import type { GameSound } from "../audio/sound";
import { SOUND } from "../audio/constants";
import type { RomReader } from "../rom/reader";
import type { PokemonData } from "../rom/pokemon";
import { ENGINE_FLAGS, MENU, PC, RAM } from "../rom/profile";
import { hallOfFamePC } from "./hall-of-fame";
import { oakRating } from "./league";
import { readMail } from "./mail";
import { printerDisconnected } from "./printer";
import { receiveItem, removeFromSlot, type ItemSlot } from "../party/bag";
import {
  BOX_NAME_PATTERN,
  PARTY_LENGTH,
  type PartyMon,
} from "../party/pokemon";
import {
  MONS_PER_BOX,
  NUM_BOXES,
  bufferMon,
  currentBox,
  depositMon,
  receivePCItem,
  restorePP,
  toBoxMon,
  withdrawnMon,
  type BoxMon,
} from "../party/storage";
import { readString, readText, type TextContext } from "./text";
import type { MartEntry, ScriptEffect, ScriptState } from "./interpreter";

type Input = number | string | undefined;
type Gen<T = void> = Generator<ScriptEffect, T, Input>;

/** What the PC routines need from the running script. */
export interface PcHost {
  state: ScriptState;
  reader: RomReader;
  data: PokemonData;
  text(): TextContext;
  /** text_ram and text_decimal values, keyed by RAM address. */
  strings: Record<number, string>;
  numbers: Record<number, number>;
  /** _PlayerDecorationMenu: true if a decoration changed. */
  decorationMenu(): Gen<boolean>;
  /** The sound engine, for the PC's boot, choice and shutdown sounds. */
  sound?: GameSound;
}

/** PokemonCenterPC's menu items (PCPCITEM_*). */
const PCPCITEM_PLAYERS_PC = 0,
  PCPCITEM_BILLS_PC = 1,
  PCPCITEM_OAKS_PC = 2,
  PCPCITEM_HALL_OF_FAME = 3,
  PCPCITEM_TURN_OFF = 4;
/** _PlayersPC's menu items (PLAYERSPCITEM_*). */
const PLAYERSPCITEM_WITHDRAW_ITEM = 0,
  PLAYERSPCITEM_DEPOSIT_ITEM = 1,
  PLAYERSPCITEM_TOSS_ITEM = 2,
  PLAYERSPCITEM_MAIL_BOX = 3,
  PLAYERSPCITEM_DECORATION = 4;
/** _BillsPC's menu items. */
const BILLSPC_WITHDRAW = 0,
  BILLSPC_DEPOSIT = 1,
  BILLSPC_CHANGE_BOX = 2,
  BILLSPC_MOVE = 3;
/** The box submenus: DEPOSIT or WITHDRAW, STATS, RELEASE, CANCEL; and
 * SWITCH, NAME, PRINT, QUIT for a box. */
const SUBMENU_TAKE = 0,
  SUBMENU_STATS = 1,
  SUBMENU_RELEASE = 2;
const BOX_SWITCH = 0,
  BOX_NAME = 1,
  BOX_PRINT = 2;
/** DelayFrames after a Bill's PC message, in overworld ticks (two frames). */
const MESSAGE_TICKS = 25,
  RELEASED_TICKS = 40;

/** A pack entry and where it came from, for TossItem's wCurItemQuantity. */
interface PackSlot extends ItemSlot {
  pocket: "items" | "balls" | "keyItems";
  index: number;
}

/** The Pokémon Center PC (engine/events/pokecenter_pc.asm), Bill's PC
 * (engine/pokemon/bills_pc_top.asm and bills_pc.asm) and Oak's PC
 * (engine/events/prof_oaks_pc.asm). The original draws its own screens;
 * here menus, lists and messages are presented natively. */
export class PcSession {
  constructor(private host: PcHost) {}

