import { config } from '../config/Config.js';
import { Rng } from '../utils/Rng.js';
import { NameGenerator } from '../utils/NameGenerator.js';
import { buildJumpNetwork } from './JumpNetwork.js';
import { assignPlanetFrames } from './PlanetFrames.js';
import { assignPlanetClasses } from './PlanetClasses.js';
import { assignStationFrames } from './StationFrames.js';
import { generateSystemContent, rollSystemComposition, settlementDensity } from './SystemGenerator.js';
import { buildEconomy } from '../economy/Economy.js';

const TAU = Math.PI * 2;
const clamp = (v, lo, hi) => Math.min(hi, Math.max(lo, v));

/**
 * The Galaxy — an immense, procedurally generated collection of star
 * systems, fully determined by its seed.
 *
 * Two-level generation (the "grand scale" design):
 *
 *  1. GALAXY ROSTER — generated once, up front, when New Game is pressed:
 *     `systemCount` lightweight records ({ id, name, type, x, y, d, zone }).
 *     This is cheap: the 90-system default is a few ms and a few hundred KB.
 *     It fixes the shape of the galaxy, where every system sits, and
 *     what KIND each one is — for the entire galaxy, from the seed alone.
 *
 *  2. SYSTEM CONTENTS — planets, moons, belts, hazards… generated LAZILY,
 *     the first time the player arrives (`ensureContent(id)`), then
 *     cached. Because each system's draw stream is derived from
 *     (seed, 'system', id), a lazy generation is identical to an eager
 *     one — so this is a pure performance choice, never a correctness one.
 *     `generateAll()` exists for exactly that, if it's ever "just as easy".
 *
 * The SHAPE (data/galaxy.json):
 *   - a seeded WIDE (2:1) field of stars (layout.field.width × height,
 *     center at the world origin) placed by Bridson Poisson-disk
 *     sampling — an even, organic field: every pair of systems stays at
 *     least minSpacing·√(width·height/N) apart, no clumps, no voids, not
 *     a grid. The 2:1 aspect matches the map plate (js/ui/MapWindow.js at
 *     the 1280×720 design size), so the fully-zoomed-out galaxy fills
 *     the plate instead of letterboxing;
 *   - the player's HOME system sits in the star nearest the configured
 *     corner (startingSystem: policy "corner", corner NE/NW/SE/SW,
 *     screen orientation — SE = lower right); "center" / "random" still
 *     work; its TYPE is always "main" (Main Sequence —
 *     startingSystem.type, the player's home is an ordinary star; the
 *     zone-mixed roll is overridden at roster build); the HOME→FAR
 *     diagonal is the galaxy's progression axis:
 *     each record carries `d` (0 at the home corner, 1 at the opposite
 *     corner) and its `zone` (near/middle/far, distribution.zones);
 *   - types mix PER ZONE (distribution.zoneMix × the type's global
 *     distribution.weight — the old per-type radiusBand is gone: type
 *     flavor is regional now), and free-space settlement density thins
 *     home→far (settlements.gradient, keyed on `d`).
 *
 * Determinism contract:
 *   same seed ⇒ same roster (positions, types, names), same contents,
 *   in any order of generation. Dev/test tools rely on this.
 *
 * Extension points for later world rules (see docs/PROJECT_NOTES.md):
 *   - FACTIONS: ASSIGNED AT ROSTER TIME by the faction pass (_assignFactions,
 *     data/factions.json) — each system's record carries `faction` (or
 *     null = neutral wild space) + `capital` (the four designated
 *     capitals: neutral + apex/mindweave/zenith). The reputation seam
 *     (js/reputation/Reputation.js → factionStanding) and the galaxy
 *     plate's faction ring layer (js/ui/GalaxyView.js) read them; reachability
 *     / combat / trade off the territories is the next layer.
 *   - COMBAT / TRADE: read difficulty and price levels off `record.d`
 *     and `record.zone` (the middle zone is where the zone borders cross
 *     — the planned contested space + transit trade hubs).
 *   - more layout knobs in data/galaxy.json `layout.field`.
 */
export class Galaxy {
  constructor(seed, params, typeDefs) {
    this.seed = seed;
    this.params = params;
    this.typeDefs = typeDefs;
    this.records = [];
    this.byId = new Map();
    this.contentCache = new Map();
    this.currentSystemId = null;
    // The STARTING system — the player's home port. Set once at roster
    // build and never moves: `currentSystemId` tracks where the player IS
    // NOW (jumps + saves move it), but the home world always belongs to
    // the starting system (SystemGenerator's isHome rule, GameScene's
    // home/star split). Without this split, lazily generated content for
    // a newly arrived system would compute isHome = true (currentSystemId
    // had already moved there) and deal it a home world of its own.
    this.homeSystemId = null;
    this.planetFrames = new Map(); // id → [frame, ...] — the frame-diversity pass
    this.planetClasses = null; // id → [class, ...] — the even-mix deal (or null, balance off)
    this.homeWorldFrame = null; // the starting system's home world frame
    this.stationFrames = new Map(); // id → [frame, ...] — the station-variant spread pass
    this.name = NameGenerator.galaxy(Rng.derive(seed, 'galaxy', 'name'));
  }

