import {
  WORKFLOW_ENGINE,
  normalizeWorkflowEngineId,
} from './contracts.mjs';

const REQUIRED_ENGINE_METHODS = Object.freeze([
  'start',
  'resume',
  'cancel',
  'getState',
  'streamEvents',
]);

function validateEngine(engine) {
  if (!engine || typeof engine !== 'object') {
    throw new Error('Workflow engine must be an object');
  }
  const id = normalizeWorkflowEngineId(engine.id, '');
  if (!id) throw new Error('Workflow engine requires a valid id');
  const missing = REQUIRED_ENGINE_METHODS.filter((method) => typeof engine[method] !== 'function');
  if (missing.length) {
    throw new Error(`Workflow engine ${id} missing methods: ${missing.join(', ')}`);
  }
  return id;
}

export function createWorkflowEngineRegistry(initialEngines = []) {
  const engines = new Map();

  function register(engine) {
    const id = validateEngine(engine);
    if (engines.has(id)) throw new Error(`Workflow engine already registered: ${id}`);
    engines.set(id, engine);
    return engine;
  }

  for (const engine of initialEngines) register(engine);

  return {
    register,
    get(id) {
      return engines.get(normalizeWorkflowEngineId(id, '')) ?? null;
    },
    has(id) {
      return engines.has(normalizeWorkflowEngineId(id, ''));
    },
    list() {
      return [...engines.values()].map((engine) => ({
        id: engine.id,
        label: engine.label ?? engine.id,
        kind: engine.kind ?? 'plugin',
        capabilities: Array.isArray(engine.capabilities) ? [...engine.capabilities] : [],
      }));
    },
  };
}

function createHttpError(response, action) {
  const error = new Error(`Workflow engine ${action} failed with HTTP ${response?.status ?? 'unknown'}`);
  error.code = 'WORKFLOW_ENGINE_HTTP_ERROR';
  error.status = response?.status ?? null;
  return error;
}

function joinUrl(baseUrl, pathname) {
  return `${String(baseUrl).replace(/\/$/, '')}/${String(pathname).replace(/^\//, '')}`;
}

export function createRemoteWorkflowEngine({
  id = WORKFLOW_ENGINE.LANGGRAPH,
  label = 'LangGraph',
  baseUrl,
  serviceToken = null,
  timeoutMs = 5000,
  fetchImpl = globalThis.fetch,
} = {}) {
  const normalizedId = normalizeWorkflowEngineId(id, '');
  const normalizedBaseUrl = String(baseUrl ?? '').trim().replace(/\/$/, '');
  if (!normalizedId) throw new Error('Remote workflow engine requires a valid id');
  if (!normalizedBaseUrl) throw new Error(`Remote workflow engine ${normalizedId} requires baseUrl`);
  if (typeof fetchImpl !== 'function') throw new Error('Remote workflow engine requires fetch');

  async function request(pathname, init = {}) {
    const controller = new AbortController();
    const timer = setTimeout(() => controller.abort(), Math.max(100, Number(timeoutMs) || 5000));
    try {
      const response = await fetchImpl(joinUrl(normalizedBaseUrl, pathname), {
        ...init,
        headers: {
          accept: 'application/json',
          ...(init.body ? { 'content-type': 'application/json' } : {}),
          ...(serviceToken ? { authorization: `Bearer ${serviceToken}` } : {}),
          ...(init.headers ?? {}),
        },
        signal: controller.signal,
      });
      if (!response?.ok) throw createHttpError(response, pathname);
      return response.json();
    } finally {
      clearTimeout(timer);
    }
  }

  return {
    id: normalizedId,
    label,
    kind: 'remote',
    capabilities: ['durable-execution', 'interrupt', 'streaming', 'executor-observability'],
    async start(spec) {
      return request('/v1/runs', { method: 'POST', body: JSON.stringify(spec) });
    },
    async resume(runId, input) {
      return request(`/v1/runs/${encodeURIComponent(runId)}/resume`, {
        method: 'POST',
        body: JSON.stringify(input ?? {}),
      });
    },
    async cancel(runId, input = {}) {
      return request(`/v1/runs/${encodeURIComponent(runId)}/cancel`, {
        method: 'POST',
        body: JSON.stringify(input),
      });
    },
    async getState(runId) {
      return request(`/v1/runs/${encodeURIComponent(runId)}`);
    },
    async *streamEvents(runId, cursor = null) {
      const query = cursor == null ? '' : `?after=${encodeURIComponent(cursor)}`;
      const result = await request(`/v1/runs/${encodeURIComponent(runId)}/events${query}`);
      for (const event of Array.isArray(result?.events) ? result.events : []) yield event;
    },
    async getExecutorJob(jobId) {
      return request(`/v1/executor-jobs/${encodeURIComponent(jobId)}`);
    },
    async *streamExecutorJobEvents(jobId, cursor = null) {
      const query = cursor == null ? '' : `?after=${encodeURIComponent(cursor)}`;
      const result = await request(
        `/v1/executor-jobs/${encodeURIComponent(jobId)}/events${query}`,
      );
      for (const event of Array.isArray(result?.events) ? result.events : []) yield event;
    },
  };
}