Add ability to install from CSV spec, and vacuum

Addition of vacuum closes #3

unpack.py

@@ -77,6 +77,21 @@ class _ResponseFile:  # pylint: disable=too-few-public-methods
 
         return response
 
+    def readline(self) -> bytes:  # pylint: disable=missing-function-docstring
+        try:
+            while not b"\n" in self.buffer:
+                self.buffer += next(self.iter)
+        except StopIteration:
+            pass
+
+        if b"\n" == self.buffer:
+            response, self.buffer = self.buffer.split(b"\n", 1)
+            return response
+        else:
+            response = self.buffer
+            self.buffer = b""
+            return response
+
 
 def unpack(
     package: Union[BinaryIO, _ResponseFile], target: str
@@ -176,3 +191,68 @@ def uninstall(name: str, target: str, records: str) -> None:
                 break
 
     os.remove(f"{records}/{name}")
+
+
+def _vacuum(root: str, delete_this: bool = False) -> None:
+    try:
+        for item in os.listdir(root):
+            _vacuum(f"{root}/{item}", True)
+    except NotADirectoryError:
+        pass
+
+    if delete_this:
+        try:
+            os.rmdir(root)
+        except OSError:
+            pass
+
+
+def vacuum(target: str, paths: Iterable[str] = ("lib",)) -> None:
+    """
+    Remove empty directories under `paths`, each relative to `target`.
+    """
+
+    for path in paths:
+        _vacuum(f"{target}/{path}")
+
+
+def parse_spec(spec_text: str) -> dict[str, tuple[str, str]]:
+    spec = {}
+
+    for full_line in spec_text.split("\n"):
+        line = full_line.strip()
+        if line:
+            name, version_hash, repo = line.split(",")
+            spec[name] = (version_hash, repo)
+
+    return spec
+
+
+def get_status(records: str) -> dict[str, str]:
+    status = {}
+
+    for name in os.listdir(records):
+        with open(f"{records}/{name}", encoding="utf-8") as f:
+            status[name] = f.readline().strip()
+
+    return status
+
+
+def install_spec(
+    spec_text: str, target: str, records: str, paths: Iterable[str] = ("lib",)
+) -> None:
+    spec = parse_spec(spec_text)
+    status = get_status(records)
+
+    for name, version in status.items():
+        if not name in spec or spec[name][0] != version:
+            uninstall(name, target, records)
+
+    vacuum(target, paths)
+    status = get_status(records)
+
+    for name, version_repo in spec.items():
+        version, repo = version_repo
+
+        if not name in status:
+            install(name, version, repo, target, records)