import { MAP_H, MAP_W, SIZE, MinHeap, clamp, hash2, lerp, smoothstep, valueNoise } from "./mapUtils.js";
import { generateMap } from "./mapPipeline.js";
import { LANDUSE } from "./landuseCodes.js";

export const PATCH_MIN_WIDTH = 48;
export const PATCH_MIN_HEIGHT = 48;
export const PATCH_MIN_AREA = 3000;

const POINT_LAYER_KEYS = [
  "villages", "geographicUrbanAnchors", "markets", "castles", "castleTowns", "castleRuins",
  "ports", "crossings", "passes", "modernCities", "satelliteCities", "stations",
  "interchanges", "industrialZones", "logisticsParks", "newTowns", "adminCenters",
  "externalGateways", "prefectureRegions",
];

const PATH_LAYER_KEYS = [
  "premodernRoads", "minorRoads", "nationalRoads", "ringRoads", "externalRoads",
  "railways", "branchRailways", "ringRailways", "externalRailways", "expressways", "externalExpressways",
  "icAccessRoads", "mainRivers", "tributaryRivers", "smallStreams", "riverPaths",
];

const ROAD_LAYER_KEYS = new Set(["premodernRoads", "minorRoads", "nationalRoads", "ringRoads", "externalRoads", "expressways", "externalExpressways", "icAccessRoads"]);
const RAIL_LAYER_KEYS = new Set(["railways", "branchRailways", "ringRailways", "externalRailways"]);
const RIVER_LAYER_KEYS = new Set(["mainRivers", "tributaryRivers", "smallStreams", "riverPaths"]);

const SEGMENT_LAYER_KEYS = ["adminBorders", "regionalPrefectureBorders", "prefectureBorder"];

const ID_FIELD_OFFSETS = new Map([
  ["adminId", 100000],
  ["municipalityId", 100000],
  ["prefectureRegionId", 200000],
  ["regionId", 300000],
  ["naturalCompartmentId", 400000],
  ["watershedId", 500000],
]);

const DISCRETE_FIELD_NAMES = new Set([
  "sea", "ocean", "lake", "prefectureMask", "landMask", "landuse",
  "adminId", "municipalityId", "prefectureRegionId", "regionId", "naturalCompartmentId", "watershedId",
]);


const ADMIN_CONTINUITY_FIELD_NAMES = new Set(["adminId", "municipalityId", "prefectureRegionId"]);
const NATURAL_CONTINUITY_FIELD_NAMES = new Set(["regionId", "naturalCompartmentId", "watershedId"]);
const CONTINUITY_FIELD_NAMES = new Set([...ADMIN_CONTINUITY_FIELD_NAMES, ...NATURAL_CONTINUITY_FIELD_NAMES]);

const SKIP_CELL_FIELDS = new Set(["flowTo"]);

function worldIndex(world, x, y) {
  if (!world || x < 0 || y < 0 || x >= world.width || y >= world.height) return -1;
  return y * world.width + x;
}

function sourceIndex(x, y) {
  if (x < 0 || y < 0 || x >= MAP_W || y >= MAP_H) return -1;
  return y * MAP_W + x;
}

function isCellField(value) {
  return ArrayBuffer.isView(value) && typeof value.length === "number" && value.length === SIZE;
}

function rectWidth(rect) {
  return Math.max(0, Math.floor(rect.x1) - Math.floor(rect.x0));
}

function rectHeight(rect) {
  return Math.max(0, Math.floor(rect.y1) - Math.floor(rect.y0));
}

function rectArea(rect) {
  return rectWidth(rect) * rectHeight(rect);
}

function normalizeRect(rect) {
  if (!rect) return null;
  const x0 = Math.floor(Math.min(rect.x0, rect.x1));
  const y0 = Math.floor(Math.min(rect.y0, rect.y1));
  const x1 = Math.ceil(Math.max(rect.x0, rect.x1));
  const y1 = Math.ceil(Math.max(rect.y0, rect.y1));
  return { x0, y0, x1, y1 };
}

function insideRect(x, y, rect) {
  return !!rect && x >= rect.x0 && y >= rect.y0 && x < rect.x1 && y < rect.y1;
}

function expandRect(rect, margin, world = null) {
  return {
    x0: Math.max(0, rect.x0 - margin),
    y0: Math.max(0, rect.y0 - margin),
    x1: Math.min(world?.width ?? Infinity, rect.x1 + margin),
    y1: Math.min(world?.height ?? Infinity, rect.y1 + margin),
  };
}

function distanceToRectEdge(x, y, rect) {
  return Math.min(x - rect.x0, y - rect.y0, rect.x1 - 1 - x, rect.y1 - 1 - y);
}

function defaultForField(name, Constructor) {
  if (name === "sea" || name === "ocean") return 1;
  if (name === "elevation") return 0.08;
  if (ID_FIELD_OFFSETS.has(name)) return -1;
  if (Constructor === Float32Array || Constructor === Float64Array) return 0;
  return 0;
}

function ensureWorldField(world, name, source) {
  if (!source || !isCellField(source)) return null;
  const Constructor = source.constructor;
  const expected = world.width * world.height;
  if (!world.fields[name] || world.fields[name].length !== expected) {
    world.fields[name] = new Constructor(expected);
    const fallback = defaultForField(name, Constructor);
    if (fallback !== 0) world.fields[name].fill(fallback);
  }
  return world.fields[name];
}

export function clipPatchRect(rect, world) {
  const normalized = normalizeRect(rect);
  if (!normalized || !world) return null;
  return {
    x0: Math.min(Math.max(normalized.x0, 0), world.width),
    y0: Math.min(Math.max(normalized.y0, 0), world.height),
    x1: Math.min(Math.max(normalized.x1, 0), world.width),
    y1: Math.min(Math.max(normalized.y1, 0), world.height),
  };
}

export function validatePatchRect(rect, world) {
  const clipped = clipPatchRect(rect, world);
  if (!clipped) return { ok: false, rect: null, reason: "No selected area." };
  const width = rectWidth(clipped);
  const height = rectHeight(clipped);
  const area = width * height;
  if (width < PATCH_MIN_WIDTH || height < PATCH_MIN_HEIGHT) {
    const parts = [];
    if (width < PATCH_MIN_WIDTH) parts.push(`minimum width ${PATCH_MIN_WIDTH} cells`);
    if (height < PATCH_MIN_HEIGHT) parts.push(`minimum height ${PATCH_MIN_HEIGHT} cells`);
    return {
      ok: false,
      rect: clipped,
      width,
      height,
      area,
      reason: `Selection is too small: ${parts.join(", ")} required. Current ${width} x ${height} cells, ${area.toLocaleString()} cells total.`,
    };
  }
  if (area < PATCH_MIN_AREA) {
    return {
      ok: false,
      rect: clipped,
      width,
      height,
      area,
      reason: `Selection area is too small: minimum area ${PATCH_MIN_AREA.toLocaleString()} cells required. Current ${area.toLocaleString()} cells.`,
    };
  }
  return { ok: true, rect: clipped, width, height, area, reason: "" };
}

