mdview: Markdown viewer with mermaid-ascii support (glow wrapper)

mdview

#!/usr/bin/env python3
"""Markdown viewer that converts mermaid diagrams to ASCII art via mermaid-ascii, then displays with glow."""

import os
import re
import subprocess
import sys
import tempfile

MERMAID_BLOCK_RE = re.compile(
    r"```mermaid\s*\n(.*?)```", re.DOTALL
)


def convert_mermaid(mermaid_src: str) -> str:
    """Convert mermaid source to ASCII art using mermaid-ascii CLI."""
    try:
        result = subprocess.run(
            ["mermaid-ascii", "-f", "-"],
            input=mermaid_src,
            capture_output=True,
            text=True,
            timeout=30,
        )
        if result.returncode == 0 and result.stdout.strip():
            return result.stdout.rstrip("\n")
    except (subprocess.TimeoutExpired, FileNotFoundError):
        pass
    # Fallback: return original as-is in a code block
    return mermaid_src.rstrip("\n")


def process_markdown(content: str) -> tuple[str, bool]:
    """Replace mermaid code blocks with ASCII art. Returns (processed_content, had_mermaid)."""
    had_mermaid = False

    def replacer(match: re.Match[str]) -> str:
        nonlocal had_mermaid
        had_mermaid = True
        mermaid_src = match.group(1)
        ascii_art = convert_mermaid(mermaid_src)
        return f"```\n{ascii_art}\n```"

    processed = MERMAID_BLOCK_RE.sub(replacer, content)
    return processed, had_mermaid


def main() -> None:
    # Separate file path from glow options
    file_path = None
    glow_args: list[str] = []

    for arg in sys.argv[1:]:
        if file_path is None and not arg.startswith("-") and os.path.isfile(arg):
            file_path = arg
        else:
            glow_args.append(arg)

    # Read markdown content
    if file_path:
        with open(file_path) as f:
            content = f.read()
    elif not sys.stdin.isatty():
        content = sys.stdin.read()
    else:
        # No file and no stdin: just run glow as-is
        os.execvp("glow", ["glow", *glow_args])

    processed, had_mermaid = process_markdown(content)

    # Disable word-wrap by default unless user explicitly sets -w
    if not any(a in ("-w", "--width") for a in glow_args):
        glow_args = ["-w", "0", *glow_args]

    if not had_mermaid and file_path:
        # No mermaid blocks: pass original file directly to glow
        os.execvp("glow", ["glow", file_path, *glow_args])

    # Write processed content to temp file for glow
    with tempfile.NamedTemporaryFile(mode="w", suffix=".md", delete=False) as tmp:
        tmp.write(processed)
        tmp_path = tmp.name

    try:
        result = subprocess.run(["glow", tmp_path, *glow_args])
        sys.exit(result.returncode)
    finally:
        os.unlink(tmp_path)


if __name__ == "__main__":
    main()