Add --pager flag for juv cat (#45)

src/juv/__init__.py

@@ -304,7 +304,14 @@ def exec_(
 @cli.command()
 @click.argument("notebook", type=click.Path(exists=True), required=True)
 @click.option("--script", is_flag=True)
-def cat(notebook: str, *, script: bool) -> None:
+@click.option(
+    "--pager",
+    type=click.STRING,
+    help="The pager to use.",
+    default=lambda: os.environ.get("JUV_PAGER"),
+    hidden=True,
+)
+def cat(notebook: str, *, script: bool, pager: str | None) -> None:
     """Print notebook contents to stdout."""
     from ._cat import cat
 
@@ -316,7 +323,7 @@ def cat(notebook: str, *, script: bool) -> None:
         )
         return
 
-    sys.stdout.write(cat(path, script=script))
+    cat(path=path, script=script, pager=pager)
 
 
 def main() -> None:

src/juv/_cat.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import re
+import sys
 from typing import TYPE_CHECKING
 
 import jupytext
@@ -41,7 +42,7 @@ def strip_python_frontmatter_comment(content: str) -> tuple[str, str]:
     return "", content
 
 
-def cat(nb: Path | dict, *, script: bool) -> str:
+def notebook_contents(nb: Path | dict, *, script: bool) -> str:
     fmt = "py:percent" if script else "md"
     notebook = nb if isinstance(nb, dict) else jupytext.read(nb)
     contents = jupytext.writes(notebook, fmt=fmt)
@@ -50,3 +51,36 @@ def cat(nb: Path | dict, *, script: bool) -> str:
     else:
         _, contents = strip_markdown_header(contents)
     return contents.lstrip()
+
+
+def cat(path: Path, *, script: bool, pager: str | None = None) -> None:
+    code = notebook_contents(path, script=script)
+
+    if pager:
+        import os
+        import subprocess
+
+        command = [pager, "-"]
+
+        # special case bat to apply syntax highlighting
+        if pager == "bat":
+            command.extend(
+                [
+                    "--language",
+                    "md" if not script else "py",
+                    "--file-name",
+                    f"{path.stem}.md" if not script else f"{path.stem}.py",
+                ]
+            )
+
+        subprocess.run(  # noqa: PLW1510, S603
+            command,
+            input=code.encode(),
+            stdout=sys.stdout,
+            stderr=sys.stderr,
+            env=os.environ,
+        )
+
+    else:
+        # otherwise, just print to stdout
+        sys.stdout.write(notebook_contents(path, script=script))

src/juv/_edit.py

@@ -4,7 +4,7 @@
 
 import jupytext
 
-from ._cat import cat
+from ._cat import notebook_contents
 
 
 class EditorAbortedError(Exception):
@@ -66,7 +66,8 @@ def edit(path: Path, editor: str) -> None:
         update["metadata"]["id"] = update["id"]
         prev_cells[update["id"]] = update
 
-    text = open_editor(cat(prev_notebook, script=False), suffix=".md", editor=editor)
+    code = notebook_contents(path, script=False)
+    text = open_editor(code, suffix=".md", editor=editor)
     new_notebook = jupytext.reads(text.strip(), fmt="md")
 
     # Update the previous notebook cells with the new ones