export function buildPatchRects(userRect, world = null) {
  const coreRect = normalizeRect(userRect);
  const width = rectWidth(coreRect);
  const height = rectHeight(coreRect);
  const shortSide = Math.max(1, Math.min(width, height));
  const desiredWrite = Math.min(96, Math.max(28, Math.floor(shortSide * 0.42)));
  const maxBySource = Math.max(0, Math.floor(Math.min((MAP_W - width) / 2, (MAP_H - height) / 2)));
  const writeMargin = Math.max(0, Math.min(desiredWrite, maxBySource));
  const desiredRepair = Math.min(120, writeMargin + Math.max(8, Math.floor(shortSide * 0.12)));
  const repairMargin = Math.max(writeMargin, Math.min(desiredRepair, maxBySource));
  const writeRect = expandRect(coreRect, writeMargin, world);
  const repairRect = expandRect(coreRect, repairMargin, world);
  const transportReachMargin = Math.max(repairMargin + 96, Math.min(260, repairMargin + Math.max(MAP_W, MAP_H)));
  const transportReachRect = expandRect(coreRect, transportReachMargin, world);
  return {
    coreRect,
    writeRect,
    repairRect,
    contextRect: repairRect,
    transportReachRect,
    blendRect: coreRect,
    userRect: writeRect,
    selectedRect: coreRect,
    writeMargin,
    repairMargin,
    transportReachMargin,
    outerMargin: writeMargin,
    innerMargin: 0,
  };
}

function patchAlpha(x, y, rects, seed = 0) {
  const writeRect = rects.writeRect || rects.userRect;
  if (!insideRect(x, y, writeRect)) return 0;
  const edge = distanceToRectEdge(x, y, writeRect);
  const margin = Math.max(1, rects.writeMargin || 1);
  const low = valueNoise(x, y, seed ^ 0x7153a9d1, 18) - 0.5;
  const mid = valueNoise(x, y, seed ^ 0x9e3779b9, 7) - 0.5;
  const noisyEdge = edge + low * margin * 0.42 + mid * margin * 0.16;
  const base = smoothstep(clamp(noisyEdge / margin));
  // Keep the expanded repair band as the actual seam.  The user's selected core
  // is still dominant, but the write edge is irregular, so coastlines and land-use
  // no longer inherit the rectangular user selection as a hard boundary.
  return clamp(base);
}

function continuityReplaceThreshold(name, x, y, rects, seed = 0) {
  const n = valueNoise(x, y, seed ^ 0x4f1bbcdc, 11) - 0.5;
  if (ADMIN_CONTINUITY_FIELD_NAMES.has(name)) return clamp(0.82 + n * 0.12, 0.70, 0.92);
  if (NATURAL_CONTINUITY_FIELD_NAMES.has(name)) return clamp(0.68 + n * 0.16, 0.54, 0.82);
  return clamp(0.46 + n * 0.20, 0.28, 0.68);
}

function continuitySegmentAllowed(x, y, nx, ny, rects, seed, minAlpha = 0.42) {
  if (!rects) return true;
  return Math.min(patchAlpha(x, y, rects, seed), patchAlpha(nx, ny, rects, seed)) >= minAlpha;
}


function sourceWindowForRects(rects) {
  const cx = (rects.coreRect.x0 + rects.coreRect.x1 - 1) / 2;
  const cy = (rects.coreRect.y0 + rects.coreRect.y1 - 1) / 2;
  return {
    worldCenterX: cx,
    worldCenterY: cy,
    sourceCenterX: (MAP_W - 1) / 2,
    sourceCenterY: (MAP_H - 1) / 2,
  };
}

function sourceCoordForWorld(window, x, y) {
  return {
    x: Math.round(x - window.worldCenterX + window.sourceCenterX),
    y: Math.round(y - window.worldCenterY + window.sourceCenterY),
  };
}

function worldCoordForSource(window, sx, sy) {
  return {
    x: Math.round(sx - window.sourceCenterX + window.worldCenterX),
    y: Math.round(sy - window.sourceCenterY + window.worldCenterY),
  };
}

function fieldIdOffset(name, seed) {
  const base = ID_FIELD_OFFSETS.get(name) || 0;
  if (!base) return 0;
  return base + ((seed >>> 0) % 997) * 10000;
}

function offsetFieldValue(name, raw, seed) {
  if (!Number.isFinite(raw) || raw < 0) return raw;
  const offset = fieldIdOffset(name, seed);
  return offset ? raw + offset : raw;
}

function isContinuityTransitionCell(x, y, rects, seed = 0, mode = "normal") {
  if (!insideRect(x, y, rects.writeRect)) return false;
  const edge = distanceToRectEdge(x, y, rects.writeRect);
  const margin = Math.max(2, rects.writeMargin || 1);
  const alpha = patchAlpha(x, y, rects, seed);
  const edgeLimit = mode === "prefecture" ? margin * 2.15 : mode === "admin" ? margin * 1.75 : margin * 1.45;
  const alphaLimit = mode === "prefecture" ? 0.995 : mode === "admin" ? 0.985 : 0.96;
  return edge <= edgeLimit || alpha < alphaLimit;
}

function addCount(bucket, key, amount = 1) {
  if (!Number.isFinite(key) || key < 0) return;
  bucket.set(key, (bucket.get(key) || 0) + amount);
}

function buildContinuityIdMappings(world, candidate, rects, window, oldFields, seed = 0) {
  const out = new Map();
  const debug = { continuityIdMappings: 0, continuityIdMappedCells: 0 };
  const dirs = [[0,0],[1,0],[-1,0],[0,1],[0,-1],[1,1],[1,-1],[-1,1],[-1,-1]];

  for (const name of CONTINUITY_FIELD_NAMES) {
    const source = candidate?.[name];
    const old = oldFields?.get(name) || world.fields?.[name];
    if (!source || !old || !isCellField(source)) continue;
    const mode = name === "prefectureRegionId" ? "prefecture" : (name === "adminId" || name === "municipalityId") ? "admin" : "natural";
    const contacts = new Map();

    for (let y = rects.writeRect.y0; y < rects.writeRect.y1; y++) {
      for (let x = rects.writeRect.x0; x < rects.writeRect.x1; x++) {
        if (!isContinuityTransitionCell(x, y, rects, seed, mode)) continue;
        const s = sourceCoordForWorld(window, x, y);
        const si = sourceIndex(s.x, s.y);
        if (si < 0) continue;
        const from = offsetFieldValue(name, source[si], seed);
        if (!Number.isFinite(from) || from < 0) continue;
        const bucket = contacts.get(from) || new Map();
        for (const [dx, dy] of dirs) {
          const nx = x + dx, ny = y + dy;
          const wi = worldIndex(world, nx, ny);
          if (wi < 0 || old[wi] < 0) continue;
          const outsideWrite = !insideRect(nx, ny, rects.writeRect);
          const weakPatch = insideRect(nx, ny, rects.writeRect) && patchAlpha(nx, ny, rects, seed) < (mode === "prefecture" ? 0.96 : 0.88);
          const edgeWeight = outsideWrite ? 6 : weakPatch ? 3 : (dx || dy ? 1 : 2);
          addCount(bucket, old[wi], edgeWeight);
        }
        contacts.set(from, bucket);
      }
    }

    const mapping = new Map();
    for (const [from, bucket] of contacts) {
      let total = 0;
      let best = -1;
      let bestCount = 0;
      for (const [to, count] of bucket) {
        total += count;
        if (count > bestCount) { best = to; bestCount = count; }
      }
      const minCount = mode === "prefecture" ? 10 : mode === "admin" ? 8 : 5;
      const minShare = mode === "prefecture" ? 0.42 : mode === "admin" ? 0.48 : 0.36;
      if (best >= 0 && bestCount >= minCount && bestCount / Math.max(1, total) >= minShare) {
        mapping.set(from, best);
      }
    }
    if (mapping.size) {
      out.set(name, mapping);
      debug.continuityIdMappings += mapping.size;
    }
  }
  out.debug = debug;
  return out;
}

