export const ANALYTICS_CONFIG_URL = "public/config/analytics.json";
export const ANALYTICS_SCHEMA_VERSION = 1;
export const ANALYTICS_USER_ID_STORAGE_KEY = "world-citybook-anonymous-user-id";
export const ANALYTICS_SESSION_STORAGE_KEY = "world-citybook-session-id";
export const ANALYTICS_OPT_OUT_STORAGE_KEY = "world-citybook-analytics-opt-out";
export const DEFAULT_ANALYTICS_API_HOST = "https://us.i.posthog.com";

let analyticsState = {
  initialized: false,
  config: normalizeAnalyticsConfig(),
  anonymousUserId: "",
  sessionId: "",
  appVersion: "",
  pageUrl: "",
  referrer: "",
  send: null,
};

export async function initAnalytics(options = {}) {
  const win = options.window || globalThis.window;
  const doc = options.document || win?.document || globalThis.document;
  const optOut = resolveAnalyticsOptOut(win);
  const config = normalizeAnalyticsConfig(options.config || await loadAnalyticsConfig(win, options.configUrl));
  const anonymousUserId = getOrCreateAnonymousUserId({
    localStorage: win?.localStorage,
    randomUUID: win?.crypto?.randomUUID?.bind(win.crypto),
  });
  const sessionId = getOrCreateSessionId({
    sessionStorage: win?.sessionStorage,
    randomUUID: win?.crypto?.randomUUID?.bind(win.crypto),
  });
  const identityOptOut = await isExcludedAnalyticsId(
    anonymousUserId,
    config.excludedDistinctIdHashes,
    win?.crypto || globalThis.crypto,
  );
  config.optOut = optOut || isLocalAnalyticsLocation(win?.location) || identityOptOut;

  analyticsState = {
    initialized: true,
    config,
    anonymousUserId,
    sessionId,
    appVersion: options.appVersion || appVersionFromDocument(doc),
    pageUrl: String(win?.location?.href || ""),
    referrer: String(doc?.referrer || ""),
    send: typeof options.send === "function" ? options.send : null,
  };

  trackEvent("site_entered", {
    path: String(win?.location?.pathname || ""),
    search: String(win?.location?.search || ""),
    title: String(doc?.title || ""),
  });

  return {
    anonymousUserId,
    sessionId,
    enabled: shouldTrackAnalytics(config),
  };
}

export function trackEvent(name, props = {}) {
  if (!analyticsState.initialized) return null;
  const event = normalizeAnalyticsEvent(name, {
    anonymousUserId: analyticsState.anonymousUserId,
    sessionId: analyticsState.sessionId,
    appVersion: analyticsState.appVersion,
    pageUrl: analyticsState.pageUrl,
    referrer: analyticsState.referrer,
    props,
  });
  if (!shouldTrackAnalytics(analyticsState.config)) return event;

  if (analyticsState.send) {
    analyticsState.send(event, analyticsState.config);
  } else if (analyticsState.config.provider === "posthog") {
    sendPostHogEvent(event, analyticsState.config);
  }
  return event;
}

export function getAnalyticsIdentity() {
  return {
    anonymousUserId: analyticsState.anonymousUserId,
    sessionId: analyticsState.sessionId,
  };
}

export function getOrCreateAnonymousUserId(options = {}) {
  return getOrCreateStoredId({
    storage: options.localStorage,
    storageKey: ANALYTICS_USER_ID_STORAGE_KEY,
    prefix: "wcb",
    randomUUID: options.randomUUID,
  });
}

export function getOrCreateSessionId(options = {}) {
  return getOrCreateStoredId({
    storage: options.sessionStorage,
    storageKey: ANALYTICS_SESSION_STORAGE_KEY,
    prefix: "wcbs",
    randomUUID: options.randomUUID,
  });
}

export function normalizeAnalyticsConfig(value = {}) {
  const provider = String(value.provider || "posthog").trim().toLowerCase();
  return {
    enabled: value.enabled === true,
    provider,
    posthogKey: String(value.posthogKey || value.apiKey || "").trim(),
    apiHost: stripTrailingSlash(value.apiHost || DEFAULT_ANALYTICS_API_HOST),
    debug: value.debug === true,
    optOut: value.optOut === true || value.optedOut === true,
    excludedDistinctIdHashes: normalizeDistinctIdHashes(value.excludedDistinctIdHashes),
  };
}

export async function isExcludedAnalyticsId(value, hashes, cryptoProvider = globalThis.crypto) {
  const normalizedHashes = normalizeDistinctIdHashes(hashes);
  if (!value || !normalizedHashes.length || !cryptoProvider?.subtle?.digest) return false;
  const bytes = new TextEncoder().encode(String(value));
  const digest = await cryptoProvider.subtle.digest("SHA-256", bytes);
  const hash = [...new Uint8Array(digest)].map((byte) => byte.toString(16).padStart(2, "0")).join("");
  return normalizedHashes.includes(hash);
}

