//
// DISCLAIMER
//
// Copyright 2016-2022 ArangoDB GmbH, Cologne, Germany
//
// 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Copyright holder is ArangoDB GmbH, Cologne, Germany
//

package internal

import (
	_ "embed"
	"encoding/base64"
	"fmt"
	"os"
	"path"
	"path/filepath"
	"sort"
	"strings"
	"text/template"
	"time"
)

//go:embed timezones.go.tmpl
var timezonesGoTemplate []byte

type Timezone struct {
	Name   string
	Offset int64
	Zone   string
	Parent string
}

type TimezoneData struct {
	Name string
	Data string
}

func RenderTimezones(root string) error {
	rootPath := path.Join(root, "pkg", "generated", "timezones")

	if _, err := os.Stat(rootPath); err != nil {
		if os.IsNotExist(err) {
			if err := os.MkdirAll(rootPath, 0755); err != nil {
				return err
			}
		} else {
			return err
		}
	}

	out, err := os.OpenFile(path.Join(rootPath, "timezones.go"), os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0644)
	if err != nil {
		return err
	}

	i, err := template.New("timezones").Parse(string(timezonesGoTemplate))
	if err != nil {
		return err
	}

	tzs, data := ListTimezones()

	if err := i.Execute(out, map[string]interface{}{
		"timezones":     tzs,
		"timezoneDatas": data,
	}); err != nil {
		return err
	}

	if err := out.Close(); err != nil {
		return err
	}

	return nil
}

func ListTimezones() ([]Timezone, []TimezoneData) {
	var zoneDirs = []string{
		// Update path according to your OS
		"/usr/share/zoneinfo/",
		"/usr/share/lib/zoneinfo/",
		"/usr/lib/locale/TZ/",
	}

	zones := map[string]time.Time{}
	datas := map[string]string{}
	dataMaps := map[string]string{}

	now := time.Now()

	var tzs []Timezone

	for _, zoneDir := range zoneDirs {
		files, err := os.ReadDir(zoneDir)
		if err != nil {
			continue
		}

		for _, file := range files {
			fn := file.Name()
			if !file.IsDir() {
				loc, err := time.LoadLocation(fn)
				if err != nil {
					continue
				}
				if file.Type()&os.ModeSymlink != os.ModeSymlink {
					data, err := os.ReadFile(path.Join(zoneDir, fn))
					if err == nil {
						datas[fn] = base64.StdEncoding.EncodeToString(data)
						dataMaps[fn] = fn
					}
				} else {
					target, err := os.Readlink(path.Join(zoneDir, fn))
					if err == nil {
						real, err := filepath.Abs(path.Join(zoneDir, target))
						if err == nil {
							dataMaps[fn] = strings.TrimLeft(real, zoneDir)
						}
					}
				}
				zones[fn] = now.In(loc)
			} else {
				if fn[0] != strings.ToUpper(fn)[0] {
					continue
				}

				if fn[1:] != strings.ToLower(fn)[1:] {
					continue
				}

				subFiles, err := os.ReadDir(path.Join(zoneDir, fn))
				if err != nil {
					continue
				}

				for _, subFile := range subFiles {
					zn := fmt.Sprintf("%s/%s", fn, subFile.Name())
					loc, err := time.LoadLocation(zn)
					if err != nil {
						continue
					}

					if subFile.Type()&os.ModeSymlink != os.ModeSymlink {
						data, err := os.ReadFile(path.Join(zoneDir, zn))
						if err == nil {
							datas[zn] = base64.StdEncoding.EncodeToString(data)
							dataMaps[zn] = zn
						}
					} else {
						target, err := os.Readlink(path.Join(zoneDir, zn))
						if err == nil {
							real, err := filepath.Abs(path.Join(zoneDir, fn, target))
							if err == nil {
								dataMaps[zn] = strings.TrimLeft(real, zoneDir)
							}
						}
					}

					zones[zn] = now.In(loc)
				}
			}
		}
	}

	var tzData []TimezoneData

	for tz, data := range datas {
		tzData = append(tzData, TimezoneData{
			Name: tz,
			Data: data,
		})
	}

	for tz, t := range zones {
		q, o := t.Zone()
		tzs = append(tzs, Timezone{
			Name:   tz,
			Offset: (int64(o) * int64(time.Second)) / int64(time.Minute),
			Zone:   q,
			Parent: dataMaps[tz],
		})
	}

	sort.Slice(tzs, func(i, j int) bool {
		return tzs[i].Name < tzs[j].Name
	})

	sort.Slice(tzData, func(i, j int) bool {
		return tzData[i].Name < tzData[j].Name
	})

	return tzs, tzData
}