import { existsSync, readFileSync, writeFileSync } from "node:fs";

import { EventEmitter } from "../utils/event-emitter.js";
import { getSettingsPath } from "../utils/paths.js";

/**
 * Supported persisted settings keys.
 */
export type SettingsData = {
  "default-mnemonic"?: string;
  currency: string;
};

/**
 * Event payloads emitted by {@link SettingsService}.
 */
export type SettingsServiceEventMap = {
  "settings-updated": {
    key: keyof SettingsData;
    value: string | undefined;
    settings: SettingsData;
  };
};

/**
 * Runtime defaults for settings that should always exist in memory.
 */
const DEFAULT_SETTINGS: SettingsData = {
  currency: "USD",
};

/**
 * Handles loading, migrating, and persisting wallet settings.
 *
 * The backing file is `<XO_CONFIG_DIR>/.wallet`. Historically it stored a raw
 * mnemonic reference string. This service migrates that legacy format to JSON:
 * `{ "default-mnemonic": "<value>", "currency": "USD" }`.
 */
export class SettingsService extends EventEmitter<SettingsServiceEventMap> {
  private readonly settingsPath: string;
  private settings: SettingsData;

  /**
   * Creates a new settings service instance.
   *
   * @param settingsPath - Optional custom settings file path (useful for tests)
   */
  constructor(settingsPath: string = getSettingsPath()) {
    super();
    this.settingsPath = settingsPath;
    this.settings = this.loadSettings();
  }

  /**
   * Returns the current settings snapshot.
   */
  public getSettings(): SettingsData {
    return { ...this.settings };
  }

  /**
   * Returns the currently selected default mnemonic reference.
   */
  public getDefaultMnemonic(): string | undefined {
    return this.settings["default-mnemonic"];
  }

  /**
   * Updates the default mnemonic reference and persists it to disk.
   */
  public setDefaultMnemonic(mnemonicRef: string): void {
    const normalizedMnemonicRef = mnemonicRef.trim();
    if (normalizedMnemonicRef.length === 0) {
      throw new Error("default-mnemonic cannot be empty");
    }

    this.settings["default-mnemonic"] = normalizedMnemonicRef;
    this.persistSettings();

    this.emit("settings-updated", {
      key: "default-mnemonic",
      value: normalizedMnemonicRef,
      settings: this.getSettings(),
    });
  }

  /**
   * Returns the selected fiat currency code (ISO-like uppercase).
   */
  public getCurrency(): string {
    return this.settings.currency;
  }

  /**
   * Updates the selected fiat currency and persists it to disk.
   */
  public setCurrency(currencyCode: string): void {
    const normalizedCurrency = this.normalizeCurrency(currencyCode);
    if (this.settings.currency === normalizedCurrency) {
      return;
    }

    this.settings.currency = normalizedCurrency;
    this.persistSettings();

    this.emit("settings-updated", {
      key: "currency",
      value: normalizedCurrency,
      settings: this.getSettings(),
    });
  }

  /**
   * Reads and normalizes the settings file from disk.
   *
   * If the file contains the old legacy format (raw mnemonic string), the
   * migrated JSON shape is written back immediately.
   */
  private loadSettings(): SettingsData {
    if (!existsSync(this.settingsPath)) {
      return { ...DEFAULT_SETTINGS };
    }

    const rawContents = readFileSync(this.settingsPath, "utf8").trim();
    if (rawContents.length === 0) {
      return { ...DEFAULT_SETTINGS };
    }

    try {
      const parsed = JSON.parse(rawContents);
      const normalized = this.normalizeSettings(parsed);
      return normalized;
    } catch {
      const migrated = this.normalizeSettings({
        "default-mnemonic": rawContents,
      });
      this.persistSettings(migrated);
      return migrated;
    }
  }

  /**
   * Writes the given settings object to disk as pretty JSON.
   *
   * @param nextSettings - Optional explicit value, defaults to in-memory state
   */
  private persistSettings(nextSettings?: SettingsData): void {
    if (nextSettings) {
      this.settings = nextSettings;
    }

    writeFileSync(
      this.settingsPath,
      `${JSON.stringify(this.settings, null, 2)}\n`,
      "utf8",
    );
  }

  /**
   * Coerces unknown input into a safe settings object.
   */
  private normalizeSettings(input: unknown): SettingsData {
    const normalized: SettingsData = {
      ...DEFAULT_SETTINGS,
    };

    if (!input || typeof input !== "object") {
      return normalized;
    }

    const maybeMnemonic = (input as Record<string, unknown>)["default-mnemonic"];
    if (typeof maybeMnemonic === "string" && maybeMnemonic.trim().length > 0) {
      normalized["default-mnemonic"] = maybeMnemonic.trim();
    }

    const maybeCurrency = (input as Record<string, unknown>).currency;
    if (typeof maybeCurrency === "string" && maybeCurrency.trim().length > 0) {
      normalized.currency = this.normalizeCurrency(maybeCurrency);
    }

    return normalized;
  }

  /**
   * Ensures currency values stay uppercase and non-empty.
   */
  private normalizeCurrency(currencyCode: string): string {
    const normalizedCurrency = currencyCode.trim().toUpperCase();
    if (normalizedCurrency.length === 0) {
      throw new Error("currency cannot be empty");
    }
    return normalizedCurrency;
  }
}