package usos

import (
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha1"
	"encoding/base64"
	"encoding/hex"
	"net/url"
	"sort"
	"strconv"
	"strings"
	"time"
)

const unreserved = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~"

func percentEncode(s string) string {
	var b strings.Builder
	for i := range len(s) {
		c := s[i]
		if strings.IndexByte(unreserved, c) >= 0 {
			b.WriteByte(c)
			continue
		}
		b.WriteByte('%')
		b.WriteString(strings.ToUpper(hex.EncodeToString([]byte{c})))
	}
	return b.String()
}

func signature(method, endpoint string, params url.Values, consumerSecret, tokenSecret string) string {
	pairs := make([]string, 0, len(params))
	for key, values := range params {
		for _, value := range values {
			pairs = append(pairs, percentEncode(key)+"="+percentEncode(value))
		}
	}
	sort.Strings(pairs)
	base := method + "&" + percentEncode(endpoint) + "&" + percentEncode(strings.Join(pairs, "&"))
	mac := hmac.New(sha1.New, []byte(percentEncode(consumerSecret)+"&"+percentEncode(tokenSecret)))
	mac.Write([]byte(base))
	return base64.StdEncoding.EncodeToString(mac.Sum(nil))
}

func nonce() string {
	buf := make([]byte, 16)
	if _, err := rand.Read(buf); err != nil {
		panic(err)
	}
	return hex.EncodeToString(buf)
}

func (c *Client) authorization(endpoint string, token *Token, params url.Values) (header string, body url.Values) {
	oauth := url.Values{
		"oauth_consumer_key":     {c.Key},
		"oauth_nonce":            {nonce()},
		"oauth_signature_method": {"HMAC-SHA1"},
		"oauth_timestamp":        {strconv.FormatInt(time.Now().Unix(), 10)},
		"oauth_version":          {"1.0"},
	}
	tokenSecret := ""
	if token != nil {
		oauth.Set("oauth_token", token.Key)
		tokenSecret = token.Secret
	}
	body = url.Values{}
	all := url.Values{}
	for key, values := range params {
		if strings.HasPrefix(key, "oauth_") {
			oauth[key] = values
		} else {
			body[key] = values
		}
		all[key] = values
	}
	for key, values := range oauth {
		all[key] = values
	}
	oauth.Set("oauth_signature", signature("POST", endpoint, all, c.Secret, tokenSecret))

	keys := make([]string, 0, len(oauth))
	for key := range oauth {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	parts := make([]string, 0, len(keys))
	for _, key := range keys {
		parts = append(parts, key+`="`+percentEncode(oauth.Get(key))+`"`)
	}
	return "OAuth " + strings.Join(parts, ", "), body
}