package base

import (
	"bytes"
	"crypto/md5"
	"encoding/hex"
	"encoding/xml"
	"errors"
	"hash"
	"io"
	"sort"
	"sync"
)

var textBufferPool = sync.Pool{
	New: func() interface{} {
		return bytes.NewBuffer(make([]byte, 0, 16<<10)) // 16KB
	},
}

// FormatMapToXML marshal map[string]string to xmlWriter with xml format, the root node name is xml.
//  NOTE: This function assumes the key of m map[string]string are legitimate xml name string
//  that does not contain the required escape character!
func FormatMapToXML(xmlWriter io.Writer, m map[string]string) (err error) {
	if xmlWriter == nil {
		return errors.New("nil xmlWriter")
	}

	if _, err = io.WriteString(xmlWriter, "<xml>"); err != nil {
		return
	}

	for k, v := range m {
		if _, err = io.WriteString(xmlWriter, "<"+k+">"); err != nil {
			return
		}
		if err = xml.EscapeText(xmlWriter, []byte(v)); err != nil {
			return
		}
		if _, err = io.WriteString(xmlWriter, "</"+k+">"); err != nil {
			return
		}
	}

	if _, err = io.WriteString(xmlWriter, "</xml>"); err != nil {
		return
	}
	return
}

//Sign 微信支付签名.
//  parameters: 待签名的参数集合
//  apiKey:     API密钥
//  fn:         func() hash.Hash, 如果 fn == nil 则默认用 md5.New
func Sign(parameters map[string]string, apiKey string, fn func() hash.Hash) string {
	ks := make([]string, 0, len(parameters))
	for k := range parameters {
		if k == "sign" {
			continue
		}
		ks = append(ks, k)
	}
	sort.Strings(ks)

	if fn == nil {
		fn = md5.New
	}
	h := fn()

	buf := make([]byte, 256)
	for _, k := range ks {
		v := parameters[k]
		if v == "" {
			continue
		}

		buf = buf[:0]
		buf = append(buf, k...)
		buf = append(buf, '=')
		buf = append(buf, v...)
		buf = append(buf, '&')
		h.Write(buf)
	}
	buf = buf[:0]
	buf = append(buf, "key="...)
	buf = append(buf, apiKey...)
	h.Write(buf)

	signature := make([]byte, h.Size()*2)
	hex.Encode(signature, h.Sum(nil))
	return string(bytes.ToUpper(signature))
}

// ParseXMLToMap parses xml reading from xmlReader and returns the first-level sub-node key-value set,
// if the first-level sub-node contains child nodes, skip it.
func ParseXMLToMap(xmlReader io.Reader) (m map[string]string, err error) {
	if xmlReader == nil {
		err = errors.New("nil xmlReader")
		return
	}

	m = make(map[string]string)
	var (
		d     = xml.NewDecoder(xmlReader)
		tk    xml.Token
		depth = 0 // current xml.Token depth
		key   string
		value bytes.Buffer
	)
	for {
		tk, err = d.Token()
		if err != nil {
			if err == io.EOF {
				err = nil
			}
			return
		}

		switch v := tk.(type) {
		case xml.StartElement:
			depth++
			switch depth {
			case 2:
				key = v.Name.Local
				value.Reset()
			case 3:
				if err = d.Skip(); err != nil {
					return
				}
				depth--
				key = "" // key == "" indicates that the node with depth==2 has children
			}
		case xml.CharData:
			if depth == 2 && key != "" {
				value.Write(v)
			}
		case xml.EndElement:
			if depth == 2 && key != "" {
				m[key] = value.String()
			}
			depth--
		}
	}
}