import { mkdirSync, readFileSync, renameSync, writeFileSync } from 'node:fs';
import { dirname } from 'node:path';

export const GPU_CRASH_WINDOW_MS = 10 * 60 * 1000;
export const GPU_CRASH_THRESHOLD = 2;

export type GpuFallbackState = {
  crashCount: number;
  lastCrashAt: number;
  reason: string;
};

function isState(value: unknown): value is GpuFallbackState {
  if (!value || typeof value !== 'object') return false;
  const record = value as Record<string, unknown>;
  return Number.isFinite(record.crashCount)
    && Number.isFinite(record.lastCrashAt)
    && typeof record.reason === 'string';
}

export function readGpuFallbackState(
  filePath: string,
  now = Date.now(),
): GpuFallbackState | null {
  try {
    const parsed: unknown = JSON.parse(readFileSync(filePath, 'utf8'));
    if (!isState(parsed)) return null;
    if (now - parsed.lastCrashAt > GPU_CRASH_WINDOW_MS) return null;
    return parsed;
  } catch {
    return null;
  }
}

export function shouldUseSoftwareRendering(input: {
  envDisabled?: boolean;
  cliDisabled?: boolean;
  state?: GpuFallbackState | null;
  now?: number;
}): boolean {
  if (input.envDisabled || input.cliDisabled) return true;
  const state = input.state;
  if (!state) return false;
  const now = input.now ?? Date.now();
  return now - state.lastCrashAt <= GPU_CRASH_WINDOW_MS
    && state.crashCount >= GPU_CRASH_THRESHOLD;
}

export function recordGpuCrash(
  filePath: string,
  reason: string,
  now = Date.now(),
): GpuFallbackState {
  const previous = readGpuFallbackState(filePath, now);
  const next: GpuFallbackState = {
    crashCount: previous ? previous.crashCount + 1 : 1,
    lastCrashAt: now,
    reason,
  };
  mkdirSync(dirname(filePath), { recursive: true });
  const temporaryPath = `${filePath}.${process.pid}.tmp`;
  writeFileSync(temporaryPath, `${JSON.stringify(next)}\n`, 'utf8');
  renameSync(temporaryPath, filePath);
  return next;
}