/**
 * Environment-scoped settings hooks.
 *
 * Abstracts the split between server-authoritative settings (persisted in
 * `settings.json` on the server, fetched via `server.getConfig`) and
 * client-only settings (persisted in localStorage).
 *
 * Live server settings always require an environment id. Primary-environment
 * access is intentionally named as such so environment-sensitive consumers
 * cannot silently read the wrong server's settings.
 */
import { useCallback, useMemo, useSyncExternalStore } from "react";
import { useAtomValue } from "@effect/atom-react";
import {
  DEFAULT_SERVER_SETTINGS,
  type EnvironmentId,
  ServerSettings,
  type ServerSettingsPatch,
} from "@t3tools/contracts";
import {
  type ClientSettingsPatch,
  type ClientSettings,
  DEFAULT_CLIENT_SETTINGS,
  type UnifiedSettings,
} from "@t3tools/contracts/settings";
import { safeErrorLogAttributes } from "@t3tools/client-runtime/errors";
import { ensureLocalApi } from "~/localApi";
import * as Struct from "effect/Struct";
import { primaryServerSettingsAtom, serverEnvironment } from "~/state/server";
import { usePrimaryEnvironment } from "~/state/environments";
import { useAtomCommand } from "~/state/use-atom-command";

const CLIENT_SETTINGS_PERSISTENCE_ERROR_SCOPE = "[CLIENT_SETTINGS]";

const clientSettingsListeners = new Set<() => void>();
const clientSettingsHydrationListeners = new Set<() => void>();
let clientSettingsSnapshot = DEFAULT_CLIENT_SETTINGS;
let clientSettingsHydrated = false;
let clientSettingsHydrationPromise: Promise<void> | null = null;
let clientSettingsHydrationGeneration = 0;

type SettingsSelector<S, T> = (settings: S) => T;

const selectClientSettingsIdentity: SettingsSelector<ClientSettings, ClientSettings> = (settings) =>
  settings;

function isObjectLike(value: unknown): value is Record<string, unknown> {
  return typeof value === "object" && value !== null;
}

export function areSettingsSelectionsEqual<T>(left: T, right: T): boolean {
  if (Object.is(left, right)) {
    return true;
  }
  if (!isObjectLike(left) || !isObjectLike(right)) {
    return false;
  }

  const leftKeys = Object.keys(left);
  const rightKeys = Object.keys(right);
  if (leftKeys.length !== rightKeys.length) {
    return false;
  }

  for (const key of leftKeys) {
    if (!Object.prototype.hasOwnProperty.call(right, key)) {
      return false;
    }
    if (!Object.is(left[key], right[key])) {
      return false;
    }
  }

  return true;
}

export function createSettingsSelectorSnapshotReader<S, T>(
  getSnapshot: () => S,
  selector: SettingsSelector<S, T>,
): () => T {
  let hasPreviousSelection = false;
  let previousSelection: T;

  return () => {
    const nextSelection = selector(getSnapshot());
    if (hasPreviousSelection && areSettingsSelectionsEqual(previousSelection, nextSelection)) {
      return previousSelection;
    }

    hasPreviousSelection = true;
    previousSelection = nextSelection;
    return nextSelection;
  };
}

function emitClientSettingsChange() {
  for (const listener of clientSettingsListeners) {
    listener();
  }
}

function emitClientSettingsHydrationChange() {
  for (const listener of clientSettingsHydrationListeners) {
    listener();
  }
}

function getClientSettingsSnapshot(): ClientSettings {
  return clientSettingsSnapshot;
}

function replaceClientSettingsSnapshot(settings: ClientSettings): void {
  clientSettingsSnapshot = settings;
  emitClientSettingsChange();
}

function setClientSettingsHydrated(nextHydrated: boolean): void {
  if (clientSettingsHydrated === nextHydrated) {
    return;
  }
  clientSettingsHydrated = nextHydrated;
  emitClientSettingsHydrationChange();
}

