package routetable_test

import (
	"math"
	"net/netip"
	"reflect"
	"testing"
	"time"

	"github.com/bits-and-blooms/bitset"

	"git.eeqj.de/sneak/routewatch/internal/routetable"
)

// originChange returns the origin change the table records for prefix and asn
// at the clock's time, announced or withdrawn, with peerCount peers.
func originChange(
	prefix netip.Prefix, asn int, announced bool, peerCount int, at time.Time,
) routetable.OriginChange {
	return routetable.OriginChange{
		Prefix:    prefix,
		OriginASN: asn,
		Announced: announced,
		PeerCount: peerCount,
		Time:      at,
	}
}

// TestOriginChangesRecordAnnouncedAndWithdrawn checks that a prefix and origin
// AS pair records an announced row when it gains its first peer, nothing for a
// second peer, and a withdrawn row when it loses its last peer.
func TestOriginChangesRecordAnnouncedAndWithdrawn(t *testing.T) {
	t.Parallel()

	now := at(0)
	table := routetable.New(routetable.Params{
		Now: func() time.Time { return now },
	})
	prefix := netip.MustParsePrefix(prefixV4)

	table.Announce(prefix, asA, routeOf(peerA, asA, 10))
	table.Announce(prefix, asA, routeOf(peerB, asA, 20))

	checkOriginChanges(t, table, []routetable.OriginChange{
		originChange(prefix, asA, true, 1, now),
	})

	table.Withdraw(prefix, peerA)
	table.Withdraw(prefix, peerB)

	checkOriginChanges(t, table, []routetable.OriginChange{
		originChange(prefix, asA, false, 0, now),
	})
}

// TestOriginChangesRecordAPeerMovingOrigin checks that a peer moving from one
// origin AS to another records a withdrawn row for the old one and an
// announced row for the new one.
func TestOriginChangesRecordAPeerMovingOrigin(t *testing.T) {
	t.Parallel()

	now := at(0)
	table := routetable.New(routetable.Params{
		Now: func() time.Time { return now },
	})
	prefix := netip.MustParsePrefix(prefixV4)

	table.Announce(prefix, asA, routeOf(peerA, asA, 10))
	table.Announce(prefix, asB, routeOf(peerA, asB, 20))

	checkOriginChanges(t, table, []routetable.OriginChange{
		originChange(prefix, asA, true, 1, now),
		originChange(prefix, asA, false, 0, now),
		originChange(prefix, asB, true, 1, now),
	})
}

// TestOriginChangesRecordPeersDown checks that PeersDown records a withdrawn
// row for each prefix and origin AS pair it empties.
func TestOriginChangesRecordPeersDown(t *testing.T) {
	t.Parallel()

	now := at(0)
	table := routetable.New(routetable.Params{
		Now: func() time.Time { return now },
	})
	v4 := netip.MustParsePrefix(prefixV4)
	v6 := netip.MustParsePrefix(prefixV6)

	table.Announce(v4, asA, routeOf(peerA, asA, 10))
	table.Announce(v6, asA, routeOf(peerA, asA, 10))
	table.Announce(v4, asB, routeOf(peerB, asB, 20))

	table.PeersDown([]string{peerA})

	// peerA carried v4 and v6 with asA; both pairs are emptied. peerB still
	// carries v4 with asB, so that pair is not.
	checkOriginChanges(t, table, []routetable.OriginChange{
		originChange(v4, asA, true, 1, now),
		originChange(v6, asA, true, 1, now),
		originChange(v4, asB, true, 2, now),
		originChange(v4, asA, false, 1, now),
		originChange(v6, asA, false, 0, now),
	})
}

// TestOriginChangesLoadRecordsNothing checks that Load records no origin
// change.
func TestOriginChangesLoadRecordsNothing(t *testing.T) {
	t.Parallel()

	table := routetable.New(routetable.Params{
		PeerNumbers: map[string]uint{peerA: 0},
	})
	prefix := netip.MustParsePrefix(prefixV4)

	peers := new(bitset.BitSet)
	peers.Set(0)

	table.Load(routetable.Change{
		Prefix:    prefix,
		OriginASN: asA,
		Peers:     peers,
		Routes:    []routetable.Route{routeOf(peerA, asA, 10)},
	})

	changes, dropped := table.TakeOriginChanges(math.MaxInt)
	if dropped != 0 || len(changes) != 0 {
		t.Errorf("TakeOriginChanges = %+v, %d; want none", changes, dropped)
	}
}

// TestOriginChangesTakeReturnsOldestFirst checks that TakeOriginChanges
// returns the changes oldest first and at most max.
func TestOriginChangesTakeReturnsOldestFirst(t *testing.T) {
	t.Parallel()

	table := routetable.New(routetable.Params{})
	prefix := netip.MustParsePrefix(prefixV4)

	table.Announce(prefix, asA, routeOf(peerA, asA, 10))
	table.Announce(prefix, asB, routeOf(peerB, asB, 20))
	table.Announce(prefix, asC, routeOf(peerC, asC, 30))

	first, dropped := table.TakeOriginChanges(2)
	if dropped != 0 {
		t.Errorf("dropped = %d, want 0", dropped)
	}

	if len(first) != 2 || first[0].OriginASN != asA || first[1].OriginASN != asB {
		t.Errorf("first TakeOriginChanges = %+v, want the first two", first)
	}

	second, _ := table.TakeOriginChanges(math.MaxInt)
	if len(second) != 1 || second[0].OriginASN != asC {
		t.Errorf("second TakeOriginChanges = %+v, want the third", second)
	}
}

