) {
    for (let next = step(at, dir); board.has(key(...next)); next = step(next, dir)) pair(next, opposite(dir), dir);
  }
  return { cells, board, featuredPorts, pair, replace, path, loop, ray };
}

const centerWirings = [[1, 0, 3, 2, 5, 4], [3, 4, 5, 0, 1, 2], [1, 0, 4, 5, 2, 3]];

function petals(design, radius, variant) {
  if (radius === 5) {
    const emphasized = flowerTrackEmphasis();
    for (const source of FLOWER_LEVEL.cells) {
      const cell = design.board.get(key(source.q, source.r));
      cell.tracks = [...source.tracks];
      for (let port = 0; port < 6; port++) if (emphasized(source, port)) design.featuredPorts.add(`${source.q},${source.r}:${port}`);
    }
    const wiring = centerWirings[mod(variant, centerWirings.length)];
    design.replace([0, 0], wiring.flatMap((b, a) => a < b ? [[a, b]] : []));
    // One gate can be rethreaded while all six petal outlines remain intact.
    if (mod(variant, 4) > 1) {
      const at = rotate([0, -2], mod(variant, 6));
      const cell = design.board.get(key(...at));
      const pairs = cell.tracks.flatMap((b, a) => a < b ? [[a, b]] : []);
      const [[a, b], [c, d]] = pairs;
      design.replace(at, [[a, c], [b, d]]);
    }
    return;
  }
  if (radius === 2) {
    // Six triangular petals: every drawn lobe belongs to one open tour.
    const circuit = [];
    for (let sector = 0; sector < 6; sector++) circuit.push(...[[0, -1], [0, -2], [1, -2], [0, -1]].map(point => rotate(point, sector)));
    const first = 1;
    const points = [...circuit.slice(first), ...circuit.slice(0, first), circuit[first]];
    design.path(points, 0, 1);
    for (let sector = 0; sector < 6; sector++) if (variant & (1 << sector)) {
      // Reverse one lobe through its two gates, preserving the open full tour.
      design.replace(rotate([0, -1], sector), [[4, 1], [0, 2]].map(pair => pair.map(port => mod(port + sector))));
    }
    return;
  }
  const rootDistance = radius - 2;
  for (let sector = 0; sector < 6; sector++) {
    const lobe = ring(1, [0, -(radius - 1)]).map(point => rotate(point, sector));
    design.loop(lobe);
    for (let distance = 1; distance <= radius; distance++) {
      const at = rotate([0, -distance], sector);
      design.pair(at, sector, (sector + 3) % 6);
    }
    const root = rotate([0, -rootDistance], sector);
    const gate = variant & (1 << sector) ? [[1, 0], [5, 3]] : [[1, 3], [5, 0]];
    design.replace(root, gate.map(pair => pair.map(port => mod(port + sector))));
  }
  const wiring = centerWirings[mod(variant, centerWirings.length)];
  for (let a = 0; a < 6; a++) if (a < wiring[a]) design.pair([0, 0], a, wiring[a]);
}

function orbits(design, radius, variant) {
  for (let distance = 1; distance <= radius; distance++) design.loop(ring(distance));
  for (let r = -radius; r <= radius; r++) design.pair([0, r], 0, 3);
  for (let distance = 1; distance <= radius; distance++) {
    // Switching one ring's gate to the opposite side changes traversal order.
    const south = mod(variant, 2 ** radius) & (1 << (distance - 1));
    const turn = south ? 3 : 0;
    const at = rotate([0, -distance], turn);
    const pairs = mod(variant + distance, 3) === 0 ? [[0, 4], [3, 2]] : [[0, 2], [3, 4]];
    design.replace(at, pairs.map(pair => pair.map(port => mod(port + turn))));
  }
}

// Complete a partly reserved route through unused ports. A cell is visited only
// once in this extension, so no new pair can consume its own earlier exit port.
function openExtension(design, start, entry, rng) {
  const queue = [{ at: start, entry, points: [start] }], seen = new Set([key(...start)]);
  for (let head = 0; head < queue.length; head++) {
    const node = queue[head], cell = design.board.get(key(...node.at));
    const options = [0, 1, 2, 3, 4, 5].filter(port => port !== node.entry && cell.tracks[port] === null);
    const phase = Math.floor(rng() * options.length);
    options.push(...options.splice(0, phase));
    for (const exit of options) {
      const next = step(node.at, exit), nextCell = design.board.get(key(...next));
      if (!nextCell) return { points: node.points, exit };
      if (nextCell.tracks[opposite(exit)] !== null || seen.has(key(...next))) continue;
      seen.add(key(...next));
      queue.push({ at: next, entry: opposite(exit), points: [...node.points, next] });
    }
  }
  return null;
}

