/**
 * @file Prestige eligibility checks, runestone calculations, and post-prestige state builder.
 * @copyright nhcarrigan
 * @license Naomi's Public License
 * @author Naomi Carrigan
 */
/* eslint-disable max-lines-per-function -- buildPostPrestigeState requires constructing a large composite state object */
import { initialGameState } from "../data/initialState.js";
import { defaultPrestigeUpgrades } from "../data/prestigeUpgrades.js";
import type {
  GameState,
  PrestigeData,
  PrestigeUpgradeCategory,
} from "@elysium/types";

const basePrestigeGoldThreshold = 1_000_000;
const thresholdScaleFactor = 5;
const runestonesPerPrestigeLevel = 10;
const milestoneInterval = 5;
const milestoneRunestonesPerInterval = 25;

/**
 * Calculates the gold threshold required for the next prestige.
 * Formula: BASE * SCALE_FACTOR^prestigeCount — each prestige makes the next threshold harder.
 * @param prestigeCount - The current number of prestiges completed.
 * @param thresholdMultiplier - An optional echo-upgrade multiplier applied to the threshold.
 * @returns The gold amount required to prestige.
 */
const calculatePrestigeThreshold = (
  prestigeCount: number,
  thresholdMultiplier = 1,
): number => {
  return (
    basePrestigeGoldThreshold
    * Math.pow(thresholdScaleFactor, prestigeCount)
    * thresholdMultiplier
  );
};

/**
 * Returns true if the player has earned enough gold to prestige.
 * @param state - The current game state.
 * @returns Whether the player is eligible for a prestige reset.
 */
const isEligibleForPrestige = (state: GameState): boolean => {
  const thresholdMultiplier
    = state.transcendence?.echoPrestigeThresholdMultiplier ?? 1;
  return (
    state.player.totalGoldEarned
    >= calculatePrestigeThreshold(state.prestige.count, thresholdMultiplier)
  );
};

const getCategoryMultiplier = (
  purchasedUpgradeIds: Array<string>,
  category: PrestigeUpgradeCategory,
): number => {
  return defaultPrestigeUpgrades.filter((upgrade) => {
    const matchesCategory = upgrade.category === category;
    const isPurchased = purchasedUpgradeIds.includes(upgrade.id);
    return matchesCategory && isPurchased;
  }).reduce((mult, upgrade) => {
    return mult * upgrade.multiplier;
  }, 1);
};

/**
 * Computes all four runestone multipliers from the purchased upgrade IDs.
 * @param purchasedUpgradeIds - The array of purchased prestige upgrade IDs.
 * @returns An object containing all four runestone multiplier values.
 */
const computeRunestoneMultipliers = (
  purchasedUpgradeIds: Array<string>,
): {
  runestonesIncomeMultiplier:  number;
  runestonesClickMultiplier:   number;
  runestonesEssenceMultiplier: number;
  runestonesCrystalMultiplier: number;
} => {
  return {
    runestonesClickMultiplier: getCategoryMultiplier(
      purchasedUpgradeIds,
      "click",
    ),
    runestonesCrystalMultiplier: getCategoryMultiplier(
      purchasedUpgradeIds,
      "crystals",
    ),
    runestonesEssenceMultiplier: getCategoryMultiplier(
      purchasedUpgradeIds,
      "essence",
    ),
    runestonesIncomeMultiplier: getCategoryMultiplier(
      purchasedUpgradeIds,
      "income",
    ),
  };
};

interface RunestoneParameters {
  totalGoldEarned:          number;
  prestigeCount:            number;
  purchasedUpgradeIds:      Array<string>;
  echoRunestoneMultiplier?: number;
}

/**
 * Calculates how many runestones the player earns from a prestige.
 * Formula: floor(sqrt(totalGoldEarned / threshold)) * RUNESTONES_PER_PRESTIGE_LEVEL * runestoneMultiplier.
 * @param parameters - The parameters for the runestone calculation.
 * @param parameters.totalGoldEarned - The total gold earned in the current run.
 * @param parameters.prestigeCount - The current prestige count.
 * @param parameters.purchasedUpgradeIds - The purchased prestige upgrade IDs.
 * @param parameters.echoRunestoneMultiplier - An optional echo-upgrade multiplier.
 * @returns The number of runestones earned.
 */
const calculateRunestones = (parameters: RunestoneParameters): number => {
  const {
    totalGoldEarned,
    prestigeCount,
    purchasedUpgradeIds,
    echoRunestoneMultiplier = 1,
  } = parameters;
  const threshold = calculatePrestigeThreshold(prestigeCount);
  const base
    = Math.floor(Math.sqrt(totalGoldEarned / threshold))
    * runestonesPerPrestigeLevel;
  const runestoneMult = getCategoryMultiplier(
    purchasedUpgradeIds,
    "runestones",
  );
  return Math.floor(base * runestoneMult * echoRunestoneMultiplier);
};

/**
 * Calculates the new prestige production multiplier.
 * Formula: 1.15^prestigeCount — exponential scaling per prestige.
 * @param prestigeCount - The new prestige count.
 * @returns The production multiplier for the new prestige level.
 */
const calculateProductionMultiplier = (
  prestigeCount: number,
): number => {
  return Math.pow(1.15, prestigeCount);
};

