feat: Initial commit for OnEver Drive centralized backup system with Windows PyQt6 agent and Proxmox LXC deployment

windows-agent/agent/chunker.py

@@ -0,0 +1,49 @@
+import math
+import hashlib
+from pathlib import Path
+from typing import Tuple
+
+def compute_file_sha256(filepath: Path, buffer_size: int = 1024 * 1024) -> str:
+    """Calculates full SHA-256 checksum of a file using streaming buffers to avoid memory overhead."""
+    hasher = hashlib.sha256()
+    with open(filepath, "rb") as f:
+        while True:
+            chunk = f.read(buffer_size)
+            if not chunk:
+                break
+            hasher.update(chunk)
+    return hasher.hexdigest()
+
+class FileChunker:
+    """Handles splitting large files into discrete chunks and calculating block hashes."""
+
+    def __init__(self, filepath: Path, chunk_size: int = 4 * 1024 * 1024):
+        self.filepath = Path(filepath).resolve()
+        if not self.filepath.exists():
+            raise FileNotFoundError(f"File {filepath} not found")
+
+        self.file_size = self.filepath.stat().st_size
+        self.chunk_size = chunk_size
+        self.total_chunks = max(1, math.ceil(self.file_size / self.chunk_size))
+        self._cached_sha256 = None
+
+    @property
+    def full_sha256(self) -> str:
+        if self._cached_sha256 is None:
+            self._cached_sha256 = compute_file_sha256(self.filepath)
+        return self._cached_sha256
+
+    def get_chunk(self, chunk_index: int) -> Tuple[bytes, str]:
+        """
+        Reads the bytes for chunk `chunk_index` and returns (chunk_data, chunk_sha256).
+        """
+        if chunk_index < 0 or chunk_index >= self.total_chunks:
+            raise IndexError(f"Chunk index {chunk_index} out of bounds (total: {self.total_chunks})")
+
+        offset = chunk_index * self.chunk_size
+        with open(self.filepath, "rb") as f:
+            f.seek(offset)
+            data = f.read(self.chunk_size)
+
+        chunk_sha256 = hashlib.sha256(data).hexdigest()
+        return data, chunk_sha256