function spiral(design, radius, rng, variant) {
  const points = ring(radius);
  for (let distance = radius - 1; distance >= 1; distance--) {
    const next = ring(distance), last = points[points.length - 1];
    const gates = next.flatMap((point, index) => direction(last, point) >= 0 ? [index] : []);
    const gate = gates[mod(variant + Math.floor(rng() * gates.length), gates.length)];
    points.push(...next.slice(gate), ...next.slice(0, gate));
  }
  points.push([0, 0]);
  // Reserve the inward tour, leaving its last entry to be paired with an exit.
  for (let i = 0; i + 1 < points.length; i++) design.pair(points[i], i ? direction(points[i], points[i - 1]) : 3, direction(points[i], points[i + 1]));
  const entry = direction([0, 0], points[points.length - 2]);
  const extension = openExtension(design, [0, 0], entry, rng);
  if (!extension) throw new Error('Spiral has no free outward connector');
  design.path(extension.points, entry, extension.exit);
}

// Reversing a short strip moves its two gates without changing cell coverage.
// This preserves the recognisable lanes and gives a true route-order variant.
function shiftFolds(points, rng, variant, radius) {
  for (let change = 0; change < mod(variant, 4); change++) {
    const candidates = [];
    for (let i = 0; i + 4 < points.length; i++) for (let j = i + 3; j < Math.min(points.length - 1, i + radius * 4 + 4); j++) {
      if (direction(points[i], points[j]) >= 0 && direction(points[i + 1], points[j + 1]) >= 0) candidates.push([i, j]);
    }
    if (candidates.length) {
      const [i, j] = candidates[Math.floor(rng() * candidates.length)];
      points.splice(i + 1, j - i, ...points.slice(i + 1, j + 1).reverse());
    } else {
      // A triangular corner lets the connection enter the next lane one cell
      // earlier. The omitted cell keeps complete secondary tracks below.
      const corners = points.flatMap((point, i) => i > 0 && i + 1 < points.length && direction(points[i - 1], points[i + 1]) >= 0 ? [i] : []);
      if (!corners.length) break;
      points.splice(corners[Math.floor(rng() * corners.length)], 1);
    }
  }
  return points;
}

function boundaryPort(design, at, preferred) {
  return [preferred, ...[0, 1, 2, 3, 4, 5].filter(port => port !== preferred)].find(port => !design.board.has(key(...step(at, port))));
}

function switchback(design, radius, rng, variant) {
  const points = [];
  for (let q = -radius; q <= radius; q++) {
    const lane = design.cells.filter(cell => cell.q === q).map(cell => [cell.q, cell.r]);
    if (mod(q + radius, 2)) lane.reverse();
    points.push(...lane);
  }
  shiftFolds(points, rng, variant, radius);
  design.path(points, boundaryPort(design, points[0], 5), boundaryPort(design, points[points.length - 1], 2));
}

function weave(design, radius, rng, variant) {
  const points = [], bottom = -Math.ceil(radius / 2), top = Math.floor(radius / 2);
  for (let row = bottom; row <= top; row++) {
    const lane = [];
    for (let q = -radius; q <= radius; q++) lane.push([q, row - Math.floor(q / 2)]);
    if (mod(row - bottom, 2)) lane.reverse();
    points.push(...lane);
  }
  shiftFolds(points, rng, variant, radius);
  design.path(points, boundaryPort(design, points[0], 5), boundaryPort(design, points[points.length - 1], 2));
}

function crossing(design, radius, variant) {
  const north = Math.floor(radius / 2), south = radius >= 4 && mod(variant, 3) === 1 ? 1 : north;
  design.loop(ring(north, [0, -north]));
  design.loop(ring(south, [0, south]));
  design.replace([0, 0], mod(variant, 2) ? [[1, 4], [5, 2]] : [[1, 2], [5, 4]]);
  const gate = [0, -north * 2];
  design.replace(gate, [[2, 0], [4, 1]]);
  design.ray(gate, 0); design.ray(gate, 1);
}

