From 895ec536982f30aded6759e0f6d09ac59277ef10 Mon Sep 17 00:00:00 2001
From: adman <adman.else@gmail.com>
Date: Tue, 21 Apr 2026 22:24:12 +0200
Subject: [PATCH] parse the world

---
 level/anvil/level_test.go |  22 ++++++++
 level/anvil/mca.go        | 103 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 125 insertions(+)
 create mode 100644 level/anvil/mca.go

diff --git a/level/anvil/level_test.go b/level/anvil/level_test.go
index bc3ca7a..71e1174 100644
--- a/level/anvil/level_test.go
+++ b/level/anvil/level_test.go
@@ -1,10 +1,13 @@
 package anvil_test
 
 import (
+	"encoding/json"
+	"fmt"
 	"os"
 	"testing"
 
 	"github.com/admin-else/strom/level/anvil"
+	"github.com/admin-else/strom/util"
 )
 
 func TestLevel(t *testing.T) {
@@ -20,3 +23,22 @@ func TestLevel(t *testing.T) {
 	}
 	t.Log(l)
 }
+
+func TestRegionFile(t *testing.T) {
+	f, err := os.Open("./testdata/testworld/region/r.0.0.mca")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	ch, err := anvil.ReadChunkHeader(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	n, err := ch.ChunkAt(f, 0, 0)
+	if err != nil {
+		return
+	}
+
+	fmt.Println(string(util.MustT(json.MarshalIndent(n, "", "  "))))
+}
diff --git a/level/anvil/mca.go b/level/anvil/mca.go
new file mode 100644
index 0000000..c2515e1
--- /dev/null
+++ b/level/anvil/mca.go
@@ -0,0 +1,103 @@
+package anvil
+
+import (
+	"compress/gzip"
+	"compress/zlib"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/admin-else/strom/nbt"
+)
+
+type CompressionStrategy uint8
+
+const (
+	ChunksWidthRegionFile = 32
+	ChunksRegionFile      = ChunksWidthRegionFile * ChunksWidthRegionFile
+)
+
+const (
+	_ CompressionStrategy = iota
+	CompressionStrategyGZIP
+	CompressionStrategyZLIB
+	CompressionStrategyNONE
+	CompressionStrategyLZ4
+)
+
+func (c CompressionStrategy) Wrap(r io.ReadCloser) (rNew io.ReadCloser, shouldClose bool, err error) {
+	switch c {
+	case CompressionStrategyGZIP:
+		shouldClose = true
+		rNew, err = gzip.NewReader(r)
+		return
+	case CompressionStrategyZLIB:
+		shouldClose = true
+		rNew, err = zlib.NewReader(r)
+		return
+	case CompressionStrategyNONE:
+		rNew = r
+		return
+	case CompressionStrategyLZ4:
+		err = fmt.Errorf("lz4 compression not supported")
+		return
+	default:
+		err = fmt.Errorf("unknown compression strategy %d", c)
+		return
+	}
+}
+
+type ChunkHeader struct {
+	Chunk, Time [ChunksRegionFile]int32
+}
+
+func ReadChunkHeader(r *os.File) (ch *ChunkHeader, err error) {
+	var h ChunkHeader
+	err = binary.Read(r, binary.BigEndian, &h)
+	if err != nil {
+		return
+	}
+	ch = &h
+	return
+}
+
+func (c *ChunkHeader) ChunkAt(f *os.File, x, z int32) (n *nbt.Tag, err error) {
+	off, size := chunkLocation(c.Chunk[chunkXZtoIndex(x, z)])
+	_, err = f.Seek(int64(off), 0)
+	if err != nil {
+		return
+	}
+	_ = size // i dont really know why mc has this maybe to point out how much space is wasted?
+	var realSize int32
+	err = binary.Read(f, binary.BigEndian, &realSize)
+	if err != nil {
+		return
+	}
+	var compressionStrategy CompressionStrategy
+	err = binary.Read(f, binary.BigEndian, &compressionStrategy)
+	if err != nil {
+		return
+	}
+	r, shouldClose, err := compressionStrategy.Wrap(f)
+	if err != nil {
+		return
+	}
+	if shouldClose {
+		defer r.Close()
+	}
+	n = &nbt.Tag{}
+	err = n.Decode(r)
+	if err != nil {
+		return
+	}
+	return
+}
+
+func chunkXZtoIndex(x, z int32) int32 {
+	return (x % ChunksWidthRegionFile) + (z%ChunksWidthRegionFile)*ChunksWidthRegionFile
+}
+
+func chunkLocation(v int32) (offset, l int32) {
+	return ((v >> 8) & 0xFFFFFF) * 4096, (v & 0xFF) * 4096
+}