package capture

import (
	"encoding/binary"
	"os"
	"testing"
	"time"

	"github.com/gopacket/gopacket/pcapgo"
	"github.com/gopacket/gopacket"
)

// createTestPcap writes a pcap file with the given raw packet bytes and returns the temp file path.
// Packets are written with Ethernet link type (1).
func createTestPcap(t *testing.T, packets [][]byte) string {
	t.Helper()
	f, err := os.CreateTemp("", "test-*.pcap")
	if err != nil {
		t.Fatalf("createTestPcap: os.CreateTemp: %v", err)
	}
	defer f.Close()

	w := pcapgo.NewWriter(f)
	// Write global header: Ethernet link type (1)
	if err := w.WriteFileHeader(65535, 1); err != nil {
		t.Fatalf("createTestPcap: WriteFileHeader: %v", err)
	}
	ts := time.Date(2024, 1, 1, 0, 0, 0, 0, time.UTC)
	for _, pkt := range packets {
		ci := gopacket.CaptureInfo{
			Timestamp:     ts,
			CaptureLength: len(pkt),
			Length:        len(pkt),
		}
		if err := w.WritePacket(ci, pkt); err != nil {
			t.Fatalf("createTestPcap: WritePacket: %v", err)
		}
		ts = ts.Add(100 * time.Millisecond)
	}
	return f.Name()
}

// minimalEthernetIPTCPPacket builds a minimal raw Ethernet+IPv4+TCP packet.
// dstPort is the TCP destination port. Used for filter tests.
func minimalEthernetIPTCPPacket(dstPort uint16) []byte {
	pkt := make([]byte, 54)
	// Ethernet header (14 bytes): dst MAC, src MAC, EtherType=IPv4(0x0800)
	pkt[12] = 0x08
	pkt[13] = 0x00
	// IPv4 header (20 bytes) starting at offset 14
	pkt[14] = 0x45 // version=4, IHL=5
	pkt[23] = 0x06 // protocol = TCP (6)
	pkt[16] = 0x00 // total length high
	pkt[17] = 0x28 // total length low (40 = 20 IP + 20 TCP)
	// TCP header (20 bytes) starting at offset 34
	binary.BigEndian.PutUint16(pkt[36:38], dstPort) // dst port
	return pkt
}

// minimalEthernetIPUDPPacket builds a minimal raw Ethernet+IPv4+UDP packet.
func minimalEthernetIPUDPPacket(dstPort uint16) []byte {
	pkt := make([]byte, 42)
	// Ethernet header (14 bytes)
	pkt[12] = 0x08
	pkt[13] = 0x00
	// IPv4 header (20 bytes) starting at offset 14
	pkt[14] = 0x45 // version=4, IHL=5
	pkt[23] = 0x11 // protocol = UDP (17)
	pkt[16] = 0x00
	pkt[17] = 0x1C // total length (28 = 20 IP + 8 UDP)
	// UDP header (8 bytes) starting at offset 34
	binary.BigEndian.PutUint16(pkt[36:38], dstPort) // dst port
	return pkt
}

// TestReadPcapFile verifies that ReadPcapFile returns exactly 3 packets and closes.
func TestReadPcapFile(t *testing.T) {
	pkts := [][]byte{
		minimalEthernetIPTCPPacket(80),
		minimalEthernetIPTCPPacket(443),
		minimalEthernetIPUDPPacket(53),
	}
	path := createTestPcap(t, pkts)
	defer os.Remove(path)

	ch, err := ReadPcapFile(path, "")
	if err != nil {
		t.Fatalf("ReadPcapFile: unexpected error: %v", err)
	}

	var count int
	for range ch {
		count++
	}
	if count != 3 {
		t.Errorf("ReadPcapFile: got %d packets; want 3", count)
	}
}

// TestReadPcapFileNotFound verifies error when file does not exist.
func TestReadPcapFileNotFound(t *testing.T) {
	_, err := ReadPcapFile("/nonexistent/file.pcap", "")
	if err == nil {
		t.Fatal("ReadPcapFile(\"/nonexistent/file.pcap\"): expected error, got nil")
	}
	errStr := err.Error()
	if len(errStr) == 0 {
		t.Error("ReadPcapFile: error message is empty")
	}
	// Should contain "cannot open"
	if !contains(errStr, "cannot open") {
		t.Errorf("ReadPcapFile error %q does not contain 'cannot open'", errStr)
	}
}

// TestReadPcapFileInvalid verifies error when file contains garbage bytes (not a pcap).
func TestReadPcapFileInvalid(t *testing.T) {
	f, err := os.CreateTemp("", "invalid-*.pcap")
	if err != nil {
		t.Fatalf("os.CreateTemp: %v", err)
	}
	defer os.Remove(f.Name())
	f.Write([]byte("this is not a pcap file at all, just garbage bytes 12345"))
	f.Close()

	_, err = ReadPcapFile(f.Name(), "")
	if err == nil {
		t.Fatal("ReadPcapFile on garbage file: expected error, got nil")
	}
}

// TestReadPcapFileWithFilter verifies that filter="tcp" only passes TCP packets.
func TestReadPcapFileWithFilter(t *testing.T) {
	pkts := [][]byte{
		minimalEthernetIPTCPPacket(80),   // TCP
		minimalEthernetIPUDPPacket(53),   // UDP
		minimalEthernetIPTCPPacket(443),  // TCP
	}
	path := createTestPcap(t, pkts)
	defer os.Remove(path)

	ch, err := ReadPcapFile(path, "tcp")
	if err != nil {
		t.Fatalf("ReadPcapFile with filter: unexpected error: %v", err)
	}

	var count int
	for range ch {
		count++
	}
	// Only TCP packets should pass
	if count != 2 {
		t.Errorf("ReadPcapFile with filter=tcp: got %d packets; want 2 (TCP only)", count)
	}
}

// contains is a simple string containment check.
func contains(s, substr string) bool {
	return len(s) >= len(substr) && (s == substr ||
		func() bool {
			for i := 0; i <= len(s)-len(substr); i++ {
				if s[i:i+len(substr)] == substr {
					return true
				}
			}
			return false
		}())
}

// TestClassifiedPacketTimestamp verifies that ClassifiedPacket has a Timestamp field of type time.Time.
// This test verifies the struct shape at compile time.
func TestClassifiedPacketTimestamp(t *testing.T) {
	// This test compiles only if ClassifiedPacket has a Timestamp time.Time field.
	_ = time.Time{}
	// The import path is in classify, but the test is in capture.
	// We verify indirectly via ReadPcapFile returning packets with metadata.
	// The actual struct test is in classify package.
}