// Copyright or © or Copr. happyDNS (2020)
//
// contact@happydns.org
//
// This software is a computer program whose purpose is to provide a modern
// interface to interact with DNS systems.
//
// This software is governed by the CeCILL license under French law and abiding
// by the rules of distribution of free software.  You can use, modify and/or
// redistribute the software under the terms of the CeCILL license as
// circulated by CEA, CNRS and INRIA at the following URL
// "http://www.cecill.info".
//
// As a counterpart to the access to the source code and rights to copy, modify
// and redistribute granted by the license, users are provided only with a
// limited warranty and the software's author, the holder of the economic
// rights, and the successive licensors have only limited liability.
//
// In this respect, the user's attention is drawn to the risks associated with
// loading, using, modifying and/or developing or reproducing the software by
// the user in light of its specific status of free software, that may mean
// that it is complicated to manipulate, and that also therefore means that it
// is reserved for developers and experienced professionals having in-depth
// computer knowledge. Users are therefore encouraged to load and test the
// software's suitability as regards their requirements in conditions enabling
// the security of their systems and/or data to be ensured and, more generally,
// to use and operate it in the same conditions as regards security.
//
// The fact that you are presently reading this means that you have had
// knowledge of the CeCILL license and that you accept its terms.

package api

import (
	"encoding/json"
	"errors"
	"io"
	"math/rand"
	"strings"
	"time"

	"github.com/julienschmidt/httprouter"
	"github.com/miekg/dns"

	"git.happydns.org/happydns/config"
)

func init() {
	router.POST("/api/resolver", ApiHandler(runResolver))
}

type resolverRequest struct {
	Resolver   string `json:"resolver"`
	Custom     string `json:"custom,omitempty"`
	DomainName string `json:"domain"`
	Type       string `json:"type"`
}

func runResolver(_ *config.Options, ps httprouter.Params, body io.Reader) Response {
	var urr resolverRequest
	err := json.NewDecoder(body).Decode(&urr)
	if err != nil {
		return APIErrorResponse{
			err: err,
		}
	}

	urr.DomainName = dns.Fqdn(urr.DomainName)

	if urr.Resolver == "custom" {
		urr.Resolver = urr.Custom
	} else if urr.Resolver == "local" {
		cConf, err := dns.ClientConfigFromFile("/etc/resolv.conf")
		if err != nil {
			return APIErrorResponse{
				err: err,
			}
		}

		urr.Resolver = cConf.Servers[rand.Intn(len(cConf.Servers))]
	}

	if strings.Count(urr.Resolver, ":") > 0 && urr.Resolver[0] != '[' {
		urr.Resolver = "[" + urr.Resolver + "]"
	}

	client := dns.Client{Timeout: time.Second * 5}

	m := new(dns.Msg)
	m.SetQuestion(urr.DomainName, dns.StringToType[urr.Type])
	m.RecursionDesired = true
	m.SetEdns0(4096, true)

	r, _, err := client.Exchange(m, urr.Resolver+":53")
	if err != nil {
		return APIErrorResponse{
			err: err,
		}
	}

	if r == nil {
		return APIErrorResponse{
			err: errors.New("response is nil"),
		}
	}
	if r.Rcode != dns.RcodeSuccess {
		return APIErrorResponse{
			err: errors.New("failed to get a valid answer"),
		}
	}

	return APIResponse{
		response: r,
	}
}