function subscribeClientSettings(listener: () => void): () => void {
  clientSettingsListeners.add(listener);
  void hydrateClientSettings();
  return () => {
    clientSettingsListeners.delete(listener);
  };
}

function getClientSettingsHydratedSnapshot(): boolean {
  return clientSettingsHydrated;
}

function subscribeClientSettingsHydration(listener: () => void): () => void {
  clientSettingsHydrationListeners.add(listener);
  void hydrateClientSettings();
  return () => {
    clientSettingsHydrationListeners.delete(listener);
  };
}

async function hydrateClientSettings(): Promise<void> {
  if (clientSettingsHydrated) {
    return;
  }
  if (clientSettingsHydrationPromise) {
    return clientSettingsHydrationPromise;
  }

  const hydrationGeneration = clientSettingsHydrationGeneration;
  const nextHydration = (async () => {
    try {
      const persistedSettings = await ensureLocalApi().persistence.getClientSettings();
      if (hydrationGeneration !== clientSettingsHydrationGeneration) {
        return;
      }
      if (persistedSettings) {
        replaceClientSettingsSnapshot({ ...DEFAULT_CLIENT_SETTINGS, ...persistedSettings });
      }
    } catch (error) {
      console.error(`${CLIENT_SETTINGS_PERSISTENCE_ERROR_SCOPE} hydrate failed`, {
        operation: "hydrate",
        ...safeErrorLogAttributes(error),
      });
    } finally {
      if (hydrationGeneration === clientSettingsHydrationGeneration) {
        setClientSettingsHydrated(true);
      }
    }
  })();

  const hydrationPromise = nextHydration.finally(() => {
    if (clientSettingsHydrationPromise === hydrationPromise) {
      clientSettingsHydrationPromise = null;
    }
  });
  clientSettingsHydrationPromise = hydrationPromise;

  return clientSettingsHydrationPromise;
}

function persistClientSettings(settings: ClientSettings): void {
  replaceClientSettingsSnapshot(settings);
  void ensureLocalApi()
    .persistence.setClientSettings(settings)
    .catch((error) => {
      console.error(`${CLIENT_SETTINGS_PERSISTENCE_ERROR_SCOPE} persist failed`, {
        operation: "persist",
        ...safeErrorLogAttributes(error),
      });
    });
}

// ── Key sets for routing patches ─────────────────────────────────────

const SERVER_SETTINGS_KEYS = new Set<string>(Struct.keys(ServerSettings.fields));

function splitPatch(patch: Partial<UnifiedSettings>): {
  serverPatch: ServerSettingsPatch;
  clientPatch: ClientSettingsPatch;
} {
  const serverPatch: Record<string, unknown> = {};
  const clientPatch: Record<string, unknown> = {};
  for (const [key, value] of Object.entries(patch)) {
    if (SERVER_SETTINGS_KEYS.has(key)) {
      serverPatch[key] = value;
    } else {
      clientPatch[key] = value;
    }
  }
  return {
    serverPatch: serverPatch as ServerSettingsPatch,
    clientPatch: clientPatch as ClientSettingsPatch,
  };
}

// ── Hooks ────────────────────────────────────────────────────────────

/**
 * Non-hook accessor for the current merged client settings snapshot.
 * Used by non-React code paths (e.g. runtime services) that need the latest
 * settings without subscribing.
 */
export function getClientSettings(): ClientSettings {
  return getClientSettingsSnapshot();
}

export function useClientSettingsHydrated(): boolean {
  return useSyncExternalStore(
    subscribeClientSettingsHydration,
    getClientSettingsHydratedSnapshot,
    () => false,
  );
}

function useSelectedClientSettings<T>(selector: SettingsSelector<ClientSettings, T>): T {
  const getSelectedSnapshot = useMemo(
    () => createSettingsSelectorSnapshotReader(getClientSettingsSnapshot, selector),
    [selector],
  );
  const getSelectedServerSnapshot = useMemo(
    () => createSettingsSelectorSnapshotReader(() => DEFAULT_CLIENT_SETTINGS, selector),
    [selector],
  );

