refactor: modularize downloader architecture

app.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"net/http"
+	"sync"
+
+	"gorm.io/gorm"
+)
+
+type App struct {
+	db         *gorm.DB
+	cfg        Config
+	queue      chan uint
+	wg         sync.WaitGroup
+	httpClient *http.Client
+	am         AMClient
+	storage    RemoteStorage
+}
+
+// AMClient isolates the music API from the task engine.
+type AMClient interface {
+	Search(keyword, source string, page, limit int) (*http.Response, error)
+	Resolve(source, rid, quality string) (playInfo, error)
+}
+
+// RemoteStorage isolates WebDAV and leaves room for S3/local backends later.
+type RemoteStorage interface {
+	Upload(localPath, remotePath string) error
+	ExistsSameSize(remotePath string, size int64) (bool, error)
+	Remove(remotePath string) error
+	MkdirAll(remoteDir string) error
+}