  /**
   * Build a galaxy from a seed (trimmed; ' abc ' and 'abc' are the same
   * galaxy). `overrides` shallow-merges over data/galaxy.json — used by
   * dev tools (e.g. a 300-system galaxy for brute-force tests).
   */
  static create(seed, overrides = {}) {
    if (seed === undefined || seed === null || String(seed).trim().length === 0) {
      throw new Error('Galaxy.create() needs a non-empty seed');
    }
    const params = { ...config.section('galaxy', {}), ...overrides };
    const typeDefs = config.get('systems.types', {});
    if (Object.keys(typeDefs).length === 0) {
      throw new Error('No system types found — is data/systems.json listed in data/manifest.json?');
    }
    const count = Math.floor(params.systemCount ?? 200);
    if (!(count >= 1)) {
      throw new Error(`galaxy.systemCount must be a whole number >= 1 (got ${params.systemCount})`);
    }
    const galaxy = new Galaxy(String(seed).trim(), params, typeDefs);
    galaxy._generate(count);
    return galaxy;
  }

  // ------------------------------------------------------------------
  // Roster generation (level 1)
  // ------------------------------------------------------------------

  _generate(count) {
    const L = this.params.layout ?? {};
    const F = L.field ?? {};
    const W = Math.max(4, Math.floor(Number(F.width) || 32000));
    const H = Math.max(4, Math.floor(Number(F.height) || 16000));
    this.fieldW = W; // the field's extent (world px, center at origin)
    this.fieldH = H;
    const halfW = W / 2;
    const halfH = H / 2;
    const minSpacing = clamp(Number(F.minSpacing) || 0.8, 0.4, 1.2);

    // The HOME CORNER (data/galaxy.json → startingSystem.corner; screen
    // orientation — y down, so SE = lower right). Two things key off it:
    // the starting-system policy (home = the star NEAREST this corner),
    // and the difficulty diagonal (d = 0 here, d = 1 at the opposite
    // corner — the galaxy's progression axis, whatever policy picks the
    // starting system).
    const start = this.params.startingSystem ?? {};
    const corner = this._cornerPoint(start.corner ?? 'SE', { halfW, halfH });
    const opp = { x: -corner.x, y: -corner.y };
    const diag2 = (corner.x - opp.x) ** 2 + (corner.y - opp.y) ** 2; // W² + H²
    const dOf = (x, y) => clamp(
      ((corner.x - x) * (corner.x - opp.x) + (corner.y - y) * (corner.y - opp.y)) / diag2,
      0, 1,
    );

    // ZONES — slices of the home→far diagonal (distribution.zones), and
    // the PER-ZONE type mix (distribution.zoneMix × each type's global
    // distribution.weight). Regional flavor replaces the old per-type
    // radiusBand: which KINDS of stars favor which region of the galaxy.
    const zones = this._zones();
    const zoneOf = (d) => (zones.find((z) => d >= z.d[0] && d < z.d[1]) ?? zones[zones.length - 1]).name;
    const mix = this.params.distribution?.zoneMix ?? {};
    const typeIds = Object.keys(this.typeDefs);
    const weightsFor = (zone) => {
      const m = mix[zone] ?? {};
      const w = {};
      for (const id of typeIds) {
        const mul = m[id] === undefined ? 1 : Math.max(0, Number(m[id]) || 0);
        w[id] = Math.max(0, this.typeDefs[id].distribution?.weight ?? 1) * mul;
      }
      return w;
    };

    const g = Rng.derive(this.seed, 'layout');

    // EVEN PLACEMENT — a Bridson Poisson-disk (blue-noise) field: every
    // pair of systems stays at least dmin apart (no clumps, no voids)
    // while the field stays organic (not a grid). dmin is a fraction of
    // the mean inter-star spacing √(width·height/N)
    // (layout.field.minSpacing).
    // Even spacing is what keeps the jump network's hop counts
    // proportional to map distance — the property the trade economy
    // leans on ("a hop is a hop").
    const dmin = minSpacing * Math.sqrt((W * H) / Math.max(1, count));
    const points = this._poissonDisk(count, { halfW, halfH }, dmin);

    const records = this.records;
    for (let i = 1; i <= count; i++) {
      const id = `S${String(i).padStart(6, '0')}`;
      const p = points[i - 1] ?? { x: g.range(-halfW, halfW), y: g.range(-halfH, halfH) };
      const d = dOf(p.x, p.y);
      const zone = zoneOf(d);
      const type = g.weighted(weightsFor(zone), typeIds[0]);
      // Name comes from a per-record fork so roster generation order can
      // never leak into it. d (0 = home corner, 1 = far corner) and zone
      // stay on the record: the settlement generator uses d (home→far
      // density), and factions/trade/combat will read difficulty off both.
      // faction/capital default to null (neutral wild space, no capital)
      // — the faction pass (_assignFactions) stamps the territories +
      // capital designations after the jump network exists.
      const name = NameGenerator.star(Rng.derive(this.seed, 'name', id));
      const rec = { id, name, type, x: p.x, y: p.y, d, zone, faction: null, capital: null };
      records.push(rec);
      this.byId.set(id, rec);
    }

    // Starting system (the player's home port).
    const policy = start.policy ?? 'corner';
    const closestTo = (px, py) =>
      records
        .slice()
        .sort((a, b) => (a.x - px) ** 2 + (a.y - py) ** 2 - ((b.x - px) ** 2 + (b.y - py) ** 2))[0]?.id ?? records[0]?.id;
    this.currentSystemId =
      policy === 'random'
        ? `S${String(g.int(1, count)).padStart(6, '0')}`
        : policy === 'center'
          ? closestTo(0, 0)
          : closestTo(corner.x, corner.y); // 'corner' (default)
    // Frozen copy of the starting system — `currentSystemId` will track
    // the player from here on (jumps, saves); the home rules must not.
    this.homeSystemId = this.currentSystemId;