// TestOriginChangesPutBackPutsRowsInFront checks that PutBackOriginChanges
// puts rows back in front, so the next TakeOriginChanges returns them first.
func TestOriginChangesPutBackPutsRowsInFront(t *testing.T) {
	t.Parallel()

	table := routetable.New(routetable.Params{})
	prefix := netip.MustParsePrefix(prefixV4)

	table.Announce(prefix, asA, routeOf(peerA, asA, 10))
	table.Announce(prefix, asB, routeOf(peerB, asB, 20))

	taken, _ := table.TakeOriginChanges(math.MaxInt)
	table.Announce(prefix, asC, routeOf(peerC, asC, 30))
	table.PutBackOriginChanges(taken)

	changes, _ := table.TakeOriginChanges(math.MaxInt)
	if len(changes) != 3 || changes[0].OriginASN != asA ||
		changes[1].OriginASN != asB || changes[2].OriginASN != asC {
		t.Errorf("TakeOriginChanges = %+v, want the put-back rows first", changes)
	}
}

// TestOriginChangesDropPastTheLimit checks that a change past 100,000 waiting
// rows is dropped and counted.
func TestOriginChangesDropPastTheLimit(t *testing.T) {
	t.Parallel()

	table := routetable.New(routetable.Params{})
	addr := netip.MustParseAddr("10.0.0.0")

	for range routetable.MaxWaitingOriginChanges + 1 {
		prefix := netip.PrefixFrom(addr, 32)
		table.Announce(prefix, asA, routeOf(peerA, asA, 10))

		addr = addr.Next()
	}

	changes, dropped := table.TakeOriginChanges(routetable.MaxWaitingOriginChanges)
	if dropped != 1 {
		t.Errorf("dropped = %d, want 1", dropped)
	}

	if len(changes) != routetable.MaxWaitingOriginChanges {
		t.Errorf("len(changes) = %d, want %d", len(changes),
			routetable.MaxWaitingOriginChanges)
	}
}

// TestOriginChangesTakeResetsTheDroppedCount checks that a TakeOriginChanges
// that reports dropped rows leaves the next one reporting none, so each drop
// is logged once, not on every later write.
func TestOriginChangesTakeResetsTheDroppedCount(t *testing.T) {
	t.Parallel()

	table := routetable.New(routetable.Params{})
	addr := netip.MustParseAddr("10.0.0.0")

	for range routetable.MaxWaitingOriginChanges + 1 {
		table.Announce(netip.PrefixFrom(addr, 32), asA, routeOf(peerA, asA, 10))
		addr = addr.Next()
	}

	_, dropped := table.TakeOriginChanges(routetable.MaxWaitingOriginChanges)
	if dropped != 1 {
		t.Fatalf("dropped = %d, want 1", dropped)
	}

	_, dropped = table.TakeOriginChanges(0)
	if dropped != 0 {
		t.Errorf("the next take's dropped = %d, want 0", dropped)
	}
}

// TestOriginChangesPutBackTrimsToTheLimit checks that putting back what a
// failed write took, after new changes filled the table again, drops the
// oldest changes past the cap and counts them, so the cap still holds. The
// clock advances one second per change, so a change's time says its age.
func TestOriginChangesPutBackTrimsToTheLimit(t *testing.T) {
	t.Parallel()

	const (
		taken = 20000
		added = 20000
	)

	now := time.Unix(0, 0)
	table := routetable.New(routetable.Params{
		Now: func() time.Time {
			now = now.Add(time.Second)

			return now
		},
	})
	addr := netip.MustParseAddr("10.0.0.0")

	announce := func(n int) {
		for range n {
			table.Announce(netip.PrefixFrom(addr, 32), asA, routeOf(peerA, asA, 10))
			addr = addr.Next()
		}
	}

	announce(routetable.MaxWaitingOriginChanges)

	takenChanges, _ := table.TakeOriginChanges(taken)

	announce(added)

	table.PutBackOriginChanges(takenChanges)

	changes, dropped := table.TakeOriginChanges(math.MaxInt)
	if dropped != added {
		t.Errorf("dropped = %d, want %d", dropped, added)
	}

	if len(changes) != routetable.MaxWaitingOriginChanges {
		t.Errorf("len(changes) = %d, want %d", len(changes),
			routetable.MaxWaitingOriginChanges)
	}

	// The put-back rows are the oldest, so they are the ones dropped. The
	// first remaining change is the one that followed them.
	if want := time.Unix(int64(added+1), 0); !changes[0].Time.Equal(want) {
		t.Errorf("first change's time = %v, want %v", changes[0].Time, want)
	}
}

// checkOriginChanges checks that TakeOriginChanges, taking every change,
// returns want.
func checkOriginChanges(
	t *testing.T, table *routetable.Table, want []routetable.OriginChange,
) {
	t.Helper()

	changes, dropped := table.TakeOriginChanges(math.MaxInt)
	if dropped != 0 {
		t.Errorf("dropped = %d, want 0", dropped)
	}

	if !reflect.DeepEqual(changes, want) {
		t.Errorf("TakeOriginChanges = %+v, want %+v", changes, want)
	}
}