// Every family lays its signature routes over part of the board and leaves the
// rest to be filled in. The filler used to pair a leftover port with the one
// straight across, which is why a board reads as a grid of long straight lines
// crossing everywhere: on a switchback board 76% of all track pairs were
// diameters and 43 of 61 cells were nothing but diameters. Two diameters in one
// cell always cross, so straight filler buys crossings as well as straightness.
// `fill` picks what a leftover port prefers instead; 'curve' asks for a bend.
function completePorts(design, family, variant, fill = 'straight') {
  for (const cell of design.cells) {
    const free = cell.tracks.flatMap((value, port) => value === null ? [port] : []);
    // Periodic completion keeps secondary rails ordered instead of random noise.
    const phase = mod(cell.q - cell.r + variant, 3);
    while (free.length) {
      const a = free.shift();
      const bend = mod(a + 1 + phase % 2);        // 60° or 120°, varied by phase
      const preferred = fill === 'curve' ? bend
        : family === 'weave' && phase === 0 ? mod(a + 1) : opposite(a);
      const b = free.splice(free.includes(preferred) ? free.indexOf(preferred) : mod(phase, free.length), 1)[0];
      cell.tracks[a] = b; cell.tracks[b] = a;
    }
  }
}

function describeRoutes(design) {
  const candidates = [];
  const reachablePairs = new Set();
  for (const start of design.cells) for (let dir = 0; dir < 6; dir++) {
    let q = start.q, r = start.r, exit = dir, bends = 0, steps = 1;
    const seen = new Set([`${q},${r}:${exit}`]), pairs = [];
    let status = 'loop';
    for (let count = 0; count <= design.cells.length * 6; count++) {
      q += DIRS[exit][0]; r += DIRS[exit][1];
      const cell = design.board.get(key(q, r));
      if (!cell) { status = 'exit'; break; }
      const enter = opposite(exit); exit = cell.tracks[enter];
      if (opposite(enter) !== exit) bends++;
      steps++;
      const signature = `${q},${r}:${exit}`;
      if (seen.has(signature)) break;
      seen.add(signature);
      if (design.featuredPorts.has(`${q},${r}:${enter}`) && design.featuredPorts.has(`${q},${r}:${exit}`)) pairs.push(pairKey(q, r, enter, exit));
    }
    if (status !== 'exit') continue;
    for (const pair of pairs) reachablePairs.add(pair);
    if (pairs.length) {
      const uniquePairs = [...new Set(pairs)];
      candidates.push({ q: start.q, r: start.r, dir, steps, bends, featuredPairs: uniquePairs.length, pairs: uniquePairs });
    }
  }
  const featured = design.cells.flatMap(cell => cell.tracks.flatMap((b, a) => a < b && reachablePairs.has(pairKey(cell.q, cell.r, a, b)) ? [{ q: cell.q, r: cell.r, a, b }] : []));
  candidates.sort((a, b) => b.featuredPairs - a.featuredPairs || b.bends - a.bends || b.steps - a.steps || a.q - b.q || a.r - b.r || a.dir - b.dir);
  // Keep witnesses for every open branch, rather than filling the list with
  // offsets along just the longest branch of a multi-petal design.
  const selected = [], uncovered = new Set(reachablePairs);
  while (uncovered.size) {
    let best = null, gain = 0;
    for (const candidate of candidates) {
      const extra = candidate.pairs.reduce((count, pair) => count + Number(uncovered.has(pair)), 0);
      if (extra > gain) { best = candidate; gain = extra; }
    }
    if (!best) break;
    selected.push(best);
    for (const pair of best.pairs) uncovered.delete(pair);
  }
  for (const candidate of candidates) {
    if (selected.length >= 36) break;
    if (!selected.includes(candidate)) selected.push(candidate);
  }
  return { featured, heroStarts: selected.map(({ pairs, ...candidate }) => candidate) };
}

export function createRouteBoard(seed, { family = 'petals', radius = 3, variant = 0, fill = 'straight' } = {}) {
  const spec = ROUTE_FAMILIES.find(candidate => candidate.id === family);
  if (!spec) throw new RangeError(`Unknown route family: ${family}`);
  if (!Number.isInteger(radius) || radius < 2 || radius > 5) throw new RangeError('Route radius must be 2–5');
  if (!Number.isInteger(variant)) throw new RangeError('Route variant must be an integer');
  const rng = random(seed), design = draft(radius);
  const gateVariant = mod(variant + (seed >>> 0), 96);
  if (family === 'petals') petals(design, radius, gateVariant);
  if (family === 'orbits') orbits(design, radius, gateVariant);
  if (family === 'spiral') spiral(design, radius, rng, gateVariant);
  if (family === 'switchback') switchback(design, radius, rng, gateVariant);
  if (family === 'weave') weave(design, radius, rng, gateVariant);
  if (family === 'crossing') crossing(design, radius, gateVariant);
  completePorts(design, family, gateVariant, fill);
  const { featured, heroStarts } = describeRoutes(design);
  return {
    version: 1, id: `route-${family}-${radius}-${seed}-${variant}`, name: `${spec.name} · 路线草图`,
    cells: design.cells, tiles: [], moveLimit: 1, rotationEnabled: true,
    routeDesign: { family, variant, seed, radius, gateVariant, featured, heroStarts },
  };
}