/**
 * Diablo II Exceptional / Elite Item Base Upgrade System.
 *
 * Implements base item quality upgrades during TreasureClass drop generation:
 * - Reads difficulty parameters from `Difficultylevels.txt` (UberCodeOddsNormal, UberCodeOddsGood,
 *   UltraCodeOddsNormal, UltraCodeOddsGood for Normal, Nightmare, Hell).
 * - Implements 1.13c disassembly logic from D2Game!6FC32380 and D2Game!6FC31880:
 *   - qf[4] (uberCodeOdds) and qf[5] (ultraCodeOdds) checks against rng.rand(1024).
 *   - Flags 0x04 (exceptional) and 0x10 (elite).
 *   - Selection priority: elite ultracode -> exceptional ubercode -> original base (normcode).
 *   - When upgraded, the item base is replaced with the upgraded base, and `isUber` is set to true.
 */
import type { D2Table } from './acts.ts'
import { parseTable } from './acts.ts'
import type { MountedArchives } from '../mpq/mount.ts'
import type { ItemBase } from './items.ts'
import type { D2Rng } from './d2-rng.ts'

/** Canonical MPQ path of `Difficultylevels.txt`. */
export const DIFFICULTY_LEVELS_TABLE_PATH = 'data\\global\\excel\\Difficultylevels.txt'

/** Bitflag set when exceptional upgrade succeeds (genFlags |= 0x04). */
export const ITEM_UPGRADE_FLAG_EXCEPTIONAL = 0x04

/** Bitflag set when elite upgrade succeeds (genFlags |= 0x10). */
export const ITEM_UPGRADE_FLAG_ELITE = 0x10

/**
 * Difficulty level odds parsed from `Difficultylevels.txt`.
 */
export interface DifficultyLevelOdds {
  readonly name: string
  readonly uberCodeOddsNormal: number
  readonly uberCodeOddsGood: number
  readonly ultraCodeOddsNormal: number
  readonly ultraCodeOddsGood: number
  // PascalCase aliases matching exact table column names
  readonly UberCodeOddsNormal: number
  readonly UberCodeOddsGood: number
  readonly UltraCodeOddsNormal: number
  readonly UltraCodeOddsGood: number
}

/**
 * Case-insensitive, whitespace-tolerant Map for looking up items/difficulties by key.
 */
export class CaseInsensitiveMap<V> extends Map<string, V> {
  private normalize(key: string): string {
    return typeof key === 'string' ? key.trim().toLowerCase() : String(key).trim().toLowerCase()
  }

  override get(key: string): V | undefined {
    return super.get(this.normalize(key))
  }

  override has(key: string): boolean {
    return super.has(this.normalize(key))
  }

  override set(key: string, value: V): this {
    return super.set(this.normalize(key), value)
  }

  override delete(key: string): boolean {
    return super.delete(this.normalize(key))
  }
}

/** Default canonical odds for standard Diablo II difficulties. */
export const DEFAULT_DIFFICULTY_LEVEL_ODDS: Record<string, DifficultyLevelOdds> = {
  Normal: {
    name: 'Normal',
    uberCodeOddsNormal: 0,
    uberCodeOddsGood: 0,
    ultraCodeOddsNormal: 0,
    ultraCodeOddsGood: 0,
    UberCodeOddsNormal: 0,
    UberCodeOddsGood: 0,
    UltraCodeOddsNormal: 0,
    UltraCodeOddsGood: 0,
  },
  Nightmare: {
    name: 'Nightmare',
    uberCodeOddsNormal: 10,
    uberCodeOddsGood: 20,
    ultraCodeOddsNormal: 0,
    ultraCodeOddsGood: 0,
    UberCodeOddsNormal: 10,
    UberCodeOddsGood: 20,
    UltraCodeOddsNormal: 0,
    UltraCodeOddsGood: 0,
  },
  Hell: {
    name: 'Hell',
    uberCodeOddsNormal: 20,
    uberCodeOddsGood: 40,
    ultraCodeOddsNormal: 30,
    ultraCodeOddsGood: 40,
    UberCodeOddsNormal: 20,
    UberCodeOddsGood: 40,
    UltraCodeOddsNormal: 30,
    UltraCodeOddsGood: 40,
  },
}