function applyContinuityMapping(idMappings, name, value) {
  const map = idMappings?.get?.(name);
  return map && map.has(value) ? map.get(value) : value;
}

function pointCandidateContinuityIds(p, key, seed = 0) {
  const ids = [];
  if (!p) return ids;
  if (key === "adminCenters") {
    for (const raw of [p.id, p.adminId, p.adminNumericId, p.municipalityId]) {
      if (Number.isFinite(raw) && raw >= 0) ids.push(offsetFieldValue("adminId", raw, seed));
    }
  } else if (key === "prefectureRegions") {
    for (const raw of [p.id, p.prefectureRegionId]) {
      if (Number.isFinite(raw) && raw >= 0) ids.push(offsetFieldValue("prefectureRegionId", raw, seed));
    }
  }
  return ids;
}

function cloneContinuityFields(world) {
  const out = new Map();
  for (const name of CONTINUITY_FIELD_NAMES) {
    const field = world?.fields?.[name];
    if (ArrayBuffer.isView(field)) out.set(name, new field.constructor(field));
  }
  return out;
}

function stabilizeContinuitySeam(world, rects, oldFields, seed = 0) {
  let restored = 0;
  let remapped = 0;
  const margin = Math.max(2, rects.writeMargin || 1);
  for (const name of CONTINUITY_FIELD_NAMES) {
    const field = world.fields?.[name];
    const old = oldFields?.get(name);
    if (!field || !old) continue;
    const isPrefecture = name === "prefectureRegionId";
    const isAdmin = name === "adminId" || name === "municipalityId";
    const preserveAlpha = isPrefecture ? 0.94 : isAdmin ? 0.90 : 0.74;
    const preserveEdge = isPrefecture ? margin * 1.25 : isAdmin ? margin : margin * 0.72;

    // First preserve the old IDs in the transition band.  This prevents the
    // writeRect edge from becoming a prefecture/municipal border.
    for (let y = rects.writeRect.y0; y < rects.writeRect.y1; y++) {
      for (let x = rects.writeRect.x0; x < rects.writeRect.x1; x++) {
        const i = worldIndex(world, x, y);
        if (i < 0 || old[i] < 0) continue;
        const edge = distanceToRectEdge(x, y, rects.writeRect);
        const a = patchAlpha(x, y, rects, seed);
        if (edge <= preserveEdge || a < preserveAlpha) {
          if (field[i] !== old[i]) { field[i] = old[i]; restored++; }
        }
      }
    }

    // Then map candidate IDs that contact an outside ID back to that outside ID.
    // This lets prefectures/municipalities cross the generated-area seam instead
    // of creating a new border exactly on the seam.
    const contacts = new Map();
    const dirs = [[1,0],[-1,0],[0,1],[0,-1]];
    for (let y = rects.writeRect.y0 + 1; y < rects.writeRect.y1 - 1; y++) {
      for (let x = rects.writeRect.x0 + 1; x < rects.writeRect.x1 - 1; x++) {
        const i = worldIndex(world, x, y);
        if (i < 0 || field[i] < 0 || old[i] === field[i]) continue;
        const a = patchAlpha(x, y, rects, seed);
        if (a < 0.98 && !isPrefecture) continue;
        for (const [dx, dy] of dirs) {
          const ni = worldIndex(world, x + dx, y + dy);
          if (ni < 0 || old[ni] < 0 || old[ni] === field[i]) continue;
          if (field[ni] === old[ni] || patchAlpha(x + dx, y + dy, rects, seed) < preserveAlpha) {
            const key = field[i];
            const bucket = contacts.get(key) || new Map();
            bucket.set(old[ni], (bucket.get(old[ni]) || 0) + 1);
            contacts.set(key, bucket);
          }
        }
      }
    }
    const mapping = new Map();
    for (const [from, bucket] of contacts) {
      let best = -1, bestCount = 0;
      for (const [to, count] of bucket) if (count > bestCount) { best = to; bestCount = count; }
      if (best >= 0 && bestCount >= (isPrefecture ? 2 : 3)) mapping.set(from, best);
    }
    if (mapping.size) {
      for (let y = rects.writeRect.y0; y < rects.writeRect.y1; y++) {
        for (let x = rects.writeRect.x0; x < rects.writeRect.x1; x++) {
          const i = worldIndex(world, x, y);
          if (i >= 0 && mapping.has(field[i])) { field[i] = mapping.get(field[i]); remapped++; }
        }
      }
    }
  }
  return { continuityCellsRestored: restored, continuityCellsRemapped: remapped };
}

function copyFullPipelineFields(world, candidate, rects, seed) {
  const window = sourceWindowForRects(rects);
  const oldSea = world.fields.sea ? new Uint8Array(world.fields.sea) : null;
  const oldContinuityFields = cloneContinuityFields(world);
  const continuityIdMappings = buildContinuityIdMappings(world, candidate, rects, window, oldContinuityFields, seed);
  let continuityIdMappedCells = 0;
  let updatedCells = 0;
  let coastCellsChanged = 0;
  let terrainCellsFullyReplaced = 0;
  let naturalRegionsUpdated = 0;
  let adminCellsReassigned = 0;
  let landUseCellsUpdated = 0;

  for (const [name, source] of Object.entries(candidate || {})) {
    if (SKIP_CELL_FIELDS.has(name) || !isCellField(source)) continue;
    const dest = ensureWorldField(world, name, source);
    if (!dest) continue;
    const isFloat = source.constructor === Float32Array || source.constructor === Float64Array;
    const isDiscrete = DISCRETE_FIELD_NAMES.has(name) || !isFloat;
    const idOffset = fieldIdOffset(name, seed);

    for (let y = rects.writeRect.y0; y < rects.writeRect.y1; y++) {
      for (let x = rects.writeRect.x0; x < rects.writeRect.x1; x++) {
        const wi = worldIndex(world, x, y);
        if (wi < 0) continue;
        const s = sourceCoordForWorld(window, x, y);
        const si = sourceIndex(s.x, s.y);
        if (si < 0) continue;
        const alpha = patchAlpha(x, y, rects, seed);
        if (alpha <= 0.005) continue;

        if (isDiscrete) {
          const threshold = continuityReplaceThreshold(name, x, y, rects, seed);
          if (alpha >= threshold) {
            const raw = source[si];
            let value = idOffset && raw >= 0 ? raw + idOffset : raw;
            if (CONTINUITY_FIELD_NAMES.has(name)) {
              const mapped = applyContinuityMapping(continuityIdMappings, name, value);
              if (mapped !== value) continuityIdMappedCells++;
              value = mapped;
            }
            if (name === "sea" && oldSea && dest[wi] !== value) coastCellsChanged++;
            if ((name === "naturalCompartmentId" || name === "watershedId" || name === "regionId") && dest[wi] !== value) naturalRegionsUpdated++;
            if ((name === "adminId" || name === "municipalityId") && dest[wi] !== value) adminCellsReassigned++;
            if (name === "landuse" && dest[wi] !== value) landUseCellsUpdated++;
            dest[wi] = value;
          }
        } else {
          const before = dest[wi] || 0;
          dest[wi] = lerp(before, source[si] || 0, alpha);
        }

        if (name === "elevation") {
          updatedCells++;
          if (alpha > 0.94) terrainCellsFullyReplaced++;
        }
      }
    }
  }

