// Copyright 2025 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.

package util

import (
	"path/filepath"
	"strings"
	"time"

	"github.com/pingcap/log"
	"github.com/pingcap/ticdc/pkg/errors"
	"github.com/pingcap/tidb/pkg/types"
	"github.com/pingcap/tidb/pkg/util/timeutil"
	"go.uber.org/zap"
)

// GetTimezone returns the timezone specified by the name
func GetTimezone(name string) (tz *time.Location, err error) {
	switch strings.ToLower(name) {
	case "", "system", "local":
		tz, err = GetLocalTimezone()
		err = errors.WrapError(errors.ErrLoadTimezone, err)
		if err == nil {
			log.Info("Use the timezone of the TiCDC server machine",
				zap.String("timezoneName", name),
				zap.String("timezone", tz.String()))
		}
	default:
		tz, err = time.LoadLocation(name)
		err = errors.WrapError(errors.ErrLoadTimezone, err)
		if err == nil {
			log.Info("Load the timezone specified by the user",
				zap.String("timezoneName", name),
				zap.String("timezone", tz.String()))
		}
	}
	return
}

// GetTimezoneFromZonefile read the timezone from file
func GetTimezoneFromZonefile(zonefile string) (tz *time.Location, err error) {
	// the linked path of `/etc/localtime` sample:
	// MacOS: /var/db/timezone/zoneinfo/Asia/Shanghai
	// Linux: /usr/share/zoneinfo/Asia/Shanghai
	region := filepath.Base(filepath.Dir(zonefile))
	zone := filepath.Base(zonefile)
	var tzName string
	if region == "zoneinfo" {
		tzName = zone
	} else {
		tzName = filepath.Join(region, zone)
	}
	tz, err = time.LoadLocation(tzName)
	err = errors.WrapError(errors.ErrLoadTimezone, err)
	return
}

// GetLocalTimezone returns the timezone in local system
func GetLocalTimezone() (*time.Location, error) {
	if time.Local.String() != "Local" {
		return time.Local, nil
	}
	str := timeutil.InferSystemTZ()
	return GetTimezoneFromZonefile(str)
}

// GetTimeZoneName returns the timezone name in a time.Location.
func GetTimeZoneName(tz *time.Location) string {
	if tz == nil {
		return ""
	}
	return tz.String()
}

// ConvertTimezone converts the timestamp to the specified timezone
func ConvertTimezone(timestamp string, location string) (string, error) {
	t, err := types.ParseTimestamp(types.StrictContext, timestamp)
	if err != nil {
		return "", err
	}

	var tz *time.Location
	switch strings.ToLower(location) {
	case "", "system", "local":
		tz, err = GetLocalTimezone()
	default:
		tz, err = time.LoadLocation(location)
	}
	if err != nil {
		log.Info("cannot load timezone location",
			zap.String("location", location), zap.Error(err))
		return "", err
	}

	err = t.ConvertTimeZone(tz, time.UTC)
	if err != nil {
		return "", err
	}

	return t.String(), nil
}