feat: add shared media assets and fix credit lifecycle

assets.go

@@ -0,0 +1,125 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"gorm.io/gorm"
+)
+
+type MediaAsset struct {
+	ID            uint      `gorm:"primaryKey" json:"id"`
+	AssetKey      string    `gorm:"uniqueIndex;size:512" json:"assetKey"`
+	Source        string    `gorm:"index;size:32" json:"source"`
+	RID           string    `gorm:"index;size:256" json:"rid"`
+	Quality       string    `gorm:"index;size:32" json:"quality"`
+	LocalPath     string    `json:"localPath,omitempty"`
+	Format        string    `json:"format,omitempty"`
+	ActualQuality string    `json:"actualQuality,omitempty"`
+	Size          int64     `json:"size"`
+	Status        string    `gorm:"index;size:20" json:"status"`
+	OwnerTaskID   uint      `gorm:"index" json:"ownerTaskId,omitempty"`
+	CreatedAt     time.Time `json:"createdAt"`
+	UpdatedAt     time.Time `json:"updatedAt"`
+}
+
+func assetKey(source, rid, quality string) string {
+	return strings.Join([]string{source, rid, quality}, "\x00")
+}
+
+func (a *App) ensureAsset(t *Task) (*MediaAsset, error) {
+	if t.AssetID != 0 {
+		var asset MediaAsset
+		if err := a.db.First(&asset, t.AssetID).Error; err == nil {
+			return &asset, nil
+		}
+	}
+	key := assetKey(t.Source, t.RID, t.Quality)
+	var asset MediaAsset
+	err := a.db.Where("asset_key = ?", key).First(&asset).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		asset = MediaAsset{AssetKey: key, Source: t.Source, RID: t.RID, Quality: t.Quality, Status: "new"}
+		if err := a.db.Create(&asset).Error; err != nil {
+			if a.db.Where("asset_key = ?", key).First(&asset).Error != nil {
+				return nil, err
+			}
+		}
+	} else if err != nil {
+		return nil, err
+	}
+	t.AssetID = asset.ID
+	if err := a.db.Model(t).Update("asset_id", asset.ID).Error; err != nil {
+		return nil, err
+	}
+	return &asset, nil
+}
+
+// acquireAsset serializes physical downloads for the same source/rid/quality.
+// A waiting task yields its worker briefly instead of creating duplicate files.
+func (a *App) acquireAsset(t *Task) (*MediaAsset, bool, error) {
+	for i := 0; i < 120; i++ {
+		asset, err := a.ensureAsset(t)
+		if err != nil {
+			return nil, false, err
+		}
+		if asset.Status == "done" && asset.LocalPath != "" {
+			if fi, statErr := os.Stat(asset.LocalPath); statErr == nil && fi.Size() > 0 {
+				t.LocalPath, t.Format, t.ActualQuality = asset.LocalPath, asset.Format, asset.ActualQuality
+				t.TotalBytes, t.DownloadedBytes, t.Progress, t.Status = fi.Size(), fi.Size(), 100, "done"
+				if err := a.db.Save(t).Error; err != nil {
+					return nil, false, err
+				}
+				return asset, true, nil
+			}
+		}
+		claimed := false
+		err = a.db.Transaction(func(tx *gorm.DB) error {
+			var current MediaAsset
+			if err := tx.First(&current, asset.ID).Error; err != nil {
+				return err
+			}
+			if current.Status == "downloading" && current.OwnerTaskID != t.ID {
+				return nil
+			}
+			current.Status, current.OwnerTaskID = "downloading", t.ID
+			if current.LocalPath == "" {
+				current.LocalPath = filepath.Join(a.cfg.DownloadDir, safe(t.Artist)+" - "+safe(t.Title)+"."+t.Format)
+			}
+			if err := tx.Save(&current).Error; err != nil {
+				return err
+			}
+			*asset = current
+			claimed = true
+			return nil
+		})
+		if err != nil {
+			return nil, false, err
+		}
+		if claimed {
+			t.LocalPath = asset.LocalPath
+			return asset, false, nil
+		}
+		time.Sleep(500 * time.Millisecond)
+	}
+	return nil, false, fmt.Errorf("timed out waiting for shared media asset")
+}
+
+func (a *App) markAssetDone(t *Task) {
+	if t.AssetID == 0 {
+		return
+	}
+	_ = a.db.Model(&MediaAsset{}).Where("id = ? AND owner_task_id = ?", t.AssetID, t.ID).Updates(map[string]any{
+		"status": "done", "owner_task_id": 0, "local_path": t.LocalPath, "format": t.Format, "actual_quality": t.ActualQuality, "size": t.DownloadedBytes,
+	}).Error
+}
+
+func (a *App) releaseAsset(t *Task) {
+	if t.AssetID == 0 {
+		return
+	}
+	_ = a.db.Model(&MediaAsset{}).Where("id = ? AND owner_task_id = ?", t.AssetID, t.ID).Updates(map[string]any{"status": "error", "owner_task_id": 0}).Error
+}