package hscontrol

import (
	"context"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/juanfont/headscale/hscontrol/types"
	"github.com/juanfont/headscale/hscontrol/types/change"
	"github.com/rs/zerolog/log"
	"gorm.io/gorm"
	"tailscale.com/tailcfg"
	"tailscale.com/types/key"
	"tailscale.com/types/ptr"
)

type AuthProvider interface {
	RegisterHandler(http.ResponseWriter, *http.Request)
	AuthURL(types.RegistrationID) string
}

func (h *Headscale) handleRegister(
	ctx context.Context,
	regReq tailcfg.RegisterRequest,
	machineKey key.MachinePublic,
) (*tailcfg.RegisterResponse, error) {
	node, ok := h.state.GetNodeByNodeKey(regReq.NodeKey)

	if ok {
		resp, err := h.handleExistingNode(node.AsStruct(), regReq, machineKey)
		if err != nil {
			return nil, fmt.Errorf("handling existing node: %w", err)
		}

		return resp, nil
	}

	if regReq.Followup != "" {
		return h.waitForFollowup(ctx, regReq)
	}

	if regReq.Auth != nil && regReq.Auth.AuthKey != "" {
		resp, err := h.handleRegisterWithAuthKey(regReq, machineKey)
		if err != nil {
			// Preserve HTTPError types so they can be handled properly by the HTTP layer
			var httpErr HTTPError
			if errors.As(err, &httpErr) {
				return nil, httpErr
			}

			return nil, fmt.Errorf("handling register with auth key: %w", err)
		}

		return resp, nil
	}

	resp, err := h.handleRegisterInteractive(regReq, machineKey)
	if err != nil {
		return nil, fmt.Errorf("handling register interactive: %w", err)
	}

	return resp, nil
}

func (h *Headscale) handleExistingNode(
	node *types.Node,
	regReq tailcfg.RegisterRequest,
	machineKey key.MachinePublic,
) (*tailcfg.RegisterResponse, error) {
	if node.MachineKey != machineKey {
		return nil, NewHTTPError(http.StatusUnauthorized, "node exist with different machine key", nil)
	}

	expired := node.IsExpired()

	// If the node is expired and this is not a re-authentication attempt,
	// force the client to re-authenticate
	if expired && regReq.Auth == nil {
		return &tailcfg.RegisterResponse{
			NodeKeyExpired:    true,
			MachineAuthorized: false,
			AuthURL:           "", // Client will need to re-authenticate
		}, nil
	}

	if !expired && !regReq.Expiry.IsZero() {
		requestExpiry := regReq.Expiry

		// The client is trying to extend their key, this is not allowed.
		if requestExpiry.After(time.Now()) {
			return nil, NewHTTPError(http.StatusBadRequest, "extending key is not allowed", nil)
		}

		// If the request expiry is in the past, we consider it a logout.
		if requestExpiry.Before(time.Now()) {
			if node.IsEphemeral() {
				c, err := h.state.DeleteNode(node.View())
				if err != nil {
					return nil, fmt.Errorf("deleting ephemeral node: %w", err)
				}

				h.Change(c)

				return nil, nil
			}
		}

		updatedNode, c, err := h.state.SetNodeExpiry(node.ID, requestExpiry)
		if err != nil {
			return nil, fmt.Errorf("setting node expiry: %w", err)
		}

		h.Change(c)

		// CRITICAL: Use the updated node view for the response
		// The original node object has stale expiry information
		node = updatedNode.AsStruct()
	}

	return nodeToRegisterResponse(node), nil
}

func nodeToRegisterResponse(node *types.Node) *tailcfg.RegisterResponse {
	return &tailcfg.RegisterResponse{
		// TODO(kradalby): Only send for user-owned nodes
		// and not tagged nodes when tags is working.
		User:           *node.User.TailscaleUser(),
		Login:          *node.User.TailscaleLogin(),
		NodeKeyExpired: node.IsExpired(),

