# Architecture

Testapp is a Python CLI built around a REPL (Read-Eval-Print Loop).

## Structure

```
src/
  __init__.py     — package marker
  main.py         — entry point; contains the REPL loop
  commands.py     — command registry and handlers
tests/
  __init__.py
  test_commands.py
  test_main.py
requirements.txt  — pytest (dev)
```

## Command registry

`src/commands.py` defines two things:

- `COMMAND_DESCRIPTIONS` — `{name: one-line description}` used by `help`
- `COMMANDS` — `{name: callable}` mapping command names to handler functions

Every handler takes no arguments and returns a string. The REPL prints that string.

To add a new command:
1. Define a handler function `_my_command() -> str`
2. Add it to `COMMAND_DESCRIPTIONS` with a description
3. Add it to `COMMANDS` under its name

## REPL loop (`src/main.py`)

```
print welcome message
loop:
  print "> " prompt
  read input → strip whitespace → lowercase
  if empty: skip
  if in COMMANDS: call handler, print result
  else: print "Unknown command" error
  on KeyboardInterrupt: exit loop cleanly
```