/**
 * Act I outdoor level maps from the DRLG port (M5 adapter).
 *
 * The 1:1 port of D2MOO's DRLG (src/game/drlg/drlg-*.ts) produces the level exactly as D2Common builds
 * it: rooms, their tile lists (DRLGROOMTILE_AddRoomMapTiles), preset units and warps. This module turns
 * one generated level into what the rest of the game consumes:
 *   - a DS1-shaped canvas ({@link Ds1}) for the isometric renderer (`buildIsoMapScene`), one cell per
 *     level tile, holding the exact (style, sequence, type) of every tile D2 placed;
 *   - the DT1 libraries those tiles come from, with a per-cell library mask so the renderer only draws
 *     variants from the library D2 picked the tile from;
 *   - DS1-shaped objects (the same (type, id) encoding a preset DS1 uses, so the bake resolves them
 *     through its existing object path);
 *   - the level's entrances (seams with their real sides from the DRLG level links, and warps from the
 *     UNIT_TILE preset units D2 creates for them) and SuperUnique landmarks.
 *
 * Nothing here decides anything about the layout: every value comes from the verified DRLG output
 * (the schema-3 dump, identical for the native oracle and the port), and anything unexpected throws.
 * The input is the normalized {@link DrlgLevelInput} so the same code maps the oracle's JSON and the
 * port's in-memory dump.
 */

import type { Ds1, Ds1Cell, Ds1Floor, Ds1Object, Ds1Wall } from '../../formats/ds1.ts'
import type { Dt1 } from '../../formats/dt1.ts'
import { dt1MaskAllows } from '../d2map.ts'
import type { DrlgDump, DumpCoord, DumpLevel, DumpTile, DumpTileRef } from './drlg-dump.ts'
import { DRLG_GetActNoFromLevelId } from './drlg-drlg.ts'
import { DRLGPRESET_GetObjectIndexFromObjPreset } from './drlg-preset.ts'
import { normalizeDrlgPath } from './drlg-source.ts'
import { DATATBLS_GetLevelDefRecord, DATATBLS_GetLvlTypesTxtRecord, DATATBLS_GetMonPresetTxtActSection } from './drlg-tables.ts'
import type { DrlgTables } from './drlg-tables.ts'
import {
  ALTDIR_EAST, ALTDIR_NORTH, ALTDIR_SOUTH, ALTDIR_WEST, DRLGTYPE_OUTDOOR, GRID2_LVL_LINK,
} from './drlg-types.ts'

/** Tiles per outdoor grid cell (the 8x8 blocks of D2DrlgOutdoorInfoStrc.pGrid). */
const TILES_PER_GRID_CELL = 8
/** Sub-tiles per tile (DUNGEON_GameTileToSubtileCoords). */
const SUBTILES_PER_TILE = 5

// D2MapTileFlags (D2DrlgDrlg.h)
const MAPTILE_HIDDEN = 0x8
const MAPTILE_LAYER_SHIFT = 14
const MAPTILE_LAYER_MASK = 0x7

// D2TileType (D2CMP.h)
const TILETYPE_FLOOR = 0
const TILETYPE_WALL_TOP_CORNER_RIGHT = 3
const TILETYPE_WALL_TOP_CORNER_LEFT = 4
const TILETYPE_SHADOW = 13

// D2C_UnitTypes
const UNIT_MONSTER = 1
const UNIT_OBJECT = 2
const UNIT_TILE = 5

/** DS1 object `type` values (the encoding DRLGPRESET_ParseDS1File reads). */
const DS1_TYPE_MONSTER = 1
const DS1_TYPE_OBJECT = 2
/** Object ids below this are ObjPreset slots; `objects.txt id + 150` otherwise (DRLGPRESET_ParseDS1File, v > 5). */
const DS1_OBJPRESET_SLOTS = 150
/**
 * Objects.txt class D2Game refuses to create from a preset unit (SUnit.cpp:1003, SUNIT_CreatePresetUnit:
 * `if (nClassId == 573) return`), so it never exists in game.
 */
const OBJECT_CLASS_INVALID_PRESET = 573

/**
 * MonPlace.txt rows D2Game turns into a fixed monster at the preset position instead of a random pack
 * (D2Game MonsterRegion.cpp:243-300, `switch (nMonPlace)`), mapped to the monster planner's landmark id.
 * Only the cases reachable from Act I outdoor presets are listed: 5 -> MONSTER_BLOODRAVEN.
 */
const MONPLACE_LANDMARKS: ReadonlyMap<number, string> = new Map([[5, 'Blood Raven']])

/** Axis-aligned rectangle in world tiles (D2DrlgCoordStrc). */
export interface DrlgRect {
  readonly x: number
  readonly y: number
  readonly width: number
  readonly height: number
}

/** Which array of the owner room's D2DrlgRoomTilesStrc a tile lives in. */
export type DrlgTileKind = 'wall' | 'floor' | 'shadow'

/** One D2DrlgTileDataStrc, placed in level coordinates. */
export interface DrlgTileInput {
  /** Identity of the tile data (owner level, room, array, index), so owned and linked copies dedupe. */
  readonly key: string
  readonly kind: DrlgTileKind
  /** Level-local tile position: owner room position + nPosX/nPosY - level position (0..W, 0..H). */
  readonly x: number
  readonly y: number
  /** D2DrlgTileDataStrc.dwFlags (D2MapTileFlags). */
  readonly flags: number
  /** D2DrlgTileDataStrc.nTileType. */
  readonly tileType: number
  /** pTile: the DT1 tile D2 picked (normalized library path, tile index), or null when none matched. */
  readonly tile: { readonly library: string; readonly index: number } | null
}

