var http = require('http')
var echarts = require('node-echarts-canvas')
var url = require('url')

function processConfig (request, response, callback) {
  var queryData = ''
  if (typeof callback !== 'function') {
    return null
  }
  if (request.method === 'GET') {
    var arg = url.parse(request.url, true).query
    if (!arg.config) {
      response.end('request parameter "config" invalid')
      return
    }
    request.config = arg.config
    callback()
  } else {
    request.on('data', function (data) {
      queryData += data
      if (queryData.length > 1e6) {
        response.end('request body too large')
      }
    })
    request.on('end', function () {
      request.config = queryData
      callback()
    })
  }
}

var server = http.createServer(function (request, response) {
  processConfig(request, response, function () {
    var config
    try {
      config = JSON.parse(request.config)
    } catch (e) {
      response.end('request parameter "config" format invalid, is not JSON')
      return
    }
    if (!config || !config.option) {
      response.end('request parameter "config" format invalid')
      return
    }

    var buffer = echarts({
      option: config.option,
      width: config.width || 600,
      height: config.height || 400
    })
    response.setHeader('Content-Type', 'image/png')
    response.write(buffer)
    response.end()
  })
})

var hostName = '0.0.0.0'
var port = 8081
server.listen(port, hostName, function () {
  console.log(`server started at port ${port}`)
})