/**
 * Quests and NPCs.
 *
 * Diablo II's quests are a small state machine per act: talk to an NPC to accept,
 * do the thing, talk again to be rewarded. `Quest.txt` holds the names and
 * descriptions (through the string table) and the objective; the dialogue itself
 * lives in code with its text in the TBL. This module models the part that is
 * structural — the states, the objective counter, the reward, and the dialogue
 * *selection* — and leaves the actual lines to the data.
 *
 * The dialogue is chosen by state rather than listed blindly, because that is the
 * behaviour that matters: an NPC who offers a quest already in progress, or who
 * forgets a completed one, is the classic quest bug.
 */
import { numberCell, resolveText, textCell } from './tables.ts'
import type { TextSource } from './tables.ts'

/** One NPC. */
export interface NpcDef {
  /** Table id. */
  readonly id: string
  /** Display name. */
  readonly name: string
  /** The quest this NPC offers, when any. */
  readonly questId: string | null
  /** Lines offered while the quest is available. */
  readonly offerLines: readonly string[]
  /** Lines offered while the quest is in progress. */
  readonly progressLines: readonly string[]
  /** Lines offered once the quest is done. */
  readonly doneLines: readonly string[]
}

/** One quest. */
export interface QuestDef {
  /** Table id. */
  readonly id: string
  /** Display name. */
  readonly name: string
  /** Description, for the quest log. */
  readonly description: string
  /** Monster id to kill, or `*` for any. */
  readonly monsterId: string
  /** How many kills complete it. */
  readonly killCount: number
  /** Experience awarded on completion. */
  readonly rewardXp: number
  /** Gold awarded on completion. */
  readonly rewardGold: number
}

/** A quest's live state. */
export interface QuestProgress {
  /** The definition. */
  readonly def: QuestDef
  /** Where it stands. */
  status: 'inactive' | 'active' | 'complete'
  /** Kills recorded so far. */
  kills: number
}

/** Raised when a quest id is used that the log does not know. */
export class QuestError extends Error {
  constructor(message: string) {
    super(message)
    this.name = 'QuestError'
  }
}

/**
 * Read one NPC row.
 *
 * @param row - the record.
 * @param rowIndex - position, for a fallback id.
 * @param text - text source for name and dialogue indices.
 * @returns the NPC.
 */
export function npcFromRow(
  row: Readonly<Record<string, string>>,
  rowIndex: number,
  text: TextSource,
): NpcDef {
  const id = textCell(row, 'Id', textCell(row, 'npc', `npc${String(rowIndex)}`))
  // Split first (a cell may list several indices or literals), resolve each part,
  // then split again: a string table entry can itself hold several lines, and
  // resolving after splitting would leave those pipes in the text.
  const lines = (column: string): string[] =>
    textCell(row, column, '')
      .split('|')
      .map(part => resolveText(part.trim(), text))
      .flatMap(resolved => resolved.split('|'))
      .map(line => line.trim())
      .filter(line => line !== '')
  return {
    id,
    name: resolveText(textCell(row, 'Name', id), text) || id,
    questId: textCell(row, 'Quest', '') || null,
    offerLines: lines('Offer'),
    progressLines: lines('Progress'),
    doneLines: lines('Done'),
  }
}

/**
 * Read every NPC in a table.
 *
 * @param table - an NPC-shaped table.
 * @param text - text source.
 * @returns the NPCs.
 */
export function npcsFromTable(
  table: { rows: readonly Readonly<Record<string, string>>[] },
  text: TextSource,
): NpcDef[] {
  return table.rows.map((row, index) => npcFromRow(row, index, text))
}

/**
 * Read one quest row.
 *
 * @param row - the record.
 * @param rowIndex - position, for a fallback id.
 * @param text - text source for name and description indices.
 * @returns the quest.
 */
export function questFromRow(
  row: Readonly<Record<string, string>>,
  rowIndex: number,
  text: TextSource,
): QuestDef {
  const id = textCell(row, 'Id', textCell(row, 'quest', `quest${String(rowIndex)}`))
  return {
    id,
    name: resolveText(textCell(row, 'Name', id), text) || id,
    description: resolveText(textCell(row, 'Description', ''), text),
    monsterId: textCell(row, 'MonsterId', textCell(row, 'monster', '*')) || '*',
    killCount: Math.max(1, numberCell(row, 'KillCount', numberCell(row, 'count', 1))),
    rewardXp: Math.max(0, numberCell(row, 'RewardXP', numberCell(row, 'xp', 0))),
    rewardGold: Math.max(0, numberCell(row, 'RewardGold', numberCell(row, 'gold', 0))),
  }
}

