export const CONTEXT_ID = "linuxcnc-2.10.0-pre0-wasm-m1-py-c1";
export const PROTOCOL_SCHEMA = 1;
let CLIENT_INSTANCE = 0;

function isObject(value) {
  return value !== null && typeof value === "object" && !Array.isArray(value);
}

function commandError(message) {
  const payload = isObject(message?.payload) ? message.payload : {};
  const reason = payload.reason ?? payload.gate_reason ?? payload.message_key ?? payload.code ?? "worker_error";
  return Object.assign(new Error(String(reason)), {
    code: payload.code ?? "worker_error",
    reason: payload.reason ?? payload.gate_reason ?? null,
    message_key: payload.message_key ?? null,
    response: message,
  });
}

export class WorkerClient {
  constructor({ worker = null, workerFactory = null, contextId = CONTEXT_ID, sessionId = null, timeoutMs = 10000, maxPending = 64 } = {}) {
    this.contextId = contextId;
    this.sessionId = sessionId ?? `ui-${++CLIENT_INSTANCE}`;
    this.timeoutMs = timeoutMs;
    this.maxPending = maxPending;
    this.worker = worker ?? (workerFactory ? workerFactory() : new Worker("../worker/sim-worker.mjs", { type: "module" }));
    this.seq = 0;
    this.pending = new Map();
    this.completed = new Map();
    this.listeners = new Set();
    this.closed = false;
    this.worker.onmessage = (event) => this.#receive(event.data);
    this.worker.onerror = (event) => this.#failAll(new Error(event?.message ?? "worker_exception"));
  }

  onMessage(listener) {
    this.listeners.add(listener);
    return () => this.listeners.delete(listener);
  }

  #emit(message) {
    for (const listener of this.listeners) listener(message);
  }

  #receive(message) {
    this.#emit(message);
    if (!isObject(message)) return;
    const operationId = message.operation_id ?? message.payload?.operation_id;
    const pending = operationId ? this.pending.get(operationId) : this.pending.get(`seq:${message.seq}`);
    if (!pending) return;
    clearTimeout(pending.timer);
    this.pending.delete(operationId ?? `seq:${message.seq}`);
    if (operationId) this.completed.set(operationId, message);
    if (message.kind === "ERROR" || message.payload?.status === "error" || message.payload?.status === "blocked") {
      pending.reject(commandError(message));
    } else pending.resolve(message);
  }

  #failAll(error) {
    for (const pending of this.pending.values()) {
      clearTimeout(pending.timer);
      pending.reject(error);
    }
    this.pending.clear();
  }

  send(kind, payload = {}, { operationId = null, timeoutMs = this.timeoutMs } = {}) {
    if (this.closed) return Promise.reject(new Error("worker_client_closed"));
    if (!Number.isSafeInteger(this.maxPending) || this.maxPending < 1) return Promise.reject(new Error("worker_client_backpressure"));
    if (operationId && this.completed.has(operationId)) return Promise.resolve(this.completed.get(operationId));
    if (operationId && this.pending.has(operationId)) return this.pending.get(operationId).promise;
    const seq = ++this.seq;
    const message = {
      schema_version: PROTOCOL_SCHEMA,
      context_id: this.contextId,
      session_id: this.sessionId,
      seq,
      kind,
      ...(operationId ? { operation_id: operationId } : {}),
      payload,
    };
    let resolvePromise;
    let rejectPromise;
    const promise = new Promise((resolve, reject) => { resolvePromise = resolve; rejectPromise = reject; });
    const pendingKey = operationId ?? `seq:${seq}`;
    const timer = setTimeout(() => {
      this.pending.delete(pendingKey);
      const error = new Error("worker_timeout");
      error.code = "worker_timeout";
      rejectPromise(error);
    }, timeoutMs);
    if (this.pending.size >= this.maxPending) {
      clearTimeout(timer);
      rejectPromise(Object.assign(new Error("worker_backpressure"), { code: "worker_backpressure" }));
      return promise;
    }
    this.pending.set(pendingKey, { promise, resolve: resolvePromise, reject: rejectPromise, timer, seq, operationId, pendingKey });
    try {
      this.worker.postMessage(message);
    } catch (error) {
      clearTimeout(timer);
      this.pending.delete(pendingKey);
      rejectPromise(error);
    }
    return promise;
  }

