cmd/lncli: add fwdinghistory support for relative times

- introduces new parser in `cmd/lncli/arg_parse.go`
- converts start_time and end_time flags to strings
- adds default value for end_time

cmd/lncli/arg_parse_test.go

@@ -0,0 +1,88 @@
+package main
+
+import (
+	"testing"
+	"time"
+)
+
+var now = time.Date(2017, 11, 10, 7, 8, 9, 1234, time.UTC)
+
+var partTimeTests = []struct {
+	in          string
+	expected    uint64
+	errExpected bool
+}{
+	{
+		"12345",
+		uint64(12345),
+		false,
+	},
+	{
+		"-0s",
+		uint64(now.Unix()),
+		false,
+	},
+	{
+		"-1s",
+		uint64(time.Date(2017, 11, 10, 7, 8, 8, 1234, time.UTC).Unix()),
+		false,
+	},
+	{
+		"-2h",
+		uint64(time.Date(2017, 11, 10, 5, 8, 9, 1234, time.UTC).Unix()),
+		false,
+	},
+	{
+		"-3d",
+		uint64(time.Date(2017, 11, 7, 7, 8, 9, 1234, time.UTC).Unix()),
+		false,
+	},
+	{
+		"-4w",
+		uint64(time.Date(2017, 10, 13, 7, 8, 9, 1234, time.UTC).Unix()),
+		false,
+	},
+	{
+		"-5M",
+		uint64(now.Unix() - 30.44*5*24*60*60),
+		false,
+	},
+	{
+		"-6y",
+		uint64(now.Unix() - 365.25*6*24*60*60),
+		false,
+	},
+	{
+		"-999999999999999999s",
+		uint64(now.Unix() - 999999999999999999),
+		false,
+	},
+	{
+		"-9999999999999999991s",
+		0,
+		true,
+	},
+	{
+		"-7z",
+		0,
+		true,
+	},
+}
+
+// Test that parsing absolute and relative times works.
+func TestParseTime(t *testing.T) {
+	for _, test := range partTimeTests {
+		actual, err := parseTime(test.in, now)
+		if test.errExpected == (err == nil) {
+			t.Fatalf("unexpected error for %s:\n%v\n", test.in, err)
+		}
+		if actual != test.expected {
+			t.Fatalf(
+				"for %s actual and expected do not match:\n%d\n%d\n",
+				test.in,
+				actual,
+				test.expected,
+			)
+		}
+	}
+}