/** One D2PresetUnitStrc of a room, after DRLGROOMTILE_AddRoomMapTiles. */
export interface DrlgUnitInput {
  /** Room index in the level's room chain. */
  readonly room: number
  /** D2C_UnitTypes. */
  readonly type: number
  /** nIndex as D2 stores it (after DRLGPRESET_ParseDS1File's MonPreset / ObjPreset conversion). */
  readonly index: number
  readonly mode: number
  /** Level-local sub-tile position (room-relative nXpos/nYpos + 5 * room offset). */
  readonly subX: number
  readonly subY: number
  readonly spawned: number
}

/** One D2RoomTileStrc (a warp of a room, sub_6FD77F00). */
export interface DrlgWarpInput {
  readonly room: number
  /** pLvlWarpTxtRecord->dwLevelId: the LvlWarp.txt `Id`, the class id of the warp's UNIT_TILE unit. */
  readonly lvlWarpId: number
  /** pDrlgRoom->pLevel->nLevelId of the destination room. */
  readonly toLevelId: number
}

/** One level-to-level D2DrlgOrthStrc of pOutdoors->pRoomData. */
export interface DrlgOrthInput {
  readonly level: number
  /** ALTDIR_*: where the neighbour lies (0 west, 1 north, 2 east, 3 south). */
  readonly dir: number
  readonly box: DrlgRect
}

/** Everything the adapter reads about one generated level. */
export interface DrlgLevelInput {
  readonly levelId: number
  readonly drlgType: number
  readonly levelType: number
  readonly coord: DrlgRect
  /** pOutdoors->dwFlags (D2DrlgOutdoorInfoStrc: link directions, river bank, ...). */
  readonly flags: number
  readonly orths: readonly DrlgOrthInput[]
  /** pOutdoors->pGrid[2] (packed grid-2 info) as dumped at the levelGrid stage. */
  readonly grid2: { readonly w: number; readonly h: number; readonly cells: readonly number[] }
  readonly tiles: readonly DrlgTileInput[]
  readonly units: readonly DrlgUnitInput[]
  readonly warps: readonly DrlgWarpInput[]
}

/** Tables the mapping needs besides the DRLG output. */
export interface DrlgMapContext {
  readonly tables: DrlgTables
  /** Parsed DT1 libraries keyed by {@link normalizeDrlgPath}. */
  readonly dt1: ReadonlyMap<string, Dt1>
  /** SuperUniques.txt `Superunique` column, by row. */
  readonly superUniqueIds: readonly string[]
}

/** Which edge of the level an entrance sits on (world-graph `Side`). */
export type DrlgSide = 'north' | 'east' | 'south' | 'west'

/**
 * A way into or out of the level: the fields of a `WildernessEntrance` (what the bake's
 * buildSceneLinks reads) except the display label, which the bake adds, plus `span` for seams.
 */
export interface DrlgEntrance {
  /** Anchor cell (tiles, level-local). */
  readonly x: number
  readonly y: number
  /** One step inside from the anchor. */
  readonly interiorX: number
  readonly interiorY: number
  readonly toLevelId: number
  readonly side: DrlgSide | null
  readonly kind: 'gate' | 'preset'
  /**
   * Seams only: the stretch of this level's edge (tiles along the side, `from` inclusive, `to`
   * exclusive) where the opening is. The bake searches the walkable gap inside it.
   */
  readonly span?: { readonly from: number; readonly to: number }
  /** Warps only: the UNIT_TILE position in sub-tiles (level-local) and its LvlWarp.txt Id. */
  readonly warp?: { readonly subX: number; readonly subY: number; readonly lvlWarpId: number }
}

/** A fixed monster the planner anchors to its preset position. */
export interface DrlgLandmark {
  /** The monster planner's id (SuperUniques.txt `Superunique`, or 'Blood Raven'). */
  readonly id: string
  readonly tileX: number
  readonly tileY: number
  readonly subX: number
  readonly subY: number
}

/** One tile reference written into the canvas, with the library D2 took it from. */
export interface DrlgCellRef {
  readonly x: number
  readonly y: number
  readonly kind: DrlgTileKind
  readonly style: number
  readonly sequence: number
  readonly type: number
  /** Index into {@link DrlgLevelMap.dt1Names}. */
  readonly library: number
  readonly hidden: boolean
}

export interface DrlgLevelMapStats {
  readonly walls: number
  readonly floors: number
  readonly shadows: number
  /** Type-4 halves skipped because the renderer draws them with their type-3 tile. */
  readonly cornerCompanions: number
  /** Tiles whose pTile is null (D2CMP found no tile): D2 draws nothing for them. */
  readonly withoutTile: number
  /** Linked tiles of other rooms drawn inside this level's canvas. */
  readonly linkedInCanvas: number
  /** Linked tiles outside the canvas (belong to the neighbour's canvas). */
  readonly linkedOutside: number
  readonly objects: number
  readonly monsters: number
  readonly skippedInvalidObjects: number
}

