import { access, readFile } from 'node:fs/promises'
import path from 'node:path'
import { pathToFileURL } from 'node:url'

export interface EasySlidesConfig {
  title: string
  description: string
  slidesDir: string
  outDir: string
  exportDir: string
  theme?: string
}

const defaults: EasySlidesConfig = {
  title: 'easy-slides',
  description: 'Markdown presentations powered by easy-slides',
  slidesDir: 'slides',
  outDir: 'dist',
  exportDir: 'exports',
}

export async function loadProjectConfig(cwd = process.cwd()): Promise<EasySlidesConfig> {
  const candidates = [
    'easy-slides.config.mjs',
    'easy-slides.config.js',
    'easy-slides.config.json',
  ]

  for (const candidate of candidates) {
    const filename = path.join(cwd, candidate)
    if (!(await exists(filename)))
      continue

    const loaded = candidate.endsWith('.json')
      ? JSON.parse(await readFile(filename, 'utf8'))
      : (await import(`${pathToFileURL(filename).href}?t=${Date.now()}`)).default

    return normalizeConfig(loaded)
  }

  return { ...defaults }
}

export function normalizeConfig(value: Partial<EasySlidesConfig> | undefined): EasySlidesConfig {
  return {
    ...defaults,
    ...value,
    slidesDir: normalizeRelativePath(value?.slidesDir ?? defaults.slidesDir, 'slidesDir'),
    outDir: normalizeRelativePath(value?.outDir ?? defaults.outDir, 'outDir'),
    exportDir: normalizeRelativePath(value?.exportDir ?? defaults.exportDir, 'exportDir'),
  }
}

function normalizeRelativePath(value: string, field: string) {
  const normalized = value.trim().replace(/[\\/]+$/, '')
  const portable = normalized.replaceAll('\\', '/')
  if (!normalized || path.isAbsolute(normalized) || portable === '..' || portable.startsWith('../'))
    throw new Error(`${field} 必须是项目内的相对路径`)
  return normalized
}

async function exists(filename: string) {
  try {
    await access(filename)
    return true
  }
  catch {
    return false
  }
}