package main

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"
)

const (
	searchEndpoint   = "https://c.y.qq.com/soso/fcgi-bin/search_for_qq_cp"
	lyricsEndpoint   = "https://c.y.qq.com/lyric/fcgi-bin/fcg_query_lyric_new.fcg"
	maxUpstreamBytes = 4 << 20
)

type song struct {
	Name     string `json:"name"`
	MID      string `json:"mid"`
	Singer   string `json:"singer"`
	Album    string `json:"album"`
	Interval int    `json:"interval"`
}

type lyricResult struct {
	Lyric string `json:"lyric"`
	Trans string `json:"trans"`
	Code  int    `json:"code"`
}

type qqAPI interface {
	Search(string, int) ([]song, error)
	Lyrics(string) (lyricResult, error)
}

type qqClient struct {
	httpClient     *http.Client
	searchEndpoint string
	lyricsEndpoint string
}

func newQQClient() *qqClient {
	transport := http.DefaultTransport.(*http.Transport).Clone()
	transport.MaxIdleConns = 8
	transport.MaxIdleConnsPerHost = 4
	transport.ResponseHeaderTimeout = 10 * time.Second
	return &qqClient{
		httpClient: &http.Client{
			Timeout:   15 * time.Second,
			Transport: transport,
			CheckRedirect: func(_ *http.Request, _ []*http.Request) error {
				return errors.New("unexpected redirect from fixed QQ Music endpoint")
			},
		},
		searchEndpoint: searchEndpoint,
		lyricsEndpoint: lyricsEndpoint,
	}
}

func (c *qqClient) Search(keyword string, limit int) ([]song, error) {
	query := url.Values{
		"format":     {"json"},
		"p":          {"1"},
		"n":          {fmt.Sprint(limit)},
		"w":          {keyword},
		"outCharset": {"utf-8"},
	}
	var response struct {
		Code    int    `json:"code"`
		Message string `json:"message"`
		Data    struct {
			Song struct {
				List []struct {
					SongName  string `json:"songname"`
					SongMID   string `json:"songmid"`
					AlbumName string `json:"albumname"`
					Interval  int    `json:"interval"`
					Singer    []struct {
						Name string `json:"name"`
					} `json:"singer"`
				} `json:"list"`
			} `json:"song"`
		} `json:"data"`
	}
	if err := c.getJSON(c.searchEndpoint, query, &response); err != nil {
		return nil, err
	}
	if response.Code != 0 {
		return nil, fmt.Errorf("QQ Music search failed: %s", response.Message)
	}
	result := make([]song, 0, len(response.Data.Song.List))
	for _, item := range response.Data.Song.List {
		if item.SongMID == "" {
			continue
		}
		names := make([]string, 0, len(item.Singer))
		for _, singer := range item.Singer {
			if singer.Name != "" {
				names = append(names, singer.Name)
			}
		}
		result = append(result, song{
			Name: item.SongName, MID: item.SongMID,
			Singer: strings.Join(names, " / "), Album: item.AlbumName, Interval: item.Interval,
		})
	}
	return result, nil
}

func (c *qqClient) Lyrics(mid string) (lyricResult, error) {
	query := url.Values{
		"format": {"json"}, "songmid": {mid}, "outCharset": {"utf-8"}, "nobase64": {"1"},
	}
	var result lyricResult
	if err := c.getJSON(c.lyricsEndpoint, query, &result); err != nil {
		return lyricResult{}, err
	}
	if result.Code != 0 || result.Lyric == "" {
		return lyricResult{}, errors.New("lyrics are not available for this track")
	}
	return result, nil
}

func (c *qqClient) getJSON(endpoint string, query url.Values, destination any) error {
	request, err := http.NewRequest(http.MethodGet, endpoint+"?"+query.Encode(), nil)
	if err != nil {
		return err
	}
	request.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 Chrome/131 Safari/537.36")
	request.Header.Set("Referer", "https://y.qq.com/")
	request.Header.Set("Origin", "https://y.qq.com")
	request.Header.Set("Accept", "application/json,text/plain,*/*")
	response, err := c.httpClient.Do(request)
	if err != nil {
		return fmt.Errorf("QQ Music request failed: %w", err)
	}
	defer response.Body.Close()
	if response.StatusCode != http.StatusOK {
		return fmt.Errorf("QQ Music returned HTTP %d", response.StatusCode)
	}
	body, err := io.ReadAll(io.LimitReader(response.Body, maxUpstreamBytes+1))
	if err != nil {
		return err
	}
	if len(body) > maxUpstreamBytes {
		return errors.New("QQ Music response exceeded the safety limit")
	}
	body = unwrapJSONP(body)
	if err := json.Unmarshal(body, destination); err != nil {
		return errors.New("QQ Music returned an invalid response")
	}
	return nil
}

func unwrapJSONP(body []byte) []byte {
	body = bytes.TrimSpace(body)
	if len(body) == 0 || body[0] == '{' || body[0] == '[' {
		return body
	}
	left := bytes.IndexByte(body, '(')
	right := bytes.LastIndexByte(body, ')')
	if left >= 0 && right > left {
		return bytes.TrimSpace(body[left+1 : right])
	}
	return body
}