  return useSyncExternalStore(
    subscribeClientSettings,
    getSelectedSnapshot,
    getSelectedServerSnapshot,
  );
}

export function mergeEnvironmentSettings(
  serverSettings: ServerSettings,
  clientSettings: ClientSettings,
): UnifiedSettings {
  return { ...serverSettings, ...clientSettings };
}

function useMergedSettings<T>(
  serverSettings: ServerSettings,
  selector: ((settings: UnifiedSettings) => T) | undefined,
): T {
  const selectMergedSettings = useCallback(
    (clientSettings: ClientSettings) => {
      const merged = mergeEnvironmentSettings(serverSettings, clientSettings);
      return selector ? selector(merged) : (merged as T);
    },
    [selector, serverSettings],
  );

  return useSelectedClientSettings(selectMergedSettings);
}

export function useClientSettings<T = ClientSettings>(
  selector?: (settings: ClientSettings) => T,
): T {
  return useSelectedClientSettings(
    selector ?? (selectClientSettingsIdentity as unknown as SettingsSelector<ClientSettings, T>),
  );
}

/** Read current settings for one environment, merged with client-local preferences. */
export function useEnvironmentSettings<T = UnifiedSettings>(
  environmentId: EnvironmentId,
  selector?: (settings: UnifiedSettings) => T,
): T {
  const serverSettings = useAtomValue(serverEnvironment.settingsValueAtom(environmentId));
  return useMergedSettings(serverSettings ?? DEFAULT_SERVER_SETTINGS, selector);
}

/** Primary-only settings access for the settings UI and other explicitly global surfaces. */
export function usePrimarySettings<T = UnifiedSettings>(
  selector?: (settings: UnifiedSettings) => T,
): T {
  return useMergedSettings(useAtomValue(primaryServerSettingsAtom), selector);
}

/**
 * Returns an updater that routes each key to the correct backing store.
 *
 * Server keys are optimistically patched in atom-backed server state, then
 * persisted via RPC. Client keys go through client persistence.
 */
function useUpdateSettingsTarget(environmentId: EnvironmentId | null) {
  const persistServerSettings = useAtomCommand(
    serverEnvironment.updateSettings,
    "server settings update",
  );
  const updateSettings = useCallback(
    (patch: Partial<UnifiedSettings>) => {
      const { serverPatch, clientPatch } = splitPatch(patch);

      if (Object.keys(serverPatch).length > 0) {
        if (environmentId) {
          void persistServerSettings({
            environmentId,
            input: { patch: serverPatch },
          });
        }
      }

      if (Object.keys(clientPatch).length > 0) {
        persistClientSettings({
          ...getClientSettingsSnapshot(),
          ...clientPatch,
        });
      }
    },
    [environmentId, persistServerSettings],
  );

  return updateSettings;
}

export function useUpdateEnvironmentSettings(environmentId: EnvironmentId) {
  return useUpdateSettingsTarget(environmentId);
}

export function useUpdatePrimarySettings() {
  return useUpdateSettingsTarget(usePrimaryEnvironment()?.environmentId ?? null);
}

export function useUpdateClientSettings() {
  return useCallback((patch: ClientSettingsPatch) => {
    persistClientSettings({
      ...getClientSettingsSnapshot(),
      ...patch,
    });
  }, []);
}

export function __resetClientSettingsPersistenceForTests(): void {
  clientSettingsHydrationGeneration += 1;
  clientSettingsSnapshot = DEFAULT_CLIENT_SETTINGS;
  clientSettingsHydrated = false;
  clientSettingsHydrationPromise = null;
  clientSettingsListeners.clear();
  clientSettingsHydrationListeners.clear();
}

export function __setClientSettingsForTests(settings: ClientSettings): void {
  clientSettingsHydrationGeneration += 1;
  clientSettingsSnapshot = settings;
  clientSettingsHydrated = true;
  clientSettingsHydrationPromise = null;
}