  // The legacy full pipeline uses `adminId` as the municipality raster and
  // assigns municipality metadata on `adminCenters`; it does not expose a
  // separate municipalityId cell field.  If an old experimental field exists,
  // keep it synchronized with the canonical legacy adminId instead of leaving
  // stale numeric/one-municipality data in regenerated patches.
  if (world.fields.adminId && !candidate?.municipalityId) {
    const expected = world.width * world.height;
    if (!world.fields.municipalityId || world.fields.municipalityId.length !== expected) {
      world.fields.municipalityId = new Int32Array(expected);
      world.fields.municipalityId.fill(-1);
    }
    const municipalityId = world.fields.municipalityId;
    const adminId = world.fields.adminId;
    for (let y = rects.writeRect.y0; y < rects.writeRect.y1; y++) {
      for (let x = rects.writeRect.x0; x < rects.writeRect.x1; x++) {
        const wi = worldIndex(world, x, y);
        if (wi >= 0) municipalityId[wi] = adminId[wi];
      }
    }
  }

  // Keep water fields coherent after all continuous fields have been blended.
  const sea = world.fields.sea;
  const ocean = world.fields.ocean;
  const lake = world.fields.lake;
  const landuse = world.fields.landuse;
  if (sea) {
    for (let y = rects.writeRect.y0; y < rects.writeRect.y1; y++) {
      for (let x = rects.writeRect.x0; x < rects.writeRect.x1; x++) {
        const i = worldIndex(world, x, y);
        if (i < 0) continue;
        if (sea[i]) {
          if (ocean) ocean[i] = 1;
          if (lake) lake[i] = 0;
          if (landuse) landuse[i] = LANDUSE.WATER || 0;
        } else {
          if (ocean) ocean[i] = 0;
          if (lake) lake[i] = 0;
        }
      }
    }
  }

  const continuityDebug = stabilizeContinuitySeam(world, rects, oldContinuityFields, seed);

  return {
    window,
    idMappings: continuityIdMappings,
    updatedCells,
    terrainCellsFullyReplaced,
    coastCellsChanged,
    naturalRegionsUpdated,
    adminCellsReassigned,
    landUseCellsUpdated,
    continuityIdMappedCells,
    continuityIdMappings: continuityIdMappings.debug?.continuityIdMappings || 0,
    ...continuityDebug,
  };
}

function smoothWaterTopology(world, rect, seaLevel = 0.30) {
  const sea = world.fields.sea;
  const ocean = world.fields.ocean;
  const lake = world.fields.lake;
  const elevation = world.fields.elevation;
  if (!sea || !elevation) return { coastCellsChanged: 0 };
  let changed = 0;
  for (let pass = 0; pass < 3; pass++) {
    const flips = [];
    for (let y = rect.y0 + 1; y < rect.y1 - 1; y++) {
      for (let x = rect.x0 + 1; x < rect.x1 - 1; x++) {
        const i = worldIndex(world, x, y);
        if (i < 0) continue;
        let seaN = 0;
        let landN = 0;
        for (let dy = -1; dy <= 1; dy++) {
          for (let dx = -1; dx <= 1; dx++) {
            if (!dx && !dy) continue;
            const ni = worldIndex(world, x + dx, y + dy);
            if (ni < 0) continue;
            if (sea[ni]) seaN++; else landN++;
          }
        }
        if (sea[i] && seaN <= 1 && elevation[i] > seaLevel - 0.035) flips.push([i, 0]);
        else if (!sea[i] && seaN >= 7 && elevation[i] < seaLevel + 0.055) flips.push([i, 1]);
      }
    }
    for (const [i, nextSea] of flips) {
      if (sea[i] === nextSea) continue;
      sea[i] = nextSea;
      if (ocean) ocean[i] = nextSea;
      if (lake) lake[i] = 0;
      if (nextSea) elevation[i] = Math.min(elevation[i], seaLevel - 0.004);
      else elevation[i] = Math.max(elevation[i], seaLevel + 0.006);
      changed++;
    }
  }
  return { coastCellsChanged: changed };
}

function recomputeSlopeAndWaterDependentFields(world, rect, seaLevel = 0.30) {
  const fields = world.fields;
  const { elevation, sea } = fields;
  if (!elevation || !sea) return;
  if (!fields.slope) fields.slope = new Float32Array(world.width * world.height);
  for (let y = rect.y0; y < rect.y1; y++) {
    for (let x = rect.x0; x < rect.x1; x++) {
      const i = worldIndex(world, x, y);
      if (i < 0) continue;
      if (sea[i]) {
        for (const key of ["slope", "river", "floodplain", "plain", "agriculture", "ridgeField", "valleyField", "coastalLowland", "naturalBarrierScore", "populationDensity", "settlementScore", "roadInfluence", "railInfluence2", "stationInfluence", "villageInfluence"]) {
          if (fields[key]) fields[key][i] = 0;
        }
        continue;
      }
      if (x > 0 && y > 0 && x < world.width - 1 && y < world.height - 1) {
        const gx = elevation[worldIndex(world, x + 1, y)] - elevation[worldIndex(world, x - 1, y)];
        const gy = elevation[worldIndex(world, x, y + 1)] - elevation[worldIndex(world, x, y - 1)];
        fields.slope[i] = clamp(Math.hypot(gx, gy) * 8.2);
      }
      if (fields.plain) fields.plain[i] = clamp((fields.plain[i] || 0) * 0.75 + (1 - (fields.slope[i] || 0)) * clamp((0.62 - elevation[i]) * 1.8) * 0.25);
      if (fields.agriculture && fields.plain) fields.agriculture[i] = clamp((fields.agriculture[i] || 0) * 0.72 + fields.plain[i] * 0.28);
    }
  }
}

function seaNeighbors(world, x, y, radius = 1) {
  let count = 0;
  for (let dy = -radius; dy <= radius; dy++) {
    for (let dx = -radius; dx <= radius; dx++) {
      if (!dx && !dy) continue;
      const i = worldIndex(world, x + dx, y + dy);
      if (i >= 0 && world.fields.sea?.[i]) count++;
    }
  }
  return count;
}

function isLand(world, x, y) {
  const i = worldIndex(world, x, y);
  return i >= 0 && !world.fields.sea?.[i];
}

function nearestLand(world, x, y, rect, radius = 10) {
  if (insideRect(x, y, rect) && isLand(world, x, y)) return { x, y };
  for (let r = 1; r <= radius; r++) {
    let best = null;
    let bestScore = Infinity;
    for (let yy = y - r; yy <= y + r; yy++) {
      for (let xx = x - r; xx <= x + r; xx++) {
        if (Math.abs(xx - x) !== r && Math.abs(yy - y) !== r) continue;
        if (!insideRect(xx, yy, rect) || !isLand(world, xx, yy)) continue;
        const i = worldIndex(world, xx, yy);
        const score = Math.hypot(xx - x, yy - y) + (world.fields.slope?.[i] || 0) * 3;
        if (score < bestScore) { bestScore = score; best = { x: xx, y: yy }; }
      }
    }
    if (best) return best;
  }
  return null;
}

