package models

import "encoding/binary"
import "testify/assert"
const HEADER = 4

const BTREE_PAGE_SIZE = 4096
const BTREE_MAX_KEY_SIZE = 1000
const BTREE_MAX_VAL_SIZE = 1000

type BNode []byte

type BTree struct {
	root uint64
	get  func(uint64) []byte
	new  func([]byte) uint64
	del  func(uint64)
}

func init() {
	noode1max := HEADER + 8 + 2 + 4 + BTREE_MAX_KEY_SIZE + BTREE_MAX_VAL_SIZE
	assert(noode1max <= BTREE_PAGE_SIZE)
}

func (node BNode) btype() uint16 {
	return binary.LittleEndian.Uint16(node[0:2])
}

func (node BNode) nkeys() uint16 {
	return binary.LittleEndian.Uint16(node[2:4])
}

func (node BNode) setHeader(btype uint16, nkeys uint16) {
	binary.LittleEndian.PutUint16(node[0:2], btype)
	binary.LittleEndian.PutUint16(node[2:4], nkeys)
}

func (node BNode) getPtr(ids uint16) uint64 {
	assert(ids < node.nkeys())
	pos := HEADER + 8*ids
	return binary.LittleEndian.Uint64(node[pos:])
}

func (node BNode) setPtr(idx uint16, val uint64) {
	assert(idx <= node.nkeys())
	pos := HEADER + 8*idx
	binary.LittleEndian.PutUint64(node[pos:], val)
}

func (node BNode) getOffset(idx uint16) uint16 {
	if (idx == 0) {
		return 0
	}
	pos := HEADER + 8*node.nkeys() + 2*(idx - 1)
	return binary.LittleEndian.Uint16(node[pos:])
}

func (node BNode) kvPos(idx uint16) (uint16) {
	assert(idx < node.nkeys())
	return 4 + 8*node.nkeys() + 2*node.nkeys() + node.getOffset(idx)
}

func(node BNode) getKey(idx uint16) []byte {
	assert(idx < node.nkeys())
	pos := node.kvPos(idx)
	klen := binary.LittleEndian.Uint16(node[pos:])
	vlen := binary.LittleEndian.Uint16(node[pos+2:])
	return node[pos+4+klen:][:vlen]
}