/**
 * OAuth persistence format and isomorphic backends (remote HTTP,
 * sessionStorage). Writes plain JSON `{ servers, idpSessions }`. On read,
 * accepts legacy persist envelopes `{ state: { servers, idpSessions },
 * version }` and promotes the inner payload.
 *
 * This module must stay browser-safe: it imports only the Node-free
 * `store-serialize` helpers, never `store-io` (which pulls `node:fs`). The
 * Node-only file backend lives in `./node/oauth-persist-file.ts`.
 */

import { serializeStore, parseStore } from "../storage/store-serialize.js";
import type { IdpSessionState } from "./storage.js";
import type { ServerOAuthState } from "./store.js";

export const OAUTH_PERSIST_STORAGE_KEY = "mcp-inspector-oauth";

export interface OAuthPersistSnapshot {
  servers: Record<string, ServerOAuthState>;
  idpSessions: Record<string, IdpSessionState>;
}

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

function snapshotFromPayload(
  payload: Partial<OAuthPersistSnapshot>,
): OAuthPersistSnapshot {
  return {
    servers: payload.servers ?? {},
    idpSessions: payload.idpSessions ?? {},
  };
}

/**
 * Parse OAuth store JSON from disk, remote API, or sessionStorage.
 * Accepts plain `{ servers, idpSessions }` or legacy `{ state, version }`.
 * `raw` may be a JSON string or an already-parsed object (e.g. from `res.json()`).
 */
export function parseOAuthPersistBlob(
  raw: string | null | unknown,
): OAuthPersistSnapshot | null {
  if (raw === null || raw === undefined) {
    return null;
  }

  const parsed = typeof raw === "string" ? (raw ? parseStore(raw) : null) : raw;

  if (!isRecord(parsed)) {
    return null;
  }

  if (isRecord(parsed.state) && "version" in parsed) {
    return snapshotFromPayload(parsed.state as Partial<OAuthPersistSnapshot>);
  }

  if ("servers" in parsed || "idpSessions" in parsed) {
    return snapshotFromPayload(parsed as Partial<OAuthPersistSnapshot>);
  }

  return null;
}

export function serializeOAuthPersistBlob(
  snapshot: OAuthPersistSnapshot,
): string {
  return serializeStore(snapshot);
}

export interface OAuthPersistBackend {
  read(): Promise<OAuthPersistSnapshot | null>;
  write(snapshot: OAuthPersistSnapshot): Promise<void>;
  remove?(): Promise<void>;
}

export interface RemoteOAuthPersistBackendOptions {
  baseUrl: string;
  storeId: string;
  authToken?: string;
  fetchFn?: typeof fetch;
}

export function createRemoteOAuthPersistBackend(
  options: RemoteOAuthPersistBackendOptions,
): OAuthPersistBackend {
  const baseUrl = options.baseUrl.replace(/\/$/, "");
  const fetchFn = options.fetchFn ?? globalThis.fetch;

  return {
    async read() {
      const headers: Record<string, string> = {};
      if (options.authToken) {
        headers["x-mcp-remote-auth"] = `Bearer ${options.authToken}`;
      }

      const res = await fetchFn(`${baseUrl}/api/storage/${options.storeId}`, {
        method: "GET",
        headers,
      });

      if (!res.ok) {
        if (res.status === 404) {
          return null;
        }
        throw new Error(`Failed to read store: ${res.status}`);
      }

      // parseOAuthPersistBlob already returns null for {} (the server's
      // missing-file response, server.ts) and for a literal null body, so no
      // empty-object guard is needed — and Object.keys(null) would throw.
      const store = await res.json();
      return parseOAuthPersistBlob(store);
    },
    async write(snapshot) {
      const headers: Record<string, string> = {
        "Content-Type": "application/json",
      };
      if (options.authToken) {
        headers["x-mcp-remote-auth"] = `Bearer ${options.authToken}`;
      }

      const res = await fetchFn(`${baseUrl}/api/storage/${options.storeId}`, {
        method: "POST",
        headers,
        body: serializeOAuthPersistBlob(snapshot),
      });

      if (!res.ok) {
        throw new Error(`Failed to write store: ${res.status}`);
      }
    },
    async remove() {
      const headers: Record<string, string> = {};
      if (options.authToken) {
        headers["x-mcp-remote-auth"] = `Bearer ${options.authToken}`;
      }

      const res = await fetchFn(`${baseUrl}/api/storage/${options.storeId}`, {
        method: "DELETE",
        headers,
      });

      if (!res.ok && res.status !== 404) {
        throw new Error(`Failed to delete store: ${res.status}`);
      }
    },
  };
}

export interface SessionOAuthPersistBackendOptions {
  storageKey?: string;
  getStorage?: () => Storage;
}

export function createSessionOAuthPersistBackend(
  options: SessionOAuthPersistBackendOptions = {},
): OAuthPersistBackend {
  const storageKey = options.storageKey ?? OAUTH_PERSIST_STORAGE_KEY;
  const getStorage = options.getStorage ?? (() => sessionStorage);

  return {
    async read() {
      return parseOAuthPersistBlob(getStorage().getItem(storageKey));
    },
    async write(snapshot) {
      getStorage().setItem(storageKey, serializeOAuthPersistBlob(snapshot));
    },
    async remove() {
      getStorage().removeItem(storageKey);
    },
  };
}