Feature/#8 date diff (#175)

pkg/stdlib/datetime/diff.go

@@ -0,0 +1,93 @@
+package datetime
+
+import (
+	"context"
+	"strings"
+
+	"github.com/MontFerret/ferret/pkg/runtime/core"
+	"github.com/MontFerret/ferret/pkg/runtime/values"
+	"github.com/pkg/errors"
+)
+
+// DateDiff returns the difference between two dates in given time unit.
+// @params date1   (DateTime) - first DateTime.
+// @params date2   (DateTime) - second DateTime.
+// @params unit    (String)   - time unit to return the difference in.
+// @params asFloat (Boolean, optional) - if true amount of unit will be as float.
+// @return (Int, Float) - difference between date1 and date2.
+func DateDiff(_ context.Context, args ...core.Value) (core.Value, error) {
+	err := core.ValidateArgs(args, 3, 4)
+	if err != nil {
+		return values.None, err
+	}
+
+	err = core.ValidateValueTypePairs(
+		core.PairValueType{Value: args[0], Types: sliceDateTime},
+		core.PairValueType{Value: args[1], Types: sliceDateTime},
+		core.PairValueType{Value: args[2], Types: sliceStringType},
+	)
+	if err != nil {
+		return values.None, err
+	}
+
+	date1 := args[0].(values.DateTime)
+	date2 := args[1].(values.DateTime)
+	unit := args[2].(values.String)
+	isFloat := values.NewBoolean(false)
+
+	if len(args) == 4 {
+		err = core.ValidateType(args[3], core.BooleanType)
+		if err != nil {
+			return values.None, err
+		}
+		isFloat = args[3].(values.Boolean)
+	}
+
+	if date1.Equal(date2.Time) {
+		if isFloat {
+			return values.NewFloat(0), nil
+		}
+		return values.NewInt(0), nil
+	}
+
+	var nsecDiff int64
+
+	if date1.After(date2.Time) {
+		nsecDiff = date1.Time.Sub(date2.Time).Nanoseconds()
+	} else {
+		nsecDiff = date2.Time.Sub(date1.Time).Nanoseconds()
+	}
+
+	unitDiff, err := nsecToUnit(float64(nsecDiff), unit.String())
+	if err != nil {
+		return values.None, err
+	}
+
+	if !isFloat {
+		return values.NewInt(int(unitDiff)), nil
+	}
+
+	return values.NewFloat(unitDiff), nil
+}
+
+func nsecToUnit(nsec float64, unit string) (float64, error) {
+	switch strings.ToLower(unit) {
+	case "y", "year", "years":
+		return nsec / 31536e12, nil
+	case "m", "month", "months":
+		return nsec / 26784e11, nil
+	case "w", "week", "weeks":
+		return nsec / 6048e11, nil
+	case "d", "day", "days":
+		return nsec / 864e11, nil
+	case "h", "hour", "hours":
+		return nsec / 36e11, nil
+	case "i", "minute", "minutes":
+		return nsec / 6e10, nil
+	case "s", "second", "seconds":
+		return nsec / 1e9, nil
+	case "f", "millisecond", "milliseconds":
+		return nsec / 1e6, nil
+	}
+	return -1, errors.Errorf("no such unit '%s'", unit)
+}