package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"sort"
	"strings"
	"time"
)

type backup struct {
	Name string
	Time time.Time
}

var (
	keep_yearly  = 1
	keep_monthly = 6
	keep_weekly  = 4
	keep_daily   = 14

	patterns = map[string]string{
		"daily":   "2006-01-02",
		"weekly":  "", // See special case in keepers()
		"monthly": "2006-01",
		"yearly":  "2006",
	}
)

func enumerate_backups() []backup {
	var backups []backup

	files, err := ioutil.ReadDir("./test/data")
	if err != nil {
		log.Fatal(err)
	}

	for _, file := range files {
		name := file.Name()
		time, err := time.Parse(time.RFC3339, strings.Split(name, "@")[1])

		if err != nil {
			log.Fatalf("Failed to parse timestamp in %s\n", name)
			continue
		}

		backups = append(backups, backup{name, time})
	}

	return backups
}

func keepers(backups []backup, rule string, keepCnt int) []backup {

	var keep []backup
	var last string

	for _, backup := range backups {
		var period string

		// Special case because there is no support for "week number" in Time.Format
		if rule == "weekly" {
			year, week := backup.Time.Local().ISOWeek()
			period = fmt.Sprintf("%d-%d", year, week)
		} else {
			period = backup.Time.Local().Format(patterns[rule])
		}

		// fmt.Printf("rule: %s, pattern: %s, t: %s, format: %s\n", rule, patterns[rule], backup.Time.Local(), period)

		if period != last {
			last = period
			keep = append(keep, backup)

			if len(keep) == keepCnt {
				break
			}
		}
	}

	return keep
}

func main() {
	backups := enumerate_backups()

	sort.Slice(backups, func(i, j int) bool {
		return backups[i].Time.After(backups[j].Time)
	})

	fmt.Println("==============  DAILY  ==============")
	for _, kept := range keepers(backups, "daily", keep_daily) {
		fmt.Printf("%s\n", kept.Name)
	}
	fmt.Println("============== WEEKLY  ==============")
	for _, kept := range keepers(backups, "weekly", keep_weekly) {
		fmt.Printf("%s\n", kept.Name)
	}
	fmt.Println("============== MONTHLY ==============")
	for _, kept := range keepers(backups, "monthly", keep_monthly) {
		fmt.Printf("%s\n", kept.Name)
	}
	fmt.Println("============== YEARLY  ==============")
	for _, kept := range keepers(backups, "yearly", keep_yearly) {
		fmt.Printf("%s\n", kept.Name)
	}
}