table.go

/*
MIT License

Copyright (c) 2023 ISSuh

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

package table

import (
	"encoding/binary"
	"os"

	"github.com/ISSuh/lsm-tree/block"
	"github.com/ISSuh/lsm-tree/logging"
)

const (
	BlockMetaOffetTypeSize = 4
)

type Table struct {
	id               int
	path             string
	file             *os.File
	fileSize         int64
	blockMetas       []block.BlockMeta
	blockMetasOffset int
}

func OpenTable(id int, path string) *Table {
	file, err := os.Open(path)
	if err != nil {
		logging.Error("OpenTable - file open fail. ", path)
		return nil
	}
	defer file.Close()

	info, err := file.Stat()
	if err != nil {
		logging.Error("OpenTable - invalid file. ", path)
		return nil
	}

	table := &Table{
		id:               id,
		path:             path,
		file:             file,
		fileSize:         info.Size(),
		blockMetas:       make([]block.BlockMeta, 0),
		blockMetasOffset: 0,
	}

	table.decodeBlockMetaOffset(table.fileSize)
	table.decodeBlockMetas(table.fileSize)
	return table
}

func (table *Table) NewTableLeader() *TableLeader {
	return &TableLeader{
		table: table,
	}
}

func (table *Table) Id() int {
	return table.id
}

func (table *Table) FileName() string {
	return table.file.Name()
}

func (table *Table) FirstKey() string {
	if len(table.blockMetas) <= 0 {
		return ""
	}
	return string(table.blockMetas[0].FirstKey())
}

func (table *Table) BlockNum() int {
	return len(table.blockMetas)
}

func (table *Table) Size() int64 {
	return table.fileSize
}

func (table *Table) LoadBlock(index int) *block.Block {
	if index >= len(table.blockMetas) {
		logging.Error("ReadBlock - invalid index. ", index)
		return nil
	}

	file, err := os.Open(table.path)
	if err != nil {
		logging.Error("OpenTable - file open fail. ", table.path)
		return nil
	}
	defer file.Close()

	table.file = file

	blockOffset := int(table.blockMetas[index].Offset())
	nextBlockOffset := 0

	nextIndex := index + 1
	if nextIndex < len(table.blockMetas) {
		nextBlockOffset = int(table.blockMetas[nextIndex].Offset())
	} else {
		nextBlockOffset = int(table.blockMetasOffset)
	}

	blockSize := nextBlockOffset - blockOffset
	blockBuffer := make([]byte, blockSize)
	n, err := table.file.ReadAt(blockBuffer, int64(blockOffset))
	if (err != nil) || (n != blockSize) {
		logging.Error("decodeBlockMetas - read error. erro : ", err, " / size n : ", n)
		return nil
	}

	block := &block.Block{}
	block.Decode(blockBuffer)
	return block
}

func (table *Table) decodeBlockMetaOffset(fileSize int64) {
	blockMetaOffsetByte := make([]byte, BlockMetaOffetTypeSize)
	n, err := table.file.ReadAt(blockMetaOffsetByte, fileSize-BlockMetaOffetTypeSize)
	if (err != nil) || (n != BlockMetaOffetTypeSize) {
		logging.Error("decodeBlockMetaOffset - read error. erro : ", err, " / size n : ", n)
		return
	}

	table.blockMetasOffset = int(binary.LittleEndian.Uint32(blockMetaOffsetByte))
}

func (table *Table) decodeBlockMetas(fileSize int64) {
	calculateblockMetasSize := fileSize - int64(table.blockMetasOffset+BlockMetaOffetTypeSize)
	blockMetasByte := make([]byte, calculateblockMetasSize)
	n, err := table.file.ReadAt(blockMetasByte, int64(table.blockMetasOffset))
	if (err != nil) || (n != int(calculateblockMetasSize)) {
		logging.Error("decodeBlockMetas - read error. erro : ", err, " / size n : ", n)
		return
	}

	table.blockMetas = block.DecodeBlockMetasFromByte(blockMetasByte)
}

type TableLeader struct {
	table *Table
}

func (leader *TableLeader) Get(key string) []byte {
	blockIndex := leader.findApproximateBlock(key)
	if blockIndex < 0 {
		return nil
	}

	block := leader.table.LoadBlock(blockIndex)
	if block == nil {
		return nil
	}

	return leader.searchOnBlock(key, block)
}

func (leader *TableLeader) findApproximateBlock(key string) int {
	blockIndex := -1
	for index, meta := range leader.table.blockMetas {
		firstKey := string(meta.FirstKey()[:])
		if key <= firstKey {
			blockIndex = index
			break
		}
	}
	return blockIndex
}

func (leader *TableLeader) searchOnBlock(key string, block *block.Block) []byte {
	iter := block.Iterator()
	for iter != nil {
		if key == iter.Key() {
			return iter.Value()
		}
		iter = iter.Next()
	}
	return nil
}