/** One mapped level. */
export interface DrlgLevelMap {
  readonly levelId: number
  readonly coord: DrlgRect
  readonly flags: number
  /** The canvas: (width + 1) x (height + 1) cells, like a DS1 of the level's size. */
  readonly ds1: Ds1
  /** DT1 libraries (normalized archive paths) in renderer library order; per-cell `dt1Mask` bits index it. */
  readonly dt1Names: readonly string[]
  readonly entrances: readonly DrlgEntrance[]
  readonly landmarks: readonly DrlgLandmark[]
  /** Every tile reference written into the canvas (for the DT1-mask ambiguity audit). */
  readonly refs: readonly DrlgCellRef[]
  readonly stats: DrlgLevelMapStats
}

/**
 * DT1 libraries DRLGROOMTILE_LoadDT1FilesForRoom loads for every room regardless of its mask
 * (DrlgRoomTile.cpp:1249-1256): they come first so a cell mask can always name them.
 */
export const DRLG_UNIVERSAL_DT1: readonly string[] = [
  'DATA\\GLOBAL\\TILES\\Act1\\Outdoors\\Blank.dt1',
  'DATA\\GLOBAL\\TILES\\Act1\\Barracks\\InvisWal.dt1',
  'DATA\\GLOBAL\\TILES\\Act1\\Barracks\\Warp.dt1',
].map(normalizeDrlgPath)

/**
 * The Act I levels D2 generates with the outdoor DRLG (Levels.txt DrlgType 3), ascending.
 *
 * @param tables - the DRLG tables.
 * @returns level ids.
 */
export function act1OutdoorLevelIds(tables: DrlgTables): number[] {
  const out: number[] = []
  for (let id = 1; id < tables.nLevelsTxtRecordCount; id += 1) {
    if (DRLG_GetActNoFromLevelId(id) !== 0) break
    if (DATATBLS_GetLevelDefRecord(tables, id).dwDrlgType === DRLGTYPE_OUTDOOR) out.push(id)
  }
  return out
}

const SIDE_OF_ALTDIR: Readonly<Record<number, DrlgSide>> = {
  [ALTDIR_WEST]: 'west',
  [ALTDIR_NORTH]: 'north',
  [ALTDIR_EAST]: 'east',
  [ALTDIR_SOUTH]: 'south',
}

function sideOfAltDir(dir: number, what: string): DrlgSide {
  const side = SIDE_OF_ALTDIR[dir]
  if (side === undefined) throw new Error(`${what}: direction ${dir} is not an ALTDIR`)
  return side
}

function emptyWall(): Ds1Wall {
  return { prop1: 0, sequence: 0, style: 0, type: 0, unknown1: 0, unknown2: 0, hidden: false }
}

function emptyFloor(): Ds1Floor {
  return { prop1: 0, sequence: 0, style: 0, unknown1: 0, unknown2: 0, hidden: false }
}

/** Mutable per-cell collector. */
interface CellBuild {
  walls: { layer: number; order: number; wall: Ds1Wall }[]
  floors: { layer: number; order: number; floor: Ds1Floor }[]
  shadows: Ds1Floor[]
  mask: number
}

/**
 * The DT1 library order for a level: the universal libraries, then the libraries of the level's
 * LvlTypes row in `File 1..32` order. Only libraries some tile uses are listed (plus the universal
 * three, which DRLGROOMTILE_LoadDT1FilesForRoom always loads).
 */
function libraryOrder(tables: DrlgTables, levelType: number, used: ReadonlySet<string>, levelId: number): string[] {
  const order: string[] = [...DRLG_UNIVERSAL_DT1]
  const listed = new Set(order)
  for (const f of DATATBLS_GetLvlTypesTxtRecord(tables, levelType).szFile) {
    if (f.length <= 1) continue
    const key = normalizeDrlgPath(f)
    if (listed.has(key) || !used.has(key)) continue
    order.push(key)
    listed.add(key)
  }
  for (const lib of used) {
    if (!listed.has(lib)) {
      throw new Error(`level ${levelId}: tile library ${lib} is neither universal nor in LvlTypes row ${levelType}`)
    }
  }
  if (order.length > 32) throw new Error(`level ${levelId}: ${order.length} DT1 libraries do not fit a 32-bit cell mask`)
  return order
}

/**
 * Map one generated Act I outdoor level.
 *
 * @param input - the level, from the DRLG dump.
 * @param ctx - tables, DT1 libraries and names.
 * @returns the mapped level.
 */
export function buildDrlgLevelMap(input: DrlgLevelInput, ctx: DrlgMapContext): DrlgLevelMap {
  const { levelId, coord } = input
  if (input.drlgType !== DRLGTYPE_OUTDOOR) throw new Error(`level ${levelId}: not an outdoor level (DrlgType ${input.drlgType})`)
  const nAct = DRLG_GetActNoFromLevelId(levelId)
  const cellsX = coord.width + 1
  const cellsY = coord.height + 1