    // The starting system is ALWAYS a MAIN SEQUENCE system (data/galaxy.json
    // → startingSystem.type, default 'main' — data/systems.json → types.main,
    // "Main Sequence"): the player's home is an ordinary star. Its type was
    // rolled from the zone mix above like every other record; override it
    // here — before the frame passes read it — so the dossier ("Main
    // Sequence system · star G"), the map plate, and the generated content
    // all agree.
    const forcedType = String(start.type ?? 'main');
    const homeRec = this.byId.get(this.currentSystemId);
    if (homeRec && this.typeDefs[forcedType]) {
      if (homeRec.type !== forcedType) homeRec.type = forcedType;
    } else {
      console.warn(
        `[orbit] startingSystem.type "${forcedType}" is not a defined system type — the starting system keeps its rolled type`,
      );
    }

    // Spatial hash for fast neighbor queries (jump ranges, proximity rules,
    // the eventual star map).
    const area = W * H;
    this.cellSize = Math.max(8, Math.sqrt(area / count) * 1.4);
    this.grid = new Map();
    for (const rec of records) {
      const key = `${Math.floor(rec.x / this.cellSize)},${Math.floor(rec.y / this.cellSize)}`;
      let cell = this.grid.get(key);
      if (!cell) {
        cell = [];
        this.grid.set(key, cell);
      }
      cell.push(rec);
    }

    // The BARREN set — the gate-only dead ends (objectCount → 0). The
    // SAME roll the content generator uses (dedicated per-system forks —
    // rollSystemComposition), so the network and the content always agree:
    // JumpNetwork keeps every barren system a LEAF of the tree (one gate —
    // in and out the same way), the maze's dead ends.
    const typeDefs = this.typeDefs ?? {};
    const barren = new Set();
    for (const record of records) {
      if (record.id === this.currentSystemId) continue; // home is exempt
      const type = typeDefs[record.type] ?? {};
      const density = settlementDensity({ params: this.params }, record);
      const composition = rollSystemComposition(
        this.seed, record, false, type.attributes?.settlements ?? {}, density, type.attributes ?? {},
      );
      if (composition.classes.length === 0) barren.add(record.id);
    }

    // The JUMP NETWORK (data/gates.json): which star each system's jump
    // gates reach. A degree-limited spanning TREE of the nearest-star
    // graph — the galaxy reads as a MAZE: (nearly) one route between any
    // two systems, dead ends at the leaves — and every barren system is
    // a dead-end LEAF (exactly one gate, in and out the same way). The
    // deliberate exception: the BRIDGES (data/gates.json → bridges)
    // cross-link the branches' middle belts, so one branch doesn't have
    // to trek back to the trunk (home) to reach another (the faction
    // design — data/factions.json). Tree edges run BOTH ways, so from any
    // system the player can reach any other and every jump has a RETURN
    // gate (no trapped sets). Each system holds 1–maxGates gates (its
    // degree, bridges included). Deterministic: same roster ⇒ same
    // network.
    const pool = Math.max(1, Math.min(count - 1, (config.get('gates.neighborPool', 8) | 0)));
    this.jumpNetwork = buildJumpNetwork({
      records,
      knn: (id) => this.neighborsOf(id, pool),
      minGates: Math.max(0, config.get('gates.minGates', 1) | 0),
      maxGates: Math.max(1, config.get('gates.maxGates', 3) | 0),
      shortcuts: config.get('gates.shortcuts', true) === true,
      barren,
      rootId: this.currentSystemId,
      bridges: config.get('gates.bridges', null),
    });
    // Defensive repairs that had to fire (0 on a healthy kNN graph).
    this.jumpNetworkRepaired = this.jumpNetwork.repaired;
    if (this.jumpNetworkRepaired > 0) {
      console.warn(`[orbit] jump network: ${this.jumpNetworkRepaired} system(s) needed a repair attach`);
    }

    // FACTIONS (data/factions.json — the faction pass): branch
    // territories + the four CAPITAL designations (neutral + apex /
    // mindweave / zenith), stamped on the roster records
    // (record.faction / record.capital). Runs after the jump network
    // (it needs the branches the tree defines) and before the frame
    // pass (independent of it — the capital planet is not a
    // composition planet, so the frame pass never sees it).
    this._assignFactions(barren);

    // PLANET CLASS BALANCE (js/galaxy/PlanetClasses.js): the galaxy-wide
    // even-mix pass — the non-home planets are dealt from ONE shared deck
    // (even per-class quotas ± the star-mix tilt; each system draws its
    // worlds weighted by its star type's table), so every class lands at
    // ~1/N of the galaxy while the star type still flavors local systems.
    // Stamped before the frame pass (the frames index the classes) and
    // read back by the content generator + the economy pass — lazy ===
    // eager, every subsystem sees the same worlds. NULL when
    // planetClassBalance.enabled === false (callers keep the old
    // per-system weighted draws).
    this.planetClasses = assignPlanetClasses({
      seed: this.seed,
      records,
      homeId: this.currentSystemId,
      params: this.params,
    });

    // FRAME DIVERSITY (js/galaxy/PlanetFrames.js): the galaxy-wide
    // (class, frame) assignment — each planet's sheet frame avoids what
    // the NEAREST stars already wear for that class, so the same face is
    // spread across the galaxy instead of clustering in one region. Fixed
    // roster order ⇒ visit-order independent; read back by the content
    // generator (planet.frame / content.homeFrame) — the lazy === eager
    // contract is preserved.
    const pool8 = Math.max(1, Math.floor(this.params.neighbors ?? 8));
    const { frames, homeFrame } = assignPlanetFrames({
      seed: this.seed,
      records,
      homeId: this.currentSystemId,
      params: this.params,
      neighborsOf: (id) => this.neighborsOf(id, pool8),
      planetClasses: this.planetClasses,
    });
    this.planetFrames = frames; // Map id → [frame, ...] (ordinal order)
    this.homeWorldFrame = homeFrame;

