Add configuration and CLI foundation

internal/timeutil/clock.go

@@ -0,0 +1,22 @@
+// Package timeutil provides time-zone, clock, and period helpers.
+package timeutil
+
+import "time"
+
+type Clock interface {
+	Now() time.Time
+}
+
+type SystemClock struct{}
+
+func (SystemClock) Now() time.Time {
+	return time.Now()
+}
+
+type FixedClock struct {
+	Time time.Time
+}
+
+func (c FixedClock) Now() time.Time {
+	return c.Time
+}

internal/timeutil/parse.go

@@ -0,0 +1,49 @@
+package timeutil
+
+import (
+	"fmt"
+	"strings"
+	"time"
+)
+
+const DateLayout = "2006-01-02"
+const LocalDateTimeLayout = "2006-01-02T15:04"
+
+func LoadLocation(name string) (*time.Location, error) {
+	location, err := time.LoadLocation(name)
+	if err == nil {
+		return location, nil
+	}
+	if strings.Contains(name, "/") {
+		return nil, fmt.Errorf("load timezone %q: %w", name, err)
+	}
+	location, chicagoErr := time.LoadLocation("America/" + name)
+	if chicagoErr == nil {
+		return location, nil
+	}
+	return nil, fmt.Errorf("load timezone %q: %w", name, err)
+}
+
+func LocalDate(now time.Time, location *time.Location) time.Time {
+	local := now.In(location)
+	return time.Date(local.Year(), local.Month(), local.Day(), 0, 0, 0, 0, location)
+}
+
+func ParseLocalDate(value string, location *time.Location) (time.Time, error) {
+	parsed, err := time.ParseInLocation(DateLayout, value, location)
+	if err != nil {
+		return time.Time{}, fmt.Errorf("parse date %q as YYYY-MM-DD: %w", value, err)
+	}
+	return parsed, nil
+}
+
+func ParseStormTime(value string, location *time.Location) (time.Time, error) {
+	if parsed, err := time.Parse(time.RFC3339, value); err == nil {
+		return parsed, nil
+	}
+	parsed, err := time.ParseInLocation(LocalDateTimeLayout, value, location)
+	if err != nil {
+		return time.Time{}, fmt.Errorf("parse storm time %q as YYYY-MM-DDTHH:MM or RFC3339: %w", value, err)
+	}
+	return parsed, nil
+}

internal/timeutil/parse_test.go

@@ -0,0 +1,49 @@
+package timeutil
+
+import (
+	"testing"
+	"time"
+)
+
+func TestLoadLocationAcceptsChicagoAlias(t *testing.T) {
+	location, err := LoadLocation("Chicago")
+	if err != nil {
+		t.Fatalf("LoadLocation() error = %v", err)
+	}
+	if location.String() != "America/Chicago" {
+		t.Fatalf("location = %q, want America/Chicago", location.String())
+	}
+}
+
+func TestParseLocalDate(t *testing.T) {
+	location := time.FixedZone("Test", -5*60*60)
+	got, err := ParseLocalDate("2026-05-29", location)
+	if err != nil {
+		t.Fatalf("ParseLocalDate() error = %v", err)
+	}
+	if got.Format(DateLayout) != "2026-05-29" {
+		t.Fatalf("date = %s, want 2026-05-29", got.Format(DateLayout))
+	}
+	if got.Location() != location {
+		t.Fatalf("location = %v, want test location", got.Location())
+	}
+}
+
+func TestParseStormTime(t *testing.T) {
+	location := time.FixedZone("Test", -5*60*60)
+	local, err := ParseStormTime("2026-05-29T18:00", location)
+	if err != nil {
+		t.Fatalf("ParseStormTime(local) error = %v", err)
+	}
+	if local.Location() != location {
+		t.Fatalf("local location = %v, want test location", local.Location())
+	}
+
+	rfc3339, err := ParseStormTime("2026-05-29T18:00:00-05:00", location)
+	if err != nil {
+		t.Fatalf("ParseStormTime(rfc3339) error = %v", err)
+	}
+	if rfc3339.Format(time.RFC3339) != "2026-05-29T18:00:00-05:00" {
+		t.Fatalf("rfc3339 = %s, want preserved offset time", rfc3339.Format(time.RFC3339))
+	}
+}