package saml

import (
	"crypto/rsa"
	"crypto/x509"
	"fmt"
	"net/http"
	"net/url"
	"strings"

	"github.com/crewjam/saml"
	"github.com/crewjam/saml/samlsp"
	"go.uber.org/zap"
)

const defaultNameIdentifier = "urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress"

type (
	SamlSPService struct {
		log *zap.Logger

		Enabled bool

		IdpURL      url.URL
		Host        url.URL
		IDPUserMeta *IdpIdentityPayload
		IDPMeta     *saml.EntityDescriptor

		sp      saml.ServiceProvider
		handler *samlsp.Middleware
	}

	SamlSPArgs struct {
		Enabled bool

		AcsURL  string
		MetaURL string
		SloURL  string

		SignRequests    bool
		SignatureMethod string

		Binding string

		// user meta from idp
		IdentityPayload IdpIdentityPayload

		IdpURL      url.URL
		Host        url.URL
		Certificate *x509.Certificate
		PrivateKey  *rsa.PrivateKey
		IdpMeta     *saml.EntityDescriptor
	}
)

// NewSamlSPService loads the certificates and registers the
// already fetched IDP metadata into the SAML middleware
func NewSamlSPService(log *zap.Logger, args SamlSPArgs) (s *SamlSPService, err error) {
	metadataURL, _ := url.Parse(args.MetaURL)
	acsURL, _ := url.Parse(args.AcsURL)
	logoutURL, _ := url.Parse(args.SloURL)

	sp := saml.ServiceProvider{
		Key:         args.PrivateKey,
		Certificate: args.Certificate,
		IDPMetadata: args.IdpMeta,

		MetadataURL: *args.Host.ResolveReference(metadataURL),
		AcsURL:      *args.Host.ResolveReference(acsURL),
		SloURL:      *args.Host.ResolveReference(logoutURL),
	}

	if args.SignRequests {
		sp.SignatureMethod = args.SignatureMethod
	}

	// default to GET
	if args.Binding == "" {
		args.Binding = saml.HTTPRedirectBinding
	}

	opts := samlsp.Options{
		URL:         args.Host,
		Key:         sp.Key,
		Certificate: sp.Certificate,
		IDPMetadata: args.IdpMeta,
	}

	// internal samlsp service
	handler, err := samlsp.New(opts)
	if err != nil {
		err = fmt.Errorf("could not init SAML SP handler: %w", err)
		return
	}

	handler.RequestTracker = samlsp.DefaultRequestTracker(opts, &handler.ServiceProvider)
	handler.ServiceProvider = sp
	handler.Binding = args.Binding

	s = &SamlSPService{
		log: log,

		Enabled: args.Enabled,

		sp:      sp,
		handler: handler,

		IdpURL:      args.IdpURL,
		Host:        args.Host,
		IDPUserMeta: &args.IdentityPayload,
	}

	return
}

func (ssp *SamlSPService) NameIdentifier() string {
	return strings.TrimPrefix(defaultNameIdentifier, "urn:oasis:names:tc:SAML:1.1:nameid-format:")
}

// GuessIdentifier tries to guess the necessary (email) key
// for external authentication
func (ssp *SamlSPService) GuessIdentifier(payload map[string][]string) string {
	tryValues := []string{
		ssp.IDPUserMeta.Identifier,
		ssp.NameIdentifier(),
		defaultNameIdentifier,
		"urn:oasis:names:tc:SAML:attribute:subject-id",
		"email",
		"mail",
	}

	for _, v := range tryValues {
		if _, ok := payload[v]; ok {
			return payload[v][0]
		}
	}

	return ""
}

func (ssp *SamlSPService) Handler() *samlsp.Middleware {
	return ssp.handler
}

// ServeHTTP enables us to use the service directly
// in the router
func (ssp *SamlSPService) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if ssp.handler == nil {
		w.WriteHeader(http.StatusServiceUnavailable)
		return
	}

	ssp.handler.ServeHTTP(w, r)
}