package api

import (
	"context"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"net/http"

	"github.com/go-chi/chi"
	"github.com/pkg/errors"
	"github.com/smallstep/certificates/acme"
	"github.com/smallstep/certificates/api"
)

func link(url, typ string) string {
	return fmt.Sprintf("<%s>;rel=\"%s\"", url, typ)
}

type payloadInfo struct {
	value       []byte
	isPostAsGet bool
	isEmptyJSON bool
}

// payloadFromContext searches the context for a payload. Returns the payload
// or an error.
func payloadFromContext(ctx context.Context) (*payloadInfo, error) {
	val, ok := ctx.Value(acme.PayloadContextKey).(*payloadInfo)
	if !ok || val == nil {
		return nil, acme.ServerInternalErr(errors.Errorf("payload expected in request context"))
	}
	return val, nil
}

// New returns a new ACME API router.
func New(acmeAuth acme.Interface) api.RouterHandler {
	return &Handler{acmeAuth}
}

// Handler is the ACME request handler.
type Handler struct {
	Auth acme.Interface
}

// Route traffic and implement the Router interface.
func (h *Handler) Route(r api.Router) {
	getLink := h.Auth.GetLinkExplicit
	// Standard ACME API
	r.MethodFunc("GET", getLink(acme.NewNonceLink, "{provisionerID}", false, nil), h.baseURLFromRequest(h.lookupProvisioner(h.addNonce(h.GetNonce))))
	r.MethodFunc("HEAD", getLink(acme.NewNonceLink, "{provisionerID}", false, nil), h.baseURLFromRequest(h.lookupProvisioner(h.addNonce(h.GetNonce))))
	r.MethodFunc("GET", getLink(acme.DirectoryLink, "{provisionerID}", false, nil), h.baseURLFromRequest(h.lookupProvisioner(h.addNonce(h.GetDirectory))))
	r.MethodFunc("HEAD", getLink(acme.DirectoryLink, "{provisionerID}", false, nil), h.baseURLFromRequest(h.lookupProvisioner(h.addNonce(h.GetDirectory))))

	extractPayloadByJWK := func(next nextHTTP) nextHTTP {
		return h.baseURLFromRequest(h.lookupProvisioner(h.addNonce(h.addDirLink(h.verifyContentType(h.parseJWS(h.validateJWS(h.extractJWK(h.verifyAndExtractJWSPayload(next)))))))))
	}
	extractPayloadByKid := func(next nextHTTP) nextHTTP {
		return h.baseURLFromRequest(h.lookupProvisioner(h.addNonce(h.addDirLink(h.verifyContentType(h.parseJWS(h.validateJWS(h.lookupJWK(h.verifyAndExtractJWSPayload(next)))))))))
	}

	r.MethodFunc("POST", getLink(acme.NewAccountLink, "{provisionerID}", false, nil), extractPayloadByJWK(h.NewAccount))
	r.MethodFunc("POST", getLink(acme.AccountLink, "{provisionerID}", false, nil, "{accID}"), extractPayloadByKid(h.GetUpdateAccount))
	r.MethodFunc("POST", getLink(acme.KeyChangeLink, "{provisionerID}", false, nil, "{accID}"), extractPayloadByKid(h.NotImplemented))
	r.MethodFunc("POST", getLink(acme.NewOrderLink, "{provisionerID}", false, nil), extractPayloadByKid(h.NewOrder))
	r.MethodFunc("POST", getLink(acme.OrderLink, "{provisionerID}", false, nil, "{ordID}"), extractPayloadByKid(h.isPostAsGet(h.GetOrder)))
	r.MethodFunc("POST", getLink(acme.OrdersByAccountLink, "{provisionerID}", false, nil, "{accID}"), extractPayloadByKid(h.isPostAsGet(h.GetOrdersByAccount)))
	r.MethodFunc("POST", getLink(acme.FinalizeLink, "{provisionerID}", false, nil, "{ordID}"), extractPayloadByKid(h.FinalizeOrder))
	r.MethodFunc("POST", getLink(acme.AuthzLink, "{provisionerID}", false, nil, "{authzID}"), extractPayloadByKid(h.isPostAsGet(h.GetAuthz)))
	r.MethodFunc("POST", getLink(acme.ChallengeLink, "{provisionerID}", false, nil, "{chID}"), extractPayloadByKid(h.GetChallenge))
	r.MethodFunc("POST", getLink(acme.CertificateLink, "{provisionerID}", false, nil, "{certID}"), extractPayloadByKid(h.isPostAsGet(h.GetCertificate)))
}

