/*
Copyright 2020 Rodrigue Chakode and contributors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package main

import (
	"bytes"
	"crypto/tls"
	"encoding/json"
	"fmt"
	"html/template"
	"net"
	"net/http"
	"net/smtp"
	"net/url"
	"strings"
	"log"

	"github.com/dpapathanasiou/go-recaptcha"
	"github.com/spf13/viper"
)

type SendMailRequest struct {
	from    string
	to      []string
	subject string
	body    string
}

type ContactRequest struct {
	Name          string `json:"name,omitempty"`
	Email         string `json:"email,omitempty"`
	Organization  string `json:"organization,omitempty"`
	Subject       string `json:"subject,omitempty"`
	Message       string `json:"message,omitempty"`
	RequestTarget string `json:"requestType,omitempty"`
	OriginURI     string `json:"originURI,omitempty"`
}

type ContactResponse struct {
	Status  string `json:"status,omitempty"`
	Message string `json:"message,omitempty"`
}

// NewSendMailRequest creates a new instance to manage send mail
func NewSendMailRequest(from string, to []string, subject string) *SendMailRequest {
	return &SendMailRequest{
		from:    from,
		to:      to,
		subject: subject,
	}
}

// Execute processes the actual email sending
func (m *SendMailRequest) Execute() error {

	mime := "MIME-version: 1.0;\nContent-Type: text/plain; charset=\"UTF-8\";\n\n"
	from := "From: " + m.from + "\n"
	subject := "Subject: " + m.subject + "\n"
	msg := []byte(from + subject + mime + "\n" + m.body)

	// Connect to the SMTP Server
	smtpServerAddr := viper.GetString("SMTP_SERVER_ADDR")
	smtpServerHost, _, _ := net.SplitHostPort(smtpServerAddr)

	// TLS config
	tlsconfig := &tls.Config{
		InsecureSkipVerify: viper.GetBool("SMTP_SKIP_VERIFY_CERT"),
		ServerName:         smtpServerHost,
	}

	// Important: call tls.Dial instead of smtp.Dial for smtp servers running on 465.
	// On port 465 ssl connection is required from the very beginning (no starttls)
	conn, err := tls.Dial("tcp", smtpServerAddr, tlsconfig)
	if err != nil {
		return fmt.Errorf("failed initiating smtp connection to host %s (%s)", smtpServerAddr, err)
	}
	defer conn.Close()

	smtpClient, err := smtp.NewClient(conn, smtpServerHost)
	if err != nil {
		return fmt.Errorf("failed creating smtp client to host %s (%s)", smtpServerHost, err)
	}
	defer smtpClient.Quit()

	// Authenticate if configured
	if viper.GetBool("SMTP_AUTHENTICATION_ENABLED") {
		smtpClientAuth := smtp.PlainAuth("",
			viper.GetString("SMTP_CLIENT_USERNAME"),
			viper.GetString("SMTP_CLIENT_PASSWORD"),
			smtpServerHost)
		if err = smtpClient.Auth(smtpClientAuth); err != nil {
			return fmt.Errorf("failed authenticating to smtp server (%s)", err)
		}
	}

	// Initialize a mail transaction
	err = smtpClient.Mail(m.from)
	if err != nil {
		return fmt.Errorf("failed issuing MAIL command (%s)", err)
	}

	// Set recipients
	for _, recipient := range m.to {
		err = smtpClient.Rcpt(recipient)
		if err != nil {
			return fmt.Errorf("failed issuing RCPT command (%s)", err)
		}
	}

	smtpWriter, err := smtpClient.Data()
	if err != nil {
		return fmt.Errorf("failed issuing DATA command (%s)", err)
	}
	defer smtpWriter.Close()

	_, err = smtpWriter.Write([]byte(msg))
	if err != nil {
		return fmt.Errorf("failed sending mail content (%s)", err)
	}

	return nil
}

// ParseTemplate parses template and bing data and process the email sending
func (m *SendMailRequest) ParseTemplate(templateFileName string, data interface{}) error {
	emailTpl, err := template.ParseFiles(templateFileName)
	if err != nil {
		return err
	}
	buf := new(bytes.Buffer)
	err = emailTpl.Execute(buf, data)
	if err != nil {
		return err
	}

	m.body = buf.String()
	return nil
}

// MuxSecAllowedDomainsHandler is a security middleware which controls allowed domains.
func MuxSecAllowedDomainsHandler(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		allowedDomains := strings.Split(viper.GetString("ALLOWED_ORIGINS"), ",")
		allowedOrigins := make(map[string]bool)

		for _, domain := range allowedDomains {
			domainTrimmed := strings.TrimSpace(domain)
			allowedOrigins[fmt.Sprintf("http://%s", domainTrimmed)] = true
			allowedOrigins[fmt.Sprintf("https://%s", domainTrimmed)] = true
			allowedOrigins[fmt.Sprintf("http://www.%s", domainTrimmed)] = true
			allowedOrigins[fmt.Sprintf("https://www.%s", domainTrimmed)] = true
		}