/**
 * Parsed collection of difficulty level upgrade odds from `Difficultylevels.txt`.
 */
export type DifficultyLevelTable = DifficultyLevelsTable

export class DifficultyLevelsTable {
  readonly all: readonly DifficultyLevelOdds[]
  readonly byName: Map<string, DifficultyLevelOdds>
  readonly normal: DifficultyLevelOdds
  readonly nightmare: DifficultyLevelOdds
  readonly hell: DifficultyLevelOdds
  readonly Normal: DifficultyLevelOdds
  readonly Nightmare: DifficultyLevelOdds
  readonly Hell: DifficultyLevelOdds

  constructor(all: DifficultyLevelOdds[], byName: Map<string, DifficultyLevelOdds>) {
    this.all = all
    this.byName = byName

    const normal = byName.get('Normal') ?? all[0] ?? DEFAULT_DIFFICULTY_LEVEL_ODDS.Normal!
    const nightmare = byName.get('Nightmare') ?? all[1] ?? DEFAULT_DIFFICULTY_LEVEL_ODDS.Nightmare!
    const hell = byName.get('Hell') ?? all[2] ?? DEFAULT_DIFFICULTY_LEVEL_ODDS.Hell!

    this.normal = normal
    this.nightmare = nightmare
    this.hell = hell
    this.Normal = normal
    this.Nightmare = nightmare
    this.Hell = hell
  }

  get(name: string): DifficultyLevelOdds | undefined {
    return this.byName.get(name)
  }

  [Symbol.iterator](): IterableIterator<DifficultyLevelOdds> {
    return this.all[Symbol.iterator]()
  }

  get length(): number {
    return this.all.length
  }
}

/**
 * Parses `Difficultylevels.txt` table rows into {@link DifficultyLevelsTable}.
 *
 * @param table - Raw parsed tab-separated D2Table.
 * @returns {@link DifficultyLevelsTable} instance.
 */
export function parseDifficultyLevelsTable(table: D2Table): DifficultyLevelsTable {
  const colMap = new Map<string, number>()
  const lowerMap = new Map<string, number>()

  table.header.forEach((name, idx) => {
    const trimmed = name.trim()
    if (!colMap.has(trimmed)) {
      colMap.set(trimmed, idx)
    }
    const lower = trimmed.toLowerCase()
    if (!lowerMap.has(lower)) {
      lowerMap.set(lower, idx)
    }
  })

  const strAt = (row: readonly string[], colName: string): string => {
    const idx = colMap.get(colName) ?? lowerMap.get(colName.toLowerCase())
    return idx !== undefined ? (row[idx] ?? '').trim() : ''
  }

  const numAt = (row: readonly string[], colName: string, fallback = 0): number => {
    const raw = strAt(row, colName)
    if (!raw) return fallback
    const val = Number(raw)
    return Number.isFinite(val) ? val : fallback
  }

  const all: DifficultyLevelOdds[] = []
  const byName = new CaseInsensitiveMap<DifficultyLevelOdds>()

  for (const row of table.rows) {
    const name = strAt(row, 'Name')
    if (!name || name === 'Expansion') {
      continue
    }

    const uberCodeOddsNormal = numAt(row, 'UberCodeOddsNormal', 0)
    const uberCodeOddsGood = numAt(row, 'UberCodeOddsGood', 0)
    const ultraCodeOddsNormal = numAt(row, 'UltraCodeOddsNormal', 0)
    const ultraCodeOddsGood = numAt(row, 'UltraCodeOddsGood', 0)

    const entry: DifficultyLevelOdds = {
      name,
      uberCodeOddsNormal,
      uberCodeOddsGood,
      ultraCodeOddsNormal,
      ultraCodeOddsGood,
      UberCodeOddsNormal: uberCodeOddsNormal,
      UberCodeOddsGood: uberCodeOddsGood,
      UltraCodeOddsNormal: ultraCodeOddsNormal,
      UltraCodeOddsGood: ultraCodeOddsGood,
    }

    all.push(entry)
    byName.set(name, entry)
  }

  return new DifficultyLevelsTable(all, byName)
}

/**
 * Loads and parses `Difficultylevels.txt` from mounted MPQ archives.
 *
 * @param archives - Mounted MPQ archives.
 * @param path - Optional override MPQ path (defaults to {@link DIFFICULTY_LEVELS_TABLE_PATH}).
 * @returns Promise resolving to {@link DifficultyLevelsTable}.
 */
export async function loadDifficultyLevels(
  archives: MountedArchives,
  path = DIFFICULTY_LEVELS_TABLE_PATH,
): Promise<DifficultyLevelsTable> {
  const bytes = await archives.read(path)
  const d2Table = parseTable(bytes)
  return parseDifficultyLevelsTable(d2Table)
}