// GetNonce just sets the right header since a Nonce is added to each response
// by middleware by default.
func (h *Handler) GetNonce(w http.ResponseWriter, r *http.Request) {
	if r.Method == "HEAD" {
		w.WriteHeader(http.StatusOK)
	} else {
		w.WriteHeader(http.StatusNoContent)
	}
}

// GetDirectory is the ACME resource for returning a directory configuration
// for client configuration.
func (h *Handler) GetDirectory(w http.ResponseWriter, r *http.Request) {
	dir, err := h.Auth.GetDirectory(r.Context())
	if err != nil {
		api.WriteError(w, err)
		return
	}
	api.JSON(w, dir)
}

// NotImplemented returns a 501 and is generally a placeholder for functionality which
// MAY be added at some point in the future but is not in any way a guarantee of such.
func (h *Handler) NotImplemented(w http.ResponseWriter, r *http.Request) {
	api.WriteError(w, acme.NotImplemented(nil).ToACME())
}

// GetAuthz ACME api for retrieving an Authz.
func (h *Handler) GetAuthz(w http.ResponseWriter, r *http.Request) {
	acc, err := acme.AccountFromContext(r.Context())
	if err != nil {
		api.WriteError(w, err)
		return
	}
	authz, err := h.Auth.GetAuthz(r.Context(), acc.GetID(), chi.URLParam(r, "authzID"))
	if err != nil {
		api.WriteError(w, err)
		return
	}

	w.Header().Set("Location", h.Auth.GetLink(r.Context(), acme.AuthzLink, true, authz.GetID()))
	api.JSON(w, authz)
}

// GetChallenge ACME api for retrieving a Challenge.
func (h *Handler) GetChallenge(w http.ResponseWriter, r *http.Request) {
	acc, err := acme.AccountFromContext(r.Context())
	if err != nil {
		api.WriteError(w, err)
		return
	}
	// Just verify that the payload was set, since we're not strictly adhering
	// to ACME V2 spec for reasons specified below.
	_, err = payloadFromContext(r.Context())
	if err != nil {
		api.WriteError(w, err)
		return
	}

	// NOTE: We should be checking that the request is either a POST-as-GET, or
	// that the payload is an empty JSON block ({}). However, older ACME clients
	// still send a vestigial body (rather than an empty JSON block) and
	// strict enforcement would render these clients broken. For the time being
	// we'll just ignore the body.
	var (
		ch   *acme.Challenge
		chID = chi.URLParam(r, "chID")
	)
	ch, err = h.Auth.ValidateChallenge(r.Context(), acc.GetID(), chID, acc.GetKey())
	if err != nil {
		api.WriteError(w, err)
		return
	}

	w.Header().Add("Link", link(h.Auth.GetLink(r.Context(), acme.AuthzLink, true, ch.GetAuthzID()), "up"))
	w.Header().Set("Location", h.Auth.GetLink(r.Context(), acme.ChallengeLink, true, ch.GetID()))
	api.JSON(w, ch)
}

// GetCertificate ACME api for retrieving a Certificate.
func (h *Handler) GetCertificate(w http.ResponseWriter, r *http.Request) {
	acc, err := acme.AccountFromContext(r.Context())
	if err != nil {
		api.WriteError(w, err)
		return
	}
	certID := chi.URLParam(r, "certID")
	certBytes, err := h.Auth.GetCertificate(acc.GetID(), certID)
	if err != nil {
		api.WriteError(w, err)
		return
	}

	block, _ := pem.Decode(certBytes)
	if block == nil {
		api.WriteError(w, acme.ServerInternalErr(errors.New("failed to decode any certificates from generated certBytes")))
		return
	}
	cert, err := x509.ParseCertificate(block.Bytes)
	if err != nil {
		api.WriteError(w, acme.Wrap(err, "failed to parse generated leaf certificate"))
		return
	}

	api.LogCertificate(w, cert)
	w.Header().Set("Content-Type", "application/pem-certificate-chain; charset=utf-8")
	w.Write(certBytes)
}