  // ---- tiles -> canvas ----
  const cells: CellBuild[] = []
  for (let i = 0; i < cellsX * cellsY; i += 1) cells.push({ walls: [], floors: [], shadows: [], mask: 0 })
  const seen = new Set<string>()
  const used = new Set<string>()
  const placed: { t: DrlgTileInput; style: number; sequence: number; type: number; hidden: boolean }[] = []
  let cornerCompanions = 0
  let withoutTile = 0
  let linkedInCanvas = 0
  let linkedOutside = 0
  const topCornerRights = new Set<string>()
  const topCornerLefts: { t: DrlgTileInput; style: number; sequence: number }[] = []

  for (const t of input.tiles) {
    if (seen.has(t.key)) continue
    seen.add(t.key)
    const linked = !t.key.startsWith(`${levelId}/`)
    if (t.x < 0 || t.y < 0 || t.x >= cellsX || t.y >= cellsY) {
      if (!linked) throw new Error(`level ${levelId}: owned tile ${t.key} at (${t.x}, ${t.y}) is outside the ${cellsX}x${cellsY} canvas`)
      linkedOutside += 1
      continue
    }
    if (linked) linkedInCanvas += 1
    if (t.tile === null) {
      withoutTile += 1
      continue
    }
    const lib = ctx.dt1.get(t.tile.library)
    if (lib === undefined) throw new Error(`level ${levelId}: tile ${t.key} uses DT1 ${t.tile.library}, which is not loaded`)
    const header = lib.tiles[t.tile.index]
    if (header === undefined) throw new Error(`level ${levelId}: tile ${t.key}: ${t.tile.library} has no tile #${t.tile.index}`)
    if (header.type !== t.tileType) {
      throw new Error(`level ${levelId}: tile ${t.key}: nTileType ${t.tileType} but DT1 tile #${t.tile.index} of ${t.tile.library} is type ${header.type}`)
    }
    const kindOk = t.kind === 'floor' ? header.type === TILETYPE_FLOOR
      : t.kind === 'shadow' ? header.type === TILETYPE_SHADOW
        : header.type !== TILETYPE_FLOOR && header.type !== TILETYPE_SHADOW
    if (!kindOk) throw new Error(`level ${levelId}: tile ${t.key} is a ${t.kind} of DT1 type ${header.type}`)
    if (header.type === TILETYPE_WALL_TOP_CORNER_LEFT) {
      // D2 stores the left half of a top corner as its own tile data next to the type-3 tile
      // (DRLGROOMTILE_InitWallTileData); buildIsoMapScene draws that half itself for every type-3 wall.
      topCornerLefts.push({ t, style: header.style, sequence: header.sequence })
      continue
    }
    if (header.type === TILETYPE_WALL_TOP_CORNER_RIGHT) topCornerRights.add(`${t.x},${t.y},${header.style},${header.sequence}`)
    used.add(t.tile.library)
    placed.push({ t, style: header.style, sequence: header.sequence, type: header.type, hidden: (t.flags & MAPTILE_HIDDEN) !== 0 })
  }
  for (const c of topCornerLefts) {
    if (!topCornerRights.has(`${c.t.x},${c.t.y},${c.style},${c.sequence}`)) {
      throw new Error(`level ${levelId}: top-corner-left tile ${c.t.key} at (${c.t.x}, ${c.t.y}) has no top-corner-right partner`)
    }
    cornerCompanions += 1
  }

  const dt1Names = libraryOrder(ctx.tables, input.levelType, used, levelId)
  const libIndex = new Map(dt1Names.map((name, i) => [name, i]))
  const refs: DrlgCellRef[] = []
  let order = 0
  let walls = 0
  let floors = 0
  let shadows = 0
  for (const p of placed) {
    const cell = cells[p.t.y * cellsX + p.t.x]!
    const library = libIndex.get(p.t.tile!.library)!
    cell.mask |= 1 << library
    const layer = (p.t.flags >>> MAPTILE_LAYER_SHIFT) & MAPTILE_LAYER_MASK
    // prop1 only marks the slot as used for the renderer; hidden tiles (warp lit tiles, etc.) are kept
    // hidden exactly as D2 adds them.
    if (p.t.kind === 'floor') {
      cell.floors.push({ layer, order: order++, floor: { prop1: 1, sequence: p.sequence, style: p.style, unknown1: 0, unknown2: 0, hidden: p.hidden } })
      floors += 1
    } else if (p.t.kind === 'shadow') {
      cell.shadows.push({ prop1: 1, sequence: p.sequence, style: p.style, unknown1: 0, unknown2: 0, hidden: p.hidden })
      shadows += 1
    } else {
      cell.walls.push({ layer, order: order++, wall: { prop1: 1, sequence: p.sequence, style: p.style, type: p.type, unknown1: 0, unknown2: 0, hidden: p.hidden } })
      walls += 1
    }
    refs.push({ x: p.t.x, y: p.t.y, kind: p.t.kind, style: p.style, sequence: p.sequence, type: p.type, library, hidden: p.hidden })
  }

  let wallLayers = 1
  let floorLayers = 1
  let shadowLayers = 1
  for (const c of cells) {
    wallLayers = Math.max(wallLayers, c.walls.length)
    floorLayers = Math.max(floorLayers, c.floors.length)
    shadowLayers = Math.max(shadowLayers, c.shadows.length)
  }
  const byLayer = <T extends { layer: number; order: number }>(a: T, b: T): number => a.layer - b.layer || a.order - b.order
  const rows: Ds1Cell[][] = []
  for (let y = 0; y < cellsY; y += 1) {
    const row: Ds1Cell[] = []
    for (let x = 0; x < cellsX; x += 1) {
      const c = cells[y * cellsX + x]!
      const cw = c.walls.sort(byLayer).map(w => w.wall)
      const cf = c.floors.sort(byLayer).map(f => f.floor)
      const cs = [...c.shadows]
      while (cw.length < wallLayers) cw.push(emptyWall())
      while (cf.length < floorLayers) cf.push(emptyFloor())
      while (cs.length < shadowLayers) cs.push(emptyFloor())
      row.push({ walls: cw, floors: cf, shadows: cs, substitutions: [], ...(c.mask !== 0 ? { dt1Mask: c.mask >>> 0 } : {}) })
    }
    rows.push(row)
  }

