package api

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/netip"
	"os/exec"
	"time"

	"github.com/awnumar/memguard"
	"github.com/rs/zerolog"
	"github.com/txn2/txeh"
	"golang.org/x/sys/unix"

	"git.omukk.dev/wrenn/sandbox/envd/internal/host"
	"git.omukk.dev/wrenn/sandbox/envd/internal/logs"
	"git.omukk.dev/wrenn/sandbox/envd/internal/shared/keys"
)

var (
	ErrAccessTokenMismatch           = errors.New("access token validation failed")
	ErrAccessTokenResetNotAuthorized = errors.New("access token reset not authorized")
)

const (
	maxTimeInPast   = 50 * time.Millisecond
	maxTimeInFuture = 5 * time.Second
)

// validateInitAccessToken validates the access token for /init requests.
// Token is valid if it matches the existing token OR the MMDS hash.
// If neither exists, first-time setup is allowed.
func (a *API) validateInitAccessToken(ctx context.Context, requestToken *SecureToken) error {
	requestTokenSet := requestToken.IsSet()

	// Fast path: token matches existing
	if a.accessToken.IsSet() && requestTokenSet && a.accessToken.EqualsSecure(requestToken) {
		return nil
	}

	// Check MMDS only if token didn't match existing
	matchesMMDS, mmdsExists := a.checkMMDSHash(ctx, requestToken)

	switch {
	case matchesMMDS:
		return nil
	case !a.accessToken.IsSet() && !mmdsExists:
		return nil // first-time setup
	case !requestTokenSet:
		return ErrAccessTokenResetNotAuthorized
	default:
		return ErrAccessTokenMismatch
	}
}

// checkMMDSHash checks if the request token matches the MMDS hash.
// Returns (matches, mmdsExists).
//
// The MMDS hash is set by the orchestrator during Resume:
//   - hash(token): requires this specific token
//   - hash(""): explicitly allows nil token (token reset authorized)
//   - "": MMDS not properly configured, no authorization granted
func (a *API) checkMMDSHash(ctx context.Context, requestToken *SecureToken) (bool, bool) {
	if a.isNotFC {
		return false, false
	}

	mmdsHash, err := a.mmdsClient.GetAccessTokenHash(ctx)
	if err != nil {
		return false, false
	}

	if mmdsHash == "" {
		return false, false
	}

	if !requestToken.IsSet() {
		return mmdsHash == keys.HashAccessToken(""), true
	}

	tokenBytes, err := requestToken.Bytes()
	if err != nil {
		return false, true
	}
	defer memguard.WipeBytes(tokenBytes)

	return keys.HashAccessTokenBytes(tokenBytes) == mmdsHash, true
}

func (a *API) PostInit(w http.ResponseWriter, r *http.Request) {
	defer r.Body.Close()

	ctx := r.Context()

	operationID := logs.AssignOperationID()
	logger := a.logger.With().Str(string(logs.OperationIDKey), operationID).Logger()

	if r.Body != nil {
		// Read raw body so we can wipe it after parsing
		body, err := io.ReadAll(r.Body)
		// Ensure body is wiped after we're done
		defer memguard.WipeBytes(body)
		if err != nil {
			logger.Error().Msgf("Failed to read request body: %v", err)
			w.WriteHeader(http.StatusBadRequest)

			return
		}

		var initRequest PostInitJSONBody
		if len(body) > 0 {
			err = json.Unmarshal(body, &initRequest)
			if err != nil {
				logger.Error().Msgf("Failed to decode request: %v", err)
				w.WriteHeader(http.StatusBadRequest)

				return
			}
		}

		// Ensure request token is destroyed if not transferred via TakeFrom.
		// This handles: validation failures, timestamp-based skips, and any early returns.
		// Safe because Destroy() is nil-safe and TakeFrom clears the source.
		defer initRequest.AccessToken.Destroy()

		a.initLock.Lock()
		defer a.initLock.Unlock()

		// Update data only if the request is newer or if there's no timestamp at all
		if initRequest.Timestamp == nil || a.lastSetTime.SetToGreater(initRequest.Timestamp.UnixNano()) {
			err = a.SetData(ctx, logger, initRequest)
			if err != nil {
				switch {
				case errors.Is(err, ErrAccessTokenMismatch), errors.Is(err, ErrAccessTokenResetNotAuthorized):
					w.WriteHeader(http.StatusUnauthorized)
				default:
					logger.Error().Msgf("Failed to set data: %v", err)
					w.WriteHeader(http.StatusBadRequest)
				}
				w.Write([]byte(err.Error()))

				return
			}
		}
	}

	go func() { //nolint:contextcheck // TODO: fix this later
		ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
		defer cancel()
		host.PollForMMDSOpts(ctx, a.mmdsChan, a.defaults.EnvVars)
	}()

	w.Header().Set("Cache-Control", "no-store")
	w.Header().Set("Content-Type", "")

	w.WriteHeader(http.StatusNoContent)
}

func (a *API) SetData(ctx context.Context, logger zerolog.Logger, data PostInitJSONBody) error {
	// Validate access token before proceeding with any action
	// The request must provide a token that is either:
	// 1. Matches the existing access token (if set), OR
	// 2. Matches the MMDS hash (for token change during resume)
	if err := a.validateInitAccessToken(ctx, data.AccessToken); err != nil {
		return err
	}

