package world

import (
	"github.com/Tnze/go-mc/data/block"
	pk "github.com/Tnze/go-mc/net/packet"
)

// Chunk store a 256*16*16 area of blocks, sharded on the Y axis into 16
// sections.
type Chunk struct {
	Sections [16]Section
}

// Section implements storage of blocks within a fixed 16*16*16 area.
type Section interface {
	// GetBlock return block status, offset can be calculate by SectionOffset.
	GetBlock(offset uint) BlockStatus
	// SetBlock is the reverse operation of GetBlock.
	SetBlock(offset uint, s BlockStatus)
}

func sectionIdx(x, y, z int) uint {
	return uint(((y & 15) << 8) | (z << 4) | x)
}

type BlockStatus uint32

type ChunkLoc struct {
	X, Z int
}

// GetBlockStatus return the state ID of the block at the given position.
func (w *World) GetBlockStatus(x, y, z int) BlockStatus {
	w.chunkLock.RLock()
	defer w.chunkLock.RUnlock()

	c := w.Chunks[ChunkLoc{x >> 4, z >> 4}]
	if c != nil && y >= 0 {
		if sec := c.Sections[y>>4]; sec != nil {
			return sec.GetBlock(sectionIdx(x&15, y&15, z&15))
		}
	}
	return 0
}

// UnloadChunk unloads a chunk from the world.
func (w *World) UnloadChunk(loc ChunkLoc) {
	w.chunkLock.Lock()
	delete(w.Chunks, loc)
	w.chunkLock.Unlock()
}

// UnaryBlockUpdate updates the block at the specified position with a new
// state ID.
func (w *World) UnaryBlockUpdate(pos pk.Position, bStateID BlockStatus) bool {
	w.chunkLock.Lock()
	defer w.chunkLock.Unlock()

	c := w.Chunks[ChunkLoc{X: pos.X >> 4, Z: pos.Z >> 4}]
	if c == nil {
		return false
	}
	sIdx, bIdx := pos.Y>>4, sectionIdx(pos.X&15, pos.Y&15, pos.Z&15)

	if sec := c.Sections[sIdx]; sec == nil {
		sec = newSectionWithSize(uint(block.BitsPerBlock))
		sec.SetBlock(bIdx, bStateID)
		c.Sections[sIdx] = sec
	} else {
		sec.SetBlock(bIdx, bStateID)
	}
	return true
}

// MultiBlockUpdate updates a packed specification of blocks within a single
// section of a chunk.
func (w *World) MultiBlockUpdate(loc ChunkLoc, sectionY int, blocks []pk.VarLong) bool {
	w.chunkLock.Lock()
	defer w.chunkLock.Unlock()

	c := w.Chunks[loc]
	if c == nil {
		return false // not loaded
	}

	sec := c.Sections[sectionY]
	if sec == nil {
		sec = newSectionWithSize(uint(block.BitsPerBlock))
		c.Sections[sectionY] = sec
	}

	for _, b := range blocks {
		bStateID := b >> 12
		x, z, y := (b>>8)&0xf, (b>>4)&0xf, b&0xf
		sec.SetBlock(sectionIdx(int(x&15), int(y&15), int(z&15)), BlockStatus(bStateID))
	}

	return true
}

//LoadChunk adds the given chunk to the world.
func (w *World) LoadChunk(x, z int, c *Chunk) {
	w.chunkLock.Lock()
	w.Chunks[ChunkLoc{X: x, Z: z}] = c
	w.chunkLock.Unlock()
}