//go:build pam

package auth

import (
	"fmt"
	"net/http"

	"github.com/msteinert/pam"
	"github.com/rs/zerolog/log"
)

type pamProvider struct{}

func NewPAM() (AuthProvider, error) {
	return pamProvider{}, nil
}

func (pamProvider) Middleware() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			pamAuth(next, w, r)
		})
	}
}

func pamAuth(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 system credentials", charset="UTF-8"`)
		http.Error(w, "HTTP Basic auth is required", http.StatusUnauthorized)
		return
	}

	t, err := pam.StartFunc("login", user, func(s pam.Style, msg string) (string, error) {
		log.Debug().Str("style", fmt.Sprintf("%v", s)).Msg(msg)
		switch s {
		case pam.PromptEchoOff:
			return pass, nil
		case pam.PromptEchoOn, pam.ErrorMsg, pam.TextInfo:
			return "", nil
		default:
			return "", fmt.Errorf("unsupported PAM conversation style: %v", s)
		}
	})
	if err != nil {
		log.Warn().Err(err).Msg("failed to start PAM conversation")
		http.Error(w, "Temporary authentication error, try again later", http.StatusServiceUnavailable)
		return
	}

	if err := t.Authenticate(0); err != nil {
		log.Debug().Str("user", user).Err(err).Msg("auth error")
		http.Error(w, "Invalid username or password", http.StatusUnauthorized)
		return
	}

	if err := t.AcctMgmt(0); err != nil {
		log.Debug().Str("user", user).Err(err).Msg("account unavailable")
		http.Error(w, "Account unavailable", http.StatusUnauthorized)
		return
	}

	user, err = t.GetItem(pam.User)
	if err != nil {
		log.Warn().Str("user", user).Err(err).Msg("failed to get PAM username")
		http.Error(w, "Temporary authentication error, try again later", http.StatusServiceUnavailable)
		return
	}

	authCtx := AuthContext{
		AuthMethod: "pam",
		UserName:   user,
	}
	ctx := NewContext(r.Context(), &authCtx)
	r = r.WithContext(ctx)
	next.ServeHTTP(w, r)
}