feat: release generic composition mapping and middleware factories

cmd/go-omni/apigen/testdata/composition/amount.go

@@ -0,0 +1,52 @@
+package amount
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"math/big"
+	"regexp"
+)
+
+// This fixture's business policy is exact decimal HALF_UP. The framework does
+// not choose its precision, rounding mode or currency.
+type Money string
+
+var decimalPattern = regexp.MustCompile(`^-?[0-9]+(\.[0-9]+)?$`)
+
+func (m Money) String() string {
+	if m == "" {
+		return "0.00"
+	}
+	return string(m)
+}
+func (m Money) MarshalJSON() ([]byte, error) { return json.Marshal(m.String()) }
+func (m *Money) UnmarshalJSON(data []byte) error {
+	var text string
+	if err := json.Unmarshal(data, &text); err != nil {
+		return err
+	}
+	if !decimalPattern.MatchString(text) {
+		return errors.New("invalid decimal")
+	}
+	value, ok := new(big.Rat).SetString(text)
+	if !ok {
+		return errors.New("invalid decimal")
+	}
+	value.Mul(value, big.NewRat(100, 1))
+	sign := value.Sign()
+	value.Abs(value)
+	cents, rem := new(big.Int), new(big.Int)
+	cents.QuoRem(value.Num(), value.Denom(), rem)
+	if rem.Mul(rem, big.NewInt(2)).Cmp(value.Denom()) >= 0 {
+		cents.Add(cents, big.NewInt(1))
+	}
+	whole, fraction := new(big.Int), new(big.Int)
+	whole.QuoRem(cents, big.NewInt(100), fraction)
+	prefix := ""
+	if sign < 0 && cents.Sign() != 0 {
+		prefix = "-"
+	}
+	*m = Money(fmt.Sprintf("%s%s.%02d", prefix, whole.String(), fraction.Int64()))
+	return nil
+}