  private get state() {
    return this.host.state;
  }
  private string(address: number) {
    return readString(this.host.reader, address, this.host.text());
  }
  private pages(address: number) {
    return readText(this.host.reader, address, this.host.text()).split("\n\n");
  }
  private *print(address: number): Gen {
    yield { kind: "text", pages: this.pages(address) };
  }
  /** BillsPC_PlaceString followed by DelayFrames: a message that stays
   * for a fixed time without waiting for a button. */
  private *placeString(text: string, ticks = MESSAGE_TICKS): Gen {
    yield { kind: "text", pages: [text], holdTicks: ticks };
  }
  /** A menu of `items`; the chosen index, or -1 for B. */
  private *menu(
    pages: string[],
    items: string[],
    details?: string[],
    selected = 0,
  ): Gen<number> {
    const choice = yield { kind: "menu", pages, items, details, selected };
    return typeof choice === "number" && choice >= 0 && choice < items.length
      ? choice
      : -1;
  }
  /** Consecutive "@"-terminated strings, as static menus store them. */
  private strings(address: number, count: number) {
    const r = this.host.reader,
      result: string[] = [];
    let p = address;
    for (let i = 0; i < count; i++) {
      result.push(this.string(p));
      while (r.byte(p++) !== 0x50);
    }
    return result;
  }
  /** A WhichPC list: a count, the item ids, then -1. */
  private indexSet(address: number, set: number) {
    const r = this.host.reader;
    let p = address;
    for (let i = 0; i < set; i++) p += r.byte(p) + 2;
    const count = r.byte(p);
    return Array.from({ length: count }, (_, i) => r.byte(p + 1 + i));
  }
  /** A jumptable of (routine, string) pointers: the item's string. */
  private itemString(table: number, item: number) {
    const r = this.host.reader,
      entry = table + item * 4 + 2;
    return this.string(r.near(entry, r.bank(entry)));
  }

  // ------------------------------------------------------------ PC menus

  /** PokemonCenterPC: a Pokémon is needed, then the PCs listed for the
   * player's progress until TURN OFF or B. */
  *pokemonCenterPC(): Gen {
    if (!this.state.party.length) {
      yield* this.print(PC["PC_CheckPartyForPokemon.PokecenterPCCantUseText"]);
      return;
    }
    // PC_PlayBootSound
    this.host.sound?.playSFX(SOUND.SFX_BOOT_PC);
    yield* this.print(PC.PokecenterPCTurnOnText);
    const whose = this.pages(PC.PokecenterPCWhoseText);
    let cursor = 0;
    for (;;) {
      // .ChooseWhichPCListToUse: PCPC_BEFORE_POKEDEX, PCPC_BEFORE_HOF, or
      // PCPC_POSTGAME once wHallOfFameCount (not the League flag) is set.
      const set = this.state.flags.has(ENGINE_FLAGS.pokedex)
        ? this.state.hallOfFameCount ? 2 : 1
        : 0;
      const items = this.indexSet(PC["PokemonCenterPC.WhichPC"], set);
      const choice = yield* this.menu(
        whose,
        items.map((item) =>
          this.itemString(PC["PokemonCenterPC.Jumptable"], item),
        ),
        undefined,
        cursor,
      );
      // PC_PlayShutdownSound when leaving; PC_PlayChoosePCSound otherwise.
      const sound = this.host.sound;
      if (choice < 0 || items[choice] === PCPCITEM_TURN_OFF) sound?.playSFX(SOUND.SFX_SHUT_DOWN_PC);
      else sound?.playSFX(SOUND.SFX_CHOOSE_PC_OPTION);
      if (choice < 0) return;
      cursor = choice;
      switch (items[choice]) {
        case PCPCITEM_BILLS_PC:
          yield* this.print(PC.PokecenterBillsPCText);
          yield* this.billsPC();
          break;
        case PCPCITEM_PLAYERS_PC:
          yield* this.print(PC.PokecenterPlayersPCText);
          yield* this.playersPC(false);
          break;
        case PCPCITEM_OAKS_PC:
          yield* this.print(PC.PokecenterOaksPCText);
          yield* this.oaksPC();
          break;
        case PCPCITEM_HALL_OF_FAME:
          yield* hallOfFamePC(
            this.host.data,
            this.state.hallOfFameTeams,
            this.state.options.textboxFrame,
            this.host.sound,
          );
          break;
        case PCPCITEM_TURN_OFF:
          yield* this.print(PC.PokecenterPCOaksClosedText);
          return;
        default:
          throw new Error("Unknown Pokémon Center PC entry.");
      }
    }
  }

