/**
 * Pokemon-style Leveling and Stat Calculation Service
 * Implements accurate Pokemon stat formulas based on pokemon_stat_calculation.md
 */

import type { PicletInstance } from '$lib/db/schema';

// Pokemon nature effects: [boosted_stat, lowered_stat] or [null, null] for neutral
export const NATURES = {
  'Hardy': [null, null],           // Neutral
  'Lonely': ['attack', 'defense'],
  'Brave': ['attack', 'speed'],
  'Adamant': ['attack', 'sp_attack'],
  'Naughty': ['attack', 'sp_defense'],
  'Bold': ['defense', 'attack'],
  'Docile': [null, null],          // Neutral
  'Relaxed': ['defense', 'speed'],
  'Impish': ['defense', 'sp_attack'],
  'Lax': ['defense', 'sp_defense'],
  'Timid': ['speed', 'attack'],
  'Hasty': ['speed', 'defense'],
  'Serious': [null, null],         // Neutral
  'Jolly': ['speed', 'sp_attack'],
  'Naive': ['speed', 'sp_defense'],
  'Modest': ['sp_attack', 'attack'],
  'Mild': ['sp_attack', 'defense'],
  'Quiet': ['sp_attack', 'speed'],
  'Bashful': [null, null],         // Neutral
  'Rash': ['sp_attack', 'sp_defense'],
  'Calm': ['sp_defense', 'attack'],
  'Gentle': ['sp_defense', 'defense'],
  'Sassy': ['sp_defense', 'speed'],
  'Careful': ['sp_defense', 'sp_attack'],
  'Quirky': [null, null],          // Neutral
} as const;

export type NatureName = keyof typeof NATURES;

// Growth rate multipliers for different tiers
const TIER_XP_MULTIPLIERS = {
  'low': 0.8,        // 20% less XP required (faster leveling)
  'medium': 1.0,     // Base XP requirements
  'high': 1.4,       // 40% more XP required (slower leveling)
  'legendary': 1.8   // 80% more XP required (much slower leveling)
} as const;

type TierType = keyof typeof TIER_XP_MULTIPLIERS;

/**
 * Convert string tier to TierType, defaulting to 'medium' for unknown values
 */
function normalizeTier(tier: string): TierType {
  if (tier in TIER_XP_MULTIPLIERS) {
    return tier as TierType;
  }
  return 'medium'; // Default fallback
}

// Base experience requirements for Medium Fast growth rate (level³)
// Other tiers will use multipliers of this base
const BASE_XP_REQUIREMENTS: number[] = [];
for (let level = 1; level <= 100; level++) {
  BASE_XP_REQUIREMENTS[level] = level * level * level;
}

export interface LevelUpInfo {
  oldLevel: number;
  newLevel: number;
  statChanges: {
    hp: number;
    attack: number;
    defense: number;
    speed: number;
  };
}

export interface NatureModifiers {
  attack: number;
  defense: number;
  speed: number;
}

/**
 * Calculate HP using Pokemon's HP formula
 * Formula: floor((2 * base_hp * level) / 100) + level + 10
 */
export function calculateHp(baseHp: number, level: number): number {
  if (level === 1) {
    return Math.max(1, Math.floor(baseHp / 10) + 11); // Special case for level 1
  }
  
  return Math.floor((2 * baseHp * level) / 100) + level + 10;
}

/**
 * Calculate non-HP stat using Pokemon's standard formula
 * Formula: floor((floor((2 * base_stat * level) / 100) + 5) * nature_modifier)
 */
export function calculateStat(baseStat: number, level: number, natureModifier: number = 1.0): number {
  if (level === 1) {
    return Math.max(1, Math.floor(baseStat / 10) + 5); // Special case for level 1
  }
  
  const baseValue = Math.floor((2 * baseStat * level) / 100) + 5;
  return Math.floor(baseValue * natureModifier);
}

/**
 * Get nature modifiers for all stats
 */
export function getNatureModifiers(nature: string): NatureModifiers {
  const natureName = nature as NatureName;
  const [boosted, lowered] = NATURES[natureName] || NATURES['Hardy'];
  
  const modifiers: NatureModifiers = {
    attack: 1.0,
    defense: 1.0,  
    speed: 1.0,
  };
  
  if (boosted) {
    (modifiers as any)[boosted] = 1.1; // +10%
  }
  if (lowered) {
    (modifiers as any)[lowered] = 0.9; // -10%
  }
  
  return modifiers;
}

/**
 * Get XP required to reach a specific level
 */
/**
 * Get XP required for a specific level based on tier
 */
export function getXpForLevel(level: number, tier: string = 'medium'): number {
  if (level < 1 || level > 100) {
    throw new Error('Level must be between 1 and 100');
  }
  const normalizedTier = normalizeTier(tier);
  const baseXp = BASE_XP_REQUIREMENTS[level];
  const multiplier = TIER_XP_MULTIPLIERS[normalizedTier];
  return Math.floor(baseXp * multiplier);
}

/**
 * Get XP required for next level
 */
/**
 * Get XP required for next level based on tier
 */
export function getXpForNextLevel(currentLevel: number, tier: string = 'medium'): number {
  if (currentLevel >= 100) return 0; // Max level
  return getXpForLevel(currentLevel + 1, tier);
}

