Javascript scraper postprocess (#4200)

* Add javascript post-process action
* Add documentation

pkg/scraper/mapped.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/robertkrimen/otto"
 	"github.com/stashapp/stash/pkg/logger"
 	"github.com/stashapp/stash/pkg/models"
 	"github.com/stashapp/stash/pkg/sliceutil/stringslice"
@@ -523,6 +524,31 @@ func (p *postProcessLbToKg) Apply(ctx context.Context, value string, q mappedQue
 	return value
 }
 
+type postProcessJavascript string
+
+func (p *postProcessJavascript) Apply(ctx context.Context, value string, q mappedQuery) string {
+	vm := otto.New()
+	if err := vm.Set("value", value); err != nil {
+		logger.Warnf("javascript failed to set value: %v", err)
+		return value
+	}
+
+	script, err := vm.Compile("", "(function() { "+string(*p)+"})()")
+	if err != nil {
+		logger.Warnf("javascript failed to compile: %v", err)
+		return value
+	}
+
+	output, err := vm.Run(script)
+	if err != nil {
+		logger.Warnf("javascript failed to run: %v", err)
+		return value
+	}
+
+	// assume output is string
+	return output.String()
+}
+
 type mappedPostProcessAction struct {
 	ParseDate    string                   `yaml:"parseDate"`
 	SubtractDays bool                     `yaml:"subtractDays"`
@@ -531,65 +557,75 @@ type mappedPostProcessAction struct {
 	Map          map[string]string        `yaml:"map"`
 	FeetToCm     bool                     `yaml:"feetToCm"`
 	LbToKg       bool                     `yaml:"lbToKg"`
+	Javascript   string                   `yaml:"javascript"`
 }
 
 func (a mappedPostProcessAction) ToPostProcessAction() (postProcessAction, error) {
 	var found string
 	var ret postProcessAction
 
+	ensureOnly := func(field string) error {
+		if found != "" {
+			return fmt.Errorf("post-process actions must have a single field, found %s and %s", found, field)
+		}
+		found = field
+		return nil
+	}
+
 	if a.ParseDate != "" {
 		found = "parseDate"
 		action := postProcessParseDate(a.ParseDate)
 		ret = &action
 	}
 	if len(a.Replace) > 0 {
-		if found != "" {
-			return nil, fmt.Errorf("post-process actions must have a single field, found %s and %s", found, "replace")
+		if err := ensureOnly("replace"); err != nil {
+			return nil, err
 		}
-		found = "replace"
 		action := postProcessReplace(a.Replace)
 		ret = &action
 	}
 	if a.SubScraper != nil {
-		if found != "" {
-			return nil, fmt.Errorf("post-process actions must have a single field, found %s and %s", found, "subScraper")
+		if err := ensureOnly("subScraper"); err != nil {
+			return nil, err
 		}
-		found = "subScraper"
 		action := postProcessSubScraper(*a.SubScraper)
 		ret = &action
 	}
 	if a.Map != nil {
-		if found != "" {
-			return nil, fmt.Errorf("post-process actions must have a single field, found %s and %s", found, "map")
+		if err := ensureOnly("map"); err != nil {
+			return nil, err
 		}
-		found = "map"
 		action := postProcessMap(a.Map)
 		ret = &action
 	}
 	if a.FeetToCm {
-		if found != "" {
-			return nil, fmt.Errorf("post-process actions must have a single field, found %s and %s", found, "feetToCm")
+		if err := ensureOnly("feetToCm"); err != nil {
+			return nil, err
 		}
-		found = "feetToCm"
 		action := postProcessFeetToCm(a.FeetToCm)
 		ret = &action
 	}
 	if a.LbToKg {
-		if found != "" {
-			return nil, fmt.Errorf("post-process actions must have a single field, found %s and %s", found, "lbToKg")
+		if err := ensureOnly("lbToKg"); err != nil {
+			return nil, err
 		}
-		found = "lbToKg"
 		action := postProcessLbToKg(a.LbToKg)
 		ret = &action
 	}
 	if a.SubtractDays {
-		if found != "" {
-			return nil, fmt.Errorf("post-process actions must have a single field, found %s and %s", found, "subtractDays")
+		if err := ensureOnly("subtractDays"); err != nil {
+			return nil, err
 		}
-		// found = "subtractDays"
 		action := postProcessSubtractDays(a.SubtractDays)
 		ret = &action
 	}
+	if a.Javascript != "" {
+		if err := ensureOnly("javascript"); err != nil {
+			return nil, err
+		}
+		action := postProcessJavascript(a.Javascript)
+		ret = &action
+	}
 
 	if ret == nil {
 		return nil, errors.New("invalid post-process action")