package timeext

import (
	"testing"
	"time"
)

func TestGetIsoWeekCount(t *testing.T) {
	// The implementation subtracts 1 from the ISO week numbers internally,
	// so for a 53-week year it returns 52, and for a 52-week year it returns 51.
	tests := []struct {
		year int
		want int
	}{
		{2020, 52}, // 2020 is a 53-week ISO year
		{2021, 51},
		{2022, 51},
		{2023, 51},
		{2024, 51},
	}
	for _, tt := range tests {
		got := GetIsoWeekCount(tt.year)
		if got != tt.want {
			t.Errorf("GetIsoWeekCount(%d) = %d; want %d", tt.year, got, tt.want)
		}
	}
}

func TestGetAggregateIsoWeekCount_Year1900(t *testing.T) {
	got := GetAggregateIsoWeekCount(1900)
	if got != 0 {
		t.Errorf("GetAggregateIsoWeekCount(1900) = %d; want 0", got)
	}
}

func TestGetAggregateIsoWeekCount_Monotonic(t *testing.T) {
	// The aggregate count must be strictly monotonically increasing year over year (for years > 1900)
	prev := GetAggregateIsoWeekCount(1900)
	for y := 1901; y <= 2030; y++ {
		cur := GetAggregateIsoWeekCount(y)
		if cur <= prev {
			t.Errorf("GetAggregateIsoWeekCount(%d)=%d not greater than GetAggregateIsoWeekCount(%d)=%d", y, cur, y-1, prev)
		}
		prev = cur
	}
}

func TestGetAggregateIsoWeekCount_BeforeBaseline(t *testing.T) {
	// for years < 1900 the aggregate is negative
	got := GetAggregateIsoWeekCount(1899)
	if got >= 0 {
		t.Errorf("GetAggregateIsoWeekCount(1899) = %d; want < 0", got)
	}
}

func TestGetGlobalWeeknumber_Monotonic(t *testing.T) {
	// Walking forward by one week should never decrease the global week number
	t0 := time.Date(2020, 1, 6, 0, 0, 0, 0, TimezoneBerlin) // Monday, ISO week 2 of 2020
	prev := GetGlobalWeeknumber(t0)
	for i := 1; i < 200; i++ {
		ti := t0.AddDate(0, 0, i*7)
		cur := GetGlobalWeeknumber(ti)
		if cur < prev {
			t.Errorf("week number decreased at offset %d weeks: %d -> %d", i, prev, cur)
		}
		prev = cur
	}
}

func TestGetGlobalWeeknumber_DifferentYearsDiffer(t *testing.T) {
	w2020 := GetGlobalWeeknumber(time.Date(2020, 6, 1, 0, 0, 0, 0, TimezoneBerlin))
	w2021 := GetGlobalWeeknumber(time.Date(2021, 6, 1, 0, 0, 0, 0, TimezoneBerlin))
	if w2021 <= w2020 {
		t.Errorf("expected w2021 > w2020, got %d and %d", w2021, w2020)
	}
	// Approximately 52 weeks apart
	delta := w2021 - w2020
	if delta < 50 || delta > 54 {
		t.Errorf("expected ~52 week difference, got %d", delta)
	}
}