cli: implement --watch option

pyproject.toml

@@ -79,6 +79,7 @@ dependencies = [
     'typer==0.13.1',               # to create the command-line interface
     "markdown==3.7",               # to convert Markdown to HTML
     "PyMuPDF==1.24.14",            # to convert PDF files to images
+    "watchdog==5.0.2",             # to poll files for updates
 ]
 classifiers = [
     "Intended Audience :: Science/Research",

rendercv/cli/commands.py

@@ -11,7 +11,7 @@ import typer
 from rich import print
 
 from .. import __version__, data, renderer
-from . import printer, utilities
+from . import printer, utilities, watcher
 
 app = typer.Typer(
     rich_markup_mode="rich",
@@ -123,6 +123,14 @@ def cli_command_render(
             help="Don't generate the PNG file.",
         ),
     ] = False,
+    watch: Annotated[
+        bool,
+        typer.Option(
+            "--watch",
+            "-w",
+            help="Automatically generate files on change.",
+        ),
+    ] = False,
     # This is a dummy argument for the help message for
     # extra_data_model_override_argumets:
     _: Annotated[
@@ -136,6 +144,32 @@ def cli_command_render(
     extra_data_model_override_argumets: typer.Context = None,  # type: ignore
 ):
     """Render a CV from a YAML input file."""
+
+    if watch:
+
+        def rerun_command():
+            cli_command_render(
+                input_file_name=input_file_name,
+                use_local_latex_command=use_local_latex_command,
+                output_folder_name=output_folder_name,
+                latex_path=latex_path,
+                pdf_path=pdf_path,
+                markdown_path=markdown_path,
+                html_path=html_path,
+                png_path=png_path,
+                dont_generate_markdown=dont_generate_markdown,
+                dont_generate_html=dont_generate_html,
+                dont_generate_png=dont_generate_png,
+                watch=False,
+                extra_data_model_override_argumets=extra_data_model_override_argumets,
+            )
+
+        file_path = utilities.string_to_file_path(input_file_name)
+        if file_path is None:
+            raise FileNotFoundError(f"Unable to find path to {input_file_name}")
+        watcher.watch_file(file_path, rerun_command)
+        return
+
     printer.welcome()
 
     input_file_path: pathlib.Path = pathlib.Path(input_file_name).absolute()

rendercv/cli/watcher.py

@@ -0,0 +1,76 @@
+"""
+The `rendercv.cli.watcher` module contains all the functions and classes that are used to watch files and emit callbacks.
+"""
+
+import os
+import pathlib
+import time
+from hashlib import sha256
+from typing import Callable
+
+from watchdog.events import FileModifiedEvent, FileSystemEventHandler
+from watchdog.observers import Observer
+from typer import Exit
+
+
+class ModifiedCVEventHandler(FileSystemEventHandler):
+    """This class handles the file changes and triggers a specified `callback` ignoring duplicate changes.
+
+    Args:
+        file_path (pathlib.Path): The path of the file to watch for.
+        callback (Callable[..., None]): The function to be called on file modification. *CALLBACK MUST BE NON-BLOCKING*
+    """
+
+    file_path: pathlib.Path
+    callback: Callable[..., None]
+    previous_hash: str = ""
+
+    def __init__(self, file_path: pathlib.Path, callback: Callable[..., None]):
+        self.callback = callback
+        self.file_path = file_path
+
+        # Handle an initial pass manually
+        self.on_modified(FileModifiedEvent(src_path=str(self.file_path)))
+
+    def on_modified(self, event: FileModifiedEvent) -> None:
+        if event.src_path != str(self.file_path):
+            # Ignore any events that aren't our file.
+            return
+
+        file_hash = sha256(open(event.src_path).read().encode("utf-8")).hexdigest()
+
+        if file_hash == self.previous_hash:
+            # Exit if file hash has not changed.
+            return
+
+        self.previous_hash = file_hash
+
+        try:
+            self.callback()
+        except Exit:
+            ...  # Suppress typer Exit so we can continue watching even if we see errors.
+
+
+def watch_file(file_path: pathlib.Path, callback: Callable[..., None]):
+    """Watch file located at `file_path` and trigger callback on file modification.
+
+    Args:
+        file_path (pathlib.Path): The path of the file to watch for.
+        callback (Callable[..., None]): The function to be called on file modification. *CALLBACK MUST BE NON-BLOCKING*
+    """
+    event_handler = ModifiedCVEventHandler(file_path, callback)
+    observer = Observer()
+
+    # If on windows we have to poll the parent directory instead of the file.
+    if os.name == "nt":
+        observer.schedule(event_handler, str(file_path.parent), recursive=False)
+    else:
+        observer.schedule(event_handler, str(file_path), recursive=False)
+
+    observer.start()
+    try:
+        while True:
+            time.sleep(1)
+    finally:
+        observer.stop()
+        observer.join()