  // ---- units -> DS1 objects, landmarks, warp entrances ----
  const objSlotOf = new Map<number, number>()
  for (let slot = DS1_OBJPRESET_SLOTS - 1; slot >= 0; slot -= 1) {
    objSlotOf.set(DRLGPRESET_GetObjectIndexFromObjPreset(nAct, slot), slot) // lowest slot wins
  }
  const monSection = DATATBLS_GetMonPresetTxtActSection(ctx.tables, nAct)
  if (monSection === null) throw new Error(`level ${levelId}: MonPreset has no act ${nAct + 1} section`)
  const nMonStats = ctx.tables.nMonStatsTxtRecordCount
  const nSU = ctx.tables.nSuperUniquesTxtRecordCount
  const monIdOf = new Map<number, number>()
  for (let i = monSection.count - 1; i >= 0; i -= 1) {
    const r = ctx.tables.monPreset[monSection.start + i]!
    let unit: number
    switch (r.nType) {
      case 0: unit = r.wPlace + nSU + nMonStats; break
      case 1: unit = r.wPlace; break
      case 2: unit = r.wPlace + nMonStats; break
      default: continue // DRLGPRESET_ParseDS1File maps it to -1, which is never allocated
    }
    monIdOf.set(unit, i) // lowest DS1 id wins (duplicates carry the same Place)
  }

  const objects: Ds1Object[] = []
  const landmarks: DrlgLandmark[] = []
  const entrances: DrlgEntrance[] = []
  let nObjects = 0
  let nMonsters = 0
  let skippedInvalidObjects = 0
  for (const u of input.units) {
    switch (u.type) {
      case UNIT_OBJECT: {
        if (u.index === OBJECT_CLASS_INVALID_PRESET) { skippedInvalidObjects += 1; break }
        if (u.index < 0) throw new Error(`level ${levelId}: object unit with class ${u.index}`)
        const slot = objSlotOf.get(u.index)
        objects.push({ type: DS1_TYPE_OBJECT, id: slot ?? u.index + DS1_OBJPRESET_SLOTS, x: u.subX, y: u.subY, flags: u.spawned })
        nObjects += 1
        break
      }
      case UNIT_MONSTER: {
        const id = monIdOf.get(u.index)
        if (id === undefined) throw new Error(`level ${levelId}: monster unit ${u.index} has no act ${nAct + 1} MonPreset row`)
        objects.push({ type: DS1_TYPE_MONSTER, id, x: u.subX, y: u.subY, flags: u.spawned })
        nMonsters += 1
        const tileX = Math.floor(u.subX / SUBTILES_PER_TILE)
        const tileY = Math.floor(u.subY / SUBTILES_PER_TILE)
        if (u.index >= nMonStats && u.index < nMonStats + nSU) {
          const su = ctx.superUniqueIds[u.index - nMonStats]
          if (su === undefined || su === '') throw new Error(`level ${levelId}: SuperUnique row ${u.index - nMonStats} has no id`)
          landmarks.push({ id: su, tileX, tileY, subX: u.subX, subY: u.subY })
        } else if (u.index >= nMonStats + nSU) {
          const special = MONPLACE_LANDMARKS.get(u.index - nMonStats - nSU)
          if (special !== undefined) landmarks.push({ id: special, tileX, tileY, subX: u.subX, subY: u.subY })
        }
        break
      }
      case UNIT_TILE: {
        const matches = input.warps.filter(w => w.room === u.room && w.lvlWarpId === u.index)
        const to = [...new Set(matches.map(w => w.toLevelId))]
        if (to.length !== 1) {
          throw new Error(`level ${levelId} room ${u.room}: UNIT_TILE ${u.index} matches ${to.length} warp destinations (${to.join(', ')})`)
        }
        const cx = Math.floor(u.subX / SUBTILES_PER_TILE)
        const cy = Math.floor(u.subY / SUBTILES_PER_TILE)
        entrances.push({
          x: cx,
          y: cy,
          interiorX: cx,
          interiorY: cy,
          toLevelId: to[0]!,
          side: null,
          kind: 'preset',
          warp: { subX: u.subX, subY: u.subY, lvlWarpId: u.index },
        })
        break
      }
      default:
        throw new Error(`level ${levelId} room ${u.room}: unexpected preset unit type ${u.type} (index ${u.index})`)
    }
  }

