const fs = require('fs')
const path = require('path')
const etag = require('etag')
const babel = require('babel-core')
const unpkgRewrite = require('babel-plugin-unpkg-rewrite')
const getMetadata = require('./utils/getMetadata')
const getFileContentType = require('./utils/getFileContentType')
const getIndexHTML = require('./utils/getIndexHTML')

/**
 * Automatically generate HTML pages that show package contents.
 */
const AutoIndex = !process.env.DISABLE_INDEX

/**
 * Maximum recursion depth for meta listings.
 */
const MaximumDepth = 128

const FileTransforms = {
  expand: function (file, dependencies, callback) {
    const options = {
      plugins: [
        unpkgRewrite(dependencies)
      ]
    }

    babel.transformFile(file, options, function (error, result) {
      callback(error, result && result.code)
    })
  }
}

/**
 * Send the file, JSON metadata, or HTML directory listing.
 */
function serveFile(req, res, next) {
  if (req.query.meta != null) {
    // Serve JSON metadata.
    getMetadata(req.packageDir, req.filename, req.stats, MaximumDepth, function (error, metadata) {
      if (error) {
        console.error(error)
        res.status(500).type('text').send(`Cannot generate metadata for ${req.packageSpec}${req.filename}`)
      } else {
        // Cache metadata for 1 year.
        res.set({
          'Cache-Control': 'public, max-age=31536000',
          'Cache-Tag': 'meta'
        }).send(metadata)
      }
    })
  } else if (req.stats.isFile()) {
    // Serve a file.
    const file = path.join(req.packageDir, req.filename)

    let contentType = getFileContentType(file)

    if (contentType === 'text/html')
      contentType = 'text/plain' // We can't serve HTML because bad people :(

    if (contentType === 'application/javascript' && req.query.module != null) {
      // Serve a JavaScript module.
      const dependencies = Object.assign({},
        req.packageConfig.peerDependencies,
        req.packageConfig.dependencies
      )

      FileTransforms.expand(file, dependencies, function (error, code) {
        if (error) {
          console.error(error)
          res.status(500).type('text').send(`Cannot generate index page for ${req.packageSpec}${req.filename}`)
        } else {
          // Cache modules for 1 year.
          res.set({
            'Content-Type': contentType,
            'Content-Length': Buffer.byteLength(code),
            'Cache-Control': 'public, max-age=31536000',
            'Cache-Tag': 'file,js-file,js-module'
          }).send(code)
        }
      })
    } else {
      // Serve some other static file.
      const tags = [ 'file' ]

      const ext = path.extname(req.filename).substr(1)

      if (ext)
        tags.push(`${ext}-file`)

      // Cache files for 1 year.
      res.set({
        'Content-Type': contentType,
        'Content-Length': req.stats.size,
        'Cache-Control': 'public, max-age=31536000',
        'Last-Modified': req.stats.mtime.toUTCString(),
        'ETag': etag(req.stats),
        'Cache-Tag': tags.join(',')
      })

      const stream = fs.createReadStream(file)

      stream.on('error', function (error) {
        console.error(`Cannot send file ${req.packageSpec}${req.filename}`)
        console.error(error)
        res.sendStatus(500)
      })

      stream.pipe(res)
    }
  } else if (AutoIndex && req.stats.isDirectory()) {
    // Serve an HTML directory listing.
    getIndexHTML(req.packageInfo, req.packageVersion, req.packageDir, req.filename, function (error, html) {
      if (error) {
        console.error(error)
        res.status(500).type('text').send(`Cannot generate index page for ${req.packageSpec}${req.filename}`)
      } else {
        // Cache HTML directory listings for 1 minute.
        res.set({
          'Cache-Control': 'public, max-age=60',
          'Cache-Tag': 'index'
        }).send(html)
      }
    })
  } else {
    res.status(403).type('text').send(`Cannot serve ${req.packageSpec}${req.filename}; it's not a file`)
  }
}

module.exports = serveFile