function pointWorldX(world, p) {
  if (Number.isFinite(p?.worldX)) return p.worldX;
  return (p?.x || 0) + (world?.originX || 0);
}

function pointWorldY(world, p) {
  if (Number.isFinite(p?.worldY)) return p.worldY;
  return (p?.y || 0) + (world?.originY || 0);
}

function tupleWorldX(world, tuple) {
  return (tuple?.[0] || 0) + (world?.originX || 0);
}

function tupleWorldY(world, tuple) {
  return (tuple?.[1] || 0) + (world?.originY || 0);
}

function sourcePointFromWorld(world, point) {
  return { ...point, x: point.x - world.originX, y: point.y - world.originY, worldX: point.x, worldY: point.y, patchGenerated: true };
}

function sourcePathFromWorld(world, path) {
  return path.map(([x, y]) => [Math.round(x - world.originX), Math.round(y - world.originY)]);
}

function transformCandidatePoint(world, window, p, key, seed = 0) {
  if (!p || !Number.isFinite(p.x) || !Number.isFinite(p.y)) return null;
  const w = worldCoordForSource(window, p.x, p.y);
  if (key === "ports") {
    const land = nearestLand(world, w.x, w.y, { x0: 0, y0: 0, x1: world.width, y1: world.height }, 8);
    if (!land || seaNeighbors(world, land.x, land.y, 2) < 2) return null;
    w.x = land.x; w.y = land.y;
  } else if (!["crossings", "passes", "externalGateways", "prefectureRegions"].includes(key) && !isLand(world, w.x, w.y)) {
    const land = nearestLand(world, w.x, w.y, { x0: 0, y0: 0, x1: world.width, y1: world.height }, 5);
    if (!land) return null;
    w.x = land.x; w.y = land.y;
  }
  const out = sourcePointFromWorld(world, { ...p, x: w.x, y: w.y });
  if (key === "adminCenters") {
    const offset = fieldIdOffset("adminId", seed);
    if (Number.isFinite(out.id)) out.id += offset;
    if (Number.isFinite(out.adminId)) out.adminId += offset;
    if (Number.isFinite(out.adminNumericId)) out.adminNumericId += offset;
    if (Number.isFinite(out.municipalityId)) out.municipalityId += offset;
    if (!Number.isFinite(out.adminId) && Number.isFinite(out.municipalityId)) out.adminId = out.municipalityId;
    if (!Number.isFinite(out.municipalityId) && Number.isFinite(out.adminId)) out.municipalityId = out.adminId;
  }
  if (key === "prefectureRegions") {
    const offset = fieldIdOffset("prefectureRegionId", seed);
    if (Number.isFinite(out.id)) out.id += offset;
    if (Number.isFinite(out.prefectureRegionId)) out.prefectureRegionId += offset;
  }
  if (key === "logisticsParks") sanitizeLogisticsPark(out);
  return out;
}

function sanitizeLogisticsPark(p) {
  if (!p) return p;
  p.name = null;
  p.labelName = null;
  p.facilityLabel = p.facilityLabel || "Logistics Park";
  p.labelStyle = "facility";
  p.suppressSettlementLabel = true;
  p.kind = "Logistics Park";
  p.population = 0;
  return p;
}

function sanitizeExistingLogistics(sourceMap) {
  let migrated = 0;
  if (!Array.isArray(sourceMap.logisticsParks)) return 0;
  for (const p of sourceMap.logisticsParks) {
    if (!p) continue;
    if (p.name || p.labelName || !p.suppressSettlementLabel) migrated++;
    sanitizeLogisticsPark(p);
  }
  for (const key of ["villages", "markets", "modernCities", "satelliteCities", "newTowns", "adminCenters"]) {
    const arr = sourceMap[key];
    if (!Array.isArray(arr)) continue;
    for (const p of arr) {
      if (!p?.name || !/\bLogistics\b/i.test(String(p.name))) continue;
      p.name = String(p.name).replace(/\s*Logistics\b/ig, "").trim() || null;
      p.labelName = p.name;
      migrated++;
    }
  }
  return migrated;
}

function transformCandidatePath(window, path) {
  const out = [];
  for (const tuple of path || []) {
    if (!Array.isArray(tuple) || tuple.length < 2) continue;
    const p = worldCoordForSource(window, tuple[0], tuple[1]);
    out.push([p.x, p.y]);
  }
  return out;
}

function splitWorldPathByRect(path, rect, keepInside) {
  const chunks = [];
  let current = [];
  for (const p of path || []) {
    const inside = insideRect(Math.round(p[0]), Math.round(p[1]), rect);
    if (inside === keepInside) current.push([Math.round(p[0]), Math.round(p[1])]);
    else {
      if (current.length >= 2) chunks.push(current);
      current = [];
    }
  }
  if (current.length >= 2) chunks.push(current);
  return chunks;
}

function pruneOldPathLayer(world, paths, rect, mode) {
  const kept = [];
  const anchors = [];
  let clipped = 0;
  for (const path of paths || []) {
    const worldPath = (path || []).map((tuple) => [Math.round(tupleWorldX(world, tuple)), Math.round(tupleWorldY(world, tuple))]);
    const touches = worldPath.some(([x, y]) => insideRect(x, y, rect));
    if (!touches) {
      kept.push(path);
      continue;
    }
    clipped++;
    let lastOutside = null;
    let wasInside = false;
    for (const [x, y] of worldPath) {
      const inside = insideRect(x, y, rect);
      if (!inside) {
        if (wasInside) anchors.push({ x, y, mode });
        lastOutside = { x, y, mode };
      } else if (lastOutside && !wasInside) {
        anchors.push(lastOutside);
      }
      wasInside = inside;
    }
    for (const chunk of splitWorldPathByRect(worldPath, rect, false)) kept.push(sourcePathFromWorld(world, chunk));
  }
  return { kept, anchors, clipped };
}

function pathCost(world, x, y, mode) {
  const i = worldIndex(world, x, y);
  if (i < 0 || world.fields.sea?.[i]) return Infinity;
  const slope = world.fields.slope?.[i] || 0;
  const river = world.fields.river?.[i] || 0;
  const plain = world.fields.plain?.[i] || 0;
  const roadInfluence = world.fields.roadInfluence?.[i] || 0;
  const pop = world.fields.populationDensity?.[i] || 0;
  const slopeMult = mode === "rail" ? 15 : 7;
  return 1 + slope * slopeMult - plain * 0.35 - roadInfluence * 0.28 - pop * 0.18 + river * 0.18;
}

