package pscrypto

import (
	"crypto/sha256"
	"fmt"
	"io"
	"sort"
	"strings"

	"github.com/shopspring/decimal"
)

// signature based sha256
func GetSign(m map[string]interface{}, merchantKey string) string {
	var w = sha256.New()
	_, _ = io.WriteString(w, sortedAndBuild(m)+merchantKey)
	return fmt.Sprintf("%x", w.Sum(nil))
}

func sortedAndBuild(m map[string]interface{}) string {
	var b strings.Builder
	l, c := len(m), 0
	keySet := make([]string, 0, l)
	for k, v := range m {
		keySet = append(keySet, k)
		if _, ok := v.(string); ok {
			c = len(k) + len(v.(string)) + 2
		} else {
			c = len(k) + 10 + 2
		}
	}

	b.Grow(c)
	sort.Strings(keySet)
	for _, k := range keySet {
		if v, ok := m[k]; ok {
			var str string
			if s, okk := v.(string); okk {
				str = s
			} else if d, okkk := v.(decimal.Decimal); okkk {
				str = d.String()
			} else {
				str = fmt.Sprintf("%v", v)
			}

			if len(str) > 0 {
				b.WriteString(k)
				b.WriteString("=")
				b.WriteString(str)
				b.WriteString("&")
			}
		}
	}
	r := strings.TrimRight(b.String(), "&")
	return r
}