/*
Rating system designed to be used in VoIP Carriers World
Copyright (C) 2013 ITsysCOM

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>
*/

package utils

import (
	"crypto/rand"
	"crypto/sha1"
	"encoding/hex"
	"errors"
	"fmt"
	"math"
	"regexp"
	"strconv"
	"strings"
	"time"
)

// Returns first non empty string out of vals. Useful to extract defaults
func FirstNonEmpty(vals ...string) string {
	for _, val := range vals {
		if len(val) != 0 {
			return val
		}
	}
	return ""
}

func SHA1(text string) string {
	hasher := sha1.New()
	hasher.Write([]byte(text))
	return fmt.Sprintf("%x", hasher.Sum(nil))
}

func FSCgrId(uuid string) string {
	return SHA1(uuid)
}

func NewTPid() string {
	return SHA1(GenUUID())
}

// helper function for uuid generation
func GenUUID() string {
	uuid := make([]byte, 16)
	n, err := rand.Read(uuid)
	if n != len(uuid) || err != nil {
		return strconv.FormatInt(time.Now().UnixNano(), 10)
	}
	// TODO: verify the two lines implement RFC 4122 correctly
	uuid[8] = 0x80 // variant bits see page 5
	uuid[4] = 0x40 // version 4 Pseudo Random, see page 7

	return hex.EncodeToString(uuid)
}

// Round return rounded version of x with prec precision.
//
// Special cases are:
//	Round(±0) = ±0
//	Round(±Inf) = ±Inf
//	Round(NaN) = NaN
func Round(x float64, prec int, method string) float64 {
	var rounder float64
	pow := math.Pow(10, float64(prec))
	intermed := x * pow
	_, frac := math.Modf(intermed)

	switch method {
	case ROUNDING_UP:
		rounder = math.Ceil(intermed)
	case ROUNDING_DOWN:
		rounder = math.Floor(intermed)
	case ROUNDING_MIDDLE:
		if frac >= 0.5 {
			rounder = math.Ceil(intermed)
		} else {
			rounder = math.Floor(intermed)
		}
	default:
		rounder = intermed
	}

	return rounder / pow
}

func ParseTimeDetectLayout(tmStr string) (time.Time, error) {
	var nilTime time.Time
	rfc3339Rule := regexp.MustCompile(`^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.+`)
	sqlRule := regexp.MustCompile(`^\d{4}-\d{2}-\d{2}\s\d{2}:\d{2}:\d{2}`)
	unixTimestampRule := regexp.MustCompile(`^\d{10}`)
	switch {
	case rfc3339Rule.MatchString(tmStr):
		return time.Parse(time.RFC3339, tmStr)
	case sqlRule.MatchString(tmStr):
		return time.Parse("2006-01-02 15:04:05", tmStr)
	case unixTimestampRule.MatchString(tmStr):
		if tmstmp, err := strconv.ParseInt(tmStr, 10, 64); err != nil {
			return nilTime, err
		} else {
			return time.Unix(tmstmp, 0), nil
		}
	case len(tmStr) == 0: // Time probably missing from request
		return nilTime, nil
	}
	return nilTime, errors.New("Unsupported time format")
}

func ParseDate(date string) (expDate time.Time, err error) {
	date = strings.TrimSpace(date)
	switch {
	case date == "*unlimited" || date == "":
		// leave it at zero
	case strings.HasPrefix(date, "+"):
		d, err := time.ParseDuration(date[1:])
		if err != nil {
			return expDate, err
		}
		expDate = time.Now().Add(d)
	case date == "*monthly":
		expDate = time.Now().AddDate(0, 1, 0) // add one month
	case strings.HasSuffix(date, "Z"):
		expDate, err = time.Parse(time.RFC3339, date)
	default:
		unix, err := strconv.ParseInt(date, 10, 64)
		if err != nil {
			return expDate, err
		}
		expDate = time.Unix(unix, 0)
	}
	return expDate, err
}

// returns a number equeal or larger than the amount that exactly
// is divisible to whole
func RoundTo(whole, amount time.Duration) time.Duration {
	a, w := float64(amount), float64(whole)
	if math.Mod(a, w) == 0 {
		return amount
	}
	return time.Duration((w - math.Mod(a, w)) + a)
}

func SplitPrefix(prefix string) []string {
	length := int(math.Max(float64(len(prefix)-1), 0))
	subs := make([]string, length)
	max := len(prefix)
	for i := 0; i < length; i++ {
		subs[i] = prefix[:max-i]
	}
	return subs
}

func CopyHour(src, dest time.Time) time.Time {
	if src.Hour() == 0 && src.Minute() == 0 && src.Second() == 0 {
		return src
	}
	return time.Date(dest.Year(), dest.Month(), dest.Day(), src.Hour(), src.Minute(), src.Second(), src.Nanosecond(), src.Location())
}

// Parses duration, considers s as time unit if not provided
func ParseDurationWithSecs(durStr string) (time.Duration, error) {
	if _, err := strconv.Atoi(durStr); err == nil { // No suffix, default to seconds
		durStr += "s"
	}
	return time.ParseDuration(durStr)
}