// Copyright 2022 The Ip2Region Authors. All rights reserved.
// Use of this source code is governed by a Apache2.0-style
// license that can be found in the LICENSE file.

// ---
// Ip2Region database v2.0 searcher.
// @Note this is a Not thread safe implementation.
//
// @Author Lion <chenxin619315@gmail.com>
// @Date   2025/12/03

package xdb

import (
	"encoding/binary"
	"fmt"
)

const (
	Structure20      = 2
	Structure30      = 3
	HeaderInfoLength = 256
	VectorIndexRows  = 256
	VectorIndexCols  = 256
	VectorIndexSize  = 8
)

// --- Index policy define

type IndexPolicy int

const (
	VectorIndexPolicy IndexPolicy = 1
	BTreeIndexPolicy  IndexPolicy = 2
)

func (i IndexPolicy) String() string {
	switch i {
	case VectorIndexPolicy:
		return "VectorIndex"
	case BTreeIndexPolicy:
		return "BtreeIndex"
	default:
		return "unknown"
	}
}

// --- Header define

type Header struct {
	// data []byte
	Version       uint16
	IndexPolicy   IndexPolicy
	CreatedAt     uint32
	StartIndexPtr uint32
	EndIndexPtr   uint32

	// since IPv6 supporting
	IPVersion       int
	RuntimePtrBytes int
}

func NewHeader(input []byte) (*Header, error) {
	if len(input) < 16 {
		return nil, fmt.Errorf("invalid input buffer")
	}

	return &Header{
		Version:       binary.LittleEndian.Uint16(input[0:]),
		IndexPolicy:   IndexPolicy(binary.LittleEndian.Uint16(input[2:])),
		CreatedAt:     binary.LittleEndian.Uint32(input[4:]),
		StartIndexPtr: binary.LittleEndian.Uint32(input[8:]),
		EndIndexPtr:   binary.LittleEndian.Uint32(input[12:]),

		IPVersion:       int(binary.LittleEndian.Uint16(input[16:])),
		RuntimePtrBytes: int(binary.LittleEndian.Uint16(input[18:])),
	}, nil
}

func (h *Header) String() string {
	return fmt.Sprintf(
		"{version:%d, index_policy:%d, created_at:%d, start_index_ptr:%d, end_index_ptr:%d, ip_version:%d, runtime_ptr_bytes:%d}",
		h.Version, h.IndexPolicy, h.CreatedAt, h.StartIndexPtr, h.EndIndexPtr, h.IPVersion, h.RuntimePtrBytes,
	)
}