package auth

import (
	"context"
	"log"
	"net/http"

	"github.com/emersion/go-imap/client"
	"github.com/emersion/go-sasl"
)

type IMAPProvider struct {
	addr string
	tls  bool
}

// Initializes a new IMAP auth provider with the given connection string.
func NewIMAP(addr string, tls bool) AuthProvider {
	prov := &IMAPProvider{addr, tls}
	conn, err := prov.dial()
	if err != nil {
		log.Fatalf("Error dialing configured IMAP auth server: %s", err.Error())
	}
	conn.Close()
	return prov
}

func (prov *IMAPProvider) Middleware() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			prov.doAuth(next, w, r)
		})
	}
}

func (prov *IMAPProvider) doAuth(next http.Handler,
	w http.ResponseWriter, r *http.Request) {
	user, pass, ok := r.BasicAuth()
	if !ok {
		w.Header().Add("WWW-Authenticate", `Basic realm="Please provide your IMAP credentials", charset="UTF-8"`)
		http.Error(w, "HTTP Basic auth is required", http.StatusUnauthorized)
		return
	}

	conn, err := prov.dial()
	if err != nil {
		http.Error(w, "Temporary authentication error, try again later", http.StatusServiceUnavailable)
		return
	}
	defer conn.Close()

	auth := sasl.NewPlainClient("", user, pass)
	if err := conn.Authenticate(auth); err != nil {
		http.Error(w, "Invalid username or password", http.StatusUnauthorized)
		return
	}

	authCtx := AuthContext{
		AuthMethod: "imap",
		UserName:   user,
	}
	ctx := context.WithValue(r.Context(), AuthCtxKey, &authCtx)
	r = r.WithContext(ctx)
	next.ServeHTTP(w, r)
}

func (prov *IMAPProvider) dial() (*client.Client, error) {
	if prov.tls {
		return client.DialTLS(prov.addr, nil)
	} else {
		return client.Dial(prov.addr)
	}
}