Crystal/src/game/party/pokemon.ts

import type { PokemonData } from "../rom/pokemon";

/** A party Pokémon with the fields of the original party_struct. */
export interface PartyMon {
  species: number;
  item: number;
  /** Move IDs; 0 marks an empty slot. */
  moves: [number, number, number, number];
  otId: number;
  ot: string;
  nickname: string;
  exp: number;
  /** HP, Attack, Defense, Speed, Special stat experience. */
  statExp: [number, number, number, number, number];
  /** Attack, Defense, Speed, Special DVs as four nibbles. */
  dvs: number;
  pp: [number, number, number, number];
  happiness: number;
  pokerus: number;
  /** Time of day and level, then gender and landmark (SetCaughtData). */
  caughtData: number;
  level: number;
  status: number;
  hp: number;
  /** Max HP, Attack, Defense, Speed, Sp. Atk, Sp. Def. */
  stats: [number, number, number, number, number, number];
}

export const PARTY_LENGTH = 6;
/** Characters a nickname can hold: the naming screen's letters and
 * symbols, plus the digits and apostrophes of default species names. */
export const NICKNAME_PATTERN = /^[A-Za-z0-9 ()":;[\]?!♂♀/.,×'é-]{1,10}$/u;
/** The same characters, for box names (up to eight). */
export const BOX_NAME_PATTERN = /^[A-Za-z0-9 ()":;[\]?!♂♀/.,×'é-]{1,8}$/u;
/** BASE_HAPPINESS */
const BASE_HAPPINESS = 70;
const MAX_STAT_VALUE = 999;
const MAX_LEVEL = 100;

/** GetSquareRoot: the first of 1..255 whose square is not below `value`. */
function squareRoot(value: number) {
  for (let root = 1; root < 255; root++) if (root * root >= value) return root;
  return 255;
}

/** DVs per stat; the HP DV is built from the low bits of the others. */
export function statDv(dvs: number, stat: number): number {
  const attack = (dvs >> 12) & 15,
    defense = (dvs >> 8) & 15,
    speed = (dvs >> 4) & 15,
    special = dvs & 15;
  if (stat === 0)
    return (
      ((attack & 1) << 3) |
      ((defense & 1) << 2) |
      ((speed & 1) << 1) |
      (special & 1)
    );
  return [attack, defense, speed, special, special][stat - 1];
}

/** CalcMonStatC for stat 0-5 (HP, Atk, Def, Spd, SpAtk, SpDef). */
export function calcStat(
  base: number,
  dvs: number,
  stat: number,
  level: number,
  statExp: readonly number[] | undefined,
): number {
  // Special attack and defense share the Special stat experience.
  const experience = statExp ? statExp[Math.min(stat, 4)] : 0;
  const bonus = statExp ? Math.floor(squareRoot(experience) / 4) : 0;
  const value = Math.floor(
    (((base + statDv(dvs, stat)) * 2 + bonus) * level) / 100,
  );
  return Math.min(MAX_STAT_VALUE, value + (stat === 0 ? level + 10 : 5));
}

export function calcStats(
  data: PokemonData,
  species: number,
  dvs: number,
  level: number,
  statExp?: readonly number[],
): PartyMon["stats"] {
  const base = data.baseData(species).stats;
  return base.map((value, stat) =>
    calcStat(value, dvs, stat, level, statExp),
  ) as PartyMon["stats"];
}

/** FillMoves for a new Pokémon: learn every move up to its level, skipping
 * repeats and shifting out the oldest move when all slots are full. */
export function initialMoves(
  data: PokemonData,
  species: number,
  level: number,
): PartyMon["moves"] {
  const moves: number[] = [];
  for (const learned of data.learnset(species)) {
    if (learned.level > level) break;
    if (moves.includes(learned.move)) continue;
    if (moves.length === 4) moves.shift();
    moves.push(learned.move);
  }
  while (moves.length < 4) moves.push(0);
  return moves as PartyMon["moves"];
}

/** SetCaughtData (SetBoxmonOrEggmonCaughtData): time of day and level,
 * then the player's gender bit and the map's landmark. */
export function caughtData(
  timeOfDay: number,
  level: number,
  gender: number,
  landmark: number,
): number {
  return (
    (((((timeOfDay + 1) & 3) << 6) | level) & 0xff) << 8 |
    (gender << 7) |
    landmark
  );
}

