package pay007

import (
	"crypto/md5"
	"encoding/hex"
	"sort"
	"strings"
)

var ignoredSignKeys = map[string]struct{}{
	"sign":      {},
	"sign_type": {},
}

// BuildSign creates the 007Pay merchant MD5 signature.
//
// Empty values, sign, and sign_type are ignored. The remaining params are
// sorted by key, joined as "a=1&b=2", appended with the app secret, then MD5
// hashed and upper-cased.
func BuildSign(params map[string]string, secret string) string {
	keys := make([]string, 0, len(params))
	for k, v := range params {
		if v == "" {
			continue
		}
		if _, ok := ignoredSignKeys[k]; ok {
			continue
		}
		keys = append(keys, k)
	}
	sort.Strings(keys)

	var b strings.Builder
	for i, k := range keys {
		if i > 0 {
			b.WriteByte('&')
		}
		b.WriteString(k)
		b.WriteByte('=')
		b.WriteString(params[k])
	}
	b.WriteString(secret)

	sum := md5.Sum([]byte(b.String()))
	return strings.ToUpper(hex.EncodeToString(sum[:]))
}

// VerifySign checks params["sign"] with the 007Pay signing rule.
func VerifySign(params map[string]string, secret string) bool {
	sign := params["sign"]
	if sign == "" {
		return false
	}
	return strings.EqualFold(BuildSign(params, secret), sign)
}