  // ---- seams ----
  entrances.push(...seamEntrances(input))

  const ds1: Ds1 = {
    version: 18,
    width: cellsX,
    height: cellsY,
    act: nAct + 1,
    substitutionType: 0,
    wallLayers,
    floorLayers,
    cells: rows,
    objects,
    npcPathOffset: null,
  }
  return {
    levelId,
    coord,
    flags: input.flags,
    ds1,
    dt1Names,
    entrances,
    landmarks,
    refs,
    stats: {
      walls, floors, shadows, cornerCompanions, withoutTile, linkedInCanvas, linkedOutside,
      objects: nObjects, monsters: nMonsters, skippedInvalidObjects,
    },
  }
}

/** How far the renderer's tile choice can stray from D2's for one mapped level. */
export interface DrlgDt1Ambiguity {
  /** DT1 libraries of the level ({@link DrlgLevelMap.dt1Names}). */
  readonly libraries: number
  /** Tile references written into the canvas. */
  readonly refs: number
  /**
   * References whose exact (style, sequence, type) group under their cell's DT1 mask holds more than
   * one tile. The renderer draws the variant with its own per-cell hash (scene fidelity 'layout'); D2
   * rolled it with the room seed (DRLGROOMTILE_GetTileCache), and the port records that roll.
   */
  readonly variantGroups: number
  /** References whose group under the cell mask spans more than one library: the renderer may draw a tile of a library D2 did not take it from. */
  readonly crossLibrary: number
  /** The same count with one pool for the whole level (no cell masks): what the cell masks prevent. */
  readonly crossLibraryLevelWide: number
}

/**
 * The DT1-mask ambiguity audit of a mapped level: resolves every tile reference the way
 * `buildIsoMapScene` does (exact style:sequence:type key, {@link dt1MaskAllows}) and counts the
 * references whose candidates are not pinned down to D2's library.
 *
 * @param map - the mapped level.
 * @param libraries - the parsed libraries of `map.dt1Names`, in that order.
 * @returns the counts.
 */
export function auditDrlgDt1Ambiguity(map: DrlgLevelMap, libraries: readonly Dt1[]): DrlgDt1Ambiguity {
  if (libraries.length !== map.dt1Names.length) {
    throw new Error(`level ${map.levelId}: ${libraries.length} libraries for ${map.dt1Names.length} DT1 names`)
  }
  // style:sequence:type -> tiles per library
  const groups = new Map<string, number[]>()
  libraries.forEach((library, at) => {
    for (const tile of library.tiles) {
      const key = `${tile.style}:${tile.sequence}:${tile.type}`
      let counts = groups.get(key)
      if (counts === undefined) {
        counts = new Array<number>(libraries.length).fill(0)
        groups.set(key, counts)
      }
      counts[at]! += 1
    }
  })
  let variantGroups = 0
  let crossLibrary = 0
  let crossLibraryLevelWide = 0
  for (const ref of map.refs) {
    const counts = groups.get(`${ref.style}:${ref.sequence}:${ref.type}`)
    if (counts === undefined || counts[ref.library] === 0) {
      throw new Error(`level ${map.levelId}: ${ref.kind} ${ref.style}:${ref.sequence}:${ref.type} at (${ref.x}, ${ref.y}) is not in its library ${map.dt1Names[ref.library]}`)
    }
    const mask = map.ds1.cells[ref.y]?.[ref.x]?.dt1Mask
    if (mask === undefined) throw new Error(`level ${map.levelId}: cell (${ref.x}, ${ref.y}) holds a tile but has no DT1 mask`)
    let tilesInCell = 0
    let librariesInCell = 0
    let librariesInLevel = 0
    counts.forEach((n, library) => {
      if (n === 0) return
      librariesInLevel += 1
      if (!dt1MaskAllows(mask, library)) return
      librariesInCell += 1
      tilesInCell += n
    })
    if (tilesInCell > 1) variantGroups += 1
    if (librariesInCell > 1) crossLibrary += 1
    if (librariesInLevel > 1) crossLibraryLevelWide += 1
  }
  return { libraries: libraries.length, refs: map.refs.length, variantGroups, crossLibrary, crossLibraryLevelWide }
}

