/**
 * @file Transcendence eligibility checks, echo calculations, and post-transcendence state builder.
 * @copyright nhcarrigan
 * @license Naomi's Public License
 * @author Naomi Carrigan
 */
import { initialGameState } from "../data/initialState.js";
import { defaultTranscendenceUpgrades } from "../data/transcendenceUpgrades.js";
import type {
  GameState,
  TranscendenceData,
  TranscendenceUpgradeCategory,
} from "@elysium/types";

/**
 * ID of the boss that must be defeated to unlock transcendence.
 */
const finalBossId = "the_absolute_one";

/**
 * Base constant used in the echo yield formula.
 */
const echoFormulaConstant = 853;

const getCategoryMultiplier = (
  purchasedIds: Array<string>,
  category: TranscendenceUpgradeCategory,
): number => {
  return defaultTranscendenceUpgrades.filter((upgrade) => {
    return upgrade.category === category && purchasedIds.includes(upgrade.id);
  }).reduce((mult, upgrade) => {
    return mult * upgrade.multiplier;
  }, 1);
};

/**
 * Computes all transcendence multipliers from the purchased upgrade IDs.
 * @param purchasedUpgradeIds - The array of purchased transcendence upgrade IDs.
 * @returns An object containing all transcendence multiplier values.
 */
const computeTranscendenceMultipliers = (
  purchasedUpgradeIds: Array<string>,
): Omit<TranscendenceData, "count" | "echoes" | "purchasedUpgradeIds"> => {
  return {
    echoCombatMultiplier: getCategoryMultiplier(
      purchasedUpgradeIds,
      "combat",
    ),
    echoIncomeMultiplier: getCategoryMultiplier(
      purchasedUpgradeIds,
      "income",
    ),
    echoMetaMultiplier: getCategoryMultiplier(
      purchasedUpgradeIds,
      "echo_meta",
    ),
    echoPrestigeRunestoneMultiplier: getCategoryMultiplier(
      purchasedUpgradeIds,
      "prestige_runestones",
    ),
    echoPrestigeThresholdMultiplier: getCategoryMultiplier(
      purchasedUpgradeIds,
      "prestige_threshold",
    ),
  };
};

/**
 * Returns true when the player is eligible to transcend:
 * they must have defeated the final boss at least once.
 * @param state - The current game state.
 * @returns Whether the player is eligible for transcendence.
 */
const isEligibleForTranscendence = (state: GameState): boolean => {
  return state.bosses.some((boss) => {
    return boss.id === finalBossId && boss.status === "defeated";
  });
};

/**
 * Calculates echo yield for a transcendence.
 * Formula: floor(CONSTANT / sqrt(prestigeCount)) × echoMetaMultiplier.
 * Fewer prestiges = more echoes (rewards efficient play).
 * Minimum prestige count of 1 is enforced to avoid division by zero.
 * @param prestigeCount - The current prestige count.
 * @param echoMetaMultiplier - The echo meta multiplier from transcendence upgrades.
 * @returns The number of echoes earned.
 */
const calculateEchoes = (
  prestigeCount: number,
  echoMetaMultiplier: number,
): number => {
  const safeCount = Math.max(prestigeCount, 1);
  const baseEchoes = echoFormulaConstant / Math.sqrt(safeCount);
  return Math.floor(baseEchoes * echoMetaMultiplier);
};

/**
 * Builds the permanent-data spread objects that survive a transcendence reset.
 * @param currentState - The game state at the time of transcendence.
 * @param transcendenceData - The newly-computed transcendence data to carry forward.
 * @returns A partial GameState object containing all data that persists through transcendence.
 */
const buildPermanentSpreads = (
  currentState: GameState,
  transcendenceData: TranscendenceData,
): Partial<GameState> => {
  return {
    transcendence: transcendenceData,
    ...currentState.codex === undefined
      ? {}
      : { codex: currentState.codex },
    ...currentState.apotheosis === undefined
      ? {}
      : { apotheosis: currentState.apotheosis },
    ...currentState.story === undefined
      ? {}
      : { story: currentState.story },
  };
};

/**
 * Builds the new game state after a transcendence (nuclear reset).
 * Wipes everything except codex, dailyChallenges, and transcendence data.
 * @param currentState - The game state at the time of transcendence.
 * @param characterName - The player's character name to carry forward.
 * @returns The new game state, transcendence data, and echoes earned.
 */
const buildPostTranscendenceState = (
  currentState: GameState,
  characterName: string,
): {
  transcendenceState: GameState;
  transcendenceData:  TranscendenceData;
  echoesEarned:       number;
} => {
  const previousTranscendence = currentState.transcendence;
  const echoMetaMultiplier = previousTranscendence?.echoMetaMultiplier ?? 1;

  const echoesEarned = calculateEchoes(
    currentState.prestige.count,
    echoMetaMultiplier,
  );
  const previousEchoes = previousTranscendence?.echoes ?? 0;
  const updatedCount = (previousTranscendence?.count ?? 0) + 1;
  const updatedPurchasedIds = previousTranscendence?.purchasedUpgradeIds ?? [];

  const transcendenceData: TranscendenceData = {
    count:               updatedCount,
    echoes:              previousEchoes + echoesEarned,
    purchasedUpgradeIds: updatedPurchasedIds,
    ...computeTranscendenceMultipliers(updatedPurchasedIds),
  };

  const freshState = initialGameState(currentState.player, characterName);
  const transcendenceState: GameState = {
    ...freshState,
    lastTickAt: Date.now(),
    ...buildPermanentSpreads(currentState, transcendenceData),
  };

  return { echoesEarned, transcendenceData, transcendenceState };
};

export {
  buildPostTranscendenceState,
  calculateEchoes,
  computeTranscendenceMultipliers,
  isEligibleForTranscendence,
};