package home

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"net/http"
	"os"
	"runtime"
	"syscall"
	"time"

	"github.com/AdguardTeam/AdGuardHome/internal/aghalg"
	"github.com/AdguardTeam/AdGuardHome/internal/aghhttp"
	"github.com/AdguardTeam/AdGuardHome/internal/aghnet"
	"github.com/AdguardTeam/AdGuardHome/internal/updater"
	"github.com/AdguardTeam/golibs/errors"
	"github.com/AdguardTeam/golibs/logutil/slogutil"
	"github.com/AdguardTeam/golibs/osutil"
	"github.com/AdguardTeam/golibs/osutil/executil"
)

// temporaryError is the interface for temporary errors from the Go standard
// library.
type temporaryError interface {
	error
	Temporary() (ok bool)
}

// handleVersionJSON is the handler for the POST /control/version.json HTTP API.
//
// TODO(a.garipov): Find out if this API used with a GET method by anyone.
func (web *webAPI) handleVersionJSON(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	l := web.logger

	resp := &versionResponse{}
	if web.conf.disableUpdate {
		resp.Disabled = true
		aghhttp.WriteJSONResponseOK(ctx, l, w, r, resp)

		return
	}

	req := &struct {
		Recheck bool `json:"recheck_now"`
	}{}

	var err error
	if r.ContentLength != 0 {
		err = json.NewDecoder(r.Body).Decode(req)
		if err != nil {
			aghhttp.ErrorAndLog(ctx, l, r, w, http.StatusBadRequest, "parsing request: %s", err)

			return
		}
	}

	err = web.requestVersionInfo(ctx, resp, req.Recheck)
	if err != nil {
		// Don't wrap the error, because it's informative enough as is.
		aghhttp.ErrorAndLog(ctx, l, r, w, http.StatusBadGateway, "%s", err)

		return
	}

	err = resp.setAllowedToAutoUpdate(ctx, l, web.tlsManager)
	if err != nil {
		// Don't wrap the error, because it's informative enough as is.
		aghhttp.ErrorAndLog(ctx, l, r, w, http.StatusInternalServerError, "%s", err)

		return
	}

	aghhttp.WriteJSONResponseOK(ctx, l, w, r, resp)
}

// requestVersionInfo sets the VersionInfo field of resp if it can reach the
// update server.  resp must not be nil.
func (web *webAPI) requestVersionInfo(
	ctx context.Context,
	resp *versionResponse,
	recheck bool,
) (err error) {
	updater := web.conf.updater
	for range 3 {
		resp.VersionInfo, err = updater.VersionInfo(ctx, recheck)
		if err == nil {
			return nil
		}

		if tmpErr, ok := errors.AsType[temporaryError](err); ok && tmpErr.Temporary() {
			// Temporary network error.  This case may happen while we're
			// restarting our DNS server.  Log and sleep for some time.
			//
			// See https://github.com/AdguardTeam/AdGuardHome/issues/934.
			const sleepTime = 2 * time.Second

			err = fmt.Errorf("temp net error: %w; sleeping for %s and retrying", err, sleepTime)
			web.logger.InfoContext(ctx, "updating version info", slogutil.KeyError, err)

			time.Sleep(sleepTime)

			continue
		}

		break
	}

	if err != nil {
		web.logger.WarnContext(ctx, "getting version info", slogutil.KeyError, err)

		return fmt.Errorf("getting version info: %w", err)
	}

	return nil
}

// handleUpdate performs an update to the latest available version procedure.
func (web *webAPI) handleUpdate(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	l := web.logger

	updater := web.conf.updater
	if updater.NewVersion() == "" {
		aghhttp.ErrorAndLog(
			ctx,
			l,
			r,
			w,
			http.StatusBadRequest,
			"update request isn't allowed now",
		)

		return
	}

	// Retain the current absolute path of the executable, since the updater is
	// likely to change the position current one to the backup directory.
	//
	// See https://github.com/AdguardTeam/AdGuardHome/issues/4735.
	execPath, err := os.Executable()
	if err != nil {
		aghhttp.ErrorAndLog(ctx, l, r, w, http.StatusInternalServerError, "getting path: %s", err)

		return
	}

	err = updater.Update(ctx, false)
	if err != nil {
		aghhttp.ErrorAndLog(ctx, l, r, w, http.StatusInternalServerError, "%s", err)

		return
	}

	aghhttp.OK(ctx, web.logger, w)

	rc := http.NewResponseController(w)
	err = rc.Flush()
	if err != nil {
		web.logger.WarnContext(ctx, "flushing response", slogutil.KeyError, err)
	}