    // STATION VARIANT SPREAD (js/galaxy/StationFrames.js): each system's
    // deep-space stations (up to two) wear spacestations.png variants
    // (data/stations.json → variants) — a frame avoids what the NEAREST
    // stars already wear, so the same station type is spread across the
    // galaxy instead of clustering in one region. Fixed roster order ⇒
    // visit-order independent; read back by the content generator
    // (settlement.stationFrame) — lazy === eager preserved.
    const { frames: stationFrames } = assignStationFrames({
      seed: this.seed,
      records,
      homeId: this.currentSystemId,
      params: this.params,
      neighborsOf: (id) => this.neighborsOf(id, pool8),
    });
    this.stationFrames = stationFrames; // Map id → [frame, ...] (station-bearing systems)

    // TRADE ECONOMY (js/economy/Economy.js): the galaxy-level trade map —
    // per-system economic classes + each good's hop-distance to its nearest
    // producer. A pure function of the seed (it re-derives the same
    // composition roll the content generator uses), so it's lazy-safe and
    // save-free; the price engine (Economy.buyPrice/sellPrice/shopFor) reads
    // it to fix each shop's prices. Distance is enforced by regional
    // availability — a good is cheap only in its home region — not by a live
    // per-trade multiplier (docs/ECONOMY.md §5).
    buildEconomy(this);
  }

  /**
   * The FACTION PASS — branch territories + the four capital designations
   * (data/factions.json; see docs/PROJECT_NOTES.md "Factions"). Runs at
   * roster build, before any content generation, so the stamp is pure
   * function of the seed (lazy === eager: content generation only READS
   * the record fields it leaves behind):
   *
   *   BRANCHES — the jump tree's top-level subtrees, rooted at the home
   *     system's gate neighbors (home has ≤ maxGates gates, so ≤ 3).
   *   NEUTRAL CAPITAL — a seeded pick among home's gate neighbors (the
   *     "always connected to the home star" rule); its system stays
   *     faction-NEUTRAL even though it roots one faction's branch
   *     (a neutral hub at the edge of that corridor).
   *   FACTION CAPITALS — one per faction (apex / mindweave / zenith): a
   *     SEEDED pick inside that faction's branch, preferred in the middle
   *     band (d in 0.37..0.63 — the home→far diagonal's middle slice),
   *     on a non-barren system (it must be able to host a planet). The
   *     branch↔faction assignment is a SEEDED SHUFFLE — a new galaxy
   *     reshuffles who sits where (never a fixed order), same seed ⇒
   *     identical placement.
   *   TERRITORY — a branch's systems at depth 2 … (maxDepth−1) (home =
   *     depth 0, its gate neighbors = depth 1) are ELIGIBLE; the ring
   *     right outside home and every branch's dead-end tips stay NEUTRAL
   *     WILD SPACE; anything not in a territory is neutral. A faction
   *     capital always sits in its faction's territory (fallbacks only
   *     when the branch is too short to have one).
   *   BALANCE (data/factions.json → balance) — fair, not equal. Two rules:
   *     CAP — each branch keeps only the min(eligible, quota) of its
   *     eligible systems, closest to the middle band (|d − 0.5|, index
   *     tiebreak — deterministic); quota = the MEDIAN of the branches'
   *     eligible sizes. The big branch's overflow stays neutral wild
   *     space (no dominant faction).
   *     FLOOR — a faction whose own branch is too small to reach
   *     balance.minTerritory absorbs systems that would otherwise stay
   *     neutral (first the branches' eligible overflow, then the richest
   *     faction's least-core systems — the nearest ones, so the territory
   *     stays contiguous). A tiny galaxy with too few eligible systems is
   *     best-effort (a working territory beats an empty one).
   *
   * @param {Set<string>|null} barren the gate-only dead ends (excluded from
   *   capital candidacy — they can't host a world)
   */
  _assignFactions(barren) {
    const FACTIONS = ['apex', 'mindweave', 'zenith'];
    const dMin = 0.37, dMax = 0.63; // the middle band (data/galaxy.json zones)
    const homeId = this.homeSystemId;

    // Branch + depth of every system — from the JUMP NETWORK's own
    // spanning tree (js/galaxy/JumpNetwork.js exposes branches/branchOf/
    // depth): the bridge pass and the faction pass must agree on the SAME
    // branch structure. (A BFS over the final gate list — tree + bridges
    // — can re-parent systems across branches, since the bridges are
    // loops; that is NOT the tree's branch structure.) The fallback below
    // is only for a network that lacks the export (defensive).
    const netBranchOf = this.jumpNetwork?.branchOf instanceof Map ? this.jumpNetwork.branchOf : null;
    const netDepth = this.jumpNetwork?.depth instanceof Map ? this.jumpNetwork.depth : null;
    let branchOf, depth;
    if (netBranchOf && netDepth) {
      branchOf = netBranchOf;
      depth = netDepth;
    } else {
      const gates = this.jumpNetwork?.gates ?? new Map();
      depth = new Map([[homeId, 0]]);
      branchOf = new Map(); // id → its branch-root id (a home neighbor)
      const q = [homeId];
      while (q.length) {
        const u = q.shift();
        const du = depth.get(u);
        for (const v of gates.get(u) ?? []) {
          if (depth.has(v)) continue;
          depth.set(v, du + 1);
          branchOf.set(v, du === 0 ? v : branchOf.get(u));
          q.push(v);
        }
      }
    }
    const branchRoots = (this.jumpNetwork?.branches ?? [...new Set(branchOf.values())]).slice().sort();
    if (branchRoots.length === 0) {
      // One-system galaxy (nothing connected to home) — no branches,
      // no capitals, no territories. The galaxy still generates.
      this.factions = null;
      return;
    }