function localPathfind(world, start, goal, rect, mode = "road", maxExpanded = 24000) {
  const sx = Math.round(start.x), sy = Math.round(start.y), gx = Math.round(goal.x), gy = Math.round(goal.y);
  if (!insideRect(sx, sy, rect) || !insideRect(gx, gy, rect)) return null;
  if (!isLand(world, sx, sy) || !isLand(world, gx, gy)) return null;
  const w = rectWidth(rect);
  const h = rectHeight(rect);
  const n = w * h;
  const dist = new Float64Array(n); dist.fill(Infinity);
  const prev = new Int32Array(n); prev.fill(-1);
  const local = (x, y) => (y - rect.y0) * w + (x - rect.x0);
  const heap = new MinHeap();
  const startId = local(sx, sy);
  dist[startId] = 0;
  heap.push({ x: sx, y: sy, f: Math.hypot(sx - gx, sy - gy), id: startId });
  let expanded = 0;
  let found = -1;
  const dirs = [[1,0],[-1,0],[0,1],[0,-1],[1,1],[1,-1],[-1,1],[-1,-1]];
  while (heap.items.length && expanded < maxExpanded) {
    const cur = heap.pop();
    if (!cur) break;
    if (cur.x === gx && cur.y === gy) { found = cur.id; break; }
    expanded++;
    for (const [dx, dy] of dirs) {
      const nx = cur.x + dx, ny = cur.y + dy;
      if (!insideRect(nx, ny, rect)) continue;
      const nid = local(nx, ny);
      const c = pathCost(world, nx, ny, mode);
      if (!Number.isFinite(c)) continue;
      const step = (dx && dy ? 1.42 : 1) * c;
      const nd = dist[cur.id] + step;
      if (nd >= dist[nid]) continue;
      dist[nid] = nd;
      prev[nid] = cur.id;
      heap.push({ x: nx, y: ny, id: nid, f: nd + Math.hypot(nx - gx, ny - gy) * 1.05 });
    }
  }
  if (found < 0) return null;
  const rev = [];
  let at = found;
  while (at >= 0) {
    const x = rect.x0 + (at % w);
    const y = rect.y0 + Math.floor(at / w);
    rev.push([x, y]);
    at = prev[at];
  }
  return rev.reverse();
}

function simplifyPath(path, keepEvery = 2) {
  if (!path || path.length <= 2) return path || [];
  const out = [path[0]];
  for (let i = 1; i < path.length - 1; i++) if (i % keepEvery === 0) out.push(path[i]);
  out.push(path[path.length - 1]);
  return out;
}

function collectInternalNetworkPoints(world, sourceMap, keys, rect, mode = "road") {
  const points = [];
  const seen = new Set();
  const add = (x, y, key, weight = 1) => {
    x = Math.round(x); y = Math.round(y);
    if (!insideRect(x, y, rect) || !isLand(world, x, y)) return;
    const sig = `${x},${y},${key}`;
    if (seen.has(sig)) return;
    seen.add(sig);
    points.push({ x, y, key, weight });
  };
  for (const key of keys) {
    for (const path of sourceMap[key] || []) {
      for (let i = 0; i < path.length; i += 4) {
        add(tupleWorldX(world, path[i]), tupleWorldY(world, path[i]), key, 1.1);
      }
    }
  }
  const featureKeys = mode === "rail"
    ? ["modernCities", "stations", "ports", "adminCenters", "industrialZones", "newTowns"]
    : ["modernCities", "ports", "markets", "villages", "adminCenters", "industrialZones", "logisticsParks", "newTowns"];
  for (const key of featureKeys) {
    for (const p of sourceMap[key] || []) {
      add(pointWorldX(world, p), pointWorldY(world, p), key, key === "adminCenters" || key === "modernCities" ? 1.8 : 1.25);
    }
  }
  return points;
}

function connectAnchors(world, sourceMap, anchors, mode, rect) {
  const keys = mode === "rail" ? ["railways", "branchRailways"] : ["nationalRoads", "minorRoads", "premodernRoads"];
  const targets = collectInternalNetworkPoints(world, sourceMap, keys, rect, mode);
  if (!targets.length) return { connectors: 0, disconnected: anchors.length };
  let connectors = 0;
  let disconnected = 0;
  const layer = mode === "rail" ? "branchRailways" : "minorRoads";
  sourceMap[layer] ||= [];
  const seen = new Set();
  const maxRange = mode === "rail" ? 260 : 300;
  for (const raw of anchors) {
    const anchorLand = nearestLand(world, raw.x, raw.y, rect, 18);
    if (!anchorLand) { disconnected++; continue; }
    const target = targets
      .map((p) => ({ ...p, d: Math.hypot(p.x - anchorLand.x, p.y - anchorLand.y) }))
      .filter((p) => p.d <= maxRange)
      .sort((a, b) => (a.d / Math.max(0.6, a.weight || 1)) - (b.d / Math.max(0.6, b.weight || 1)))[0];
    if (!target) { disconnected++; continue; }
    const sig = `${anchorLand.x},${anchorLand.y}:${target.x},${target.y}:${mode}`;
    if (seen.has(sig)) continue;
    seen.add(sig);
    const searchRect = expandRect(rect, 8, world);
    const path = localPathfind(world, anchorLand, target, searchRect, mode, 42000);
    if (!path || path.length < 2) { disconnected++; continue; }
    sourceMap[layer].push(sourcePathFromWorld(world, simplifyPath(path, mode === "rail" ? 3 : 2)));
    connectors++;
  }
  return { connectors, disconnected };
}

function nearestNetworkPoint(world, sourceMap, keys, point, rect, maxDistance = 80) {
  let best = null;
  let bestD = maxDistance;
  for (const key of keys) {
    for (const path of sourceMap[key] || []) {
      for (let i = 0; i < path.length; i += 5) {
        const x = Math.round(tupleWorldX(world, path[i]));
        const y = Math.round(tupleWorldY(world, path[i]));
        if (!insideRect(x, y, rect) || !isLand(world, x, y)) continue;
        const d = Math.hypot(point.x - x, point.y - y);
        if (d < bestD) { bestD = d; best = { x, y, key }; }
      }
    }
  }
  return best;
}

function ensureSettlementRoadCoverage(world, sourceMap, rect) {
  const keys = ["nationalRoads", "minorRoads", "premodernRoads"];
  const featureKeys = ["modernCities", "ports", "markets", "adminCenters", "villages"];
  sourceMap.minorRoads ||= [];
  let connectors = 0;
  const seen = new Set();
  for (const key of featureKeys) {
    for (const p of sourceMap[key] || []) {
      const start = nearestLand(world, pointWorldX(world, p), pointWorldY(world, p), rect, 10);
      if (!start || !insideRect(start.x, start.y, rect)) continue;
      const target = nearestNetworkPoint(world, sourceMap, keys, start, rect, key === "villages" ? 36 : 58);
      if (!target || Math.hypot(target.x - start.x, target.y - start.y) < 5) continue;
      const sig = `${start.x},${start.y}:${target.x},${target.y}`;
      if (seen.has(sig)) continue;
      seen.add(sig);
      const path = localPathfind(world, start, target, rect, "road", 28000);
      if (!path || path.length < 2) continue;
      sourceMap.minorRoads.push(sourcePathFromWorld(world, simplifyPath(path, 2)));
      connectors++;
    }
  }
  return connectors;
}