	// The background context is used because the underlying functions wrap it
	// with timeout and shut down the server, which handles current request.  It
	// also should be done in a separate goroutine for the same reason.
	go web.finishUpdate(context.Background(), execPath)
}

// versionResponse is the response for /control/version.json endpoint.
type versionResponse struct {
	updater.VersionInfo
	Disabled bool `json:"disabled"`
}

// maxPrivilegedPort is the maximum port number.  This only applies to Unix, as
// on Windows, [aghnet.CanBindPrivilegedPorts] always returns `true`, `nil`.
const maxPrivilegedPort = 1024

// setAllowedToAutoUpdate sets CanAutoUpdate to true if AdGuard Home is actually
// allowed to perform an automatic update by the OS.  l and tlsMgr must not be
// nil.
func (vr *versionResponse) setAllowedToAutoUpdate(
	ctx context.Context,
	l *slog.Logger,
	tlsMgr *tlsManager,
) (err error) {
	if vr.CanAutoUpdate != aghalg.NBTrue {
		return nil
	}

	canUpdate := true
	if tlsConfUsesPrivilegedPorts(tlsMgr.extendedTLSConfig()) ||
		config.HTTPConfig.Address.Port() < maxPrivilegedPort ||
		config.DNS.Port < maxPrivilegedPort {
		canUpdate, err = aghnet.CanBindPrivilegedPorts(ctx, l)
		if err != nil {
			return fmt.Errorf("checking ability to bind privileged ports: %w", err)
		}
	}

	vr.CanAutoUpdate = aghalg.BoolToNullBool(canUpdate)

	return nil
}

// tlsConfUsesPrivilegedPorts returns true if the provided TLS configuration
// indicates that privileged ports are used.  c must be valid.
func tlsConfUsesPrivilegedPorts(c *tlsConfigSettings) (ok bool) {
	return c.Enabled && (c.PortHTTPS < maxPrivilegedPort ||
		c.PortDNSOverTLS < maxPrivilegedPort ||
		c.PortDNSOverQUIC < maxPrivilegedPort)
}

// finishUpdate completes an update procedure.  It is intended to be used as a
// goroutine.
func (web *webAPI) finishUpdate(
	ctx context.Context,
	execPath string,
) {
	defer slogutil.RecoverAndExit(ctx, web.logger, osutil.ExitCodeFailure)

	web.logger.InfoContext(ctx, "stopping all tasks")

	// Ignore the error because, according to the documentation, this method
	//  always returns nil error.
	err := web.Shutdown(ctx)
	if err != nil {
		// Should never happen.
		web.logger.WarnContext(ctx, "shutting down web", slogutil.KeyError, err)
	}

	cleanup(ctx, web.logger, web.hostsContainer)
	cleanupAlways(ctx, web.logger, web.pidFilePath)

	if runtime.GOOS == "windows" {
		web.finalizeWindowsUpdate(ctx, execPath)

		os.Exit(osutil.ExitCodeSuccess)
	}

	web.logger.InfoContext(ctx, "restarting", "exec_path", execPath, "args", os.Args[1:])
	err = syscall.Exec(execPath, os.Args, os.Environ())
	if err != nil {
		panic(fmt.Errorf("restarting: %w", err))
	}
}

// finalizeWindowsUpdate completes an update procedure on windows.
func (web *webAPI) finalizeWindowsUpdate(
	ctx context.Context,
	execPath string,
) {
	var commandConf *executil.CommandConfig

	if web.conf.runningAsService {
		// NOTE: We can't restart the service via "kardianos/service" package,
		// because it kills the process first we can't start a new instance,
		// because Windows doesn't allow it.
		//
		// TODO(a.garipov): Recheck the claim above.
		commandConf = &executil.CommandConfig{
			Path: "cmd",
			Args: []string{"/c", "net stop AdGuardHome & net start AdGuardHome"},
		}
	} else {
		commandConf = &executil.CommandConfig{
			Path:   execPath,
			Args:   os.Args[1:],
			Stdin:  os.Stdin,
			Stdout: os.Stdout,
			Stderr: os.Stderr,
		}
	}

	web.logger.InfoContext(ctx, "restarting", "exec_path", execPath, "args", os.Args[1:])

	var cmd executil.Command
	cmd, err := web.cmdCons.New(ctx, commandConf)
	if err != nil {
		panic(fmt.Errorf("constructing cmd: %w", err))
	}

	err = cmd.Start(ctx)
	if err != nil {
		panic(fmt.Errorf("restarting: %w", err))
	}
}
