imgmath.py

"""Render math in HTML via dvipng or dvisvgm."""

import base64
import re
import shutil
import subprocess
import tempfile
from os import path
from subprocess import CalledProcessError
from typing import Any, Dict, List, Optional, Tuple

from docutils import nodes
from docutils.nodes import Element

import sphinx
from sphinx import package_dir
from sphinx.application import Sphinx
from sphinx.builders import Builder
from sphinx.config import Config
from sphinx.errors import SphinxError
from sphinx.locale import _, __
from sphinx.util import logging, sha1
from sphinx.util.math import get_node_equation_number, wrap_displaymath
from sphinx.util.osutil import ensuredir
from sphinx.util.png import read_png_depth, write_png_depth
from sphinx.util.template import LaTeXRenderer
from sphinx.writers.html import HTMLTranslator

logger = logging.getLogger(__name__)

templates_path = path.join(package_dir, 'templates', 'imgmath')

__all__ = ()


class MathExtError(SphinxError):
    category = 'Math extension error'

    def __init__(
        self, msg: str, stderr: Optional[str] = None, stdout: Optional[str] = None
    ) -> None:
        if stderr:
            msg += '\n[stderr]\n' + stderr
        if stdout:
            msg += '\n[stdout]\n' + stdout
        super().__init__(msg)


class InvokeError(SphinxError):
    """errors on invoking converters."""


SUPPORT_FORMAT = ('png', 'svg')

depth_re = re.compile(r'\[\d+ depth=(-?\d+)\]')
depthsvg_re = re.compile(r'.*, depth=(.*)pt')
depthsvgcomment_re = re.compile(r'<!-- DEPTH=(-?\d+) -->')


def read_svg_depth(filename: str) -> Optional[int]:
    """Read the depth from comment at last line of SVG file
    """
    with open(filename, encoding="utf-8") as f:
        for line in f:  # noqa: B007
            pass
        # Only last line is checked
        matched = depthsvgcomment_re.match(line)
        if matched:
            return int(matched.group(1))
        return None


def write_svg_depth(filename: str, depth: int) -> None:
    """Write the depth to SVG file as a comment at end of file
    """
    with open(filename, 'a', encoding="utf-8") as f:
        f.write('\n<!-- DEPTH=%s -->' % depth)


def generate_latex_macro(image_format: str,
                         math: str, config: Config, confdir: str = '') -> str:
    """Generate LaTeX macro."""
    variables = {
        'fontsize': config.imgmath_font_size,
        'baselineskip': int(round(config.imgmath_font_size * 1.2)),
        'preamble': config.imgmath_latex_preamble,
        'tightpage': '' if image_format == 'png' else ',tightpage',
        'math': math
    }

    if config.imgmath_use_preview:
        template_name = 'preview.tex_t'
    else:
        template_name = 'template.tex_t'

    for template_dir in config.templates_path:
        template = path.join(confdir, template_dir, template_name)
        if path.exists(template):
            return LaTeXRenderer().render(template, variables)

    return LaTeXRenderer(templates_path).render(template_name, variables)


def ensure_tempdir(builder: Builder) -> str:
    """Create temporary directory.

    use only one tempdir per build -- the use of a directory is cleaner
    than using temporary files, since we can clean up everything at once
    just removing the whole directory (see cleanup_tempdir)
    """
    if not hasattr(builder, '_imgmath_tempdir'):
        builder._imgmath_tempdir = tempfile.mkdtemp()  # type: ignore

    return builder._imgmath_tempdir  # type: ignore


def compile_math(latex: str, builder: Builder) -> str:
    """Compile LaTeX macros for math to DVI."""
    tempdir = ensure_tempdir(builder)
    filename = path.join(tempdir, 'math.tex')
    with open(filename, 'w', encoding='utf-8') as f:
        f.write(latex)

    # build latex command; old versions of latex don't have the
    # --output-directory option, so we have to manually chdir to the
    # temp dir to run it.
    command = [builder.config.imgmath_latex, '--interaction=nonstopmode']
    # add custom args from the config file
    command.extend(builder.config.imgmath_latex_args)
    command.append('math.tex')

    try:
        subprocess.run(command, capture_output=True, cwd=tempdir, check=True,
                       encoding='ascii')
        return path.join(tempdir, 'math.dvi')
    except OSError as exc:
        logger.warning(__('LaTeX command %r cannot be run (needed for math '
                          'display), check the imgmath_latex setting'),
                       builder.config.imgmath_latex)
        raise InvokeError from exc
    except CalledProcessError as exc:
        raise MathExtError('latex exited with error', exc.stderr, exc.stdout) from exc


