refactor: modularize downloader architecture

am_client.go

@@ -0,0 +1,61 @@
+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+)
+
+type AMAPIClient struct {
+	BaseURL string
+	HTTP    *http.Client
+}
+
+func (c *AMAPIClient) Search(keyword, source string, page, limit int) (*http.Response, error) {
+	u, err := url.Parse(strings.TrimRight(c.BaseURL, "/") + "/search")
+	if err != nil {
+		return nil, err
+	}
+	q := u.Query()
+	q.Set("keyword", keyword)
+	q.Set("source", source)
+	q.Set("page", strconv.Itoa(page))
+	q.Set("limit", strconv.Itoa(limit))
+	u.RawQuery = q.Encode()
+	return c.HTTP.Get(u.String())
+}
+
+func (c *AMAPIClient) Resolve(source, rid, quality string) (playInfo, error) {
+	u, err := url.Parse(strings.TrimRight(c.BaseURL, "/") + "/song/play-url")
+	if err != nil {
+		return playInfo{}, err
+	}
+	q := u.Query()
+	q.Set("source", source)
+	q.Set("rid", rid)
+	q.Set("level", quality)
+	u.RawQuery = q.Encode()
+	resp, err := c.HTTP.Get(u.String())
+	if err != nil {
+		return playInfo{}, err
+	}
+	defer resp.Body.Close()
+	var x struct {
+		Code    int      `json:"code"`
+		Data    playInfo `json:"data"`
+		Message string   `json:"message"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&x); err != nil {
+		return playInfo{}, err
+	}
+	if x.Code != 0 || x.Data.URL == "" {
+		if x.Message == "" {
+			x.Message = "music API returned no playable URL"
+		}
+		return playInfo{}, errors.New(x.Message)
+	}
+	return x.Data, nil
+}