2 files changed, 83 insertions, 15 deletions

diff --git a/downloader/download_manager.go b/downloader/download_manager.go
index fb7e883..004efc1 100644
--- a/downloader/download_manager.go
+++ b/downloader/download_manager.go
@@ -1,15 +1,89 @@
 package downloader
 
+import (
+	"time"
+)
+
 // DownloadManager handles a download for a particular song.
 type DownloadManager struct {
 	Url string
 
-	dlChans []<-chan []byte
+	Start    time.Duration
+	Duration time.Duration
+	End      time.Duration
+
+	pb chan (<-chan []byte)
+
+	info videoInfo
 }
 
-func NewDownload(url string) DownloadManager {
-	return DownloadManager{
-		Url:     url,
-		dlChans: []<-chan []byte{},
+const clipTime = 10 * time.Second
+const preloadCount = 5
+
+func NewDownload(url string, startTime, dur time.Duration) (*DownloadManager, error) {
+	vInfo, err := info(url)
+	if err != nil {
+		return nil, err
+	}
+
+	if dur == 0 {
+		dur = vInfo.Duration - startTime
 	}
+
+	dl := &DownloadManager{
+		Url: url,
+
+		Start:    startTime,
+		Duration: dur,
+		End:      startTime + dur,
+
+		pb:   make(chan (<-chan []byte), preloadCount),
+		info: *vInfo,
+	}
+
+	go dl.schedule()
+
+	return dl, nil
+}
+
+func (d *DownloadManager) SendOn(ch chan<- []byte) <-chan struct{} {
+	out := make(chan struct{}, 1)
+
+	go func() {
+		defer close(out)
+		for c := range d.pb {
+			for b := range c {
+				ch <- b
+			}
+		}
+	}()
+
+	return out
+}
+
+func (d *DownloadManager) schedule() {
+	go func() {
+		defer close(d.pb)
+		for i := 0; ; i++ {
+			clipStart := time.Duration(i)*clipTime + d.Start
+			clipEnd := time.Duration(i+1)*clipTime + d.Start
+
+			if clipStart >= d.End {
+				return
+			}
+
+			dur := clipTime
+			if clipEnd > d.End {
+				dur = d.End - clipStart
+			}
+
+			ch, err := d.download(clipStart, dur)
+			if err != nil {
+				log.Errorf("error setting up download: %q", err)
+				return
+			}
+
+			d.pb <- ch
+		}
+	}()
 }
diff --git a/downloader/downloader.go b/downloader/downloader.go
index 793cd22..95c022f 100644
--- a/downloader/downloader.go
+++ b/downloader/downloader.go
@@ -75,18 +75,11 @@ func info(inUrl string) (*videoInfo, error) {
 	return &v, err
 }
 
-func Download(inUrl string, startTime time.Duration, duration time.Duration) (<-chan []byte, error) {
-	vInfo, err := info(inUrl)
-	if err != nil {
-		return nil, err
-	}
-
+func (d *DownloadManager) download(startTime, duration time.Duration) (<-chan []byte, error) {
 	startSecond := int(startTime.Seconds())
-	dur := int(duration.Seconds())
-
 	args := []string{
 		"-ss", strconv.Itoa(startSecond),
-		"-i", vInfo.Url.String(),
+		"-i", d.info.Url.String(),
 		"-c:a", "pcm_s16le",
 		"-f", "wav",
 		"-ar", "48000",
@@ -94,7 +87,8 @@ func Download(inUrl string, startTime time.Duration, duration time.Duration) (<-
 		"-vn", "-y",
 	}
 
-	if dur > 0 {
+	dur := int(duration.Seconds())
+	if dur > 0 && startTime+duration < d.info.Duration {
 		args = append(args, "-t", strconv.Itoa(dur))
 	}