Exercise: Composite
This exercise puts the Composite pattern into code.
Scenario
A file-system tree holds two kinds of nodes: files and directories. A file's size is fixed.
A directory's size is the sum of all its children — which may themselves be directories. The
tree starts with an implicit directory named "root". All names in the tree are unique.
Commands
| Command | Behavior | Output |
|---|---|---|
["mkdir", name, parent] | Create a directory named name inside parent | (none) |
["file", name, parent, size] | Create a file named name with the given integer size inside parent | (none) |
["size", name] | Report the total size under name | "<name>: <total size>", or "<name> not found" |
Example
Input
6 mkdir docs root file readme.md docs 400 file guide.md docs 600 size docs size root size missing
Output
docs: 1000 root: 1000 missing not found
Explanation
A `docs` directory is created inside `root`, then two files totalling 1000 bytes are added to it. Querying `docs` returns 1000 — the sum of its children. Querying `root` also returns 1000 because `docs` is its only child and the recursion propagates up. Querying `missing` demonstrates the "not found" case: a name that was never created returns the error message rather than a size.
Your task
Create the two concrete node classes used by the dispatcher below the Node abstract class in the editor: File(Node) with a size() that returns its stored byte count, and Directory(Node) with an add(node) method and a size() that sums children recursively. Do not modify Node or run_filesystem.