/**
 * The level's seams to its outdoor/preset neighbours, one per level link (pOutdoors->pRoomData).
 *
 * Outdoor-outdoor links are the grid-2 cells DRLGOUTPLACE_PlaceAct1245OutdoorBorders flags
 * GRID2_LVL_LINK: the border cell in the middle of each linked vertex edge, which gets the open border
 * preset (picked file 3, or 4 on the Burial Grounds). Links whose vertex edge carries flag 2 (the town
 * transition, the Monastery Gate approach) get no border cell: their opening is the neighbour-specific
 * preset, somewhere along the shared edge, so the whole shared stretch is the span.
 */
function seamEntrances(input: DrlgLevelInput): DrlgEntrance[] {
  const { levelId, coord, grid2 } = input
  const out: DrlgEntrance[] = []
  if (grid2.w * TILES_PER_GRID_CELL !== coord.width || grid2.h * TILES_PER_GRID_CELL !== coord.height) {
    throw new Error(`level ${levelId}: grid-2 ${grid2.w}x${grid2.h} does not cover ${coord.width}x${coord.height} tiles`)
  }
  const linkCellsOf = new Map<number, { gx: number; gy: number }[]>()
  for (let gy = 0; gy < grid2.h; gy += 1) {
    for (let gx = 0; gx < grid2.w; gx += 1) {
      if (!(grid2.cells[gy * grid2.w + gx]! & GRID2_LVL_LINK)) continue
      const onW = gx === 0
      const onE = gx === grid2.w - 1
      const onN = gy === 0
      const onS = gy === grid2.h - 1
      if (Number(onW) + Number(onE) + Number(onN) + Number(onS) !== 1) {
        throw new Error(`level ${levelId}: level-link cell (${gx}, ${gy}) is not on exactly one border`)
      }
      const dir = onW ? ALTDIR_WEST : onE ? ALTDIR_EAST : onN ? ALTDIR_NORTH : ALTDIR_SOUTH
      // World tiles covered by the cell along its side.
      const horizontal = dir === ALTDIR_NORTH || dir === ALTDIR_SOUTH
      const from = (horizontal ? coord.x + gx * TILES_PER_GRID_CELL : coord.y + gy * TILES_PER_GRID_CELL)
      const to = from + TILES_PER_GRID_CELL
      const owners = input.orths.filter(o => {
        if (o.dir !== dir) return false
        const lo = horizontal ? o.box.x : o.box.y
        const hi = lo + (horizontal ? o.box.width : o.box.height)
        return from >= lo && to <= hi
      })
      if (owners.length !== 1) {
        throw new Error(`level ${levelId}: level-link cell (${gx}, ${gy}) matches ${owners.length} neighbour links`)
      }
      const list = linkCellsOf.get(owners[0]!.level) ?? []
      list.push({ gx, gy })
      linkCellsOf.set(owners[0]!.level, list)
    }
  }

  for (const o of input.orths) {
    const side = sideOfAltDir(o.dir, `level ${levelId} link to ${o.level}`)
    const horizontal = side === 'north' || side === 'south'
    const cellsOnLink = linkCellsOf.get(o.level) ?? []
    let from: number
    let to: number
    if (cellsOnLink.length > 1) {
      throw new Error(`level ${levelId}: ${cellsOnLink.length} level-link cells for the link to ${o.level}`)
    } else if (cellsOnLink.length === 1) {
      const c = cellsOnLink[0]!
      from = (horizontal ? c.gx : c.gy) * TILES_PER_GRID_CELL
      to = from + TILES_PER_GRID_CELL
    } else {
      // Shared edge of the two rectangles, in level-local tiles along the side.
      const lo = horizontal ? Math.max(coord.x, o.box.x) : Math.max(coord.y, o.box.y)
      const hi = horizontal
        ? Math.min(coord.x + coord.width, o.box.x + o.box.width)
        : Math.min(coord.y + coord.height, o.box.y + o.box.height)
      if (hi <= lo) throw new Error(`level ${levelId}: the link to ${o.level} (${side}) shares no edge`)
      from = lo - (horizontal ? coord.x : coord.y)
      to = hi - (horizontal ? coord.x : coord.y)
    }
    const mid = Math.floor((from + to - 1) / 2)
    const edgeX = side === 'west' ? 0 : side === 'east' ? coord.width - 1 : mid
    const edgeY = side === 'north' ? 0 : side === 'south' ? coord.height - 1 : mid
    const inX = side === 'west' ? 1 : side === 'east' ? coord.width - 2 : mid
    const inY = side === 'north' ? 1 : side === 'south' ? coord.height - 2 : mid
    out.push({
      x: edgeX,
      y: edgeY,
      interiorX: inX,
      interiorY: inY,
      toLevelId: o.level,
      side,
      kind: 'gate',
      span: { from, to },
    })
  }
  return out
}

/** Which tile array a {@link DumpTileRef} names, as the adapter's tile kind. */
const TILE_KIND_OF_ARRAY = { w: 'wall', f: 'floor', r: 'shadow' } as const

/**
 * The adapter input for one level of a schema-3 DRLG dump.
 *
 * The native oracle's JSON and the port's `dumpAct1` have the same shape, so both go through the same
 * mapping and a comparison of the two compares like with like. The dump must come from an act run with
 * activation: every room of the level activated, `mapTiles` being the final state after all of them.
 *
 * - tiles: each room's own tile data, i.e. the entries DRLGROOMTILE_InitWallTileData /
 *   InitFloorTileData / InitShadowTileData filled (`pTileGrid->nWalls/nFloors/nShadows` of the
 *   `pTiles` arrays; the rest of each allocation stays zeroed and is never drawn), then the tiles the
 *   room's pMapLinks point at (DRLGROOMTILE_LinkedTileDataManager's merge of shared room edges, which
 *   reaches rooms of the neighbouring level across a seam).
 * - units: `mapTiles.units`, the room's pPresetUnits after DRLGROOMTILE_AddRoomMapTiles (so with the
 *   UNIT_TILE units of DRLGROOMTILE_AddWarp), moved from room-relative to level-local sub-tiles.
 * - warps: the room's pRoomTiles chain.
 *
 * @param dump - schema-3 dump of an act run with activation.
 * @param levelId - the level to map.
 * @param tables - the DRLG tables the dump was made with (for LvlWarp.txt rows).
 * @returns the adapter input.
 */
export function drlgLevelInputFromDump(dump: DrlgDump, levelId: number, tables: DrlgTables): DrlgLevelInput {
  if (dump.schema !== 3) throw new Error(`DRLG dump schema ${String(dump.schema)}, expected 3`)
  const act = dump.act.find(a => a.id === levelId)
  if (act === undefined) throw new Error(`level ${levelId}: not in the dump's act section`)
  const levelsById = new Map<number, DumpLevel>(dump.levels.map(l => [l.id, l]))
  const level = levelsById.get(levelId)
  if (level === undefined) throw new Error(`level ${levelId}: not generated in the dump`)
  const levelGrid = level.levelGrid
  if (!levelGrid) throw new Error(`level ${levelId}: the dump has no levelGrid stage (not an outdoor level)`)
  const grid2 = levelGrid.grids[2]
  if (!grid2) throw new Error(`level ${levelId}: pGrid[2] was never allocated`)
  if (level.activation.length !== level.rooms.length) {
    throw new Error(`level ${levelId}: ${level.activation.length} of ${level.rooms.length} rooms activated (the dump must be made with activation)`)
  }
  const [levelX, levelY, levelW, levelH] = act.coord
  // pOutdoors->pCoord is a union over nWidth, nHeight, nGridWidth, nGridHeight (8-tile grid cells).
  const [, , gridW, gridH] = levelGrid.coord
  if (gridW * TILES_PER_GRID_CELL !== levelW || gridH * TILES_PER_GRID_CELL !== levelH) {
    throw new Error(`level ${levelId}: outdoor grid ${gridW}x${gridH} does not cover the ${levelW}x${levelH} tiles of the level`)
  }

