package comfunc

import (
	"fmt"
	"os"
	"regexp"
	"strconv"
	"strings"
	"time"
)

// Environ like os.Environ, but will returns key-value map[string]string data.
func Environ() map[string]string {
	envList := os.Environ()
	envMap := make(map[string]string, len(envList))

	for _, str := range envList {
		nodes := strings.SplitN(str, "=", 2)
		if len(nodes) < 2 {
			envMap[nodes[0]] = ""
		} else {
			envMap[nodes[0]] = nodes[1]
		}
	}
	return envMap
}

var (
	// TIP: extend unit d,w.  eg: "1d", "2w"
	// time.ParseDuration() is max support hour "h".
	durStrReg = regexp.MustCompile(`^(-?\d+)(ns|us|µs|ms|s|m|h|d|w)$`)

	// match long duration string. eg: "1hour", "2hours", "3minutes", "4mins", "5days", "1weeks", "1month"
	// time.ParseDuration() is not supported.
	durStrRegL = regexp.MustCompile(`^(-?\d+)([hdmsw][a-zA-Z]{2,8})$`)
)

// IsDuration check the string is a duration string.
func IsDuration(s string) bool {
	if s == "0" || durStrReg.MatchString(s) {
		return true
	}
	return durStrRegL.MatchString(s)
}

// ToDuration parses a duration string. such as "300ms", "-1.5h" or "2h45m".
// Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
//
// Diff of time.ParseDuration:
//   - support extend unit d, w at the end of string. such as "1d", "2w".
//   - support long string unit at end. such as "1hour", "2hours", "3minutes", "4mins", "5days", "1weeks".
//
// If the string is not a valid duration string, it will return an error.
func ToDuration(s string) (time.Duration, error) {
	ln := len(s)
	if ln == 0 {
		return 0, fmt.Errorf("empty duration string")
	}

	s = strings.ToLower(s)
	if s == "0" {
		return 0, nil
	}

	// extend unit d,w, time.ParseDuration() is not supported. eg: "1d", "2w"
	if lastUnit := s[ln-1]; lastUnit == 'd' {
		s = s + "ay"
	} else if lastUnit == 'w' {
		s = s + "eek"
	}

	// long unit, time.ParseDuration() is not supported. eg: "-3sec" => [3sec -3 sec]
	ss := durStrRegL.FindStringSubmatch(s)
	if len(ss) == 3 {
		num, unit := ss[1], ss[2]

		// convert to short unit
		switch unit {
		case "month", "months":
			// max unit is hour, so need convert by 24 * 30 * n
			n, _ := strconv.Atoi(num)
			s = strconv.Itoa(n*24*30) + "h"
		case "week", "weeks":
			// max unit is hour, so need convert by 24 * 7 * n
			n, _ := strconv.Atoi(num)
			s = strconv.Itoa(n*24*7) + "h"
		case "day", "days":
			// max unit is hour, so need convert by 24 * n
			n, _ := strconv.Atoi(num)
			s = strconv.Itoa(n*24) + "h"
		case "hour", "hours":
			s = num + "h"
		case "min", "mins", "minute", "minutes":
			s = num + "m"
		case "sec", "secs", "second", "seconds":
			s = num + "s"
		}
	}

	return time.ParseDuration(s)
}