  /** _PlayersHousePC: returns true when a decoration changed, which makes
   * the script reload the room. */
  *playersHousePC(): Gen<boolean> {
    this.host.sound?.playSFX(SOUND.SFX_BOOT_PC);
    yield* this.print(PC.PlayersPCTurnOnText);
    return yield* this.playersPC(true);
  }

  /** _PlayersPC: PLAYERSPC_NORMAL or PLAYERSPC_HOUSE. A changed
   * decoration closes the PC. */
  private *playersPC(house: boolean): Gen<boolean> {
    const items = this.indexSet(PC["PlayersPCMenuData.WhichPC"], house ? 1 : 0);
    const names = items.map((item) =>
      this.itemString(PC["PlayersPCMenuData.PlayersPCMenuPointers"], item),
    );
    const ask = this.pages(PC.PlayersPCAskWhatDoText);
    let cursor = 0;
    for (;;) {
      const choice = yield* this.menu(ask, names, undefined, cursor);
      if (choice < 0) return false;
      cursor = choice;
      switch (items[choice]) {
        case PLAYERSPCITEM_WITHDRAW_ITEM:
          yield* this.withdrawItems();
          break;
        case PLAYERSPCITEM_DEPOSIT_ITEM:
          yield* this.depositItems();
          break;
        case PLAYERSPCITEM_TOSS_ITEM:
          yield* this.tossItems();
          break;
        case PLAYERSPCITEM_MAIL_BOX:
          yield* this.mailbox();
          break;
        case PLAYERSPCITEM_DECORATION:
          if (yield* this.host.decorationMenu()) return true;
          break;
        default:
          // LOG OFF and TURN OFF.
          return false;
      }
    }
  }

  // ----------------------------------------------------------- mailbox

  /** _PlayerMailBoxMenu and MailboxPC: the MAIL listed by author, each with
   * READ MAIL, PUT IN PACK, ATTACH MAIL or CANCEL, until B or CANCEL. */
  private *mailbox(): Gen {
    if (!this.state.mailbox.length)
      return yield* this.print(PC["_PlayerMailBoxMenu.EmptyMailboxText"]);
    const actions = this.strings(PC["MailboxPC.SubMenuData"] + 2, 4);
    let cursor = 0;
    for (;;) {
      const mailbox = this.state.mailbox;
      const index = yield* this.menu(
        [],
        [
          ...mailbox.map((mail) => mail.author),
          this.string(PC["ScrollingMenu_UpdateDisplay.CancelString"]),
        ],
        undefined,
        Math.min(cursor, mailbox.length),
      );
      if (index < 0 || index >= mailbox.length) return;
      cursor = index;
      const action = yield* this.menu([], actions);
      if (action === 0) yield* readMail(this.host.data, mailbox[index], this.state.options.textboxFrame);
      else if (action === 1) yield* this.putMailInPack(index);
      else if (action === 2) yield* this.attachMail(index);
    }
  }
  /** MailboxPC.PutInPack: the MAIL item goes to the pack without its
   * message (DeleteMailFromPC). */
  private *putMailInPack(index: number): Gen {
    const ok = yield {
      kind: "yesno",
      pages: this.pages(PC["MailboxPC.MailMessageLostText"]),
    };
    if (!ok) return;
    const mailbox = this.state.mailbox;
    if (!receiveItem(this.host.data, this.state.bag, mailbox[index].type, 1))
      return yield* this.print(PC["MailboxPC.MailPackFullText"]);
    mailbox.splice(index, 1);
    yield* this.print(PC["MailboxPC.MailClearedPutAwayText"]);
  }
  /** MailboxPC.AttachMail: the party menu until a Pokémon that is not an
   * Egg and holds nothing is chosen (MoveMailFromPCToParty), or B. */
  private *attachMail(index: number): Gen {
    const r = this.host.reader,
      party = this.state.party;
    // PlacePartyMenuText with wPartyMenuActionText 0: "Choose a POKéMON."
    const prompt = this.string(
      r.near(MENU.PartyMenuStrings, r.bank(MENU.PartyMenuStrings)),
    );
    for (;;) {
      const slot = yield* this.menu(
        [prompt],
        party.map((mon) => mon.nickname),
        this.monDetails(party),
      );
      if (slot < 0) return;
      const mon = party[slot];
      if (mon.egg) {
        yield* this.print(PC["MailboxPC.MailEggText"]);
        continue;
      }
      if (mon.item) {
        yield* this.print(PC["MailboxPC.MailAlreadyHoldingItemText"]);
        continue;
      }
      const [mail] = this.state.mailbox.splice(index, 1);
      mon.item = mail.type;
      mon.mail = mail;
      return yield* this.print(PC["MailboxPC.MailMovedFromBoxText"]);
    }
  }

