Stash rating system (#2830)

* add rating100 fields to represent rating range 1-100
* deprecate existing (1-5) rating fields
* add half- and quarter-star options for rating system
* add decimal rating system option

Co-authored-by: WithoutPants <53250216+WithoutPants@users.noreply.github.com>

pkg/models/rating.go

@@ -0,0 +1,69 @@
+package models
+
+import (
+	"fmt"
+	"io"
+	"math"
+	"strconv"
+)
+
+type RatingSystem string
+
+const (
+	FiveStar             = "FiveStar"
+	FivePointFiveStar    = "FivePointFiveStar"
+	FivePointTwoFiveStar = "FivePointTwoFiveStar"
+	// TenStar              = "TenStar"
+	// TenPointFiveStar     = "TenPointFiveStar"
+	// TenPointTwoFiveStar  = "TenPointTwoFiveStar"
+	TenPointDecimal = "TenPointDecimal"
+)
+
+func (e RatingSystem) IsValid() bool {
+	switch e {
+	// case FiveStar, FivePointFiveStar, FivePointTwoFiveStar, TenStar, TenPointFiveStar, TenPointTwoFiveStar, TenPointDecimal:
+	case FiveStar, FivePointFiveStar, FivePointTwoFiveStar, TenPointDecimal:
+		return true
+	}
+	return false
+}
+
+func (e RatingSystem) String() string {
+	return string(e)
+}
+
+func (e *RatingSystem) UnmarshalGQL(v interface{}) error {
+	str, ok := v.(string)
+	if !ok {
+		return fmt.Errorf("enums must be strings")
+	}
+
+	*e = RatingSystem(str)
+	if !e.IsValid() {
+		return fmt.Errorf("%s is not a valid RatingSystem", str)
+	}
+	return nil
+}
+
+func (e RatingSystem) MarshalGQL(w io.Writer) {
+	fmt.Fprint(w, strconv.Quote(e.String()))
+}
+
+const (
+	maxRating100 = 100
+	maxRating5   = 5
+	minRating5   = 1
+	minRating100 = 20
+)
+
+// Rating100To5 converts a 1-100 rating to a 1-5 rating.
+// Values <= 30 are converted to 1. Otherwise, rating is divided by 20 and rounded to the nearest integer.
+func Rating100To5(rating100 int) int {
+	val := math.Round((float64(rating100) / 20))
+	return int(math.Max(minRating5, math.Min(maxRating5, val)))
+}
+
+// Rating5To100 converts a 1-5 rating to a 1-100 rating
+func Rating5To100(rating5 int) int {
+	return int(math.Max(minRating100, math.Min(maxRating100, float64(rating5*20))))
+}