package bolt

import (
	"bytes"
	"unsafe"
)

const maxPageSize = 0x8000
const minKeyCount = 2

const pageHeaderSize = int(unsafe.Offsetof(((*page)(nil)).data))

const minPageKeys = 2
const fillThreshold = 250 // 25%

const (
	p_branch = 0x01
	p_leaf   = 0x02
	p_meta   = 0x04
)

type pgid uint64

type page struct {
	id    pgid
	flags uint32
	lower uint16
	upper uint16
	count uint32
	data  uintptr
}

// meta returns a pointer to the metadata section of the page.
func (p *page) meta() (*meta, error) {
	// Exit if page is not a meta page.
	if (p.flags & p_meta) == 0 {
		return nil, InvalidMetaPageError
	}

	// Cast the meta section and validate before returning.
	m := (*meta)(unsafe.Pointer(&p.ptr))
	if err := m.validate(); err != nil {
		return nil, err
	}
	return m, nil
}

// init initializes a page as a new meta page.
func (p *page) init(pageSize int) {
	p.flags = p_meta
	m := (*meta)(unsafe.Pointer(&p.ptr))
	m.magic = magic
	m.version = version
	m.pageSize = uint32(pageSize)
	m.pgid = 1
	m.buckets.root = 0
}