package imapx

import (
	"testing"

	"github.com/emersion/go-imap/v2"
)

// metaBatches must tile the sequence 1..total into contiguous, non-overlapping
// windows of at most batchSize, covering every message exactly once. A single
// unbounded FETCH 1:* is what wedges large mailboxes; batching keeps each
// command short so the server stays responsive and ctx can be checked between
// windows.
func TestMetaBatches(t *testing.T) {
	cases := []struct {
		total, size uint32
		want        []imap.SeqRange
	}{
		{0, 1000, nil},
		{1, 1000, []imap.SeqRange{{Start: 1, Stop: 1}}},
		{1000, 1000, []imap.SeqRange{{Start: 1, Stop: 1000}}},
		{1001, 1000, []imap.SeqRange{{Start: 1, Stop: 1000}, {Start: 1001, Stop: 1001}}},
		{2500, 1000, []imap.SeqRange{{Start: 1, Stop: 1000}, {Start: 1001, Stop: 2000}, {Start: 2001, Stop: 2500}}},
	}
	for _, c := range cases {
		got := metaBatches(c.total, c.size)
		if len(got) != len(c.want) {
			t.Fatalf("total=%d size=%d: got %d windows %v, want %d %v", c.total, c.size, len(got), got, len(c.want), c.want)
		}
		for i := range got {
			if got[i] != c.want[i] {
				t.Fatalf("total=%d size=%d window %d: got %+v want %+v", c.total, c.size, i, got[i], c.want[i])
			}
		}
	}
}

// Every window must be within 1..total and the windows must be gap-free so no
// message is skipped or fetched twice.
func TestMetaBatchesCoverage(t *testing.T) {
	const total, size = 4321, 1000
	got := metaBatches(total, size)
	if got[0].Start != 1 {
		t.Fatalf("first window must start at 1, got %d", got[0].Start)
	}
	if last := got[len(got)-1]; last.Stop != total {
		t.Fatalf("last window must stop at total=%d, got %d", total, last.Stop)
	}
	for i := 1; i < len(got); i++ {
		if got[i].Start != got[i-1].Stop+1 {
			t.Fatalf("gap/overlap between window %d (%+v) and %d (%+v)", i-1, got[i-1], i, got[i])
		}
	}
}