  // ------------------------------------------------------ item storage

  private itemEntries(slots: ItemSlot[]): MartEntry[] {
    const data = this.host.data;
    return slots.map((slot) => ({
      item: slot.item,
      name: data.itemName(slot.item),
      price: 0,
      owned: slot.quantity,
    }));
  }
  /** The item named by PartyMonItemName (wStringBuffer1 and 2) and the
   * quantity text_decimal shows (wItemQuantityChange). */
  private nameItem(item: number, quantity?: number) {
    const name = this.host.data.itemName(item);
    this.host.strings[RAM.stringBuffer1] = name;
    this.host.strings[RAM.stringBuffer2] = name;
    if (quantity !== undefined)
      this.host.numbers[RAM.itemQuantityChange] = quantity;
  }
  /** SelectQuantityToToss for a stack, unless _CheckTossableItem makes it
   * always one. Returns 0 if cancelled. */
  private *quantity(
    mode: "withdraw" | "deposit" | "toss",
    slot: ItemSlot,
    prompt: number,
  ): Gen<number> {
    if (this.host.data.itemUnsellable(slot.item)) return 1;
    this.nameItem(slot.item);
    const chosen = yield {
      kind: "martquantity",
      mode,
      item: slot.item,
      name: this.host.data.itemName(slot.item),
      price: 0,
      max: slot.quantity,
      prompt: readText(this.host.reader, prompt, this.host.text()),
      selected: 1,
    };
    return typeof chosen === "number" &&
      Number.isInteger(chosen) &&
      chosen >= 1 &&
      chosen <= slot.quantity
      ? chosen
      : 0;
  }

  /** PlayerWithdrawItemMenu: into the matching pack pocket. */
  private *withdrawItems(): Gen {
    const items = this.state.pcItems;
    for (;;) {
      const index = yield {
        kind: "martlist",
        mode: "withdraw",
        entries: this.itemEntries(items),
        selected: 0,
      };
      const slot = typeof index === "number" ? items[index] : undefined;
      if (!slot) return;
      const quantity = yield* this.quantity(
        "withdraw",
        slot,
        PC["PlayerWithdrawItemMenu.PlayersPCHowManyWithdrawText"],
      );
      if (!quantity) continue;
      const item = slot.item;
      if (!receiveItem(this.host.data, this.state.bag, item, quantity)) {
        yield* this.print(
          PC["PlayerWithdrawItemMenu.PlayersPCNoRoomWithdrawText"],
        );
        continue;
      }
      removeFromSlot(items, index as number, item, quantity);
      this.nameItem(item, quantity);
      yield* this.print(
        PC["PlayerWithdrawItemMenu.PlayersPCWithdrewItemsText"],
      );
    }
  }

