package index

import (
	"TsDB2/DB/core/index/btree"
	"TsDB2/DB/core/page"
	"bytes"
	"encoding/binary"
)

// BTreeHandler — B+ 树二级索引 (IndexTypeBTree)
// 叶子条目: [key(keyLen) + PKID(8B BE)]
type BTreeHandler struct{}

func init() {
	Compose.RegisterHandler(page.IndexTypeBTree, &BTreeHandler{})
	// 向后兼容：旧数据库中 IndexTypeStr=3 的索引统一用 BTreeHandler 处理
	Compose.RegisterHandler(page.IndexTypeStr, &BTreeHandler{})

	// 二级 B+ 树分裂参数 —— 写死在本文件, 不随索引元数据传递。
	// 二级键分布随机且允许重复, 对半分(50)时平均填充率最高, 故保持 50/50。
	btree.SBTSplitCfg = btree.SplitConfig{SplitPercent: 50, SequentialRight: false}
}

func (h *BTreeHandler) Insert(handle page.HandleDb, entryPage *uint32, indexKey []byte, pkID uint64, rowData []byte, keyLen int) (uint32, error) {
	entry := make([]byte, keyLen+8)
	copy(entry[:keyLen], indexKey)
	binary.BigEndian.PutUint64(entry[keyLen:], pkID)
	rootPID := *entryPage
	newRoot, err := btree.SBTInsert(rootPID, entry, handle)
	if err != nil {
		return 0, err
	}
	*entryPage = newRoot
	return newRoot, nil
}

func (h *BTreeHandler) Search(handle page.HandleDb, entryPage uint32, indexKey []byte, keyLen int, resolve RowResolver) ([]byte, bool) {
	rootPID := entryPage
	if rootPID == 0 {
		return nil, false
	}
	pkID, found := btree.SBTSearch(rootPID, indexKey[:keyLen], handle)
	if !found {
		return nil, false
	}
	// 二级索引不存行数据: 回表由索引自己完成 (上层无需知道主键索引是谁)
	if resolve != nil {
		if row, ok := resolve(pkID); ok {
			return row, true
		}
		return nil, false
	}
	pkBuf := make([]byte, 8)
	binary.BigEndian.PutUint64(pkBuf, pkID)
	return pkBuf, true
}

func (h *BTreeHandler) Delete(handle page.HandleDb, entryPage *uint32, indexKey []byte, pkID uint64, keyLen int) error {
	rootPID := *entryPage
	if rootPID == 0 {
		return page.ErrNotFound
	}
	// 二级索引允许重复 key, 用 (key, pkID) 精确定位本行的条目。
	// pkID 未知(为 0)时退回按 key 搜索一个条目。
	if pkID == 0 {
		pk, found := btree.SBTSearch(rootPID, indexKey[:keyLen], handle)
		if !found {
			return page.ErrNotFound
		}
		pkID = pk
	}
	newRoot, err := btree.SBTDeleteWithPKID(rootPID, indexKey[:keyLen], pkID, handle)
	if err != nil {
		return err
	}
	*entryPage = newRoot
	return nil
}

func (h *BTreeHandler) Update(handle page.HandleDb, entryPage *uint32, oldKey, newKey, rowData []byte, pkID uint64, keyLen int) error {
	// 二级索引条目只存 [key + pkID], 不含行数据:
	//   键未变 → 无事可做 (过去"先删再插"会让条目在重复 key 区段里错位, 属于多余动作)
	//   键变了 → 按 (oldKey, pkID) 精确删旧条目, 再插新条目
	if bytes.Equal(oldKey, newKey) {
		return nil
	}
	if oldKey != nil {
		if err := h.Delete(handle, entryPage, oldKey, pkID, len(oldKey)); err != nil && err != page.ErrNotFound {
			return err
		}
	}
	_, err := h.Insert(handle, entryPage, newKey, pkID, rowData, len(newKey))
	return err
}

// IsRowStore 二级索引不承载行数据
func (h *BTreeHandler) IsRowStore() bool { return false }

// ResolveRow 二级索引无法按 pkID 取行, 由调用方的回表函数负责
func (h *BTreeHandler) ResolveRow(handle page.HandleDb, entryPage uint32, pkID uint64, cache *[]DPRange) ([]byte, bool) {
	return nil, false
}

// SearchAll 查找相同 key 下的所有 pkID
func (h *BTreeHandler) SearchAll(handle page.HandleDb, entryPage uint32, indexKey []byte, keyLen int) ([]uint64, bool) {
	rootPID := entryPage
	if rootPID == 0 {
		return nil, false
	}
	return btree.SBTSearchAll(rootPID, indexKey[:keyLen], handle)
}

func (h *BTreeHandler) GetDataPageIDs(handle page.HandleDb, entryPage uint32) []uint32 {
	// 二级索引没有 DataPage, 返回空
	return nil
}

func (h *BTreeHandler) ReadDataPageRows(handle page.HandleDb, dpID uint32) [][]byte {
	// 二级索引没有 DataPage
	return nil
}

func (h *BTreeHandler) RangeScan(handle page.HandleDb, entryPage uint32,
	startKey, endKey []byte, startInclusive, endInclusive bool, reverse bool,
	callback func(row []byte) bool) error {
	return btree.SBTRangeScan(entryPage, handle, startKey, endKey, startInclusive, endInclusive, reverse, callback)
}