/**
 * ItemBase with optional tier code linkages (normcode, ubercode, ultracode).
 */
export interface UpgradableItemBase extends ItemBase {
  readonly normcode?: string | undefined
  readonly ubercode?: string | undefined
  readonly ultracode?: string | undefined
  readonly code?: string | undefined
}

/**
 * Result of rolling an item base upgrade.
 */
export interface BaseUpgradeResult {
  /** The resulting item base (original or exceptional/elite). */
  readonly base: ItemBase
  /** Whether the base was upgraded to exceptional or elite tier. */
  readonly isUber: boolean
}

/**
 * Checks whether a base code is valid for upgrade (non-empty and not 'xxx').
 */
function isValidUpgradeCode(code: unknown): code is string {
  if (typeof code !== 'string') {
    return false
  }
  const trimmed = code.trim()
  return trimmed.length > 0 && trimmed.toLowerCase() !== 'xxx'
}

/**
 * Rolls exceptional / elite base upgrade for an item base.
 *
 * Disassembly reference:
 * - D2Game!6FC32380 (drop roll loop):
 *   `if (qf[4] && (rng.rand(1024) < qf[4])) genFlags |= 0x04`
 *   `if (qf[5] && (rng.rand(1024) < qf[5])) genFlags |= 0x10`
 * - D2Game!6FC31880 (base upgrade dispatch):
 *   - If genFlags & 0x10 (elite): check base `ultracode`. If valid and !== 'xxx', use ultracode.
 *   - Else if genFlags & 0x04 (exceptional): check base `ubercode`. If valid and !== 'xxx', use ubercode.
 *   - Otherwise keep original `normcode`.
 * - When upgraded:
 *   - Replaces item base with the exceptional/elite base (providing the new base's `qlvl` / `level`).
 *   - `isUber` flag is set to true.
 *
 * @param base - Original item base (usually normal tier).
 * @param qf4 - Uber code odds (qf[4], e.g. UberCodeOddsNormal or UberCodeOddsGood).
 * @param qf5 - Ultra code odds (qf[5], e.g. UltraCodeOddsNormal or UltraCodeOddsGood).
 * @param rng - Diablo II PRNG instance.
 * @param lookupBase - Lookup function resolving a 3-4 letter item code to an {@link ItemBase}.
 * @returns {@link BaseUpgradeResult} containing the new or original base and `isUber`.
 */
export function rollBaseUpgrade(
  base: ItemBase,
  qf4: number,
  qf5: number,
  rng: D2Rng,
  lookupBase: (code: string) => ItemBase | undefined,
): BaseUpgradeResult {
  let genFlags = 0

  if (qf4 > 0 && rng.rand(1024) < qf4) {
    genFlags |= ITEM_UPGRADE_FLAG_EXCEPTIONAL
  }

  if (qf5 > 0 && rng.rand(1024) < qf5) {
    genFlags |= ITEM_UPGRADE_FLAG_ELITE
  }

  const uBase = base as Partial<UpgradableItemBase>
  const rawUltra = uBase.ultracode
  const rawUber = uBase.ubercode

  const ultracode = isValidUpgradeCode(rawUltra) ? rawUltra.trim() : undefined
  const ubercode = isValidUpgradeCode(rawUber) ? rawUber.trim() : undefined

  let targetCode: string | undefined
  if ((genFlags & ITEM_UPGRADE_FLAG_ELITE) && ultracode) {
    targetCode = ultracode
  } else if ((genFlags & ITEM_UPGRADE_FLAG_EXCEPTIONAL) && ubercode) {
    targetCode = ubercode
  }

  if (targetCode) {
    const upgraded = lookupBase(targetCode) ?? lookupBase(targetCode.toLowerCase())
    if (upgraded) {
      return { base: upgraded, isUber: true }
    }
    // If elite was selected but lookup failed, fall back to exceptional if rolled and valid
    if (
      (genFlags & ITEM_UPGRADE_FLAG_ELITE) &&
      (genFlags & ITEM_UPGRADE_FLAG_EXCEPTIONAL) &&
      ubercode &&
      targetCode !== ubercode
    ) {
      const fallbackUber = lookupBase(ubercode) ?? lookupBase(ubercode.toLowerCase())
      if (fallbackUber) {
        return { base: fallbackUber, isUber: true }
      }
    }
  }

  return { base, isUber: false }
}

/** Alias for rollBaseUpgrade conforming to spec nomenclature. */
export const upgradeItemBase = rollBaseUpgrade