    // Per-branch node lists + the branch's max depth (territory bounds).
    const nodesOf = new Map(branchRoots.map((b) => [b, []]));
    for (const [id, b] of branchOf) nodesOf.get(b).push(id);
    const maxDepthOf = new Map();
    for (const b of branchRoots) {
      let m = 1;
      for (const id of nodesOf.get(b)) m = Math.max(m, depth.get(id) ?? 1);
      maxDepthOf.set(b, m);
    }
    // TERRITORY = the branch's middle systems (depth 2 … maxDepth−1):
    // the depth-1 ring at home and the branch tips stay neutral.
    const eligibleOf = new Map();
    for (const b of branchRoots) {
      eligibleOf.set(
        b,
        (nodesOf.get(b) ?? []).filter((id) => {
          const d = depth.get(id) ?? 0;
          return d >= 2 && d <= (maxDepthOf.get(b) ?? 1) - 1;
        }),
      );
    }
    // BALANCE (data/factions.json → balance) — fair, not equal:
    //   CAP — quota = the MEDIAN of the branches' eligible sizes: the big
    //     branch keeps only its systems nearest the middle band (|d − 0.5|
    //     — the "middle of the galaxy" design, where the bridges sit too;
    //     index tiebreak for determinism) and its overflow stays NEUTRAL
    //     WILD SPACE (no dominant faction);
    //   FLOOR — minTerritory: a faction whose own branch is too small is
    //     lifted up out of the neutral wild space (the floor pass below —
    //     a working territory beats a one-system sliver).
    const balanceCfg = config.get('factions.balance', {});
    const minTerritory = Math.max(1, Math.floor(Number(balanceCfg.minTerritory) || 5));
    const sizes = branchRoots.map((b) => eligibleOf.get(b).length).sort((x, y) => x - y);
    const quota = sizes.length ? sizes[Math.floor((sizes.length - 1) / 2)] : 0;
    const index = new Map(this.records.map((r, i) => [r.id, i]));
    const midRank = (id) => Math.abs((this.byId.get(id)?.d ?? 0.5) - 0.5);
    const inBand = (id) => {
      const rec = this.byId.get(id);
      return !!rec && rec.d >= dMin && rec.d <= dMax;
    };
    const isBarren = (id) => barren instanceof Set && barren.has(id);

    // Branch↔faction: a SEEDED SHUFFLE of the three factions across the
    // branches — a faction's branch is its HOME territory (the floor pass
    // below can lend it neighboring space). Fewer than three branches ⇒ a
    // faction's home branch is null and its territory is built entirely
    // from borrowed space (the "nice to have" relaxation; its capital
    // still lands in its own territory).
    const assign = Rng.derive(this.seed, 'factions', 'assign').shuffle(FACTIONS);
    const branchFaction = new Map();
    branchRoots.forEach((b, i) => branchFaction.set(b, assign[i % assign.length]));
    const factionBranch = new Map(
      FACTIONS.map((f) => [f, branchRoots.find((b) => branchFaction.get(b) === f) ?? null]),
    );

    // BASE TERRITORY (per FACTION): the faction's home branch keeps its
    // min(eligible, quota) systems closest to the middle band.
    const territoryOf = new Map(FACTIONS.map((f) => [f, new Set()]));
    for (const f of FACTIONS) {
      const b = factionBranch.get(f);
      if (!b) continue;
      const elig = eligibleOf.get(b) ?? [];
      territoryOf.set(
        f,
        new Set(
          elig
            .slice()
            .sort((a, c) => midRank(a) - midRank(c) || index.get(a) - index.get(c))
            .slice(0, Math.min(elig.length, quota)),
        ),
      );
    }