  /** The pack as DepositSellPack lists it: items, balls and key items,
   * with the pocket and index each entry comes from. */
  private packSlots(): PackSlot[] {
    const bag = this.state.bag;
    return [
      ...bag.items.map((slot, index) => ({
        ...slot,
        pocket: "items" as const,
        index,
      })),
      ...bag.balls.map((slot, index) => ({
        ...slot,
        pocket: "balls" as const,
        index,
      })),
      ...bag.keyItems.map((item, index) => ({
        item,
        quantity: 1,
        pocket: "keyItems" as const,
        index,
      })),
    ];
  }
  /** PlayerDepositItemMenu: from any pocket into the PC. */
  private *depositItems(): Gen {
    if (!this.packSlots().length) {
      yield* this.print(PC["PlayerDepositItemMenu.PlayersPCNoItemsText"]);
      return;
    }
    for (;;) {
      const slots = this.packSlots();
      const choice = yield {
        kind: "martlist",
        mode: "deposit",
        entries: this.itemEntries(slots),
        selected: 0,
      };
      const slot = typeof choice === "number" ? slots[choice] : undefined;
      if (!slot) return;
      const quantity = yield* this.quantity(
        "deposit",
        slot,
        PC["PlayerDepositItemMenu.PlayersPCHowManyDepositText"],
      );
      if (!quantity) continue;
      if (!receivePCItem(this.state.pcItems, slot.item, quantity)) {
        yield* this.print(
          PC["PlayerDepositItemMenu.PlayersPCNoRoomDepositText"],
        );
        continue;
      }
      const bag = this.state.bag;
      if (slot.pocket === "keyItems") bag.keyItems.splice(slot.index, 1);
      else removeFromSlot(bag[slot.pocket], slot.index, slot.item, quantity);
      this.nameItem(slot.item, quantity);
      yield* this.print(PC["PlayerDepositItemMenu.PlayersPCDepositItemsText"]);
    }
  }

  /** PlayerTossItemMenu and TossItemFromPC. */
  private *tossItems(): Gen {
    const items = this.state.pcItems;
    for (;;) {
      const index = yield {
        kind: "martlist",
        mode: "toss",
        entries: this.itemEntries(items),
        selected: 0,
      };
      const slot = typeof index === "number" ? items[index] : undefined;
      if (!slot) return;
      if (this.host.data.itemUnsellable(slot.item)) {
        yield* this.print(PC["TossItemFromPC.ItemsTooImportantText"]);
        continue;
      }
      const quantity = yield* this.quantity(
        "toss",
        slot,
        PC["TossItemFromPC.ItemsTossOutHowManyText"],
      );
      if (!quantity) continue;
      const item = slot.item;
      this.nameItem(item, quantity);
      const confirmed = yield {
        kind: "yesno",
        pages: this.pages(PC["TossItemFromPC.ItemsThrowAwayText"]),
      };
      if (!confirmed) continue;
      removeFromSlot(items, index as number, item, quantity);
      this.nameItem(item, quantity);
      yield* this.print(PC["TossItemFromPC.ItemsDiscardedText"]);
    }
  }

  // --------------------------------------------------------- Bill's PC

  /** GetBoxName: the saved name, or SetDefaultBoxNames' "BOX" and number. */
  boxName(box: number) {
    return (
      this.state.storage.names[box] ??
      `${this.string(PC["SetDefaultBoxNames.Box"])}${box + 1}`
    );
  }
  private monDetails(mons: { level: number }[]) {
    return [...mons.map((mon) => `:L${mon.level}`), ""];
  }

  /** _BillsPC: the top menu until SEE YA! or B. */
  private *billsPC(): Gen {
    if (!this.state.party.length) {
      yield* this.print(PC["_BillsPC.PCGottaHavePokemonText"]);
      return;
    }
    const names = this.strings(PC["_BillsPC.strings"], 5);
    const what = this.pages(PC["_BillsPC.PCWhatText"]);
    let cursor = 0;
    for (;;) {
      const choice = yield* this.menu(what, names, undefined, cursor);
      if (choice < 0) return;
      cursor = choice;
      if (choice === BILLSPC_WITHDRAW) yield* this.withdrawMons();
      else if (choice === BILLSPC_DEPOSIT) yield* this.depositMons();
      else if (choice === BILLSPC_CHANGE_BOX) yield* this.changeBox();
      else if (choice === BILLSPC_MOVE) yield* this.movePKMNMenu();
      else return;
    }
  }

