package main

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"github.com/btcsuite/btclog"
	"github.com/jrick/logrotate/rotator"
	"github.com/lightninglabs/loop"
	"github.com/lightninglabs/loop/lndclient"
	"github.com/lightningnetwork/lnd/build"
)

// Loggers per subsystem.  A single backend logger is created and all subsystem
// loggers created from it will write to the backend.  When adding new
// subsystems, add the subsystem logger variable here and to the
// subsystemLoggers map.
//
// Loggers can not be used before the log rotator has been initialized with a
// log file.  This must be performed early during application startup by
// calling initLogRotator.
var (
	logWriter = &build.LogWriter{}

	// backendLog is the logging backend used to create all subsystem
	// loggers.  The backend must not be used before the log rotator has
	// been initialized, or data races and/or nil pointer dereferences will
	// occur.
	backendLog = btclog.NewBackend(logWriter)

	// logRotator is one of the logging outputs.  It should be closed on
	// application shutdown.
	logRotator *rotator.Rotator

	loopdLog     = build.NewSubLogger("LOOPD", backendLog.Logger)
	loopLog      = build.NewSubLogger("LOOP", backendLog.Logger)
	lndClientLog = build.NewSubLogger("LNDC", backendLog.Logger)
)

func init() {
	loop.UseLogger(loopLog)
	lndclient.UseLogger(lndClientLog)
}

// initLogRotator initializes the logging rotator to write logs to logFile and
// create roll files in the same directory.  It must be called before the
// package-global log rotator variables are used.
func initLogRotator(logFile string, maxLogFileSize int, maxLogFiles int) {
	logDir, _ := filepath.Split(logFile)
	err := os.MkdirAll(logDir, 0700)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to create log directory: %v\n", err)
		os.Exit(1)
	}
	r, err := rotator.New(
		logFile, int64(maxLogFileSize*1024), false, maxLogFiles,
	)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to create file rotator: %v\n", err)
		os.Exit(1)
	}

	pr, pw := io.Pipe()
	go r.Run(pr)

	logWriter.RotatorPipe = pw
	logRotator = r
}

// subsystemLoggers maps each subsystem identifier to its associated logger.
var subsystemLoggers = map[string]btclog.Logger{
	"LOOPD": loopdLog,
	"LOOP":  loopLog,
	"LNDC":  lndClientLog,
}

// setLogLevel sets the logging level for provided subsystem.  Invalid
// subsystems are ignored.  Uninitialized subsystems are dynamically created as
// needed.
func setLogLevel(subsystemID string, logLevel string) {
	// Ignore invalid subsystems.
	logger, ok := subsystemLoggers[subsystemID]
	if !ok {
		return
	}

	// Defaults to info if the log level is invalid.
	level, _ := btclog.LevelFromString(logLevel)
	logger.SetLevel(level)
}

// setLogLevels sets the log level for all subsystem loggers to the passed
// level. It also dynamically creates the subsystem loggers as needed, so it
// can be used to initialize the logging system.
func setLogLevels(logLevel string) {
	// Configure all sub-systems with the new logging level.  Dynamically
	// create loggers as needed.
	for subsystemID := range subsystemLoggers {
		setLogLevel(subsystemID, logLevel)
	}
}

// logClosure is used to provide a closure over expensive logging operations so
// don't have to be performed when the logging level doesn't warrant it.
type logClosure func() string

// String invokes the underlying function and returns the result.
func (c logClosure) String() string {
	return c()
}

// newLogClosure returns a new closure over a function that returns a string
// which itself provides a Stringer interface so that it can be used with the
// logging system.
func newLogClosure(c func() string) logClosure {
	return logClosure(c)
}

// parseAndSetDebugLevels attempts to parse the specified debug level and set
// the levels accordingly. An appropriate error is returned if anything is
// invalid.
func parseAndSetDebugLevels(debugLevel string) error {
	// When the specified string doesn't have any delimiters, treat it as
	// the log level for all subsystems.
	if !strings.Contains(debugLevel, ",") && !strings.Contains(debugLevel, "=") {
		// Validate debug log level.
		if !validLogLevel(debugLevel) {
			str := "The specified debug level [%v] is invalid"
			return fmt.Errorf(str, debugLevel)
		}

		// Change the logging level for all subsystems.
		setLogLevels(debugLevel)

		return nil
	}

	// Split the specified string into subsystem/level pairs while detecting
	// issues and update the log levels accordingly.
	for _, logLevelPair := range strings.Split(debugLevel, ",") {
		if !strings.Contains(logLevelPair, "=") {
			str := "The specified debug level contains an invalid " +
				"subsystem/level pair [%v]"
			return fmt.Errorf(str, logLevelPair)
		}

		// Extract the specified subsystem and log level.
		fields := strings.Split(logLevelPair, "=")
		subsysID, logLevel := fields[0], fields[1]

		// Validate subsystem.
		if _, exists := subsystemLoggers[subsysID]; !exists {
			str := "The specified subsystem [%v] is invalid -- " +
				"supported subsystems %v"
			return fmt.Errorf(str, subsysID, supportedSubsystems())
		}

		// Validate log level.
		if !validLogLevel(logLevel) {
			str := "The specified debug level [%v] is invalid"
			return fmt.Errorf(str, logLevel)
		}

		setLogLevel(subsysID, logLevel)
	}

	return nil
}

// validLogLevel returns whether or not logLevel is a valid debug log level.
func validLogLevel(logLevel string) bool {
	switch logLevel {
	case "trace":
		fallthrough
	case "debug":
		fallthrough
	case "info":
		fallthrough
	case "warn":
		fallthrough
	case "error":
		fallthrough
	case "critical":
		fallthrough
	case "off":
		return true
	}
	return false
}

// supportedSubsystems returns a sorted slice of the supported subsystems for
// logging purposes.
func supportedSubsystems() []string {
	// Convert the subsystemLoggers map keys to a slice.
	subsystems := make([]string, 0, len(subsystemLoggers))
	for subsysID := range subsystemLoggers {
		subsystems = append(subsystems, subsysID)
	}

	// Sort the subsystems for stable display.
	sort.Strings(subsystems)
	return subsystems
}