// Package cli runs netwatch-server from its command line: the
// check-cidr and prepare-data-dir subcommands, which bin/entrypoint.sh
// runs before it starts the server, and, given no arguments, the
// server, with the fx wiring.
package cli

import (
	"context"
	"fmt"
	"io"
	"log/slog"
	"os"
	"os/user"

	"sneak.berlin/go/netwatch/internal/config"
	"sneak.berlin/go/netwatch/internal/globals"
	"sneak.berlin/go/netwatch/internal/handlers"
	"sneak.berlin/go/netwatch/internal/healthcheck"
	"sneak.berlin/go/netwatch/internal/logger"
	"sneak.berlin/go/netwatch/internal/middleware"
	"sneak.berlin/go/netwatch/internal/reportbuf"
	"sneak.berlin/go/netwatch/internal/server"

	"go.uber.org/dig"
	"go.uber.org/fx"
	"go.uber.org/fx/fxevent"
)

// usageExitCode is what Main returns for a command line it does not
// understand, the usual exit code for a usage error.
const usageExitCode = 2

// Main runs netwatch-server with args, its command line after the
// program's name, and returns the exit code. With no args, Main runs
// the server by calling serve with appname and version, the name and
// version the server logs and reports, and returns serve's exit code.
// With "check-cidr CIDR" or "prepare-data-dir DATA_DIR" it runs that
// subcommand, which writes its errors to stderr. Any other args get a
// one-line usage message on stderr and exit code 2. main passes
// os.Stderr and RunServer; the tests pass a buffer and a function of
// their own, so that no test starts the server.
func Main(
	stderr io.Writer,
	appname, version string,
	args []string,
	serve func(appname, version string) int,
) int {
	// "netwatch-server check-cidr CIDR" exits 1, with the error, if
	// this server would refuse CIDR in its TRUSTED_PROXIES.
	// bin/entrypoint.sh runs it on each entry it gives nginx.
	if len(args) == 2 && args[0] == "check-cidr" {
		return checkCIDR(stderr, args[1])
	}

	// "netwatch-server prepare-data-dir DATA_DIR" gets DATA_DIR ready
	// for the netwatch user, or exits 1 with the error; see
	// reportbuf.PrepareDataDir. bin/entrypoint.sh runs it as root
	// before it starts this server as that user.
	if len(args) == 2 && args[0] == "prepare-data-dir" {
		return prepareDataDir(stderr, "/data", args[1], "netwatch")
	}

	// Any other command line is refused, so that a mistyped one does
	// not start the server.
	if len(args) > 0 {
		_, _ = fmt.Fprintln(stderr,
			"usage: netwatch-server [check-cidr CIDR | prepare-data-dir DATA_DIR]")

		return usageExitCode
	}

	return serve(appname, version)
}

// checkCIDR returns 0 if the server would take cidr in its
// TRUSTED_PROXIES, and otherwise writes the error to stderr and
// returns 1.
func checkCIDR(stderr io.Writer, cidr string) int {
	_, err := middleware.ParseTrustedProxies([]string{cidr})
	if err != nil {
		_, _ = fmt.Fprintln(stderr, err)

		return 1
	}

	return 0
}

// prepareDataDir gets dataDir ready for the user named username with
// reportbuf.PrepareDataDir, volume being where the data volume is
// mounted, and returns 0. Otherwise it writes the error to stderr and
// returns 1.
func prepareDataDir(stderr io.Writer, volume, dataDir, username string) int {
	owner, err := user.Lookup(username)
	if err != nil {
		_, _ = fmt.Fprintln(stderr, err)

		return 1
	}

	err = reportbuf.PrepareDataDir(volume, dataDir, owner)
	if err != nil {
		_, _ = fmt.Fprintf(stderr, "DATA_DIR '%s': %v\n", dataDir, err)

		return 1
	}

	return 0
}

// RunServer runs the server until it is told to stop, with appname and
// version as the name and version it logs and reports, and returns the
// exit code. If the server fails to start, to listen or to stop, it
// returns 1. A failed start logs one line with the error's cause, such
// as the setting refused and why, as the server's last line.
func RunServer(appname, version string) int {
	globals.Appname = appname
	globals.Version = version

	var log *logger.Logger

	app := fx.New(
		// fx logs each step of starting and stopping, errors included,
		// at debug level through the server's own logger: they show
		// only with DEBUG set, and off a terminal they are JSON like
		// every other line.
		fx.WithLogger(func(log *logger.Logger) fxevent.Logger {
			fxLog := &fxevent.SlogLogger{Logger: log.Get()}
			fxLog.UseLogLevel(slog.LevelDebug)
			fxLog.UseErrorLevel(slog.LevelDebug)

			return fxLog
		}),
		fx.Provide(
			config.New,
			globals.New,
			handlers.New,
			healthcheck.New,
			logger.New,
			middleware.New,
			reportbuf.New,
			server.New,
		),
		// First, so that log is set for the error below even when a
		// setting stops the start.
		fx.Populate(&log),
		fx.Invoke(
			// Before the server, so that the name and version are
			// logged even when a setting stops the start.
			func(log *logger.Logger) { log.Identify() },
			func(*server.Server) {},
		),
	)

	startCtx, cancelStart := context.WithTimeout(
		context.Background(), app.StartTimeout())
	defer cancelStart()

	err := app.Start(startCtx)
	if err != nil {
		// fx wraps a constructor's error in its own text; the cause
		// alone names the setting. log is nil only if fx failed
		// before it built the logger.
		cause := dig.RootCause(err)
		if log == nil {
			_, _ = fmt.Fprintln(os.Stderr, cause)
		} else {
			log.Get().Error("cannot start", "error", cause)
		}

		return 1
	}

	// A signal, or the server asking to stop after a listen error.
	shutdown := <-app.Wait()

	stopCtx, cancelStop := context.WithTimeout(
		context.Background(), app.StopTimeout())
	defer cancelStop()

	err = app.Stop(stopCtx)
	if err != nil {
		log.Get().Error("cannot stop cleanly", "error", err)

		return 1
	}

	return shutdown.ExitCode
}