Add resumable downloads, download paths, queue controls and history

internal/jobs/slots.go

@@ -2,38 +2,57 @@ package jobs
 
 import (
 	"context"
+	"slices"
 	"sync"
 	"time"
 )
 
 const slotWaitInterval = 500 * time.Millisecond
 
+const (
+	queueFirst = "first"
+	queueUp    = "up"
+	queueDown  = "down"
+)
+
 type slotLimiter struct {
-	mutex  sync.Mutex
-	active int
+	mutex   sync.Mutex
+	active  int
+	waiting []string
 }
 
-func (limiter *slotLimiter) acquire(ctx context.Context, limit func() int) bool {
+func (limiter *slotLimiter) enqueue(id string) {
+	limiter.mutex.Lock()
+	defer limiter.mutex.Unlock()
+	if !slices.Contains(limiter.waiting, id) {
+		limiter.waiting = append(limiter.waiting, id)
+	}
+}
+
+func (limiter *slotLimiter) acquire(ctx context.Context, id string, limit func() int) bool {
+	limiter.enqueue(id)
 	ticker := time.NewTicker(slotWaitInterval)
 	defer ticker.Stop()
 	for {
-		if limiter.tryAcquire(limit()) {
+		if limiter.tryAcquire(id, limit()) {
 			return true
 		}
 		select {
 		case <-ctx.Done():
+			limiter.remove(id)
 			return false
 		case <-ticker.C:
 		}
 	}
 }
 
-func (limiter *slotLimiter) tryAcquire(limit int) bool {
+func (limiter *slotLimiter) tryAcquire(id string, limit int) bool {
 	limiter.mutex.Lock()
 	defer limiter.mutex.Unlock()
-	if limiter.active >= limit {
+	if limiter.active >= limit || len(limiter.waiting) == 0 || limiter.waiting[0] != id {
 		return false
 	}
+	limiter.waiting = limiter.waiting[1:]
 	limiter.active++
 	return true
 }
@@ -43,3 +62,39 @@ func (limiter *slotLimiter) release() {
 	defer limiter.mutex.Unlock()
 	limiter.active--
 }
+
+func (limiter *slotLimiter) remove(id string) {
+	limiter.mutex.Lock()
+	defer limiter.mutex.Unlock()
+	limiter.waiting = slices.DeleteFunc(limiter.waiting, func(waitingID string) bool {
+		return waitingID == id
+	})
+}
+
+func (limiter *slotLimiter) position(id string) int {
+	limiter.mutex.Lock()
+	defer limiter.mutex.Unlock()
+	return slices.Index(limiter.waiting, id) + 1
+}
+
+func (limiter *slotLimiter) reorder(id, direction string) bool {
+	limiter.mutex.Lock()
+	defer limiter.mutex.Unlock()
+	index := slices.Index(limiter.waiting, id)
+	if index < 0 {
+		return false
+	}
+
+	target := index
+	switch direction {
+	case queueFirst:
+		target = 0
+	case queueUp:
+		target = max(index-1, 0)
+	case queueDown:
+		target = min(index+1, len(limiter.waiting)-1)
+	}
+	limiter.waiting = slices.Delete(limiter.waiting, index, index+1)
+	limiter.waiting = slices.Insert(limiter.waiting, target, id)
+	return true
+}