  // ------------------------------------------------ MOVE PKMN W/O MAIL

  /** BillsPC_MovePKMNMenu: refused while a party Pokémon holds MAIL
   * (IsAnyMonHoldingMail), then StartMoveMonWOMail_SaveGame's question. The
   * native session saves by itself, so no save messages follow. */
  private *movePKMNMenu(): Gen {
    const r = this.host.reader;
    const mail = new Set<number>();
    for (let p = MENU.MailItems; r.byte(p) !== 0xff; p++) mail.add(r.byte(p));
    if (this.state.party.some((mon) => mail.has(mon.item)))
      return yield* this.print(PC["BillsPC_MovePKMNMenu.PCMonHoldingMailText"]);
    const ok = yield { kind: "yesno", pages: this.pages(PC.MoveMonWOMailSaveText) };
    if (ok) yield* this.moveWithoutMail();
  }
  /** wBillsPC_LoadedBox: 0 is the party, 1-14 the boxes. */
  private loadedBox(box: number): (PartyMon | BoxMon)[] {
    return box ? this.state.storage.boxes[box - 1] : this.state.party;
  }
  private loadedBoxName(box: number) {
    return box
      ? this.boxName(box - 1)
      : this.string(PC["BillsPC_BoxName.PartyPKMN"]);
  }
  /** Choose the party or a box (left and right in the original). */
  private *chooseLoadedBox(prompt: string, selected: number): Gen<number> {
    const boxes = Array.from({ length: NUM_BOXES + 1 }, (_, box) => box);
    return yield* this.menu(
      [prompt],
      boxes.map((box) => this.loadedBoxName(box)),
      boxes.map((box) => `${this.loadedBox(box).length}/${box ? MONS_PER_BOX : PARTY_LENGTH}`),
      selected,
    );
  }
  /** _MovePKMNWithoutMail: choose a Pokémon in the party or a box, MOVE it
   * (STATS shows it) and choose where it goes; the list is presented per
   * box instead of with left and right. */
  private *moveWithoutMail(): Gen {
    const data = this.host.data;
    const choose = this.string(PC.PCString_ChooseaPKMN),
      where = this.string(PC.PCString_MoveToWhere),
      cancel = this.string(PC["BillsPC_RefreshTextboxes.CancelString"]),
      options = this.strings(PC["_MovePKMNWithoutMail.MenuData"] + 2, 3);
    let loaded = this.state.storage.current + 1;
    for (;;) {
      const from = yield* this.chooseLoadedBox(choose, loaded);
      if (from < 0) return;
      loaded = from;
      const list = this.loadedBox(from);
      const index = yield* this.menu(
        [`${this.loadedBoxName(from)}\n${choose}`],
        [...list.map((mon) => mon.nickname), cancel],
        this.monDetails(list),
      );
      if (index < 0 || index >= list.length) continue;
      const action = yield* this.menu([this.string(PC.PCString_WhatsUp)], options);
      if (action === 1) {
        const mon = list[index];
        yield {
          kind: "stats",
          mon: from ? bufferMon(data, mon as BoxMon) : structuredClone(mon as PartyMon),
        };
        continue;
      }
      if (action !== 0) continue;
      // BillsPC_CheckMail_PreventBlackout, even within the party.
      if (!from && !(yield* this.partyMonMayLeave(index))) continue;
      // Where: a box, then the position to insert before.
      for (;;) {
        const to = yield* this.chooseLoadedBox(where, from);
        if (to < 0) break;
        const destination = this.loadedBox(to);
        const position = yield* this.menu(
          [`${this.loadedBoxName(to)}\n${where}`],
          [...destination.map((mon) => mon.nickname), "▶"],
          this.monDetails(destination),
          destination.length,
        );
        if (position < 0) continue;
        // BillsPC_CheckSpaceInDestination
        if (
          to !== from &&
          destination.length >= (to ? MONS_PER_BOX : PARTY_LENGTH)
        ) {
          yield* this.placeString(this.string(PC.PCString_TheresNoRoom));
          continue;
        }
        yield* this.placeString(
          this.string(PC["MovePKMNWithoutMail_InsertMon.Saving_LeaveOn"]),
          10,
        );
        this.insertMon(from, index, to, position);
        loaded = to;
        break;
      }
    }
  }
  /** MovePKMNWithoutMail_InsertMon: remove, then insert before `position`
   * (one earlier when moving down the same list, .CheckTrivialMove). A
   * boxed Pokémon joining the party gets CalcBufferMonStats' full HP;
   * InsertPokemonIntoBox restores the PP. */
  private insertMon(from: number, index: number, to: number, position: number) {
    const data = this.host.data;
    const source = this.loadedBox(from);
    const [moved] = source.splice(index, 1);
    if (from === to && index < position) position--;
    if (to) {
      const stored = from ? (moved as BoxMon) : toBoxMon(moved as PartyMon);
      restorePP(data, stored);
      this.state.storage.boxes[to - 1].splice(position, 0, stored);
    } else
      this.state.party.splice(
        position,
        0,
        from ? bufferMon(data, moved as BoxMon) : (moved as PartyMon),
      );
  }