    // FLOOR PASS (balance.minTerritory — no faction left with a sliver):
    // a faction below the floor absorbs systems that would otherwise stay
    // NEUTRAL, in this order —
    //   1. eligible OVERFLOW of any branch (eligible but unowned — the
    //      branch with the most of it, then the system nearest the
    //      recipient, so the region stays contiguous);
    //   2. the richest faction still above the floor (its system farthest
    //      from the middle band — the least core — nearest the recipient).
    // Deterministic (branch/faction order + index tiebreaks); a tiny
    // galaxy with too few eligible systems is best-effort (the loop stops
    // when there is nothing left to give).
    const owned = new Set();
    for (const f of FACTIONS) for (const id of territoryOf.get(f)) owned.add(id);
    const centroid = (ids) => {
      let x = 0, y = 0, n = 0;
      for (const id of ids) {
        const rec = this.byId.get(id);
        if (rec) { x += rec.x; y += rec.y; n += 1; }
      }
      return n > 0 ? { x: x / n, y: y / n } : null;
    };
    const dist2 = (id, c) => {
      const rec = this.byId.get(id);
      if (!rec || !c) return 0;
      const dx = rec.x - c.x;
      const dy = rec.y - c.y;
      return dx * dx + dy * dy;
    };
    const distPts = (p, q) => {
      if (!p || !q) return Infinity;
      const dx = p.x - q.x;
      const dy = p.y - q.y;
      return dx * dx + dy * dy;
    };
    const allEligible = branchRoots.flatMap((b) => eligibleOf.get(b) ?? []);
    for (const f of FACTIONS) {
      const terr = territoryOf.get(f);
      while (terr.size < minTerritory) {
        const anchor = terr.size > 0
          ? centroid([...terr])
          : centroid(factionBranch.get(f) ? (nodesOf.get(factionBranch.get(f)) ?? []) : allEligible);
        // 1) The biggest unowned eligible overflow, nearest the recipient.
        let best = null; // { count, dist, free }
        for (const b of branchRoots) {
          const free = (eligibleOf.get(b) ?? []).filter((id) => !owned.has(id));
          if (free.length === 0) continue;
          const dist = distPts(centroid(free), anchor);
          if (!best || best.count < free.length || (best.count === free.length && best.dist > dist)) {
            best = { count: free.length, dist, free };
          }
        }
        if (best) {
          const pickId = best.free
            .slice()
            .sort((a, c) => dist2(a, anchor) - dist2(c, anchor) || index.get(a) - index.get(c))[0];
          terr.add(pickId);
          owned.add(pickId);
          continue;
        }
        // 2) Nothing unowned left — the richest faction still above the
        //    floor lends its least-core system, nearest the recipient.
        let donor = null; // { faction, size, dist }
        for (const d of FACTIONS) {
          if (d === f) continue;
          const t = territoryOf.get(d);
          if (t.size <= minTerritory) continue;
          const dist = distPts(centroid([...t]), anchor);
          if (!donor || donor.size < t.size || (donor.size === t.size && donor.dist > dist)) {
            donor = { faction: d, size: t.size, dist };
          }
        }
        if (!donor) break; // nothing left to give — best effort
        const donorTerr = territoryOf.get(donor.faction);
        const pickId = [...donorTerr]
          .sort((a, c) => midRank(c) - midRank(a) || dist2(a, anchor) - dist2(c, anchor) || index.get(a) - index.get(c))[0];
        donorTerr.delete(pickId);
        terr.add(pickId);
        // `owned` is unchanged — the system stays owned, just re-owned.
      }
    }

    // NEUTRAL CAPITAL — one of home's gate neighbors (seeded pick).
    const neutralId = Rng.derive(this.seed, 'factions', 'neutral').pick(branchRoots);

    // FACTION CAPITALS — one per faction, inside its (post-floor) territory
    // (seeded): a faction built from borrowed space still gets its seat in
    // its own territory.
    const taken = new Set([neutralId]);
    const capitals = {};
    for (const f of FACTIONS) {
      const b = factionBranch.get(f);
      const nodes = b ? (nodesOf.get(b) ?? []) : [];
      const free = (ids) => ids.filter((id) => !taken.has(id) && !isBarren(id));
      const terr = [...territoryOf.get(f)];
      // Tiered candidacy: middle-band territory → any territory → any free
      // home-branch system (tiny-branch fallback — a working capital beats
      // no capital).
      let cands = free(terr).filter((id) => inBand(id));
      if (cands.length === 0) cands = free(terr);
      if (cands.length === 0) cands = free(nodes);
      if (cands.length === 0) cands = branchRoots.filter((id) => id !== neutralId);
      const capitalId = Rng.derive(this.seed, 'factions', 'capital', f).pick(cands);
      if (!capitalId) continue;
      const rec = this.byId.get(capitalId);
      if (rec) {
        rec.capital = f;
        rec.faction = f; // its seat — even on a fallback outside the territory
      }
      taken.add(capitalId);
      capitals[f] = capitalId;
    }
    // The neutral capital's stamp (its system stays faction-neutral).
    {
      const rec = this.byId.get(neutralId);
      if (rec) {
        rec.capital = 'neutral';
        rec.faction = null;
      }
    }

    // TERRITORIES — every system in a faction's final territory takes its
    // faction (its capital already carries the stamp); the neutral hub is
    // explicitly exempt; everything else stays NEUTRAL WILD SPACE.
    for (const f of FACTIONS) {
      for (const id of territoryOf.get(f)) {
        if (id === neutralId) continue;
        const rec = this.byId.get(id);
        if (rec && !rec.capital) rec.faction = f; // a capital keeps its own
      }
    }

    // The pass's output (UI/tests read this; the records carry the rest).
    this.factions = {
      neutralCapital: neutralId,
      capitals,
      branches: branchRoots,
      branchFaction: Object.fromEntries(branchFaction),
      // BALANCE — the CAP (median quota) + the FLOOR (min territory):
      quota,
      minTerritory,
      // PER-FACTION final territories (the floor pass can cross branches —
      // this is the truth; `territories` below is the branch view).
      factionTerritories: Object.fromEntries(FACTIONS.map((f) => [f, [...territoryOf.get(f)].sort()])),
      // Each branch's systems that ended up in a territory (its home
      // faction's kept systems, minus any it lent out — sorted).
      territories: Object.fromEntries(
        branchRoots.map((b) => [b, (nodesOf.get(b) ?? []).filter((id) => owned.has(id)).sort()]),
      ),
    };
    const missing = FACTIONS.filter((f) => !capitals[f]);
    if (missing.length > 0) {
      console.warn(`[orbit] factions: no capital placed for ${missing.join(', ')} (degenerate branch layout)`);
    }
  }

