Add CLI option to render package README.

readme_renderer/__main__.py

@@ -1,19 +1,34 @@
 import argparse
+import email
 from readme_renderer.rst import render
+from pkg_resources import get_distribution
 import sys
 
 
-if __name__ == '__main__':
+def __main__(args=None):
     parser = argparse.ArgumentParser(
         description="Renders a .rst README to HTML",
     )
-    parser.add_argument('input', help="Input README file",
-                        type=argparse.FileType('r'))
+    parser.add_argument("-p", "--package", help="Get README from package metadata",
+                        action="store_true")
+    parser.add_argument('input', help="Input README file or package name")
     parser.add_argument('-o', '--output', help="Output file (default: stdout)",
                         type=argparse.FileType('w'), default='-')
-    args = parser.parse_args()
+    args = parser.parse_args(args)
 
-    rendered = render(args.input.read(), stream=sys.stderr)
+    if args.package:
+        distribution = get_distribution(args.input)
+        pkg_info = distribution.get_metadata(distribution.PKG_INFO)
+        message = email.message_from_string(pkg_info)
+        source = message.get_payload()
+    else:
+        with open(args.input) as fp:
+            source = fp.read()
+    rendered = render(source, stream=sys.stderr)
     if rendered is None:
         sys.exit(1)
     print(rendered, file=args.output)
+
+
+if __name__ == '__main__':
+    __main__()

tests/test_cli.py

@@ -0,0 +1,39 @@
+import pathlib
+import pytest
+from readme_renderer.__main__ import __main__
+import tempfile
+from unittest import mock
+
+
+@pytest.mark.parametrize("input_file", ["test_CommonMark_001.md", "test_rst_003.rst"])
+@pytest.mark.parametrize("output_file", [False, True])
+def test_cli_input_file(input_file, output_file):
+    input_file = pathlib.Path("tests/fixtures", input_file)
+
+    if output_file:
+        with tempfile.TemporaryDirectory() as tmpdir:
+            output = pathlib.Path(tmpdir) / "output.html"
+            __main__(["-o", str(output), str(input_file)])
+            with output.open() as fp:
+                result = fp.read()
+    else:
+        with mock.patch("builtins.print") as print_:
+            __main__([str(input_file)])
+            print_.assert_called_once()
+            (result,), _ = print_.call_args
+
+    with input_file.with_suffix(".html").open() as fp:
+        expected = fp.read()
+    assert result.strip() == expected.strip()
+
+
+@pytest.mark.parametrize("package, contains", [
+    ("readme_renderer", "Readme Renderer is a library that will safely render"),
+    ("docutils", "Docutils is a modular system for processing documentation"),
+])
+def test_cli_package(package, contains):
+    with mock.patch("builtins.print") as print_:
+        __main__(["-p", package])
+        print_.assert_called_once()
+        (result,), _ = print_.call_args
+    assert contains in result