package backup

import "testing"

// TestTier2FitsHeadroom covers the size-aware rootfs-headroom guard that protects the ~8 GB guest
// rootfs from being filled by a Tier 2 SSD copy (reserve = max(2 GB, 20% of total)).
func TestTier2FitsHeadroom(t *testing.T) {
	cases := []struct {
		name                     string
		availGB, totalGB, unitGB float64
		want                     bool
	}{
		// 8 GB rootfs, ~2.4 GB free: a tiny unit fits (reserve = 2 GB), a 1 GB unit does NOT.
		{"8G rootfs, tiny unit fits", 2.4, 8.0, 0.02, true},
		{"8G rootfs, 1G unit refused", 2.4, 8.0, 1.0, false},
		{"8G rootfs, 0.3G unit fits", 2.4, 8.0, 0.3, true},
		// Reserve is the larger of 2 GB and 20%: on 8 GB, 20% = 1.6 GB < 2 GB, so 2 GB applies.
		{"8G rootfs exactly at 2G reserve", 2.0, 8.0, 0.0, true},
		{"8G rootfs just under reserve", 2.0, 8.0, 0.01, false},
		// Large drive: 20% reserve dominates (204.8 GB on a 1 TB drive).
		{"1TB drive, 50G unit fits", 500.0, 1024.0, 50.0, true},
		{"1TB drive, 320G unit refused (under 20% reserve)", 500.0, 1024.0, 320.0, false},
	}
	for _, c := range cases {
		if got := tier2FitsHeadroom(c.availGB, c.totalGB, c.unitGB); got != c.want {
			t.Errorf("%s: tier2FitsHeadroom(avail=%.2f,total=%.2f,unit=%.2f)=%v want %v",
				c.name, c.availGB, c.totalGB, c.unitGB, got, c.want)
		}
	}
}