function mergePointLayers(world, sourceMap, candidate, rects, window, seed, idMappings = null) {
  let preservedExternalEntities = 0;
  let regeneratedInternalEntities = 0;
  let invalidPortsRemoved = 0;
  for (const key of POINT_LAYER_KEYS) {
    const oldArr = Array.isArray(sourceMap[key]) ? sourceMap[key] : [];
    const kept = [];
    for (const p of oldArr) {
      if (!p) continue;
      const wx = Math.round(pointWorldX(world, p));
      const wy = Math.round(pointWorldY(world, p));
      const inWrite = insideRect(wx, wy, rects.writeRect);
      const alpha = inWrite ? patchAlpha(wx, wy, rects, seed) : 0;
      if (!inWrite || alpha < 0.34) {
        if (key === "ports" && inWrite && (!isLand(world, wx, wy) || seaNeighbors(world, wx, wy, 2) < 2)) { invalidPortsRemoved++; continue; }
        kept.push(p);
        if (!inWrite) preservedExternalEntities++;
      }
    }
    const generated = [];
    for (const p of candidate[key] || []) {
      const candidateIds = pointCandidateContinuityIds(p, key, seed);
      if (key === "adminCenters" && candidateIds.some((id) => applyContinuityMapping(idMappings, "adminId", id) !== id || applyContinuityMapping(idMappings, "municipalityId", id) !== id)) {
        continue;
      }
      if (key === "prefectureRegions" && candidateIds.some((id) => applyContinuityMapping(idMappings, "prefectureRegionId", id) !== id)) {
        continue;
      }
      const q = transformCandidatePoint(world, window, p, key, seed);
      if (!q) continue;
      const wx = Math.round(pointWorldX(world, q));
      const wy = Math.round(pointWorldY(world, q));
      if (!insideRect(wx, wy, rects.writeRect)) continue;
      if (patchAlpha(wx, wy, rects, seed) < 0.42) continue;
      generated.push(q);
    }
    sourceMap[key] = [...kept, ...generated];
    regeneratedInternalEntities += generated.length;
  }
  return { preservedExternalEntities, regeneratedInternalEntities, invalidPortsRemoved };
}

function mergePathLayers(world, sourceMap, candidate, rects, window, seed) {
  let roadAnchors = [];
  let railAnchors = [];
  let roadsClipped = 0;
  let railsClipped = 0;
  let regeneratedPaths = 0;
  for (const key of PATH_LAYER_KEYS) {
    const oldArr = Array.isArray(sourceMap[key]) ? sourceMap[key] : [];
    const mode = RAIL_LAYER_KEYS.has(key) ? "rail" : ROAD_LAYER_KEYS.has(key) ? "road" : RIVER_LAYER_KEYS.has(key) ? "river" : "path";
    const pruned = pruneOldPathLayer(world, oldArr, rects.writeRect, mode);
    if (mode === "rail") { railAnchors = railAnchors.concat(pruned.anchors); railsClipped += pruned.clipped; }
    else if (mode === "road") { roadAnchors = roadAnchors.concat(pruned.anchors); roadsClipped += pruned.clipped; }
    const next = [...pruned.kept];
    for (const path of candidate[key] || []) {
      const worldPath = transformCandidatePath(window, path);
      const chunks = splitWorldPathByRect(worldPath, rects.writeRect, true)
        .map((chunk) => chunk.filter(([x, y]) => mode === "river" || isLand(world, x, y) || patchAlpha(x, y, rects, seed) > 0.90))
        .filter((chunk) => chunk.length >= 2);
      for (const chunk of chunks) {
        if (chunk.some(([x, y]) => patchAlpha(x, y, rects, seed) >= 0.40)) {
          next.push(sourcePathFromWorld(world, simplifyPath(chunk, mode === "rail" ? 3 : 2)));
          regeneratedPaths++;
        }
      }
    }
    sourceMap[key] = next;
  }
  const transportRect = rects.transportReachRect || rects.repairRect || rects.writeRect;
  const roadConn = connectAnchors(world, sourceMap, roadAnchors, "road", transportRect);
  const railConn = connectAnchors(world, sourceMap, railAnchors, "rail", transportRect);
  const settlementRoadConnectors = ensureSettlementRoadCoverage(world, sourceMap, transportRect);
  return {
    roadsClipped,
    railsClipped,
    regeneratedPaths,
    roadConnectorsCreated: roadConn.connectors + settlementRoadConnectors,
    railwayConnectorsCreated: railConn.connectors,
    disconnectedRoadComponents: roadConn.disconnected,
    disconnectedRailComponents: railConn.disconnected,
  };
}

function segmentTouchesRect(world, seg, rect) {
  if (!Array.isArray(seg) || seg.length < 2) return false;
  return insideRect(tupleWorldX(world, seg[0]), tupleWorldY(world, seg[0]), rect)
    || insideRect(tupleWorldX(world, seg[1]), tupleWorldY(world, seg[1]), rect);
}

function buildBoundarySegmentsFromField(world, fieldName, rect, options = {}) {
  const field = world.fields[fieldName];
  const sea = world.fields.sea;
  const rects = options.rects || null;
  const seed = options.seed || 0;
  const minAlpha = Number.isFinite(options.minAlpha) ? options.minAlpha : 0;
  if (!field) return [];
  const out = [];
  for (let y = rect.y0; y < rect.y1; y++) {
    for (let x = rect.x0; x < rect.x1; x++) {
      const i = worldIndex(world, x, y);
      if (i < 0 || sea?.[i]) continue;
      const id = field[i];
      if (id < 0) continue;
      const right = worldIndex(world, x + 1, y);
      if (x + 1 < rect.x1 && right >= 0 && !sea?.[right] && field[right] >= 0 && field[right] !== id && continuitySegmentAllowed(x, y, x + 1, y, rects, seed, minAlpha)) {
        out.push([[x + 0.5 - world.originX, y - world.originY], [x + 0.5 - world.originX, y + 1 - world.originY]]);
      }
      const down = worldIndex(world, x, y + 1);
      if (y + 1 < rect.y1 && down >= 0 && !sea?.[down] && field[down] >= 0 && field[down] !== id && continuitySegmentAllowed(x, y, x, y + 1, rects, seed, minAlpha)) {
        out.push([[x - world.originX, y + 0.5 - world.originY], [x + 1 - world.originX, y + 0.5 - world.originY]]);
      }
    }
  }
  return out;
}

function mergeCandidateCompartmentDebugSegments(world, sourceMap, candidate, rects, window, seed = 0) {
  const debug = sourceMap.adminDebug || {};
  debug.compartmentBorders ||= [];
  let added = 0;
  for (const seg of candidate?.adminDebug?.compartmentBorders || []) {
    if (!Array.isArray(seg) || seg.length < 2) continue;
    const a = worldCoordForSource(window, seg[0]?.[0], seg[0]?.[1]);
    const b = worldCoordForSource(window, seg[1]?.[0], seg[1]?.[1]);
    const mx = (a.x + b.x) * 0.5;
    const my = (a.y + b.y) * 0.5;
    if (!insideRect(mx, my, rects.writeRect) || patchAlpha(mx, my, rects, seed) < 0.38) continue;
    debug.compartmentBorders.push(sourcePathFromWorld(world, [[a.x, a.y], [b.x, b.y]]));
    added++;
  }
  sourceMap.adminDebug = debug;
  return added;
}

function mergeSegmentLayers(world, sourceMap, rects, seed = 0) {
  for (const key of SEGMENT_LAYER_KEYS) {
    const oldArr = Array.isArray(sourceMap[key]) ? sourceMap[key] : [];
    sourceMap[key] = oldArr.filter((seg) => !segmentTouchesRect(world, seg, rects.writeRect));
  }
  sourceMap.adminBorders ||= [];
  sourceMap.adminBorders.push(...buildBoundarySegmentsFromField(world, "adminId", rects.writeRect, { rects, seed, minAlpha: 0.58 }));
  sourceMap.regionalPrefectureBorders ||= [];
  sourceMap.regionalPrefectureBorders.push(...buildBoundarySegmentsFromField(world, "prefectureRegionId", rects.writeRect, { rects, seed, minAlpha: 0.72 }));
  sourceMap.prefectureBorder ||= [];

