// SPDX-FileCopyrightText: 2026 Echolot contributors
// SPDX-License-Identifier: GPL-3.0-or-later

package session

import "testing"

func TestTrainBufferKeepsHeadAndDeclaresTruncation(t *testing.T) {
	s := &Session{}
	over := trainCap + 100
	for i := 0; i < over; i++ {
		s.RecordTrainPacket(7, TrainEntry{Seq: uint32(i), Size: 64})
	}
	tr, ok := s.TrainView(7)
	if !ok {
		t.Fatal("train not found")
	}
	if tr.Received != over {
		t.Fatalf("Received = %d, want %d — the count must include unbuffered packets", tr.Received, over)
	}
	if len(tr.Entries) != trainCap {
		t.Fatalf("buffered %d entries, want the cap %d", len(tr.Entries), trainCap)
	}
	if !tr.Truncated {
		t.Fatal("overflow must be declared, not silent")
	}
	// The head must survive: it is what a ring buffer would have lost.
	if tr.Entries[0].Seq != 0 || tr.Entries[trainCap-1].Seq != trainCap-1 {
		t.Fatalf("buffer kept seqs %d..%d, want the head 0..%d",
			tr.Entries[0].Seq, tr.Entries[trainCap-1].Seq, trainCap-1)
	}
}

func TestTrainEvictionDropsOldestTrain(t *testing.T) {
	s := &Session{}
	for id := uint32(0); id < maxTrains+2; id++ {
		s.RecordTrainPacket(id, TrainEntry{Seq: 1})
	}
	if _, ok := s.TrainView(0); ok {
		t.Fatal("oldest train should have been evicted")
	}
	if _, ok := s.TrainView(1); ok {
		t.Fatal("second-oldest train should have been evicted")
	}
	if _, ok := s.TrainView(maxTrains + 1); !ok {
		t.Fatal("newest train missing")
	}
	if got := len(s.Trains()); got != maxTrains {
		t.Fatalf("holding %d trains, want %d", got, maxTrains)
	}
}

func TestTrainViewReturnsACopy(t *testing.T) {
	s := &Session{}
	s.RecordTrainPacket(3, TrainEntry{Seq: 10})
	tr, _ := s.TrainView(3)
	tr.Entries[0].Seq = 99
	again, _ := s.TrainView(3)
	if again.Entries[0].Seq != 10 {
		t.Fatal("TrainView leaked the internal slice")
	}
}