def convert_dvi_to_image(command: List[str], name: str) -> Tuple[str, str]:
    """Convert DVI file to specific image format."""
    try:
        ret = subprocess.run(command, capture_output=True, check=True, encoding='ascii')
        return ret.stdout, ret.stderr
    except OSError as exc:
        logger.warning(__('%s command %r cannot be run (needed for math '
                          'display), check the imgmath_%s setting'),
                       name, command[0], name)
        raise InvokeError from exc
    except CalledProcessError as exc:
        raise MathExtError('%s exited with error' % name, exc.stderr, exc.stdout) from exc


def convert_dvi_to_png(dvipath: str, builder: Builder, out_path: str) -> Optional[int]:
    """Convert DVI file to PNG image."""
    name = 'dvipng'
    command = [builder.config.imgmath_dvipng, '-o', out_path, '-T', 'tight', '-z9']
    command.extend(builder.config.imgmath_dvipng_args)
    if builder.config.imgmath_use_preview:
        command.append('--depth')
    command.append(dvipath)

    stdout, stderr = convert_dvi_to_image(command, name)

    depth = None
    if builder.config.imgmath_use_preview:
        for line in stdout.splitlines():
            matched = depth_re.match(line)
            if matched:
                depth = int(matched.group(1))
                write_png_depth(out_path, depth)
                break

    return depth


def convert_dvi_to_svg(dvipath: str, builder: Builder, out_path: str) -> Optional[int]:
    """Convert DVI file to SVG image."""
    name = 'dvisvgm'
    command = [builder.config.imgmath_dvisvgm, '-o', out_path]
    command.extend(builder.config.imgmath_dvisvgm_args)
    command.append(dvipath)

    stdout, stderr = convert_dvi_to_image(command, name)

    depth = None
    if builder.config.imgmath_use_preview:
        for line in stderr.splitlines():  # not stdout !
            matched = depthsvg_re.match(line)
            if matched:
                depth = round(float(matched.group(1)) * 100 / 72.27)  # assume 100ppi
                write_svg_depth(out_path, depth)
                break

    return depth


def render_math(
    self: HTMLTranslator,
    math: str,
) -> Tuple[Optional[str], Optional[int]]:
    """Render the LaTeX math expression *math* using latex and dvipng or
    dvisvgm.

    Return the image absolute filename and the "depth",
    that is, the distance of image bottom and baseline in pixels, if the
    option to use preview_latex is switched on.

    Error handling may seem strange, but follows a pattern: if LaTeX or dvipng
    (dvisvgm) aren't available, only a warning is generated (since that enables
    people on machines without these programs to at least build the rest of the
    docs successfully).  If the programs are there, however, they may not fail
    since that indicates a problem in the math source.
    """
    image_format = self.builder.config.imgmath_image_format.lower()
    if image_format not in SUPPORT_FORMAT:
        raise MathExtError('imgmath_image_format must be either "png" or "svg"')

    latex = generate_latex_macro(image_format,
                                 math,
                                 self.builder.config,
                                 self.builder.confdir)

    filename = f"{sha1(latex.encode()).hexdigest()}.{image_format}"
    generated_path = path.join(self.builder.outdir, self.builder.imagedir, 'math', filename)
    ensuredir(path.dirname(generated_path))
    if path.isfile(generated_path):
        if image_format == 'png':
            depth = read_png_depth(generated_path)
        elif image_format == 'svg':
            depth = read_svg_depth(generated_path)
        return generated_path, depth

    # if latex or dvipng (dvisvgm) has failed once, don't bother to try again
    if hasattr(self.builder, '_imgmath_warned_latex') or \
       hasattr(self.builder, '_imgmath_warned_image_translator'):
        return None, None

    # .tex -> .dvi
    try:
        dvipath = compile_math(latex, self.builder)
    except InvokeError:
        self.builder._imgmath_warned_latex = True  # type: ignore
        return None, None

    # .dvi -> .png/.svg
    try:
        if image_format == 'png':
            depth = convert_dvi_to_png(dvipath, self.builder, generated_path)
        elif image_format == 'svg':
            depth = convert_dvi_to_svg(dvipath, self.builder, generated_path)
    except InvokeError:
        self.builder._imgmath_warned_image_translator = True  # type: ignore
        return None, None

    return generated_path, depth


def render_maths_to_base64(image_format: str, generated_path: Optional[str]) -> str:
    with open(generated_path, "rb") as f:
        encoded = base64.b64encode(f.read()).decode(encoding='utf-8')
    if image_format == 'png':
        return f'data:image/png;base64,{encoded}'
    if image_format == 'svg':
        return f'data:image/svg+xml;base64,{encoded}'
    raise MathExtError('imgmath_image_format must be either "png" or "svg"')


def clean_up_files(app: Sphinx, exc: Exception) -> None:
    if exc:
        return