  const debug = sourceMap.adminDebug || {};
  debug.compartmentBorders = (debug.compartmentBorders || []).filter((seg) => !segmentTouchesRect(world, seg, rects.writeRect));
  debug.compartmentBorders.push(...buildBoundarySegmentsFromField(world, "naturalCompartmentId", rects.writeRect, { rects, seed, minAlpha: 0.40 }));
  sourceMap.adminDebug = debug;
  return {
    adminBordersRebuilt: sourceMap.adminBorders.length,
    prefectureBordersRebuilt: sourceMap.regionalPrefectureBorders.length,
    compartmentBordersRebuilt: debug.compartmentBorders.length,
  };
}

function repairLanduseAndPopulation(world, rects) {
  const landuse = world.fields.landuse;
  if (!landuse) return { landUseCellsUpdated: 0 };
  let updated = 0;
  for (let y = rects.writeRect.y0; y < rects.writeRect.y1; y++) {
    for (let x = rects.writeRect.x0; x < rects.writeRect.x1; x++) {
      const i = worldIndex(world, x, y);
      if (i < 0) continue;
      if (world.fields.sea?.[i]) {
        if (landuse[i] !== (LANDUSE.WATER || 0)) updated++;
        landuse[i] = LANDUSE.WATER || 0;
        continue;
      }
      if (landuse[i] === (LANDUSE.WATER || 0)) {
        const slope = world.fields.slope?.[i] || 0;
        const ag = world.fields.agriculture?.[i] || 0;
        landuse[i] = slope > 0.42 ? LANDUSE.FOREST : ag > 0.28 ? LANDUSE.FARMLAND : LANDUSE.RURAL;
        updated++;
      }
    }
  }
  return { landUseCellsUpdated: updated };
}

function countSea(world, rect) {
  let seaCount = 0;
  let total = 0;
  for (let y = rect.y0; y < rect.y1; y++) {
    for (let x = rect.x0; x < rect.x1; x++) {
      const i = worldIndex(world, x, y);
      if (i < 0) continue;
      total++;
      if (world.fields.sea?.[i]) seaCount++;
    }
  }
  return { seaCount, total, seaRatio: total ? seaCount / total : 0 };
}

function terrainLabel(candidate, fallback) {
  return candidate?.terrainTemplate?.terrainTypeLabel || candidate?.terrainDebug?.terrainTypeLabel || fallback;
}

function terrainId(candidate, fallback) {
  return candidate?.terrainTemplate?.terrainType || candidate?.terrainDebug?.terrainType || fallback;
}

export function generatePatch(world, userRectInput, options = {}) {
  const validation = validatePatchRect(userRectInput, world);
  if (!validation.ok) return { ok: false, ...validation };

  const rects = buildPatchRects(validation.rect, world);
  const terrainType = options.terrainType || "auto";
  const seed = Number.isFinite(options.seed) ? options.seed >>> 0 : ((world?.seed || 0) + 1013904223) >>> 0;
  const variant = Number.isFinite(options.variant) ? Math.max(0, Math.floor(options.variant)) >>> 0 : 0;
  const candidate = generateMap(seed, { terrainType, legacyTerrain: true, onProgress: () => {} });
  const sourceMap = world.sourceMap || (world.sourceMap = {});
  const logisticsLabelsMigrated = sanitizeExistingLogistics(sourceMap);

  const fieldDebug = copyFullPipelineFields(world, candidate, rects, seed);
  const waterDebug = smoothWaterTopology(world, rects.writeRect, candidate.seaLevel || world.sourceMap?.seaLevel || 0.30);
  recomputeSlopeAndWaterDependentFields(world, rects.repairRect, candidate.seaLevel || world.sourceMap?.seaLevel || 0.30);
  const pointDebug = mergePointLayers(world, sourceMap, candidate, rects, fieldDebug.window, seed, fieldDebug.idMappings);
  const pathDebug = mergePathLayers(world, sourceMap, candidate, rects, fieldDebug.window, seed);
  const segmentDebug = mergeSegmentLayers(world, sourceMap, rects, seed);
  const candidateCompartmentSegmentsAdded = mergeCandidateCompartmentDebugSegments(world, sourceMap, candidate, rects, fieldDebug.window, seed);
  const landDebug = repairLanduseAndPopulation(world, rects);
  sanitizeExistingLogistics(sourceMap);

  const seaStats = countSea(world, rects.coreRect);
  const label = terrainLabel(candidate, terrainType);
  const id = terrainId(candidate, terrainType);
  const humanGeography = {
    ok: true,
    modernCities: (sourceMap.modernCities || []).filter((p) => insideRect(pointWorldX(world, p), pointWorldY(world, p), rects.writeRect)).length,
    ports: (sourceMap.ports || []).filter((p) => insideRect(pointWorldX(world, p), pointWorldY(world, p), rects.writeRect)).length,
    villages: (sourceMap.villages || []).filter((p) => insideRect(pointWorldX(world, p), pointWorldY(world, p), rects.writeRect)).length,
    ...pointDebug,
    ...pathDebug,
    adminCellsReassigned: fieldDebug.adminCellsReassigned,
    continuityCellsRestored: fieldDebug.continuityCellsRestored || 0,
    continuityCellsRemapped: fieldDebug.continuityCellsRemapped || 0,
    continuityIdMappings: fieldDebug.continuityIdMappings || 0,
    continuityIdMappedCells: fieldDebug.continuityIdMappedCells || 0,
    landUseCellsUpdated: fieldDebug.landUseCellsUpdated + landDebug.landUseCellsUpdated,
    logisticsLabelsMigrated,
    ...segmentDebug,
    candidateCompartmentSegmentsAdded,
  };

  const record = {
    ...rects.coreRect,
    coreRect: { ...rects.coreRect },
    writeRect: { ...rects.writeRect },
    repairRect: { ...rects.repairRect },
    contextRect: { ...rects.contextRect },
    blendRect: { ...rects.blendRect },
    terrainType: id,
    label,
    seed,
    variant,
    patchGenerationMode: "legacy-full-pipeline",
    updatedCells: fieldDebug.updatedCells,
    terrainCellsFullyReplaced: fieldDebug.terrainCellsFullyReplaced,
    coastCellsChanged: fieldDebug.coastCellsChanged + waterDebug.coastCellsChanged,
    naturalRegionsUpdated: fieldDebug.naturalRegionsUpdated,
    naturalRegionFragmentsMerged: 0,
    seaRatio: seaStats.seaRatio,
    humanGeography,
    createdAt: Date.now(),
  };
  world.generatedRects = [...(world.generatedRects || []), record];
  world.invalidatedRects = [...(world.invalidatedRects || []), { ...rects.writeRect }];
  world.lastPatchResult = record;

  return {
    ok: true,
    validation,
    rects,
    terrainType: id,
    label,
    seed,
    variant,
    patchGenerationMode: "legacy-full-pipeline",
    updatedCells: record.updatedCells,
    terrainCellsFullyReplaced: record.terrainCellsFullyReplaced,
    coastCellsChanged: record.coastCellsChanged,
    naturalRegionsUpdated: record.naturalRegionsUpdated,
    naturalRegionFragmentsMerged: 0,
    seaRatio: seaStats.seaRatio,
    humanGeography,
  };
}