const express = require('express')
const util = require('util')
const exec = util.promisify(require('child_process').exec)
const path = require('path')
const fs = require('fs')
const fsp = fs.promises

const strs = [
  '%sdmn         IN    A     %ip',
  '%sdmn         IN    AAAA  %ip'
]

const router = express.Router()
const cfgLoader = require(path.join('..', '..', 'config-loader'))(path.join(__dirname, 'config.json'), {
  named: '/var/named/',
  tokens: {}
})

let memcache = {}

function fmtip (i, sd, ip) {
  return strs[i].replace('%sdmn', sd).replace('%ip', ip)
}

async function updateSerial (zonefile, contents) {
  let returnContents = contents != null
  if (!contents) {
    contents = await fsp.readFile(zonefile, {encoding: 'utf8'})
  }

  // Split the file into lines
  let lines = contents.split('\n')

  // Find 'serial'
  let prv = false
  let found = false
  for (let i in lines) {
    if (found) break

    let line = lines[i]
    if (line.indexOf('SOA') !== -1) {
      prv = true
      continue
    }

    if (prv && line.toLowerCase().indexOf('serial') !== -1) {
      // Ladies and gentlemen, we got 'em
      found = true
      line = line.replace(/\d+/, Math.floor(Date.now() / 1000))
      lines[i] = line
      break
    }

    if (prv) {
      if (line.indexOf(',') === -1 && line.indexOf('(') === -1 
        && line.indexOf(')') === -1 && line.indexOf('IN') === -1) {
        found = true
        line = line.replace(/\d+/, Math.floor(Date.now() / 1000))
        lines[i] = line
        break
      } else {
        // Just give up, not in this script's readability scope..
        break
      }
    }

    prv = false
  }

  contents = lines.join('\n')
  if (!found) return contents
  if (returnContents) return contents
  await fsp.writeFile(zonefile, contents)
}

async function updateZone (cfg, v4, v6) {
  let zone = cfg.domain + '.zone'
  let zfile = path.join(cfg.root, zone)
  await fsp.access(zfile, fs.constants.F_OK | fs.constants.W_OK)

  if (!memcache[cfg.token]) {
    memcache[cfg.token] = {}
  } else if (memcache[cfg.token]['v4'] === v4 && memcache[cfg.token]['v6'] === v6) {
    // Don't update when it's identical
    return false
  }

  memcache[cfg.token].v6 = v6
  memcache[cfg.token].v4 = v4

  // If subdomain exists, use that file instead and update serial on primary
  if (cfg.subdomain && cfg.subdomain !== '@') {
    let zone2 = cfg.subdomain + '.' + zone
    let zfile2 = path.join(cfg.root, zone2)
    await fsp.access(zfile2, fs.constants.F_OK | fs.constants.W_OK)

    let file = '; GENERATED BY DYNDNS'

    if (v4) {
      file += '\n' + fmtip(0, cfg.subdomain, v4)
    }

    if (v6) {
      file += '\n' + fmtip(1, cfg.subdomain, v6)
    }

    await fsp.writeFile(zfile2, file)
    await updateSerial(zfile)
    await exec('rndc reload ' + cfg.domain)
    return true
  }

  // Subdomain not set, just update '@' target in main zone file
  let zoneFile = await fsp.readFile(zfile, {encoding: 'utf8'})
  let atlines = []
  let lines = zoneFile.split('\n')
  for (let i in lines) {
    let line = lines[i]
    if (line.indexOf('@') === 0 && line.indexOf('SOA') === -1 && line.indexOf('A') !== -1) {
      atlines.push(i)
    }
  }