    if hasattr(app.builder, '_imgmath_tempdir'):
        try:
            shutil.rmtree(app.builder._imgmath_tempdir)
        except Exception:
            pass

    if app.builder.config.imgmath_embed:
        # in embed mode, the images are still generated in the math output dir
        # to be shared across workers, but are not useful to the final document
        try:
            shutil.rmtree(path.join(app.builder.outdir, app.builder.imagedir, 'math'))
        except Exception:
            pass


def get_tooltip(self: HTMLTranslator, node: Element) -> str:
    if self.builder.config.imgmath_add_tooltips:
        return ' alt="%s"' % self.encode(node.astext()).strip()
    return ''


def html_visit_math(self: HTMLTranslator, node: nodes.math) -> None:
    try:
        rendered_path, depth = render_math(self, '$' + node.astext() + '$')
    except MathExtError as exc:
        msg = str(exc)
        sm = nodes.system_message(msg, type='WARNING', level=2,
                                  backrefs=[], source=node.astext())
        sm.walkabout(self)
        logger.warning(__('display latex %r: %s'), node.astext(), msg)
        raise nodes.SkipNode from exc

    if rendered_path is None:
        # something failed -- use text-only as a bad substitute
        self.body.append('<span class="math">%s</span>' %
                         self.encode(node.astext()).strip())
    else:
        if self.builder.config.imgmath_embed:
            image_format = self.builder.config.imgmath_image_format.lower()
            img_src = render_maths_to_base64(image_format, rendered_path)
        else:
            bname = path.basename(rendered_path)
            relative_path = path.join(self.builder.imgpath, 'math', bname)
            img_src = relative_path.replace(path.sep, '/')
        c = f'<img class="math" src="{img_src}"' + get_tooltip(self, node)
        if depth is not None:
            c += f' style="vertical-align: {-depth:d}px"'
        self.body.append(c + '/>')
    raise nodes.SkipNode


def html_visit_displaymath(self: HTMLTranslator, node: nodes.math_block) -> None:
    if node['nowrap']:
        latex = node.astext()
    else:
        latex = wrap_displaymath(node.astext(), None, False)
    try:
        rendered_path, depth = render_math(self, latex)
    except MathExtError as exc:
        msg = str(exc)
        sm = nodes.system_message(msg, type='WARNING', level=2,
                                  backrefs=[], source=node.astext())
        sm.walkabout(self)
        logger.warning(__('inline latex %r: %s'), node.astext(), msg)
        raise nodes.SkipNode from exc
    self.body.append(self.starttag(node, 'div', CLASS='math'))
    self.body.append('<p>')
    if node['number']:
        number = get_node_equation_number(self, node)
        self.body.append('<span class="eqno">(%s)' % number)
        self.add_permalink_ref(node, _('Permalink to this equation'))
        self.body.append('</span>')

    if rendered_path is None:
        # something failed -- use text-only as a bad substitute
        self.body.append('<span class="math">%s</span></p>\n</div>' %
                         self.encode(node.astext()).strip())
    else:
        if self.builder.config.imgmath_embed:
            image_format = self.builder.config.imgmath_image_format.lower()
            img_src = render_maths_to_base64(image_format, rendered_path)
        else:
            bname = path.basename(rendered_path)
            relative_path = path.join(self.builder.imgpath, 'math', bname)
            img_src = relative_path.replace(path.sep, '/')
        self.body.append(f'<img src="{img_src}"' + get_tooltip(self, node) +
                         '/></p>\n</div>')
    raise nodes.SkipNode


def setup(app: Sphinx) -> Dict[str, Any]:
    app.add_html_math_renderer('imgmath',
                               (html_visit_math, None),
                               (html_visit_displaymath, None))

    app.add_config_value('imgmath_image_format', 'png', 'html')
    app.add_config_value('imgmath_dvipng', 'dvipng', 'html')
    app.add_config_value('imgmath_dvisvgm', 'dvisvgm', 'html')
    app.add_config_value('imgmath_latex', 'latex', 'html')
    app.add_config_value('imgmath_use_preview', False, 'html')
    app.add_config_value('imgmath_dvipng_args',
                         ['-gamma', '1.5', '-D', '110', '-bg', 'Transparent'],
                         'html')
    app.add_config_value('imgmath_dvisvgm_args', ['--no-fonts'], 'html')
    app.add_config_value('imgmath_latex_args', [], 'html')
    app.add_config_value('imgmath_latex_preamble', '', 'html')
    app.add_config_value('imgmath_add_tooltips', True, 'html')
    app.add_config_value('imgmath_font_size', 12, 'html')
    app.add_config_value('imgmath_embed', False, 'html', [bool])
    app.connect('build-finished', clean_up_files)
    return {'version': sphinx.__display_version__, 'parallel_read_safe': True}