	if data.Timestamp != nil {
		// Check if current time differs significantly from the received timestamp
		if shouldSetSystemTime(time.Now(), *data.Timestamp) {
			logger.Debug().Msgf("Setting sandbox start time to: %v", *data.Timestamp)
			ts := unix.NsecToTimespec(data.Timestamp.UnixNano())
			err := unix.ClockSettime(unix.CLOCK_REALTIME, &ts)
			if err != nil {
				logger.Error().Msgf("Failed to set system time: %v", err)
			}
		} else {
			logger.Debug().Msgf("Current time is within acceptable range of timestamp %v, not setting system time", *data.Timestamp)
		}
	}

	if data.EnvVars != nil {
		logger.Debug().Msg(fmt.Sprintf("Setting %d env vars", len(*data.EnvVars)))

		for key, value := range *data.EnvVars {
			logger.Debug().Msgf("Setting env var for %s", key)
			a.defaults.EnvVars.Store(key, value)
		}
	}

	if data.AccessToken.IsSet() {
		logger.Debug().Msg("Setting access token")
		a.accessToken.TakeFrom(data.AccessToken)
	} else if a.accessToken.IsSet() {
		logger.Debug().Msg("Clearing access token")
		a.accessToken.Destroy()
	}

	if data.HyperloopIP != nil {
		go a.SetupHyperloop(*data.HyperloopIP)
	}

	if data.DefaultUser != nil && *data.DefaultUser != "" {
		logger.Debug().Msgf("Setting default user to: %s", *data.DefaultUser)
		a.defaults.User = *data.DefaultUser
	}

	if data.DefaultWorkdir != nil && *data.DefaultWorkdir != "" {
		logger.Debug().Msgf("Setting default workdir to: %s", *data.DefaultWorkdir)
		a.defaults.Workdir = data.DefaultWorkdir
	}

	if data.VolumeMounts != nil {
		for _, volume := range *data.VolumeMounts {
			logger.Debug().Msgf("Mounting %s at %q", volume.NfsTarget, volume.Path)

			go a.setupNfs(context.WithoutCancel(ctx), volume.NfsTarget, volume.Path)
		}
	}

	return nil
}

func (a *API) setupNfs(ctx context.Context, nfsTarget, path string) {
	commands := [][]string{
		{"mkdir", "-p", path},
		{"mount", "-v", "-t", "nfs", "-o", "mountproto=tcp,mountport=2049,proto=tcp,port=2049,nfsvers=3,noacl", nfsTarget, path},
	}

	for _, command := range commands {
		data, err := exec.CommandContext(ctx, command[0], command[1:]...).CombinedOutput()

		logger := a.getLogger(err)

		logger.
			Strs("command", command).
			Str("output", string(data)).
			Msg("Mount NFS")

		if err != nil {
			return
		}
	}
}

func (a *API) SetupHyperloop(address string) {
	a.hyperloopLock.Lock()
	defer a.hyperloopLock.Unlock()

	if err := rewriteHostsFile(address, "/etc/hosts"); err != nil {
		a.logger.Error().Err(err).Msg("failed to modify hosts file")
	} else {
		a.defaults.EnvVars.Store("WRENN_EVENTS_ADDRESS", fmt.Sprintf("http://%s", address))
	}
}

const eventsHost = "events.wrenn.local"

func rewriteHostsFile(address, path string) error {
	hosts, err := txeh.NewHosts(&txeh.HostsConfig{
		ReadFilePath:  path,
		WriteFilePath: path,
	})
	if err != nil {
		return fmt.Errorf("failed to create hosts: %w", err)
	}

	// Update /etc/hosts to point events.wrenn.local to the hyperloop IP
	// This will remove any existing entries for events.wrenn.local first
	ipFamily, err := getIPFamily(address)
	if err != nil {
		return fmt.Errorf("failed to get ip family: %w", err)
	}

	if ok, current, _ := hosts.HostAddressLookup(eventsHost, ipFamily); ok && current == address {
		return nil // nothing to be done
	}

	hosts.AddHost(address, eventsHost)

	return hosts.Save()
}

var (
	ErrInvalidAddress       = errors.New("invalid IP address")
	ErrUnknownAddressFormat = errors.New("unknown IP address format")
)

func getIPFamily(address string) (txeh.IPFamily, error) {
	addressIP, err := netip.ParseAddr(address)
	if err != nil {
		return txeh.IPFamilyV4, fmt.Errorf("failed to parse IP address: %w", err)
	}

	switch {
	case addressIP.Is4():
		return txeh.IPFamilyV4, nil
	case addressIP.Is6():
		return txeh.IPFamilyV6, nil
	default:
		return txeh.IPFamilyV4, fmt.Errorf("%w: %s", ErrUnknownAddressFormat, address)
	}
}

// shouldSetSystemTime returns true if the current time differs significantly from the received timestamp,
// indicating the system clock should be adjusted. Returns true when the sandboxTime is more than
// maxTimeInPast before the hostTime or more than maxTimeInFuture after the hostTime.
func shouldSetSystemTime(sandboxTime, hostTime time.Time) bool {
	return sandboxTime.Before(hostTime.Add(-maxTimeInPast)) || sandboxTime.After(hostTime.Add(maxTimeInFuture))
}