import os from "node:os";
import { execFile } from "node:child_process";

/**
 * Jedyna brama do lokalnych procesów Pythona (segmentacja, recolor, studio).
 *
 * Każdy proces ładuje modele (torch + BiRefNet/DINO/SAM ≈ 1,5–2,5 GB RAM),
 * więc równoległe wywołania z workera i z tras HTTP potrafiły zapchać
 * 8 GB RAM do 99% i zamrozić maszynę. Zasady:
 *  - co najwyżej VILMAL_PY_CONCURRENCY procesów naraz (domyślnie 1), reszta czeka w kolejce FIFO;
 *  - wątki BLAS/torch ograniczone (VILMAL_PY_THREADS, domyślnie 2 z nproc);
 *  - proces dostaje niższy priorytet systemowy, żeby UI i serwer HTTP zostały responsywne.
 */
const limit = Math.max(1, Number(process.env.VILMAL_PY_CONCURRENCY ?? 1));
const threads = String(Math.max(1, Number(process.env.VILMAL_PY_THREADS ?? Math.min(2, os.cpus().length))));
let active = 0;
const waiting: Array<() => void> = [];

async function acquire(): Promise<void> {
  if (active < limit) {
    active++;
    return;
  }
  await new Promise<void>((resolve) => waiting.push(resolve));
}

function release(): void {
  const next = waiting.shift();
  if (next) next();
  else active--;
}

/** Stan kolejki — do statusu zadań w UI. */
export function pythonQueueState(): { active: number; waiting: number; limit: number } {
  return { active, waiting: waiting.length, limit };
}

export interface PyResult {
  stdout: string;
  stderr: string;
}

export class PyError extends Error {
  constructor(message: string, readonly stdout: string, readonly stderr: string) {
    super(message);
  }
}

export async function runPython(
  args: string[],
  opts: { cwd?: string; env?: NodeJS.ProcessEnv; timeoutMs: number; maxBuffer?: number }
): Promise<PyResult> {
  await acquire();
  try {
    const py = process.env.VILMAL_PYTHON ?? "python";
    return await new Promise<PyResult>((resolve, reject) => {
      const child = execFile(
        py,
        args,
        {
          cwd: opts.cwd,
          env: {
            ...(opts.env ?? process.env),
            OMP_NUM_THREADS: threads,
            MKL_NUM_THREADS: threads,
            OPENBLAS_NUM_THREADS: threads,
            VILMAL_PY_THREADS: threads,
            PYTHONIOENCODING: "utf-8",
          },
          timeout: opts.timeoutMs,
          maxBuffer: opts.maxBuffer ?? 16 * 1024 * 1024,
          windowsHide: true,
        },
        (err, stdout, stderr) => {
          if (err) reject(new PyError(err.message, String(stdout ?? ""), String(stderr ?? "")));
          else resolve({ stdout: String(stdout), stderr: String(stderr) });
        }
      );
      if (child.pid) {
        try {
          os.setPriority(child.pid, os.constants.priority.PRIORITY_BELOW_NORMAL);
        } catch {
          /* brak uprawnień do zmiany priorytetu — proces działa z domyślnym */
        }
      }
    });
  } finally {
    release();
  }
}