package geo

import (
	"bytes"
	"context"
	"encoding/binary"
	"errors"
	"os"
	"path/filepath"
	"testing"
	"time"
)

// pathologicalMMDB builds a structurally valid IPv4 database of 32 nodes
// whose two children are both the next node: 2^32 network paths through 32
// nodes (code review R8-1).
func pathologicalMMDB(t *testing.T) string {
	t.Helper()
	const nodes = 32
	var buf bytes.Buffer
	rec := func(v uint32) { buf.Write([]byte{byte(v >> 16), byte(v >> 8), byte(v)}) } // 24-bit records
	for i := 0; i < nodes; i++ {
		next := uint32(i + 1)
		if i == nodes-1 {
			next = nodes + 16 // data section offset 0
		}
		rec(next)
		rec(next)
	}
	buf.Write(make([]byte, 16)) // data section separator
	buf.WriteByte(0xE0)         // the one record: an empty map
	str := func(s string) { buf.WriteByte(0x40 | byte(len(s))); buf.WriteString(s) }
	u16 := func(v uint16) { buf.WriteByte(0xA2); binary.Write(&buf, binary.BigEndian, v) }
	u32 := func(v uint32) { buf.WriteByte(0xC4); binary.Write(&buf, binary.BigEndian, v) }
	buf.WriteString("\xAB\xCD\xEFMaxMind.com")
	buf.WriteByte(0xE0 | 9) // metadata map, 9 keys
	str("node_count")
	u32(nodes)
	str("record_size")
	u16(24)
	str("ip_version")
	u16(4)
	str("database_type")
	str("Pathological")
	str("languages")
	buf.Write([]byte{0x00, 0x04}) // array of 0
	str("binary_format_major_version")
	u16(2)
	str("binary_format_minor_version")
	u16(0)
	str("build_epoch")
	buf.Write([]byte{0x08, 0x02}) // uint64, 8 bytes
	binary.Write(&buf, binary.BigEndian, uint64(time.Now().Unix()))
	str("description")
	buf.WriteByte(0xE0) // empty map
	p := filepath.Join(t.TempDir(), "dag.mmdb")
	if err := os.WriteFile(p, buf.Bytes(), 0o644); err != nil {
		t.Fatal(err)
	}
	return p
}

func TestOpenMMDBRefusesAPathologicalTreeInTime(t *testing.T) {
	p := pathologicalMMDB(t)
	start := time.Now()
	_, err := OpenMMDBVerified(context.Background(), p)
	if !errors.Is(err, ErrSearchTreeTooLarge) {
		t.Fatalf("err = %v, want ErrSearchTreeTooLarge", err)
	}
	if d := time.Since(start); d > 5*time.Second {
		t.Fatalf("took %s", d)
	}
	// The real fixtures still open.
	for _, f := range []string{"GeoIP2-City-Test.mmdb", "GeoIP2-Country-Test.mmdb", "MaxMind-DB-test-ipv4-24.mmdb"} {
		m, err := OpenMMDBVerified(context.Background(), "testdata/"+f)
		if err != nil {
			t.Fatalf("%s: %v", f, err)
		}
		m.Close()
	}
}

// TestRealDatabaseOpensVerified runs only with GEOIP_REAL_MMDB set to a real
// database (DB-IP Lite, GeoLite2): the bounded walk must accept it.
func TestRealDatabaseOpensVerified(t *testing.T) {
	p := os.Getenv("GEOIP_REAL_MMDB")
	if p == "" {
		t.Skip("set GEOIP_REAL_MMDB to a real .mmdb")
	}
	start := time.Now()
	m, err := OpenMMDBVerified(context.Background(), p)
	if err != nil {
		t.Fatal(err)
	}
	m.Close()
	t.Logf("%s verified in %s", m.Source(), time.Since(start))
}