  /** BillsPC_CheckMail_PreventBlackout for a party Pokémon: the last one,
   * or the last that has not fainted, stays, and one holding MAIL
   * (wBillsPC_MonHasMail) must have it removed first. */
  private *partyMonMayLeave(index: number): Gen<boolean> {
    const party = this.state.party;
    let text: number | undefined;
    if (party.length < 2) text = PC.PCString_ItsYourLastPKMN;
    else if (party.every((mon, i) => i === index || !mon.hp))
      text = PC.PCString_NoMoreUsablePKMN;
    else if (this.host.data.itemIsMail(party[index].item))
      text = PC.PCString_RemoveMail;
    if (text === undefined) return true;
    yield* this.placeString(this.string(text));
    return false;
  }
  /** ReleasePKMN_ByePKMN: the species name, not the nickname. */
  private *released(species: number): Gen {
    yield* this.placeString(
      this.string(PC.PCString_ReleasedPKMN),
      RELEASED_TICKS,
    );
    yield* this.placeString(
      `${this.string(PC.PCString_Bye)} ${this.host.data.speciesName(species)}!`,
    );
  }
  private *confirmRelease(): Gen<boolean> {
    return Boolean(
      yield { kind: "yesno", pages: [this.string(PC.PCString_ReleasePKMN)] },
    );
  }

  /** _DepositPKMN: choose a party Pokémon, then DEPOSIT, STATS or RELEASE. */
  private *depositMons(): Gen {
    const party = this.state.party,
      options = this.strings(PC["BillsPCDepositMenuHeader.MenuData"] + 2, 4);
    for (;;) {
      const index = yield* this.menu(
        [
          `${this.string(PC["BillsPC_BoxName.PartyPKMN"])}\n${this.string(PC.PCString_ChooseaPKMN)}`,
        ],
        [
          ...party.map((mon) => mon.nickname),
          this.string(PC["BillsPC_RefreshTextboxes.CancelString"]),
        ],
        this.monDetails(party),
      );
      if (index < 0 || index >= party.length) return;
      for (;;) {
        const action = yield* this.menu(
          [this.string(PC.PCString_WhatsUp)],
          options,
        );
        const mon = party[index];
        if (action === SUBMENU_TAKE) {
          if (!(yield* this.partyMonMayLeave(index))) break;
          if (!depositMon(this.host.data, this.state.storage, mon)) {
            yield* this.placeString(this.string(PC.PCString_BoxFull));
            continue;
          }
          party.splice(index, 1);
          yield* this.placeString(
            `${this.string(PC.PCString_Stored)}${mon.nickname}!`,
          );
          break;
        }
        if (action === SUBMENU_STATS) {
          yield { kind: "stats", mon: structuredClone(mon) };
          continue;
        }
        if (action !== SUBMENU_RELEASE) break;
        if (!(yield* this.partyMonMayLeave(index))) break;
        if (mon.egg) {
          yield* this.placeString(this.string(PC.PCString_NoReleasingEGGS));
          break;
        }
        if (!(yield* this.confirmRelease())) continue;
        party.splice(index, 1);
        yield* this.released(mon.species);
        break;
      }
    }
  }

