Generate cover image (#376)

* Make mutating metadata ops mutation
* Implement scene generate screenshot
* Remove fetch policy on metadata mutations
* Port UI changes to v2.5
* Set generated image in database

pkg/manager/task_generate_screenshot.go

@@ -0,0 +1,84 @@
+package manager
+
+import (
+	"context"
+	"io/ioutil"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/stashapp/stash/pkg/database"
+	"github.com/stashapp/stash/pkg/ffmpeg"
+	"github.com/stashapp/stash/pkg/logger"
+	"github.com/stashapp/stash/pkg/models"
+)
+
+type GenerateScreenshotTask struct {
+	Scene        models.Scene
+	ScreenshotAt *float64
+}
+
+func (t *GenerateScreenshotTask) Start(wg *sync.WaitGroup) {
+	defer wg.Done()
+
+	scenePath := t.Scene.Path
+	probeResult, err := ffmpeg.NewVideoFile(instance.FFProbePath, scenePath)
+
+	if err != nil {
+		logger.Error(err.Error())
+		return
+	}
+
+	var at float64
+	if t.ScreenshotAt == nil {
+		at = float64(probeResult.Duration) * 0.2
+	} else {
+		at = *t.ScreenshotAt
+	}
+
+	checksum := t.Scene.Checksum
+	normalPath := instance.Paths.Scene.GetScreenshotPath(checksum)
+
+	// we'll generate the screenshot, grab the generated data and set it
+	// in the database. We'll use SetSceneScreenshot to set the data
+	// which also generates the thumbnail
+
+	logger.Debugf("Creating screenshot for %s", scenePath)
+	makeScreenshot(*probeResult, normalPath, 2, probeResult.Width, at)
+
+	f, err := os.Open(normalPath)
+	if err != nil {
+		logger.Errorf("Error reading screenshot: %s", err.Error())
+		return
+	}
+	defer f.Close()
+
+	coverImageData, err := ioutil.ReadAll(f)
+	if err != nil {
+		logger.Errorf("Error reading screenshot: %s", err.Error())
+		return
+	}
+
+	ctx := context.TODO()
+	tx := database.DB.MustBeginTx(ctx, nil)
+
+	qb := models.NewSceneQueryBuilder()
+	updatedTime := time.Now()
+	updatedScene := models.ScenePartial{
+		ID:        t.Scene.ID,
+		UpdatedAt: &models.SQLiteTimestamp{Timestamp: updatedTime},
+	}
+
+	updatedScene.Cover = &coverImageData
+	err = SetSceneScreenshot(t.Scene.Checksum, coverImageData)
+	_, err = qb.Update(updatedScene, tx)
+	if err != nil {
+		logger.Errorf("Error setting screenshot: %s", err.Error())
+		return
+	}
+
+	if err := tx.Commit(); err != nil {
+		logger.Errorf("Error setting screenshot: %s", err.Error())
+		return
+	}
+}