package server

import (
	"bytes"
	"context"
	"crypto/rand"
	"encoding/binary"
	"errors"
	"fmt"
	"log"
	"net/mail"
	"os"
	"runtime"
	"strconv"
	"time"

	"github.com/99designs/gqlgen/graphql"
	"github.com/martinlindhe/base36"
	"github.com/vaughan0/go-ini"
	gomail "gopkg.in/mail.v2"

	"git.sr.ht/~sircmpwn/core-go/auth"
)

// Provides a graphql.RecoverFunc which will print the stack trace, and if
// debug mode is not enabled, email it to the administrator.
func EmailRecover(config ini.File, debug bool, srv string) graphql.RecoverFunc {
	return func(ctx context.Context, _origErr interface{}) error {
		var (
			ok      bool
			origErr error
		)
		if origErr, ok = _origErr.(error); !ok {
			log.Printf("Unexpected error in recover: %v\n", origErr)
			return fmt.Errorf("internal system error")
		}

		if errors.Is(origErr, context.Canceled) {
			return origErr
		}

		if errors.Is(origErr, context.DeadlineExceeded) {
			return origErr
		}

		if origErr.Error() == "pq: canceling statement due to user request" {
			return origErr
		}

		stack := make([]byte, 32768) // 32 KiB
		i := runtime.Stack(stack, false)
		log.Println(origErr.Error())
		log.Println(string(stack[:i]))
		if debug {
			return fmt.Errorf("internal system error")
		}

		to, ok := config.Get("mail", "error-to")
		if !ok {
			return fmt.Errorf("internal system error")
		}
		from, _ := config.Get("mail", "error-from")
		portStr, ok := config.Get("mail", "smtp-port")
		if !ok {
			return fmt.Errorf("internal system error")
		}
		port, _ := strconv.Atoi(portStr)
		host, _ := config.Get("mail", "smtp-host")
		user, _ := config.Get("mail", "smtp-user")
		pass, _ := config.Get("mail", "smtp-password")

		m := gomail.NewMessage()
		sender, err := mail.ParseAddress(from)
		if err != nil {
			log.Fatalf("Failed to parse sender address")
		}
		m.SetAddressHeader("From", sender.Address, sender.Name)
		recipient, err := mail.ParseAddress(to)
		if err != nil {
			log.Fatalf("Failed to parse recipient address")
		}
		m.SetAddressHeader("To", recipient.Address, recipient.Name)
		m.SetHeader("Message-ID", generateMessageID())
		m.SetHeader("Subject", fmt.Sprintf(
			"[%s] GraphQL query error: %v", srv, origErr))

		quser := auth.ForContext(ctx)
		octx := graphql.GetOperationContext(ctx)

		m.SetBody("text/plain", fmt.Sprintf(`Error occured processing GraphQL request:

%v

When running the following query on behalf of %s <%s>:

%s

The following stack trace was produced:

%s`, origErr, quser.Username, quser.Email, octx.RawQuery, string(stack[:i])))

		d := gomail.NewDialer(host, port, user, pass)
		if err := d.DialAndSend(m); err != nil {
			log.Printf("Error sending email: %v\n", err)
		}
		return fmt.Errorf("internal system error")
	}
}

// Generates an RFC 2822-compliant Message-Id based on the informational draft
// "Recommendations for generating Message IDs", for lack of a better
// authoritative source.
func generateMessageID() string {
	var (
		now   bytes.Buffer
		nonce []byte = make([]byte, 8)
	)
	binary.Write(&now, binary.BigEndian, time.Now().UnixNano())
	rand.Read(nonce)
	hostname, err := os.Hostname()
	if err != nil {
		hostname = "localhost"
	}
	return fmt.Sprintf("<%s.%s@%s>",
		base36.EncodeBytes(now.Bytes()),
		base36.EncodeBytes(nonce),
		hostname)
}