/** GeneratePartyMonStats for a Pokémon given by a script (not a wild or
 * trainer battle): random DVs, level-up moves, full PP and HP. */
export function generatePartyMon(
  data: PokemonData,
  options: {
    species: number;
    level: number;
    item: number;
    otId: number;
    ot: string;
    dvs: number;
    caughtData: number;
  },
): PartyMon {
  const { species, level } = options;
  if (!Number.isInteger(level) || level < 1 || level > 100)
    throw new Error("Invalid level.");
  const moves = initialMoves(data, species, level);
  const stats = calcStats(data, species, options.dvs, level);
  return {
    species,
    item: options.item,
    moves,
    otId: options.otId,
    ot: options.ot,
    nickname: data.speciesName(species),
    exp: data.expAtLevel(data.baseData(species).growthRate, level),
    statExp: [0, 0, 0, 0, 0],
    dvs: options.dvs,
    pp: moves.map((move) => (move ? data.move(move).pp : 0)) as PartyMon["pp"],
    happiness: BASE_HAPPINESS,
    pokerus: 0,
    caughtData: options.caughtData,
    level,
    status: 0,
    hp: stats[0],
    stats,
  };
}

/** CalcLevel: the highest level whose experience the total reaches. */
export function levelForExp(
  data: PokemonData,
  species: number,
  exp: number,
): number {
  const growth = data.baseData(species).growthRate;
  let level = 1;
  while (level < MAX_LEVEL && data.expAtLevel(growth, level + 1) <= exp)
    level++;
  return level;
}

/** ComputeMaxPP for a move with `ups` PP Ups: each adds a fifth of the base
 * PP, clamped to 7, so a 40 PP move maxes at 61 instead of overflowing the
 * packed byte at 64. The PP Ups stay in the top two bits. */
export function maxPP(data: PokemonData, move: number, ups: number): number {
  const base = data.move(move).pp;
  return (ups << 6) | (base + Math.min(Math.floor(base / 5), 7) * ups);
}

/** The box_struct fields of a stored Pokémon: everything but status, HP
 * and stats. */
export function validBoxFields(value: unknown): boolean {
  const mon = value as PartyMon;
  const integer = (value: unknown, min: number, max: number): value is number =>
    Number.isInteger(value) && Number(value) >= min && Number(value) <= max;
  const tuple = (value: unknown, length: number, max: number) =>
    Array.isArray(value) &&
    value.length === length &&
    value.every((item) => integer(item, 0, max));
  try {
    return (
      Boolean(mon) &&
      typeof mon === "object" &&
      integer(mon.species, 1, 251) &&
      integer(mon.item, 0, 255) &&
      tuple(mon.moves, 4, 251) &&
      integer(mon.otId, 0, 0xffff) &&
      typeof mon.ot === "string" &&
      /^[A-Za-z0-9 -]{1,7}$/.test(mon.ot) &&
      typeof mon.nickname === "string" &&
      NICKNAME_PATTERN.test(mon.nickname) &&
      integer(mon.exp, 0, 0xffffff) &&
      tuple(mon.statExp, 5, 0xffff) &&
      integer(mon.dvs, 0, 0xffff) &&
      tuple(mon.pp, 4, 255) &&
      integer(mon.happiness, 0, 255) &&
      integer(mon.pokerus, 0, 255) &&
      integer(mon.caughtData, 0, 0xffff) &&
      integer(mon.level, 1, 100)
    );
  } catch {
    return false;
  }
}

/** Validate a stored Pokémon against the ROM's rules before restoring it. */
export function validPartyMon(
  data: PokemonData,
  value: unknown,
): value is PartyMon {
  const mon = value as PartyMon;
  const integer = (value: unknown, min: number, max: number): value is number =>
    Number.isInteger(value) && Number(value) >= min && Number(value) <= max;
  try {
    if (
      !validBoxFields(mon) ||
      !integer(mon.status, 0, 255) ||
      !Array.isArray(mon.stats) ||
      mon.stats.length !== 6 ||
      !mon.stats.every((stat) => integer(stat, 0, MAX_STAT_VALUE)) ||
      !integer(mon.hp, 0, mon.stats[0])
    )
      return false;
    // GiveExperiencePoints awards stat experience after every victory, but
    // CalcMonStats only runs on a level-up (or a later PC recalculation).
    // Preserve legitimate pending gains instead of silently applying them on
    // load. Stored stats must stay inside the ROM-derived possible range.
    const minimum = calcStats(data, mon.species, mon.dvs, mon.level);
    const maximum = calcStats(data, mon.species, mon.dvs, mon.level, mon.statExp);
    return mon.stats.every((stat, index) =>
      stat >= minimum[index] && stat <= maximum[index]);
  } catch {
    return false;
  }
}