import { existsSync, readFileSync, statSync } from 'fs';

const MB = 1024 * 1024;
/** At or above this the package is refused: GitHub warns at 50 MB and rejects at 100 MB. */
export const PATCH_MAX_BYTES = 49 * MB;
export const PATCH_WARN_BYTES = 10 * MB;
export const PATCH_BINARY_FILE_WARN_BYTES = 1 * MB;

export interface PatchSizeReport {
  bytes: number;
  errors: string[];
  warnings: string[];
}

function fmt(bytes: number): string {
  return `${(bytes / MB).toFixed(1)} MB`;
}

/** Binary files in a `git diff --binary` patch whose size exceeds the threshold. */
export function largeBinaryFiles(
  patchText: string,
  thresholdBytes = PATCH_BINARY_FILE_WARN_BYTES
): { path: string; bytes: number }[] {
  const out: { path: string; bytes: number }[] = [];
  const lines = patchText.split('\n');
  let current = '';
  for (let i = 0; i < lines.length; i++) {
    const line = lines[i];
    const header = /^diff --git a\/.* b\/(.*)$/.exec(line);
    if (header) {
      current = header[1];
      continue;
    }
    if (line === 'GIT binary patch') {
      const m = /^(?:literal|delta) (\d+)$/.exec(lines[i + 1] ?? '');
      const bytes = m ? parseInt(m[1], 10) : 0;
      if (bytes > thresholdBytes) out.push({ path: current, bytes });
    }
  }
  return out;
}

export function checkWorkspacePatchSize(patchPath: string): PatchSizeReport {
  const report: PatchSizeReport = { bytes: 0, errors: [], warnings: [] };
  if (!existsSync(patchPath)) return report;
  report.bytes = statSync(patchPath).size;
  if (report.bytes >= PATCH_MAX_BYTES) {
    report.errors.push(
      `environment/workspace.patch is ${fmt(report.bytes)} — the limit is ${fmt(PATCH_MAX_BYTES)}. ` +
        'Remove large files (model weights, datasets, archives, build output) and regenerate the patch; ' +
        'use a tiny dummy fixture or a stub instead.'
    );
    return report;
  }
  if (report.bytes >= PATCH_WARN_BYTES) {
    report.warnings.push(
      `environment/workspace.patch is ${fmt(report.bytes)} (limit ${fmt(PATCH_MAX_BYTES)}) — ` +
        'check it contains only what the task needs'
    );
  }
  for (const f of largeBinaryFiles(readFileSync(patchPath, 'latin1'))) {
    report.warnings.push(
      `workspace.patch adds a ${fmt(f.bytes)} binary file: ${f.path} — ` +
        'prefer a tiny dummy fixture (e.g. a small random-init checkpoint) or a stub'
    );
  }
  return report;
}