		if len(r.Header["Origin"]) == 0 || len(r.Header["Referer"]) == 0 {
			rawHeader, _ := json.Marshal(r.Header)
			log.Println("request with unexpected headers", string(rawHeader))
			w.WriteHeader(http.StatusForbidden)
			return
		}

		reqOrigin := r.Header["Origin"][0]
		if _, domainFound := allowedOrigins[reqOrigin]; !domainFound {
			log.Println("not allowed origin", reqOrigin)
			w.WriteHeader(http.StatusForbidden)
			return
		}

		// Send the allowed origin back as CORS header
		w.Header().Set("Access-Control-Allow-Origin", r.Header["Origin"][0])

		next.ServeHTTP(w, r)
	})
}

// MuxSecReCaptchaHandler is a security middleware which verifies the challenge code from
// the reCaptcha human verification system (provided by Google).
func MuxSecReCaptchaHandler(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		recaptchaResponse, found := r.Form["g-recaptcha-response"]

		if found {
			remoteIp, _, _ := net.SplitHostPort(r.RemoteAddr)
			recaptchaPrivateKey := viper.GetString("RECAPTCHA_PRIVATE_KEY")

			recaptcha.Init(recaptchaPrivateKey)

			result, err := recaptcha.Confirm(remoteIp, recaptchaResponse[0])
			if err != nil {
				log.Println("reCaptcha server error:", err.Error())
				w.WriteHeader(http.StatusForbidden)
				return
			}

			if !result {
				w.WriteHeader(http.StatusForbidden)
				return
			}
		}

		next.ServeHTTP(w, r)
	})
}

// SendMail handles HTTP request to send email
func SendMail(httpResp http.ResponseWriter, httpReq *http.Request) {
	httpReq.ParseForm()

	contactRequest := ContactRequest{
		Name:          httpReq.FormValue("name"),
		Email:         strings.TrimSpace(httpReq.FormValue("email")),
		Organization:  httpReq.FormValue("organization"),
		Subject:       httpReq.FormValue("subject"),
		Message:       httpReq.FormValue("message"),
		RequestTarget: httpReq.FormValue("target"),
		OriginURI:     httpReq.FormValue("requestOrigin"),
	}

	recipients := []string{viper.GetString("CONTACT_REPLY_BCC_EMAIL")}

	userData, _ := json.Marshal(contactRequest)
	log.Println("New Request:", string(userData))

	templateData := struct {
		Name         string
		Email        string
		Organization string
		Subject      string
		Message      string
	}{
		Name:         contactRequest.Name,
		Email:        contactRequest.Email,
		Organization: contactRequest.Organization,
		Subject:      contactRequest.Subject,
		Message:      contactRequest.Message,
	}

	replyTplFile := viper.GetString("TEMPLATE_CONTACT_REQUEST_REPLY")
	if replyTplFile == "" {
		replyTplFile = "./templates/template_reply_contact_request.txt"
	}

	contactEmail := viper.GetString("CONTACT_REPLY_EMAIL")
	sendMailReq := NewSendMailRequest(
		contactEmail,
		recipients,
		contactRequest.Subject,
	)
	err := sendMailReq.ParseTemplate(replyTplFile, templateData)

	contactResponse := ContactResponse{}
	if err == nil {
		err := sendMailReq.Execute()
		if err != nil {
			log.Println(err.Error())
			contactResponse.Status = "error"
			contactResponse.Message = fmt.Sprintf("An internal error occurred, please try later or send us an email at %s.", viper.GetString("CONTACT_REPLY_BCC_EMAIL"))
		} else {
			contactResponse.Status = "success"
			contactResponse.Message = "Thank you for your message."
		}
	} else {
		log.Println(err.Error())
		contactResponse.Status = "error"
		contactResponse.Message = "Invalid request, please review your input and try again."
	}

	if contactRequest.OriginURI != "" {
		originURL, err := url.Parse(contactRequest.OriginURI)
		if err != nil {
			log.Printf("error parsing the origin URL %s (%s)", originURL, err.Error())
			originURL = &url.URL{} // continue with default (empty) url
		}

		q := originURL.Query()
		q.Set("status", contactResponse.Status)
		q.Set("message", contactResponse.Message)
		originURL.RawQuery = q.Encode()

		httpResp.Header().Set("Location", originURL.String())
		httpResp.WriteHeader(http.StatusSeeOther)
	} else {
		httpResp.WriteHeader(http.StatusOK)
	}

	respRawData, _ := json.Marshal(contactResponse)

	httpResp.Header().Set("Content-Type", "application/json; charset=UTF-8")
	httpResp.Write(respRawData)
}