// Character service: create and retrieve characters with derived stats and energy.
const { getDb } = require('../db');
const { AppError } = require('../utils/errors');
const { getBaseStats } = require('../game/classes');
const { calcDerived, computeEnergy, ENERGY_MAX } = require('../game/stats');
const { computeEnergy: computeEnergyPure } = require('../game/energy');

const ENERGY_UPDATED_AT_DEFAULT = Date.now();

function wrapStmts(db) {
  return {
    findByUserId: db.prepare(
      'SELECT * FROM characters WHERE user_id = ?'
    ),
    findByName: db.prepare(
      'SELECT id FROM characters WHERE name = ? COLLATE NOCASE'
    ),
    insertCharacter: db.prepare(
      `INSERT INTO characters
       (user_id, name, class, level, xp, gold, str, agi, int, vit,
        unspent_points, hp_current, energy, energy_updated_at, kills, deaths, created_at)
       VALUES (?, ?, ?, 1, 0, 50, ?, ?, ?, ?, 0, ?, ?, ?, 0, 0, ?)`
    ),
  };
}

let cachedStmts;

function getStmts() {
  if (!cachedStmts) {
    const db = getDb();
    cachedStmts = wrapStmts(db);
  }
  return cachedStmts;
}

/**
 * Create a new character for the current user.
 */
function createCharacter(userId, name, classKey) {
  const db = getDb();
  const stmts = getStmts();
  const baseStats = getBaseStats(classKey);
  const now = Date.now();

  // Check if user already has a character
  const existing = stmts.findByUserId.get(userId);
  if (existing) {
    throw new AppError('HERO_EXISTS', 'You already have a character.', 409);
  }

  // Check if name is taken
  const nameCheck = stmts.findByName.get(name);
  if (nameCheck) {
    throw new AppError('NAME_TAKEN', 'Hero name is already taken.', 409);
  }

  const hpCurrent = 50 + baseStats.vit * 10 + 5; // level 1: 50 + vit*10 + level*5

  const result = stmts.insertCharacter.run(
    userId, name, classKey,
    baseStats.str, baseStats.agi, baseStats.int, baseStats.vit,
    hpCurrent, ENERGY_MAX, ENERGY_UPDATED_AT_DEFAULT, now
  );

  return { id: result.lastInsertRowid };
}

/**
 * Get character profile with derived stats and current energy.
 */
function getCharacterProfile(userId) {
  const stmts = getStmts();
  const character = stmts.findByUserId.get(userId);

  if (!character) {
    return null;
  }

  // Compute derived stats (with no equipment bonuses for now)
  const derived = calcDerived(
    { str: character.str, agi: character.agi, int: character.int, vit: character.vit },
    character.level,
    character.class
  );

  // Compute current energy with lazy regen
  const energy = computeEnergy(character.energy, character.energy_updated_at, Date.now());

  // Update energy in DB if it changed
  if (energy.energy !== character.energy || energy.updatedAtMs !== character.energy_updated_at) {
    const updateEnergy = getDb().prepare(
      'UPDATE characters SET energy = ?, energy_updated_at = ? WHERE id = ?'
    );
    updateEnergy.run(energy.energy, energy.updatedAtMs, character.id);

    // Refresh character data
    Object.assign(character, { energy: energy.energy, energy_updated_at: energy.updatedAtMs });
  }

  // Calculate next energy tick
  const now = Date.now();
  const nextTickMs = character.energy_updated_at + (ENERGY_MAX - character.energy) * 180 * 1000;
  const nextTickSec = Math.max(0, Math.ceil((nextTickMs - now) / 1000));

  return {
    character: {
      id: character.id,
      name: character.name,
      class: character.class,
      level: character.level,
      xp: character.xp,
      gold: character.gold,
      str: character.str,
      agi: character.agi,
      int: character.int,
      vit: character.vit,
      unspent_points: character.unspent_points,
      hp_current: character.hp_current,
      maxHp: derived.maxHp,
      kills: character.kills,
      deaths: character.deaths,
    },
    derived: {
      maxHp: derived.maxHp,
      attack: derived.attack,
      defense: derived.defense,
      speed: derived.speed,
      critChance: derived.critChance,
      critMult: derived.critMult,
    },
    energy: {
      current: character.energy,
      max: ENERGY_MAX,
      nextTickInSec: nextTickSec,
    },
  };
}

/**
 * Spend energy from a character. Runs in a transaction.
 * First applies lazy energy regen, then deducts the cost.
 * @param {number} characterId - the character's ID
 * @param {number} cost - energy to spend
 * @returns {object} { energy, updatedAtMs } new energy state
 */
function spendEnergy(characterId, cost) {
  const db = getDb();
  const now = Date.now();

  // Validate cost
  if (typeof cost !== 'number' || cost <= 0 || !Number.isInteger(cost)) {
    throw new AppError('VALIDATION_ERROR', 'Cost must be a positive integer.', 400);
  }

  // Get character
  const character = db.prepare('SELECT * FROM characters WHERE id = ?').get(characterId);
  if (!character) {
    throw new AppError('NOT_FOUND', 'Character not found.', 404);
  }

  // Compute current energy with lazy regen
  const energy = computeEnergyPure(character.energy, character.energy_updated_at, now);

  // Check if enough energy
  if (energy.energy < cost) {
    throw new AppError('INSUFFICIENT_ENERGY', `Not enough energy. Have ${energy.energy}, need ${cost}.`, 422);
  }

  // Deduct energy in a transaction
  const updateEnergy = db.transaction((newEnergy, newUpdatedAt, cid) => {
    db.prepare('UPDATE characters SET energy = ?, energy_updated_at = ? WHERE id = ?').run(newEnergy, newUpdatedAt, cid);
  });

  updateEnergy(energy.energy - cost, energy.updatedAtMs, characterId);

  return { energy: energy.energy - cost, updatedAtMs: energy.updatedAtMs };
}

module.exports = { createCharacter, getCharacterProfile, spendEnergy };