  if (atlines.length === 0) throw new Error('I dont know what to do with this zone file.')
  let set6 = false
  let set4 = false
  for (let j in atlines) {
    let line = lines[atlines[j]]
    if (line.indexOf('AAAA') !== -1) {
      if (set6 || v6 === null) {
        lines.splice(atlines[j], 1)
        continue
      }
      if (v6) {
        lines[atlines[j]] = fmtip(1, '@', v6)
        set6 = true
      } else if (v4 && atlines.length !== 1) {
        lines[atlines[j]] = fmtip(0, '@', v4)
        set4 = true
      }
      if (v4 && atlines.length === 1) {
        lines.splice(atlines[j], 0, fmtip(0, '@', v4))
        set4 = true
      }
    } else {
      if (set4 || v4 === null) {
        lines.splice(atlines[j], 1)
        continue
      }
      if (v4) {
        lines[atlines[j]] = fmtip(0, '@', v4)
        set4 = true
      } else if (v6 && atlines.length !== 1) {
        lines[atlines[j]] = fmtip(1, '@', v6)
        set6 = true
      }
      if (v6 && atlines.length === 1) {
        lines.splice(atlines[j], 0, fmtip(1, '@', v6))
        set6 = true
      }
    }
  }

  zoneFile = await updateSerial(null, lines.join('\n'))
  if (!zoneFile) throw new Error('I dont know what to do with this zone file.')
  await fsp.writeFile(zfile, zoneFile)
  await exec('rndc reload ' + cfg.domain)
}

function validv4 (ipaddress) {  
  if (/^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/.test(ipaddress)) {  
    return true
  }
  return false
}

function validv6 (value) {
  // See https://blogs.msdn.microsoft.com/oldnewthing/20060522-08/?p=31113 and
  // https://4sysops.com/archives/ipv6-tutorial-part-4-ipv6-address-syntax/
  const components = value.split(':')
  if (components.length < 2 || components.length > 8) {
    return false
  }

  if (components[0] !== '' || components[1] !== '') {
    // Address does not begin with a zero compression ("::")
    if (!components[0].match(/^[\da-f]{1,4}/i)) {
      // Component must contain 1-4 hex characters
      return false
    }
  }

  let numberOfZeroCompressions = 0
  for (let i = 1; i < components.length; ++i) {
    if (components[i] === '') {
      // We're inside a zero compression ("::")
      ++numberOfZeroCompressions
      if (numberOfZeroCompressions > 1) {
        // Zero compression can only occur once in an address
        return false
      }
      continue
    }
    if (!components[i].match(/^[\da-f]{1,4}/i)) {
      // Component must contain 1-4 hex characters
      return false
    }
  }

  return true
}

async function init () {
  let config = await cfgLoader
  await fsp.access(config.named, fs.constants.F_OK)

  router.post('/', async (req, res, next) => {
    let token = req.header('token') || req.body.token

    // Check token
    if (!token || !config.tokens[token]) return res.status(402).send('Forbidden')

    let v4 = null
    let qv4 = req.query.ipv4 || req.body.ipv4

    let v6 = null
    let qv6 = req.query.ipv6 || req.body.ipv6

    // Lets begin our trials
    // Determine Address from request headers
    if (req.header('http_x_forwarded_for')) {
      v4 = req.header('http_x_forwarded_for')
    } else if (req.header('remote_addr')) {
      v4 = req.header('remote_addr')
    } else {
      v4 = req.connection.remoteAddress
    }

    if (!validv4(v4)) {
      v6 = v4
      v4 = null
    }

    // IPv4
    if (qv4 && validv4(qv4)) {
      v4 = qv4
    }

    if (qv4 === 'ignore') {
      v4 = null
    }

    // IPv6
    if (qv6 && validv6(qv6)) {
      v6 = qv6
    }

    if (qv6 === 'ignore') {
      v6 = null
    }

    if (v4 === null && v6 === null) {
      res.send('Nothing to do')
    }

    try {
      await updateZone(Object.assign({
        token: token,
        root: config.named,
      }, config.tokens[token]), v4, v6)
    } catch (e) {
      console.error(e.stack)
      return res.status(500).send('Internal Server Error')
    }

    res.status(204).end()
  })

  return router
}

module.exports = init