  const place = (key: string, kind: DrlgTileKind, room: DumpCoord, t: DumpTile): DrlgTileInput => ({
    key,
    kind,
    x: room[0] + t[2] - levelX,
    y: room[1] + t[3] - levelY,
    flags: t[5] >>> 0,
    tileType: t[7],
    tile: t[6] === null ? null : { library: normalizeDrlgPath(t[6][0]), index: t[6][1] },
  })
  const initialised = (level: DumpLevel, room: number, array: 'w' | 'f' | 'r'): { list: readonly DumpTile[]; count: number } => {
    const mt = level.activation[room]!.mapTiles
    const [list, count] = array === 'w' ? [mt.walls, mt.nWalls] : array === 'f' ? [mt.floors, mt.nFloors] : [mt.roofs, mt.nShadows]
    if (count < 0 || count > list.length) {
      throw new Error(`level ${level.id} room ${room}: ${count} initialised ${TILE_KIND_OF_ARRAY[array]} tiles but ${list.length} allocated`)
    }
    return { list, count }
  }

  const tiles: DrlgTileInput[] = []
  const units: DrlgUnitInput[] = []
  const warps: DrlgWarpInput[] = []
  level.rooms.forEach((room, r) => {
    const what = `level ${levelId} room ${r}`
    const mt = level.activation[r]!.mapTiles
    for (const array of ['w', 'f', 'r'] as const) {
      const { list, count } = initialised(level, r, array)
      for (let i = 0; i < count; i += 1) {
        tiles.push(place(`${levelId}/${r}/${array}/${i}`, TILE_KIND_OF_ARRAY[array], room.coord, list[i]!))
      }
    }
    for (const [, ref] of mt.links) {
      if (ref === null) throw new Error(`${what}: a map link without a tile`)
      const [refLevel, refRoom, array, index] = ref
      const owner = levelsById.get(refLevel)
      const ownerRoom = owner?.rooms[refRoom]
      if (owner === undefined || ownerRoom === undefined || owner.activation[refRoom] === undefined) {
        throw new Error(`${what}: linked tile ${ref.join('/')} is in a room the dump did not activate`)
      }
      const { list, count } = initialised(owner, refRoom, array)
      if (index < 0 || index >= count) {
        throw new Error(`${what}: linked tile ${ref.join('/')} is not one of the owner's ${count} initialised tiles`)
      }
      tiles.push(place(ref.join('/'), TILE_KIND_OF_ARRAY[array], ownerRoom.coord, list[index]!))
    }
    const subDX = SUBTILES_PER_TILE * (room.coord[0] - levelX)
    const subDY = SUBTILES_PER_TILE * (room.coord[1] - levelY)
    for (const [type, index, mode, x, y, spawned] of mt.units) {
      units.push({ room: r, type, index, mode, subX: x + subDX, subY: y + subDY, spawned })
    }
    for (const [destination, row] of mt.warps) {
      if (destination === null) throw new Error(`${what}: a warp without a destination room`)
      const record = tables.lvlWarp[row]
      if (record === undefined) throw new Error(`${what}: warp to level ${destination[0]} has LvlWarp.txt row ${row}`)
      warps.push({ room: r, lvlWarpId: record.dwLevelId, toLevelId: destination[0] })
    }
  })

  const orths: DrlgOrthInput[] = levelGrid.roomData.map(o => {
    if (o.level < 0 || o.box === null) throw new Error(`level ${levelId}: an outdoor link without a neighbour level`)
    return { level: o.level, dir: o.dir, box: { x: o.box[0], y: o.box[1], width: o.box[2], height: o.box[3] } }
  })
  return {
    levelId,
    drlgType: act.drlgType,
    levelType: act.levelType,
    coord: { x: levelX, y: levelY, width: levelW, height: levelH },
    flags: levelGrid.flags >>> 0,
    orths,
    grid2,
    tiles,
    units,
    warps,
  }
}