  hello() { return this.send("HELLO", {}); }
  attach(operationId = "session-attach") { return this.send("SESSION_ATTACH", {}, { operationId }); }
  loadWorkspace(rootPath = "/workspace", configuration = undefined, hal = undefined, operationId = "workspace-load") {
    return this.send("LOAD_WORKSPACE", { root_path: rootPath, ...(configuration ? { configuration } : {}), ...(hal ? { hal } : {}) }, { operationId });
  }
  loadProgram(source, path = "program.ngc", operationId = `program-load-${this.seq + 1}`) {
    return this.send("PROGRAM_LOAD", { source, path }, { operationId });
  }
  runProgram(operationId = `program-run-${this.seq + 1}`) { return this.send("PROGRAM_RUN", {}, { operationId }); }
  pauseProgram(operationId = `program-pause-${this.seq + 1}`) { return this.send("PROGRAM_PAUSE", {}, { operationId }); }
  resumeProgram(operationId = `program-resume-${this.seq + 1}`) { return this.send("PROGRAM_RESUME", {}, { operationId }); }
  abortProgram(operationId = `program-abort-${this.seq + 1}`) { return this.send("PROGRAM_ABORT", {}, { operationId }); }
  restartProgram(operationId = `program-restart-${this.seq + 1}`) { return this.send("PROGRAM_RESTART", {}, { operationId }); }
  stepProgram(operationId = `program-step-${this.seq + 1}`) { return this.send("PROGRAM_STEP", {}, { operationId }); }
  seekProgram(line, operationId = `program-seek-${this.seq + 1}`) { return this.send("PROGRAM_SEEK", { line }, { operationId }); }
  mdi(block, operationId = `mdi-${this.seq + 1}`) { return this.send("MDI_EXECUTE", { block }, { operationId }); }
  step(cycles = 1, operationId = `step-${this.seq + 1}`) { return this.send("SIM_STEP", { cycles }, { operationId }); }
  async stepMany(cycles = 1, { chunk = 1, operationPrefix = "batch-step" } = {}) {
    if (!Number.isSafeInteger(cycles) || cycles < 0 || cycles > 1000000 || !Number.isSafeInteger(chunk) || chunk < 1 || chunk > 1000000) return Promise.reject(Object.assign(new Error("worker_step_batch_invalid"), { code: "worker_step_batch_invalid" }));
    const responses = [];
    let remaining = cycles;
    let index = 0;
    while (remaining > 0) {
      const amount = Math.min(chunk, remaining);
      responses.push(await this.step(amount, `${operationPrefix}-${index}`));
      remaining -= amount; index += 1;
    }
    return { status: "verified", cycles, chunks: responses.length, last: responses.at(-1) ?? null };
  }
  cancel(operationId, reason = "cancel_requested") {
    const pending = this.pending.get(operationId);
    if (!pending) return Promise.resolve({ status: "verified", cancelled: false, operation_id: operationId });
    clearTimeout(pending.timer);
    this.pending.delete(operationId);
    pending.reject(Object.assign(new Error("worker_cancelled"), { code: "worker_cancelled", reason }));
    const seq = ++this.seq;
    const message = { schema_version: PROTOCOL_SCHEMA, context_id: this.contextId, session_id: this.sessionId, seq, kind: "CANCEL", operation_id: `cancel:${operationId}`, payload: { operation_id: operationId, reason } };
    try { this.worker.postMessage(message); } catch { /* cancellation is local even if transport is closed */ }
    return Promise.resolve({ status: "verified", cancelled: true, operation_id: operationId });
  }
  snapshot(operationId = `snapshot-${this.seq + 1}`) { return this.send("SNAPSHOT_REQUEST", {}, { operationId }); }
  checkpoint(operationId = `checkpoint-${this.seq + 1}`) { return this.send("CHECKPOINT", {}, { operationId }); }
  close() {
    if (this.closed) return;
    this.closed = true;
    this.#failAll(new Error("worker_client_closed"));
    this.worker.terminate?.();
  }
}