		// Headscale does not implement the concept of machine authorization
		// so we always return true here.
		// Revisit this if #2176 gets implemented.
		MachineAuthorized: true,
	}
}

func (h *Headscale) waitForFollowup(
	ctx context.Context,
	regReq tailcfg.RegisterRequest,
) (*tailcfg.RegisterResponse, error) {
	fu, err := url.Parse(regReq.Followup)
	if err != nil {
		return nil, NewHTTPError(http.StatusUnauthorized, "invalid followup URL", err)
	}

	followupReg, err := types.RegistrationIDFromString(strings.ReplaceAll(fu.Path, "/register/", ""))
	if err != nil {
		return nil, NewHTTPError(http.StatusUnauthorized, "invalid registration ID", err)
	}

	if reg, ok := h.state.GetRegistrationCacheEntry(followupReg); ok {
		select {
		case <-ctx.Done():
			return nil, NewHTTPError(http.StatusUnauthorized, "registration timed out", err)
		case node := <-reg.Registered:
			if node == nil {
				return nil, NewHTTPError(http.StatusUnauthorized, "node not found", nil)
			}
			return nodeToRegisterResponse(node), nil
		}
	}

	return nil, NewHTTPError(http.StatusNotFound, "followup registration not found", nil)
}

func (h *Headscale) handleRegisterWithAuthKey(
	regReq tailcfg.RegisterRequest,
	machineKey key.MachinePublic,
) (*tailcfg.RegisterResponse, error) {
	node, changed, err := h.state.HandleNodeFromPreAuthKey(
		regReq,
		machineKey,
	)
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, NewHTTPError(http.StatusUnauthorized, "invalid pre auth key", nil)
		}
		var perr types.PAKError
		if errors.As(err, &perr) {
			return nil, NewHTTPError(http.StatusUnauthorized, perr.Error(), nil)
		}

		return nil, err
	}

	// If node is not valid, it means an ephemeral node was deleted during logout
	if !node.Valid() {
		h.Change(changed)
		return nil, nil
	}

	// This is a bit of a back and forth, but we have a bit of a chicken and egg
	// dependency here.
	// Because the way the policy manager works, we need to have the node
	// in the database, then add it to the policy manager and then we can
	// approve the route. This means we get this dance where the node is
	// first added to the database, then we add it to the policy manager via
	// nodesChangedHook and then we can auto approve the routes.
	// As that only approves the struct object, we need to save it again and
	// ensure we send an update.
	// This works, but might be another good candidate for doing some sort of
	// eventbus.
	// TODO(kradalby): This needs to be ran as part of the batcher maybe?
	// now since we dont update the node/pol here anymore
	routeChange := h.state.AutoApproveRoutes(node)

	if _, _, err := h.state.SaveNode(node); err != nil {
		return nil, fmt.Errorf("saving auto approved routes to node: %w", err)
	}

	if routeChange && changed.Empty() {
		changed = change.NodeAdded(node.ID())
	}
	h.Change(changed)

	// TODO(kradalby): I think this is covered above, but we need to validate that.
	// // If policy changed due to node registration, send a separate policy change
	// if policyChanged {
	// 	policyChange := change.PolicyChange()
	// 	h.Change(policyChange)
	// }

	user := node.User()

	return &tailcfg.RegisterResponse{
		MachineAuthorized: true,
		NodeKeyExpired:    node.IsExpired(),
		User:              *user.TailscaleUser(),
		Login:             *user.TailscaleLogin(),
	}, nil
}

func (h *Headscale) handleRegisterInteractive(
	regReq tailcfg.RegisterRequest,
	machineKey key.MachinePublic,
) (*tailcfg.RegisterResponse, error) {
	registrationId, err := types.NewRegistrationID()
	if err != nil {
		return nil, fmt.Errorf("generating registration ID: %w", err)
	}

	nodeToRegister := types.RegisterNode{
		Node: types.Node{
			Hostname:   regReq.Hostinfo.Hostname,
			MachineKey: machineKey,
			NodeKey:    regReq.NodeKey,
			Hostinfo:   regReq.Hostinfo,
			LastSeen:   ptr.To(time.Now()),
		},
		Registered: make(chan *types.Node),
	}

	if !regReq.Expiry.IsZero() {
		nodeToRegister.Node.Expiry = &regReq.Expiry
	}

	h.state.SetRegistrationCacheEntry(
		registrationId,
		nodeToRegister,
	)

	log.Info().Msgf("Starting node registration using key: %s", registrationId)

	return &tailcfg.RegisterResponse{
		AuthURL: h.authProvider.AuthURL(registrationId),
	}, nil
}