package report

import (
	"testing"
	"time"
)

func on(s string) time.Time {
	t, err := time.Parse("2006-01-02", s)
	if err != nil {
		panic(err)
	}
	return t
}

// The axis opens on the month that has just ended, whatever the index holds.
func TestPeriodsDefaultsToLastMonth(t *testing.T) {
	ps := Periods(on("2026-08-23"), []string{"2026-08", "2026-07", "2026-06"})
	p := ps[DefaultIndex(ps)]
	if p.Label != LastMonth {
		t.Fatalf("default = %q, want %q", p.Label, LastMonth)
	}
	if p.From != "2026-07-01" || p.To != "2026-07-31" {
		t.Errorf("last month = %s…%s, want the whole of July", p.From, p.To)
	}
	if p.Span != "2026-07" {
		t.Errorf("span = %q, want the month it stands for", p.Span)
	}
}

// An index that stops short of last month still opens there: an empty report
// for the window asked for beats a full one for a window nobody chose.
func TestPeriodsDefaultsToLastMonthWithNothingInIt(t *testing.T) {
	ps := Periods(on("2026-08-23"), []string{"2026-03", "2026-02"})
	if p := ps[DefaultIndex(ps)]; p.Label != LastMonth {
		t.Fatalf("default = %q, want %q", p.Label, LastMonth)
	}
}

// The named windows come first, widest to narrowest, and the months follow in
// reverse order, skipping the ones the named windows already name.
func TestPeriodsOrder(t *testing.T) {
	ps := Periods(on("2026-08-23"), []string{"2026-09", "2026-08", "2026-07", "2026-06", "2026-01"})
	var got []string
	for _, p := range ps {
		got = append(got, p.Label)
	}
	want := []string{
		"all time", "this year", "last 12 months", "last 3 months",
		"this month", LastMonth, "2026-06", "2026-01",
	}
	if len(got) != len(want) {
		t.Fatalf("periods = %v, want %v", got, want)
	}
	for i := range want {
		if got[i] != want[i] {
			t.Fatalf("periods = %v, want %v", got, want)
		}
	}
}

// A month is bounded by its own length, not by a fixed 30 or 31 days.
func TestPeriodsMonthEnds(t *testing.T) {
	ps := Periods(on("2026-03-15"), []string{"2026-02"})
	p := ps[DefaultIndex(ps)]
	if p.From != "2026-02-01" || p.To != "2026-02-28" {
		t.Errorf("February 2026 = %s…%s, want the 1st to the 28th", p.From, p.To)
	}
}

// A rolling window runs to the end of this month rather than to the last
// complete one: it is asked in order to see what is happening now.
func TestPeriodsRollingWindows(t *testing.T) {
	ps := Periods(on("2026-08-23"), nil)
	for _, tc := range []struct{ label, from, to string }{
		{"last 3 months", "2026-06-01", "2026-08-31"},
		{"last 12 months", "2025-09-01", "2026-08-31"},
		{"this year", "2026-01-01", "2026-12-31"},
	} {
		var found bool
		for _, p := range ps {
			if p.Label != tc.label {
				continue
			}
			found = true
			if p.From != tc.from || p.To != tc.to {
				t.Errorf("%s = %s…%s, want %s…%s", tc.label, p.From, p.To, tc.from, tc.to)
			}
		}
		if !found {
			t.Errorf("no %q window", tc.label)
		}
	}
}

// All time is unbounded on both sides, so nothing has to special-case it.
func TestPeriodsAllTimeIsUnbounded(t *testing.T) {
	ps := Periods(on("2026-08-23"), []string{"2026-01"})
	if ps[0].Label != "all time" || ps[0].From != "" || ps[0].To != "" {
		t.Errorf("first window = %+v, want an unbounded all time", ps[0])
	}
}