  /**
   * The home→far zones (data/galaxy.json → distribution.zones),
   * validated and sorted by `d`. A single fallback zone when the config
   * is missing/malformed — the galaxy still generates.
   */
  _zones() {
    const raw = this.params.distribution?.zones;
    const out = (Array.isArray(raw) ? raw : [])
      .filter(
        (z) =>
          z &&
          typeof z.name === 'string' &&
          Array.isArray(z.d) &&
          z.d.length === 2 &&
          Number.isFinite(z.d[0]) &&
          Number.isFinite(z.d[1]) &&
          z.d[1] > z.d[0],
      )
      .map((z) => ({ name: z.name, d: [clamp(z.d[0], 0, 1), clamp(z.d[1], 0, 1)] }))
      .sort((a, b) => a.d[0] - b.d[0]);
    return out.length ? out : [{ name: 'all', d: [0, 1] }];
  }

  /** A corner of the field (screen orientation — y DOWN). */
  _cornerPoint(name, { halfW, halfH }) {
    const CORNERS = { NE: [1, -1], NW: [-1, -1], SE: [1, 1], SW: [-1, 1] };
    const key = String(name ?? 'SE').toUpperCase();
    const [sx, sy] = CORNERS[key] ?? CORNERS.SE;
    return { x: sx * halfW, y: sy * halfH };
  }

  /**
   * Even star placement: exactly `n` points in the field
   * [−halfW, halfW] × [−halfH, halfH], every pair at least `d0` apart
   * (Bridson / Poisson disk). If the field can't hold `n` points at
   * `d0` (dense config), retry a few times with a relaxed spacing; as a
   * last resort pad with random points — a working galaxy beats a
   * perfect one. Deterministic: each attempt draws from its own seeded
   * fork (seed, 'layout', 'poisson', attempt).
   */
  _poissonDisk(n, { halfW, halfH }, d0) {
    if (n <= 0) return [];
    let d = Math.max(1, d0);
    let pts = null;
    for (let attempt = 0; attempt < 8; attempt++) {
      const rng = Rng.derive(this.seed, 'layout', 'poisson', attempt);
      pts = this._bridson(n, { halfW, halfH }, d, rng);
      if (pts.length >= n) break;
      d *= 0.88; // not enough room — loosen the spacing and retry
    }
    const rng = Rng.derive(this.seed, 'layout', 'poisson', 'pad');
    while (pts.length < n) {
      pts.push({ x: rng.range(-halfW, halfW), y: rng.range(-halfH, halfH) });
    }
    return pts.slice(0, n);
  }

  /**
   * Bridson's algorithm: grow a Poisson-disk of points in the field,
   * stopping once `n` points are placed (or the frontier is exhausted).
   * Pure — deterministic for a given (n, halfW, halfH, d, rng stream).
   */
  _bridson(n, { halfW, halfH }, d, rng) {
    if (n <= 0) return [];
    const cell = d / Math.SQRT2;
    const grid = new Map(); // "cx,cy" → [point, …]
    const pts = [];
    const active = []; // indices into pts (Bridson's active list)
    const inside = (p) =>
      p.x >= -halfW && p.x <= halfW && p.y >= -halfH && p.y <= halfH;
    const keyOf = (p) =>
      `${Math.floor((p.x + halfW) / cell)},${Math.floor((p.y + halfH) / cell)}`;
    const free = (p) => {
      const cx = Math.floor((p.x + halfW) / cell);
      const cy = Math.floor((p.y + halfH) / cell);
      for (let ax = -2; ax <= 2; ax++) {
        for (let ay = -2; ay <= 2; ay++) {
          const bucket = grid.get(`${cx + ax},${cy + ay}`);
          if (!bucket) continue;
          for (const q of bucket) {
            const dx = q.x - p.x;
            const dy = q.y - p.y;
            if (dx * dx + dy * dy < d * d) return false;
          }
        }
      }
      return true;
    };
    const place = (p) => {
      pts.push(p);
      active.push(pts.length - 1);
      const k = keyOf(p);
      const bucket = grid.get(k);
      if (bucket) bucket.push(p);
      else grid.set(k, [p]);
    };
    // Seed the frontier with one random interior point.
    place({ x: rng.range(-halfW, halfW), y: rng.range(-halfH, halfH) });
    while (active.length > 0 && pts.length < n) {
      const i = rng.int(0, active.length - 1);
      const p = pts[active[i]];
      let placed = false;
      for (let t = 0; t < 30 && !placed; t++) {
        // Sample a candidate in the annulus [d, 2d) around p.
        const r = d * (1 + rng.next());
        const a = rng.next() * TAU;
        const q = { x: p.x + r * Math.cos(a), y: p.y + r * Math.sin(a) };
        if (!inside(q) || !free(q)) continue;
        place(q);
        placed = true;
      }
      if (!placed) active.splice(i, 1); // p can never yield a neighbor
    }
    return pts;
  }

  // ------------------------------------------------------------------
  // Queries
  // ------------------------------------------------------------------

  /**
   * The k nearest systems to a world-space point (k=1 by default).
   * Ring-expands the spatial hash; exact as long as k systems exist.
   */
  nearest(x, y, k = 1) {
    const c = this.cellSize;
    const cx = Math.floor(x / c);
    const cy = Math.floor(y / c);
    const best = [];
    const consider = (rec) => {
      const d2 = (rec.x - x) ** 2 + (rec.y - y) ** 2;
      best.push({ d2, record: rec });
      best.sort((a, b) => a.d2 - b.d2);
      if (best.length > k) best.length = k;
    };
    const maxRing = Math.min(1024, Math.ceil(Math.hypot(this.fieldW ?? 32000, this.fieldH ?? 16000) / c) + 1);
    for (let ring = 0; ring <= maxRing; ring++) {
      for (let dx = -ring; dx <= ring; dx++) {
        for (let dy = -ring; dy <= ring; dy++) {
          if (Math.max(Math.abs(dx), Math.abs(dy)) !== ring) continue;
          const cell = this.grid.get(`${cx + dx},${cy + dy}`);
          if (cell) for (const rec of cell) consider(rec);
        }
      }
      // Everything left unscanned is at least ring·c away; if the kth
      // best is already closer, the answer is final.
      if (best.length >= k) {
        const bound = ring * c;
        if (best[k - 1].d2 <= bound * bound) break;
      }
    }
    return best.slice(0, k).map((e) => e.record);
  }