export function isLocalAnalyticsLocation(location) {
  let hostname = String(location?.hostname || "").trim().toLowerCase();
  if (!hostname && location?.href) {
    try {
      hostname = new URL(String(location.href)).hostname.toLowerCase();
    } catch {
      return false;
    }
  }
  return hostname === "localhost" || hostname === "127.0.0.1" || hostname === "::1";
}

export function normalizeAnalyticsEvent(name, options = {}) {
  return {
    name: String(name || "").trim(),
    properties: sanitizeProperties({
      anonymous_user_id: options.anonymousUserId,
      session_id: options.sessionId,
      schema_version: ANALYTICS_SCHEMA_VERSION,
      app_version: options.appVersion,
      page_url: options.pageUrl,
      referrer: options.referrer,
      ...options.props,
    }),
  };
}

export function shouldTrackAnalytics(config = analyticsState.config) {
  return config?.enabled === true
    && config.provider === "posthog"
    && Boolean(config.posthogKey)
    && config.optOut !== true;
}

async function loadAnalyticsConfig(win, configUrl = ANALYTICS_CONFIG_URL) {
  const fetcher = win?.fetch || globalThis.fetch;
  if (typeof fetcher !== "function") return {};
  try {
    const response = await fetcher(configUrl, { cache: "no-store" });
    if (!response?.ok) return {};
    return await response.json();
  } catch {
    return {};
  }
}

function sendPostHogEvent(event, config) {
  const body = JSON.stringify({
    api_key: config.posthogKey,
    event: event.name,
    distinct_id: event.properties.anonymous_user_id,
    properties: event.properties,
  });
  const url = `${config.apiHost}/capture/`;

  const nav = globalThis.navigator;
  if (nav?.sendBeacon && globalThis.Blob) {
    const blob = new Blob([body], { type: "application/json" });
    if (nav.sendBeacon(url, blob)) return;
  }

  globalThis.fetch?.(url, {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body,
    keepalive: true,
    mode: "no-cors",
  }).catch(() => {});
}

function getOrCreateStoredId({ storage, storageKey, prefix, randomUUID }) {
  const existing = safeStorageGet(storage, storageKey);
  if (isValidAnalyticsId(existing, prefix)) return existing;

  const id = `${prefix}_${createRandomId(randomUUID)}`;
  safeStorageSet(storage, storageKey, id);
  return id;
}

function createRandomId(randomUUID) {
  if (typeof randomUUID === "function") return String(randomUUID());
  const random = Math.random().toString(36).slice(2, 12);
  const time = Date.now().toString(36);
  return `${time}-${random}`;
}

function isValidAnalyticsId(value, prefix) {
  return typeof value === "string" && value.startsWith(`${prefix}_`) && value.length > prefix.length + 4;
}

function safeStorageGet(storage, key) {
  try {
    return storage?.getItem?.(key) || "";
  } catch {
    return "";
  }
}

function safeStorageSet(storage, key, value) {
  try {
    storage?.setItem?.(key, value);
  } catch {
    // Analytics must never break the product experience.
  }
}

function safeStorageRemove(storage, key) {
  try {
    storage?.removeItem?.(key);
  } catch {
    // Analytics must never break the product experience.
  }
}

function resolveAnalyticsOptOut(win) {
  const storage = win?.localStorage;
  const params = new URLSearchParams(String(win?.location?.search || ""));
  if (truthyParam(params.get("analytics_opt_in"))) {
    safeStorageRemove(storage, ANALYTICS_OPT_OUT_STORAGE_KEY);
  }
  if (truthyParam(params.get("analytics_opt_out"))) {
    safeStorageSet(storage, ANALYTICS_OPT_OUT_STORAGE_KEY, "1");
    return true;
  }
  return safeStorageGet(storage, ANALYTICS_OPT_OUT_STORAGE_KEY) === "1";
}

function truthyParam(value) {
  return ["1", "true", "yes", "on"].includes(String(value || "").trim().toLowerCase());
}

function appVersionFromDocument(doc) {
  const script = doc?.querySelector?.('script[src*="src/app.js"]');
  const src = script?.getAttribute("src") || "";
  return src.match(/[?&]v=([^&]+)/)?.[1] || "";
}

function stripTrailingSlash(value) {
  return String(value || "").trim().replace(/\/+$/u, "");
}

function normalizeDistinctIdHashes(value) {
  const items = Array.isArray(value) ? value : String(value || "").split(/[\s,;]+/u);
  return [...new Set(items
    .map((item) => String(item || "").trim().toLowerCase())
    .filter((item) => /^[a-f0-9]{64}$/u.test(item)))];
}

function sanitizeProperties(value) {
  return Object.fromEntries(
    Object.entries(value)
      .filter(([, item]) => item !== undefined && item !== null && item !== "")
      .map(([key, item]) => [key, item instanceof Date ? item.toISOString() : item]),
  );
}