feat: add CLI log file output

src/batdetect2/cli/base.py

@@ -1,5 +1,7 @@
 """BatDetect2 command line interface."""
 
+from pathlib import Path
+
 import click
 
 from batdetect2.cli.ascii import BATDETECT_ASCII_ART
@@ -22,8 +24,17 @@ BatDetect2
     count=True,
     help="Increase verbosity. -v for INFO, -vv for DEBUG.",
 )
+@click.option(
+    "--log-file",
+    type=click.Path(path_type=Path),
+    help="Write CLI logs to a file in addition to the terminal.",
+)
 @click.pass_context
-def cli(ctx: click.Context, verbose: int = 0):
+def cli(
+    ctx: click.Context,
+    verbose: int = 0,
+    log_file: Path | None = None,
+) -> None:
     """Run the BatDetect2 CLI.
 
     Use subcommands to run processing, training, evaluation, and dataset
@@ -37,4 +48,4 @@ def cli(ctx: click.Context, verbose: int = 0):
 
     from batdetect2.logging import enable_logging
 
-    enable_logging(verbose)
+    enable_logging(verbose, log_file=log_file)

src/batdetect2/logging.py

@@ -50,7 +50,7 @@ __all__ = [
 ]
 
 
-def enable_logging(level: int):
+def enable_logging(level: int, log_file: Path | None = None) -> None:
     logger.remove()
 
     if level == 0:
@@ -61,6 +61,11 @@ def enable_logging(level: int):
         log_level = "DEBUG"
 
     logger.add(sys.stderr, level=log_level)
+
+    if log_file is not None:
+        log_file.parent.mkdir(parents=True, exist_ok=True)
+        logger.add(log_file, level=log_level)
+
     logger.enable("batdetect2")
 
 

tests/test_cli/test_base.py

@@ -1,18 +1,58 @@
 """Behavior-focused tests for top-level CLI command discovery."""
 
+from pathlib import Path
+
 from click.testing import CliRunner
 
 from batdetect2.cli import cli
 
 
+BASE_DIR = Path(__file__).parent.parent.parent
+
+
 def test_cli_base_help_lists_main_commands() -> None:
     """User story: discover available workflows from top-level help."""
 
     result = CliRunner().invoke(cli, ["--help"])
 
     assert result.exit_code == 0
+    assert "--log-file" in result.output
     assert "process" in result.output
     assert "train" in result.output
     assert "evaluate" in result.output
     assert "data" in result.output
     assert "detect" in result.output
+
+
+def test_cli_writes_logs_to_file_and_terminal(
+    tmp_path: Path,
+    tiny_checkpoint_path: Path,
+) -> None:
+    """User story: save CLI logs to a file while keeping terminal output."""
+
+    output_dir = tmp_path / "eval_out"
+    log_file = tmp_path / "logs" / "cli.log"
+
+    result = CliRunner().invoke(
+        cli,
+        [
+            "--log-file",
+            str(log_file),
+            "-v",
+            "evaluate",
+            str(BASE_DIR / "example_data" / "dataset.yaml"),
+            "--model",
+            str(tiny_checkpoint_path),
+            "--base-dir",
+            str(BASE_DIR),
+            "--workers",
+            "0",
+            "--output-dir",
+            str(output_dir),
+        ],
+    )
+
+    assert result.exit_code == 0
+    assert "Initiating evaluation process..." in result.output
+    assert log_file.exists()
+    assert "Initiating evaluation process..." in log_file.read_text()