  /** The k nearest OTHER systems to a system (jump-range candidate list). */
  neighborsOf(id, k = null) {
    const rec = this.byId.get(id);
    if (!rec) throw new Error(`Unknown system "${id}"`);
    const need = k ?? Math.floor(this.params.neighbors ?? 8);
    const out = [];
    for (const cand of this.nearest(rec.x, rec.y, need + 1)) {
      if (cand.id !== id) out.push(cand);
      if (out.length >= need) break;
    }
    return out;
  }

  /**
   * The other systems this system's jump gates jump to — the star
   * RECORDS ({ id, name, x, y }), ordered with the "road home" (parent)
   * edge first, then the local shortcuts. minGates–maxGates entries for
   * n > 1 (data/gates.json); empty for a one-system galaxy.
   */
  jumpGatesFor(id) {
    const rec = this.byId.get(id);
    if (!rec) throw new Error(`Unknown system "${id}"`);
    return (this.jumpNetwork.gates.get(id) ?? []).map((tid) => this.byId.get(tid)).filter(Boolean);
  }

  /** @returns {object} the player's current (starting) system record */
  currentSystem() {
    return this.byId.get(this.currentSystemId) ?? this.records[0];
  }

  /** True when the system is the player's STARTING one — the only system
   *  whose central body is the home world (a star, in every other). Stable
   *  across jumps, unlike a `currentSystemId` comparison. */
  isHomeSystem(id) {
    return id === this.homeSystemId;
  }

  // ------------------------------------------------------------------
  // Contents (level 2, lazy)
  // ------------------------------------------------------------------

  /**
   * Generate (once) and return a system's full contents. Safe to call from
   * "the player arrived here" — the result is identical to what an
   * up-front generateAll() would have produced.
   */
  ensureContent(id) {
    const cached = this.contentCache.get(id);
    if (cached) return cached;
    const record = this.byId.get(id);
    if (!record) throw new Error(`Unknown system "${id}"`);
    const content = generateSystemContent(this, record);
    this.contentCache.set(id, content);
    return content;
  }

  /** Alias of ensureContent() — reads nicer at call sites. */
  contentOf(id) {
    return this.ensureContent(id);
  }

  /**
   * Eager mode: generate every system now. Deterministically identical to
   * lazy generation (per-system seeded streams) — use it if profiling ever
   * shows "just do it all at once" is fine.
   */
  generateAll() {
    for (const rec of this.records) this.ensureContent(rec.id);
    return this;
  }

  get generatedCount() {
    return this.contentCache.size;
  }

  /**
   * The NEUTRAL CAPITAL as a destination target (data/factions.json —
   * the faction pass's designation): the system id + the capital world's
   * object id. The OBJECT vocabulary is the map's discoveryId (js/scenes/
   * GameScene.js: planets carry `discoveryId = rec.name`) — the same id
   * MapWindow's SET DESTINATION passes and the arrival/compass/plate
   * lookups read, so the capital world is the final stop the same way a
   * clicked planet would be. The capital world is the system's OUTERMOST
   * planet (js/galaxy/SystemGenerator.js converts it: `p.capital`). The
   * 'Leaving the Nest' quest's last brief (data/comms.json:
   * trestle-brief-3 — Trestle "sends the coordinates") hands this to the
   * scene's setDestination on acknowledgment (js/scenes/GameScene.js →
   * _commEnded).
   * @returns {{systemId: string, objectId: (string|null)}|null} null when
   *   the faction pass never designated one (degenerate one-system galaxy)
   */
  neutralCapitalTarget() {
    const sysId = this.factions?.neutralCapital;
    if (!sysId || !this.byId.has(sysId)) return null;
    const content = this.ensureContent(sysId);
    const cap = (content.planets ?? []).find((p) => p.capital) ?? null;
    return { systemId: sysId, objectId: cap ? cap.name : null };
  }

  // ------------------------------------------------------------------

  /** Debug/console summary. */
  summary() {
    const byType = {};
    for (const r of this.records) byType[r.type] = (byType[r.type] ?? 0) + 1;
    const byZone = {};
    for (const r of this.records) byZone[r.zone] = (byZone[r.zone] ?? 0) + 1;
    return {
      name: this.name,
      seed: this.seed,
      systems: this.records.length,
      byType,
      byZone,
      generated: this.generatedCount,
      currentSystemId: this.currentSystemId,
      // FACTIONS (the faction pass — data/factions.json): branch map +
      // the four capital system ids (a null capital = placement failed
      // for that faction, logged at roster build).
      factions: this.factions ? {
        neutralCapital: this.factions.neutralCapital,
        capitals: this.factions.capitals,
        branches: this.factions.branches,
        branchFaction: this.factions.branchFaction,
        quota: this.factions.quota,
        territories: this.factions.territories,
      } : null,
      jumpNetworkEdges: this.jumpNetwork ? [...this.jumpNetwork.gates.values()].reduce((n, t) => n + t.length, 0) : null,
      jumpNetworkBridges: this.jumpNetwork?.bridges ?? [],
    };
  }
}