/**
 * Returns the milestone runestone bonus for the given prestige count.
 * Every MILESTONE_INTERVAL prestiges awards milestone_number * MILESTONE_RUNESTONES_PER_INTERVAL stones.
 * @param prestigeCount - The prestige count after the current prestige.
 * @returns The milestone runestone bonus, or 0 if not a milestone prestige.
 */
const calculateMilestoneBonus = (prestigeCount: number): number => {
  if (prestigeCount % milestoneInterval !== 0) {
    return 0;
  }
  const milestoneNumber = prestigeCount / milestoneInterval;
  return milestoneNumber * milestoneRunestonesPerInterval;
};

/**
 * Generates the reset game state after a prestige.
 * Carries over prestige data and runestones; resets everything else.
 * @param currentState - The game state at the time of the prestige.
 * @param characterName - The player's character name to carry forward.
 * @returns The new game state, prestige data, and runestone counts.
 */
const buildPostPrestigeState = (
  currentState: GameState,
  characterName: string,
): {
  prestigeState:       GameState;
  prestigeData:        PrestigeData;
  runestonesEarned:    number;
  milestoneRunestones: number;
} => {
  const {
    autoPrestigeEnabled,
    count:              currentPrestigeCount,
    purchasedUpgradeIds,
    runestones:         currentRunestones,
  } = currentState.prestige;
  const echoRunestoneMultiplier
    = currentState.transcendence?.echoPrestigeRunestoneMultiplier ?? 1;
  const runestonesEarned = calculateRunestones({
    echoRunestoneMultiplier: echoRunestoneMultiplier,
    prestigeCount:           currentPrestigeCount,
    purchasedUpgradeIds:     purchasedUpgradeIds,
    totalGoldEarned:         currentState.player.totalGoldEarned,
  });
  const updatedPrestigeCount = currentPrestigeCount + 1;
  const milestoneRunestones = calculateMilestoneBonus(updatedPrestigeCount);

  const prestigeData: PrestigeData = {
    count:                updatedPrestigeCount,
    lastPrestigedAt:      Date.now(),
    productionMultiplier: calculateProductionMultiplier(updatedPrestigeCount),
    purchasedUpgradeIds:  purchasedUpgradeIds,
    runestones:
      currentRunestones + runestonesEarned + milestoneRunestones,
    ...computeRunestoneMultipliers(purchasedUpgradeIds),
    ...autoPrestigeEnabled === undefined
      ? {}
      : { autoPrestigeEnabled },
  };

  const freshState = initialGameState(currentState.player, characterName);

  // Compute current-run contributions to accumulate into lifetime totals
  const runBossesDefeated = currentState.bosses.filter((boss) => {
    return boss.status === "defeated";
  }).length;
  const runQuestsCompleted = currentState.quests.filter((quest) => {
    return quest.status === "completed";
  }).length;
  let runAdventurersRecruited = 0;
  for (const adventurer of currentState.adventurers) {
    runAdventurersRecruited = runAdventurersRecruited + adventurer.count;
  }
  const runAchievementsUnlocked = currentState.achievements.filter(
    (achievement) => {
      return achievement.unlockedAt !== null;
    },
  ).length;

  const prestigeState: GameState = {
    ...freshState,
    // Achievements are permanent — earned achievements survive all prestiges
    achievements: currentState.achievements,
    lastTickAt:   Date.now(),

    /*
     * Fold current-run totals into lifetime stats so the GameState reflects
     * the true all-time values immediately after prestige.
     */
    player: {
      ...freshState.player,
      lifetimeAchievementsUnlocked:
        freshState.player.lifetimeAchievementsUnlocked
        + runAchievementsUnlocked,
      lifetimeAdventurersRecruited:
        freshState.player.lifetimeAdventurersRecruited
        + runAdventurersRecruited,
      lifetimeBossesDefeated:
        freshState.player.lifetimeBossesDefeated + runBossesDefeated,
      lifetimeClicks:
        freshState.player.lifetimeClicks + currentState.player.totalClicks,
      lifetimeGoldEarned:
        freshState.player.lifetimeGoldEarned
        + currentState.player.totalGoldEarned,
      lifetimeQuestsCompleted:
        freshState.player.lifetimeQuestsCompleted + runQuestsCompleted,
    },
    prestige: prestigeData,
    // Codex lore persists across prestiges — players keep their discovered entries
    ...currentState.codex === undefined
      ? {}
      : { codex: currentState.codex },
    // Transcendence data is permanent — never wiped by prestige
    ...currentState.transcendence === undefined
      ? {}
      : { transcendence: currentState.transcendence },
    // Apotheosis data is eternal — never wiped by prestige
    ...currentState.apotheosis === undefined
      ? {}
      : { apotheosis: currentState.apotheosis },
    // Story chapter progress is permanent — survives all resets
    ...currentState.story === undefined
      ? {}
      : { story: currentState.story },
  };

  return {
    milestoneRunestones,
    prestigeData,
    prestigeState,
    runestonesEarned,
  };
};

export {
  buildPostPrestigeState,
  calculateMilestoneBonus,
  calculatePrestigeThreshold,
  calculateProductionMultiplier,
  calculateRunestones,
  computeRunestoneMultipliers,
  isEligibleForPrestige,
};