import { existsSync } from 'node:fs';
import { delimiter, dirname, isAbsolute, join, resolve } from 'node:path';

export type PythonRuntimeSource = 'configured' | 'bundled' | 'system';

export type PythonRuntime = {
  executable: string;
  binDir: string;
  source: PythonRuntimeSource;
};

export type PythonRuntimeOptions = {
  isPackaged: boolean;
  resourcesPath: string;
  appPath: string;
  platform: NodeJS.Platform;
  arch: string;
  configuredPath?: string;
};

function configuredRuntime(configuredPath: string | undefined, appPath: string): PythonRuntime | null {
  const trimmed = configuredPath?.trim();
  if (!trimmed) return null;
  const executable = isAbsolute(trimmed) ? trimmed : resolve(appPath, trimmed);
  if (!existsSync(executable)) return null;
  return { executable, binDir: dirname(executable), source: 'configured' };
}

function bundledExecutable(resourcesPath: string, platform: NodeJS.Platform): string {
  return platform === 'win32'
    ? join(resourcesPath, 'python', 'python.exe')
    : join(resourcesPath, 'python', 'bin', 'python3');
}

export function resolvePythonRuntime(options: PythonRuntimeOptions): PythonRuntime {
  const configured = configuredRuntime(options.configuredPath, options.appPath);
  if (configured) return configured;

  const executable = bundledExecutable(options.resourcesPath, options.platform);
  if (existsSync(executable)) {
    return { executable, binDir: dirname(executable), source: 'bundled' };
  }

  if (options.isPackaged) {
    throw new Error(`Bundled Python runtime is missing: ${executable}`);
  }

  return {
    executable: options.platform === 'win32' ? 'python' : 'python3',
    binDir: '',
    source: 'system',
  };
}

export function prependPythonToPath(
  environment: Record<string, string>,
  runtime: PythonRuntime,
  platform: NodeJS.Platform = process.platform,
): Record<string, string> {
  const result = { ...environment, NIANCODE_PYTHON_PATH: runtime.executable };
  if (!runtime.binDir) return result;

  const existingKey = Object.keys(result).find((key) => key.toLowerCase() === 'path');
  const pathKey = platform === 'win32' && existingKey ? existingKey : 'PATH';
  const existingPath = result[pathKey];
  result[pathKey] = existingPath ? `${runtime.binDir}${delimiter}${existingPath}` : runtime.binDir;
  return result;
}