  /** _WithdrawPKMN: choose a Pokémon in the current box, then WITHDRAW,
   * STATS or RELEASE. */
  private *withdrawMons(): Gen {
    const options = this.strings(PC["BillsPC_Withdraw.MenuData"] + 2, 4);
    for (;;) {
      const box = currentBox(this.state.storage);
      const index = yield* this.menu(
        [
          `${this.boxName(this.state.storage.current)}\n${this.string(PC.PCString_ChooseaPKMN)}`,
        ],
        [
          ...box.map((mon) => mon.nickname),
          this.string(PC["BillsPC_RefreshTextboxes.CancelString"]),
        ],
        this.monDetails(box),
      );
      if (index < 0 || index >= box.length) return;
      for (;;) {
        const action = yield* this.menu(
          [this.string(PC.PCString_WhatsUp)],
          options,
        );
        const mon = box[index];
        if (action === SUBMENU_TAKE) {
          if (this.state.party.length >= PARTY_LENGTH) {
            yield* this.placeString(this.string(PC.PCString_PartyFull));
            continue;
          }
          box.splice(index, 1);
          this.state.party.push(withdrawnMon(this.host.data, mon));
          yield* this.placeString(
            `${this.string(PC.PCString_Got)}${mon.nickname}!`,
          );
          break;
        }
        if (action === SUBMENU_STATS) {
          // CalcTempmonStats: stats from stat experience, full HP, no status.
          yield { kind: "stats", mon: withdrawnMon(this.host.data, mon) };
          continue;
        }
        if (action !== SUBMENU_RELEASE) break;
        if (mon.egg) {
          yield* this.placeString(this.string(PC.PCString_NoReleasingEGGS));
          continue;
        }
        if (!(yield* this.confirmRelease())) continue;
        box.splice(index, 1);
        yield* this.released(mon.species);
        break;
      }
    }
  }

  /** _ChangeBox: choose a box, then SWITCH, NAME, PRINT or QUIT. */
  private *changeBox(): Gen {
    const storage = this.state.storage,
      options = this.strings(PC["BillsPC_ChangeBoxSubmenu.MenuData"] + 2, 4),
      current = this.string(PC["BillsPC_PrintBoxName.Current"]),
      outOf = this.string(PC["BillsPC_PrintBoxCountAndCapacity.OutOf20"]);
    let cursor = 0;
    for (;;) {
      const names = Array.from({ length: NUM_BOXES }, (_, box) =>
        this.boxName(box),
      );
      const box = yield* this.menu(
        [
          `${current}\n${this.boxName(storage.current)}\n${this.string(PC["BillsPC_PlaceChooseABoxString.ChooseABox"])}`,
        ],
        names,
        storage.boxes.map((mons) => `${mons.length}${outOf}`),
        cursor,
      );
      if (box < 0) return;
      cursor = box;
      const action = yield* this.menu(
        [this.string(PC.PCString_WhatsUp)],
        options,
      );
      if (action === BOX_SWITCH) {
        if (box === storage.current) continue;
        // ChangeBoxSaveGame: the native session saves continuously, so the
        // switch itself is what the confirmation commits.
        const confirmed = yield {
          kind: "yesno",
          pages: this.pages(PC.ChangeBoxSaveText),
        };
        if (confirmed) storage.current = box;
      } else if (action === BOX_NAME) {
        const name = yield {
          kind: "name",
          pages: [this.string(PC["NamingScreenJumptable.BoxNameString"])],
          current: names[box],
          max: 8,
        };
        if (typeof name !== "string" || (name && !BOX_NAME_PATTERN.test(name)))
          throw new Error("Invalid box name.");
        // InitString: a blank name keeps the box's name.
        if (!/^ *$/.test(name)) storage.names[box] = name;
      } else if (action === BOX_PRINT) {
        if (!storage.boxes[box].length)
          yield* this.placeString(
            this.string(PC["BillsPC_PlaceEmptyBoxString_SFX.NoMonString"]),
          );
        else
          yield* printerDisconnected(this.host.reader, this.state.options.textboxFrame);
      }
    }
  }

  // ----------------------------------------------------------- Oak's PC

  /** ProfOaksPC: an optional Pokédex rating from OakRatings. */
  private *oaksPC(): Gen {
    const r = this.host.reader;
    const rate = yield {
      kind: "yesno",
      pages: this.pages(PC.OakPCText1),
    };
    if (rate) {
      yield* this.print(PC.OakPCText2);
      const { seen, caught } = this.state.pokedex;
      this.host.strings[RAM.stringBuffer3] = String(seen.size);
      this.host.strings[RAM.stringBuffer4] = String(caught.size);
      yield* this.print(PC.OakPCText3);
      yield* this.print(oakRating(r, caught.size).text);
    }
    yield* this.print(PC.OakPCText4);
  }
}