/**
 * Read every quest in a table.
 *
 * @param table - a `Quest.txt`-shaped table.
 * @param text - text source.
 * @returns the quests.
 */
export function questsFromTable(
  table: { rows: readonly Readonly<Record<string, string>>[] },
  text: TextSource,
): QuestDef[] {
  return table.rows.map((row, index) => questFromRow(row, index, text))
}

/** A reward handed out when a quest completes. */
export interface QuestReward {
  /** Quest that completed. */
  readonly questId: string
  /** Experience awarded. */
  readonly xp: number
  /** Gold awarded. */
  readonly gold: number
}

/**
 * The player's quest log.
 */
export class QuestLog {
  private readonly progress = new Map<string, QuestProgress>()

  /**
   * @param quests - the quests the log tracks.
   */
  constructor(quests: readonly QuestDef[]) {
    for (const quest of quests) {
      this.progress.set(quest.id, { def: quest, status: 'inactive', kills: 0 })
    }
  }

  /**
   * Rebuild a log from saved progress.
   *
   * @param quests - the quest definitions.
   * @param states - saved status and counters, matched by id.
   * @returns the log.
   */
  static restore(
    quests: readonly QuestDef[],
    states: readonly { readonly id: string; readonly status: QuestProgress['status']; readonly kills: number }[],
  ): QuestLog {
    const log = new QuestLog(quests)
    for (const saved of states) {
      const entry = log.progress.get(saved.id)
      if (entry === undefined) continue
      entry.status = saved.status
      entry.kills = Math.max(0, saved.kills)
    }
    return log
  }

  /** Every quest's progress, in table order. */
  get all(): readonly QuestProgress[] {
    return [...this.progress.values()]
  }

  /** The quests currently in progress. */
  get active(): readonly QuestProgress[] {
    return this.all.filter(entry => entry.status === 'active')
  }

  /**
   * Read one quest's progress.
   *
   * @param id - the quest id.
   * @returns the progress, or undefined when unknown.
   */
  get(id: string): QuestProgress | undefined {
    return this.progress.get(id)
  }

  /**
   * Accept a quest.
   *
   * @param id - the quest id.
   * @returns true when it moved from inactive to active.
   */
  accept(id: string): boolean {
    const entry = this.progress.get(id)
    if (entry === undefined) throw new QuestError(`unknown quest "${id}"`)
    if (entry.status !== 'inactive') return false
    entry.status = 'active'
    return true
  }

  /**
   * Record a kill, advancing every active quest that wants that monster.
   *
   * @param monsterId - the monster's table id.
   * @returns the quests this kill completed.
   */
  recordKill(monsterId: string): QuestReward[] {
    const rewards: QuestReward[] = []
    for (const entry of this.progress.values()) {
      if (entry.status !== 'active') continue
      const wanted = entry.def.monsterId
      // `*` means any monster, which is how a "kill N of anything" quest reads.
      if (wanted !== '*' && wanted !== monsterId) continue
      entry.kills += 1
      if (entry.kills >= entry.def.killCount) {
        entry.status = 'complete'
        rewards.push({ questId: entry.def.id, xp: entry.def.rewardXp, gold: entry.def.rewardGold })
      }
    }
    return rewards
  }
}

/**
 * The lines an NPC says right now.
 *
 * @param npc - the NPC.
 * @param log - the quest log.
 * @returns the lines, empty when there is nothing to say.
 */
export function npcDialog(npc: NpcDef, log: QuestLog): string[] {
  if (npc.questId === null) return [...npc.offerLines]
  const entry = log.get(npc.questId)
  if (entry === undefined) return [...npc.offerLines]
  switch (entry.status) {
    case 'inactive': return [...npc.offerLines]
    case 'active': return [...npc.progressLines]
    case 'complete': return [...npc.doneLines]
    /* v8 ignore next -- the status union is closed above. */
    default: return []
  }
}