Torrent Queuing for Botched torrent (#83)

* Implement a queue for handling failed torrent

* Add checks for getting slots

* Few other cleanups, change some function names

internal/utils/error.go

@@ -0,0 +1,47 @@
+package utils
+
+import "errors"
+
+type HTTPError struct {
+	StatusCode int
+	Message    string
+	Code       string
+}
+
+func (e *HTTPError) Error() string {
+	return e.Message
+}
+
+var HosterUnavailableError = &HTTPError{
+	StatusCode: 503,
+	Message:    "Hoster is unavailable",
+	Code:       "hoster_unavailable",
+}
+
+var TrafficExceededError = &HTTPError{
+	StatusCode: 503,
+	Message:    "Traffic exceeded",
+	Code:       "traffic_exceeded",
+}
+
+var ErrLinkBroken = &HTTPError{
+	StatusCode: 404,
+	Message:    "File is unavailable",
+	Code:       "file_unavailable",
+}
+
+var TorrentNotFoundError = &HTTPError{
+	StatusCode: 404,
+	Message:    "Torrent not found",
+	Code:       "torrent_not_found",
+}
+
+var TooManyActiveDownloadsError = &HTTPError{
+	StatusCode: 509,
+	Message:    "Too many active downloads",
+	Code:       "too_many_active_downloads",
+}
+
+func IsTooManyActiveDownloadsError(err error) bool {
+	return errors.As(err, &TooManyActiveDownloadsError)
+}