/**
 * Calculate XP progress percentage for current level
 */
/**
 * Get XP progress percentage towards next level based on tier
 */
export function getXpProgress(currentXp: number, currentLevel: number, tier: string = 'medium'): number {
  if (currentLevel >= 100) return 100;
  
  const currentLevelXp = getXpForLevel(currentLevel, tier);
  const nextLevelXp = getXpForLevel(currentLevel + 1, tier);
  const xpIntoLevel = currentXp - currentLevelXp;
  const xpNeededForLevel = nextLevelXp - currentLevelXp;
  
  return Math.min(100, Math.max(0, (xpIntoLevel / xpNeededForLevel) * 100));
}

/**
 * Get current XP towards next level in X/Y format
 */
export function getXpTowardsNextLevel(currentXp: number, currentLevel: number, tier: string = 'medium'): {
  current: number;
  needed: number;
  percentage: number;
} {
  if (currentLevel >= 100) {
    return { current: 0, needed: 0, percentage: 100 };
  }
  
  const currentLevelXp = getXpForLevel(currentLevel, tier);
  const nextLevelXp = getXpForLevel(currentLevel + 1, tier);
  const xpIntoLevel = Math.max(0, currentXp - currentLevelXp);
  const xpNeededForLevel = nextLevelXp - currentLevelXp;
  const percentage = Math.min(100, Math.max(0, (xpIntoLevel / xpNeededForLevel) * 100));
  
  return {
    current: xpIntoLevel,
    needed: xpNeededForLevel,
    percentage
  };
}

/**
 * Recalculate all stats for a Piclet based on current level and nature
 */
export function recalculatePicletStats(instance: PicletInstance): PicletInstance {
  const natureModifiers = getNatureModifiers(instance.nature);
  
  // Calculate new stats
  const newMaxHp = calculateHp(instance.baseHp, instance.level);
  const newAttack = calculateStat(instance.baseAttack, instance.level, natureModifiers.attack);
  const newDefense = calculateStat(instance.baseDefense, instance.level, natureModifiers.defense);
  const newSpeed = calculateStat(instance.baseSpeed, instance.level, natureModifiers.speed);
  
  // Field stats are 80% of main stats (existing logic)
  const newFieldAttack = Math.floor(newAttack * 0.8);
  const newFieldDefense = Math.floor(newDefense * 0.8);
  
  // Maintain current HP ratio when stats change
  const hpRatio = instance.maxHp > 0 ? instance.currentHp / instance.maxHp : 1;
  const newCurrentHp = Math.ceil(newMaxHp * hpRatio);
  
  return {
    ...instance,
    maxHp: newMaxHp,
    currentHp: newCurrentHp,
    attack: newAttack,
    defense: newDefense,
    speed: newSpeed,
    fieldAttack: newFieldAttack,
    fieldDefense: newFieldDefense
  };
}

/**
 * Process potential level up and return results
 */
export function processLevelUp(instance: PicletInstance): {
  newInstance: PicletInstance;
  levelUpInfo: LevelUpInfo | null;
} {
  const requiredXp = getXpForNextLevel(instance.level, instance.tier);
  
  // Check if level up is possible
  if (instance.level >= 100 || instance.xp < requiredXp) {
    return { newInstance: instance, levelUpInfo: null };
  }
  
  // Calculate old stats for comparison
  const oldStats = {
    hp: instance.maxHp,
    attack: instance.attack,
    defense: instance.defense,
    speed: instance.speed
  };
  
  // Level up the Piclet
  const leveledUpInstance = {
    ...instance,
    level: instance.level + 1
  };
  
  // Recalculate stats with new level
  const newInstance = recalculatePicletStats(leveledUpInstance);
  
  // Heal to full HP on level up (Pokemon tradition)
  const finalInstance = {
    ...newInstance,
    currentHp: newInstance.maxHp
  };
  
  // Calculate stat changes
  const statChanges = {
    hp: finalInstance.maxHp - oldStats.hp,
    attack: finalInstance.attack - oldStats.attack,
    defense: finalInstance.defense - oldStats.defense,
    speed: finalInstance.speed - oldStats.speed
  };
  
  const levelUpInfo: LevelUpInfo = {
    oldLevel: instance.level,
    newLevel: finalInstance.level,
    statChanges
  };
  
  return { newInstance: finalInstance, levelUpInfo };
}

/**
 * Calculate XP gained from defeating a Piclet in battle
 * Based on Pokemon formula: (baseExpYield * level) / 7
 */
export function calculateBattleXp(defeatedPiclet: PicletInstance, participantCount: number = 1): number {
  // Use BST as basis for exp yield (common Pokemon approach)
  const bst = defeatedPiclet.baseHp + defeatedPiclet.baseAttack + defeatedPiclet.baseDefense + 
             defeatedPiclet.baseSpeed + defeatedPiclet.baseFieldAttack + defeatedPiclet.baseFieldDefense;
  
  // Convert BST to exp yield (roughly BST/4, minimum 50)
  const baseExpYield = Math.max(50, Math.floor(bst / 4));
  
  // Pokemon formula
  const baseXp = Math.floor((baseExpYield * defeatedPiclet.level) / 7);
  
  // Divide among participants
  return Math.max(1, Math.floor(baseXp / participantCount));
}

/**
 * Check if a level up should occur and process it recursively
 * (Handles multiple level ups from large XP gains)
 */
export function processAllLevelUps(instance: PicletInstance): {
  newInstance: PicletInstance;
  levelUpInfo: LevelUpInfo[];
} {
  const levelUps: LevelUpInfo[] = [];
  let currentInstance = instance;
  
  // Process level ups until no more are possible
  while (currentInstance.level < 100) {
    const result = processLevelUp(currentInstance);
    
    if (result.levelUpInfo) {
      levelUps.push(result.levelUpInfo);
      currentInstance = result.newInstance;
    } else {
      break;
    }
  }
  
  return {
    newInstance: currentInstance,
    levelUpInfo: levelUps
  };
}