import fs from 'fs'
import path from 'path'

function uniqueCandidates(candidates) {
  return [...new Set(candidates.filter(Boolean))]
}

function hasServerDataDir(root) {
  const normalizedRoot = String(root || '').replace(/\/+$/, '')
  return fs.existsSync(`${normalizedRoot}/server/data`)
}

export function resolveProjectRoot() {
  const envRoot = process.env.APP_ROOT ? process.env.APP_ROOT.trim() : ''
  const cwd = process.cwd()
  const parent = path.resolve(cwd, '..')

  const candidates = uniqueCandidates([envRoot, cwd, parent])
  for (const root of candidates) {
    if (hasServerDataDir(root)) return root
  }

  return cwd
}

export function getProjectPath(...segments) {
  return path.join(resolveProjectRoot(), ...segments)
}

export function getServerDataPath(...segments) {
  // Validate segments: only allow simple filenames/dirnames (no path separators)
  const SEGMENT_RE = /^[a-zA-Z0-9._-]+$/
  for (const s of segments) {
    if (!SEGMENT_RE.test(String(s || ''))) {
      throw new Error(`Invalid data path segment: ${String(s)}`)
    }
  }

  const dataDir = getProjectPath('server', 'data')
  const candidate = path.join(dataDir, ...segments)
  const resolved = path.resolve(candidate)
  const resolvedDataDir = path.resolve(dataDir)
  if (!resolved.startsWith(resolvedDataDir + path.sep) && resolved !== resolvedDataDir) {
    throw new Error('Resolved data path is outside server/data')
  }

  return resolved
}