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()

	resp := &versionResponse{}
	if web.conf.disableUpdate {
		resp.Disabled = true
		aghhttp.WriteJSONResponseOK(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,
				web.logger,
				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, web.logger, r, w, http.StatusBadGateway, "%s", err)

		return
	}

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

		return
	}

	aghhttp.WriteJSONResponseOK(w, r, resp)
}

// requestVersionInfo sets the VersionInfo field of resp if it can reach the
// update server.
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
		}

		var terr temporaryError
		if errors.As(err, &terr) && terr.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 {
		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 finishUpdate(
		context.Background(),
		web.logger,
		web.cmdCons,
		execPath,
		web.conf.runningAsService,
	)
}

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

// 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.config()) ||
		config.HTTPConfig.Address.Port() < 1024 ||
		config.DNS.Port < 1024 {
		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.
func tlsConfUsesPrivilegedPorts(c *tlsConfigSettings) (ok bool) {
	return c.Enabled && (c.PortHTTPS < 1024 || c.PortDNSOverTLS < 1024 || c.PortDNSOverQUIC < 1024)
}

// finishUpdate completes an update procedure.  It is intended to be used as a
// goroutine.  l and cmdCons must not be nil.
func finishUpdate(
	ctx context.Context,
	l *slog.Logger,
	cmdCons executil.CommandConstructor,
	execPath string,
	runningAsService bool,
) {
	defer slogutil.RecoverAndExit(ctx, l, osutil.ExitCodeFailure)

	l.InfoContext(ctx, "stopping all tasks")

	cleanup(ctx)
	cleanupAlways()

	var err error
	if runtime.GOOS == "windows" {
		if 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.
			var cmd executil.Command
			cmd, err = cmdCons.New(ctx, &executil.CommandConfig{
				Path: "cmd",
				Args: []string{"/c", "net stop AdGuardHome & net start AdGuardHome"},
			})
			if err != nil {
				panic(fmt.Errorf("constructing cmd: %w", err))
			}

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

			os.Exit(osutil.ExitCodeSuccess)
		}

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

		var cmd executil.Command
		cmd, err = cmdCons.New(ctx, &executil.CommandConfig{
			Path:   execPath,
			Args:   os.Args[1:],
			Stdin:  os.Stdin,
			Stdout: os.Stdout,
			Stderr: os.Stderr,
		})
		if err != nil {
			panic(fmt.Errorf("constructing cmd: %w", err))
		}

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

		os.Exit(osutil.ExitCodeSuccess)
	}

	l.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))
	}
}
