package timeutil

import (
	"testing"
	"time"
)

func TestPeriodOverlapUsesHalfOpenIntervals(t *testing.T) {
	start := time.Date(2026, 5, 29, 6, 0, 0, 0, time.UTC)
	left := Period{Start: start, End: start.Add(time.Hour)}
	touching := Period{Start: start.Add(time.Hour), End: start.Add(2 * time.Hour)}
	overlapping := Period{Start: start.Add(30 * time.Minute), End: start.Add(90 * time.Minute)}

	if left.Overlaps(touching) {
		t.Fatal("touching half-open periods overlap, want false")
	}
	if !left.Overlaps(overlapping) {
		t.Fatal("overlapping periods do not overlap, want true")
	}
}

func TestClockWindowHandlesOvernight(t *testing.T) {
	location := time.FixedZone("Test", -5*60*60)
	date := time.Date(2026, 5, 29, 12, 0, 0, 0, location)
	start, _ := ParseClock("22:00")
	end, _ := ParseClock("06:00")

	window := ClockWindow(date, location, start, end)
	if got := window.Start.Format("2006-01-02T15:04"); got != "2026-05-29T22:00" {
		t.Fatalf("Start = %s, want 2026-05-29T22:00", got)
	}
	if got := window.End.Format("2006-01-02T15:04"); got != "2026-05-30T06:00" {
		t.Fatalf("End = %s, want 2026-05-30T06:00", got)
	}
}

func TestClockWindowUsesCivilTimeAcrossDSTTransitions(t *testing.T) {
	location, err := LoadLocation("America/Chicago")
	if err != nil {
		t.Fatalf("LoadLocation() error = %v", err)
	}
	tests := []struct {
		name      string
		date      time.Time
		start     string
		end       string
		wantStart string
		wantEnd   string
	}{
		{
			name:      "spring-forward daytime",
			date:      time.Date(2026, time.March, 8, 12, 0, 0, 0, location),
			start:     "00:00",
			end:       "06:00",
			wantStart: "2026-03-08T00:00:00-06:00",
			wantEnd:   "2026-03-08T06:00:00-05:00",
		},
		{
			name:      "fall-back daytime",
			date:      time.Date(2026, time.November, 1, 12, 0, 0, 0, location),
			start:     "00:00",
			end:       "06:00",
			wantStart: "2026-11-01T00:00:00-05:00",
			wantEnd:   "2026-11-01T06:00:00-06:00",
		},
		{
			name:      "spring-forward overnight",
			date:      time.Date(2026, time.March, 8, 12, 0, 0, 0, location),
			start:     "22:00",
			end:       "06:00",
			wantStart: "2026-03-08T22:00:00-05:00",
			wantEnd:   "2026-03-09T06:00:00-05:00",
		},
		{
			name:      "spring-forward end of day",
			date:      time.Date(2026, time.March, 8, 12, 0, 0, 0, location),
			start:     "18:00",
			end:       "24:00",
			wantStart: "2026-03-08T18:00:00-05:00",
			wantEnd:   "2026-03-09T00:00:00-05:00",
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			start, err := ParseClock(tt.start)
			if err != nil {
				t.Fatalf("ParseClock(%q) error = %v", tt.start, err)
			}
			end, err := ParseClock(tt.end)
			if err != nil {
				t.Fatalf("ParseClock(%q) error = %v", tt.end, err)
			}

			window := ClockWindow(tt.date, location, start, end)
			if got := window.Start.Format(time.RFC3339); got != tt.wantStart {
				t.Fatalf("Start = %s, want %s", got, tt.wantStart)
			}
			if got := window.End.Format(time.RFC3339); got != tt.wantEnd {
				t.Fatalf("End = %s, want %s", got, tt.wantEnd)
			}
		})
	}
}