import type { AuthUser, MockServerConfig, OnMessageHook, ResourceItem } from '../types.ts';

const NAMED = [
  'tables',
  'views',
  'queries',
  'requestReplies',
  'eventHandlers',
  'eventSchemas',
] as const;

function mergeUsers(a: AuthUser[] = [], b: AuthUser[] = []): AuthUser[] {
  const users = new Map(a.map((user) => [user.username, user]));
  for (const user of b) users.set(user.username, user);
  return [...users.values()];
}

function mergeResources(a: ResourceItem[] = [], b: ResourceItem[] = []): ResourceItem[] {
  const resources = new Map<string, ResourceItem>();
  for (const resource of [...a, ...b]) {
    resources.set(`${resource.RESOURCE_TYPE}:${resource.RESOURCE_NAME}`, resource);
  }
  return [...resources.values()];
}

// Both hooks, in order: the second sees what the first returned, and a
// message the first handled (false) goes no further.
function chainHooks(first: OnMessageHook, second: OnMessageHook): OnMessageHook {
  return (message, ctx) => {
    const hooked = first(message, ctx);
    if (hooked === false) return false;
    return second(hooked ?? message, ctx) ?? hooked;
  };
}

function mergeTwo(base: MockServerConfig, over: MockServerConfig): MockServerConfig {
  const merged: MockServerConfig = { ...base };
  for (const [key, value] of Object.entries(over)) {
    if (value !== undefined) (merged as Record<string, unknown>)[key] = value;
  }
  for (const key of NAMED) {
    if (base[key] && over[key]) merged[key] = { ...base[key], ...over[key] } as never;
  }
  if (base.auth && over.auth) {
    merged.auth = {
      ...base.auth,
      ...over.auth,
      users: mergeUsers(base.auth.users, over.auth.users),
    };
  }
  if (base.additionalResources && over.additionalResources) {
    merged.additionalResources = mergeResources(base.additionalResources, over.additionalResources);
  }
  // The later config's routes are tried first.
  if (base.httpRoutes && over.httpRoutes) {
    merged.httpRoutes = [...over.httpRoutes, ...base.httpRoutes];
  }
  if (base.onMessage && over.onMessage) {
    merged.onMessage = chainHooks(base.onMessage, over.onMessage);
  }
  return merged;
}

/**
 * Merges mock-server configs into one, later configs over earlier ones:
 * `createMockServer(mergeConfigs(platformPreset(), appConfig))`.
 *
 * - tables, views, queries, requestReplies, eventHandlers, eventSchemas: by
 *   name, a later entry replacing an earlier one whole.
 * - auth.users: by username, a later user replacing an earlier one; the other
 *   auth settings, setting by setting.
 * - additionalResources: both lists, without repeats.
 * - httpRoutes: both, the later config's tried first. onMessage: both, in order.
 * - Anything else (resources, fidelity, defaultEventHandler, productName, ...):
 *   the later config's, when it sets one.
 */
export function mergeConfigs(...configs: MockServerConfig[]): MockServerConfig {
  return configs.reduce<MockServerConfig>((merged, config) => mergeTwo(merged, config), {});
}