#!/usr/bin/env python3
'''
NAME
    latex2img - Converts LaTeX source to PNG or SVG file

SYNOPSIS
    latex2img [options] INFILE

DESCRIPTION
    This filter reads LaTeX source text from the input file
    INFILE (or stdin if INFILE is -) and renders it to PNG image file.
    Typically used to render math equations.

    Requires latex(1), dvipng(1) and/or dvisvgm(1) commands and LaTeX math
    packages.

OPTIONS
    -D DPI
        Set the output resolution for PNG images to DPI dots per inch. Use
        this option to scale the output PNG image size.

    -o OUTFILE
        The file name of the output file. If not specified the output file is
        named like INFILE but with an extension matching the chosen output
        image format, .png for PNG images and .svg for SVG images.

    -m
        Skip if the output image file is newer than the INFILE.
        Compares timestamps on INFILE and OUTFILE. If
        INFILE is - (stdin) then compares MD5 checksum stored in file
        named like OUTFILE but with a .md5 file name extension.
        The .md5 file is created if the -m option is used and the
        INFILE is - (stdin).

    -v
        Verbosely print processing information to stderr.

    --help, -h
        Print this documentation.

    --version
        Print program version number.

SEE ALSO
    latex(1), dvipng(1), dvisvgm(1)

AUTHOR
    Written by Stuart Rackham, <srackham@gmail.com>
    The code was inspired by Kjell Magne Fauske's code:
    http://fauskes.net/nb/htmleqII/

    See also:
    http://www.amk.ca/python/code/mt-math
    http://code.google.com/p/latexmath2png/

COPYING
    Copyright (C) 2002-2013 Stuart Rackham.
    Copyright (C) 2013-2020 AsciiDoc Contributors.

    Free use of this software is granted under the terms of the GNU General
    Public License version 2 (GPLv2).
'''

import os
import sys
import tempfile
from hashlib import md5

VERSION = '0.2.0'

# Include LaTeX packages and commands here.
TEX_HEADER = r'''\documentclass{article}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{amssymb}
\usepackage{bm}
\newcommand{\mx}[1]{\mathbf{\bm{#1}}} % Matrix command
\newcommand{\vc}[1]{\mathbf{\bm{#1}}} % Vector command
\newcommand{\T}{\text{T}}             % Transpose
\pagestyle{empty}
\begin{document}'''

TEX_FOOTER = r'''\end{document}'''

# Globals.
verbose = False


class EApp(Exception):
    pass     # Application specific exception.


def print_stderr(line):
    sys.stderr.write(line + os.linesep)


def print_verbose(line):
    if verbose:
        print_stderr(line)


def write_file(filename, data, mode='w', encoding='utf-8'):
    if 'b' in mode:
        encoding = None
    with open(filename, mode, encoding=encoding) as f:
        f.write(data)


def read_file(filename, mode='r', encoding='utf-8'):
    if 'b' in mode:
        encoding = None
    with open(filename, mode, encoding=encoding) as f:
        return f.read()


def run(cmd):
    global verbose
    if verbose:
        cmd += ' 1>&2'
    else:
        cmd += ' 2>%s 1>&2' % os.devnull
    print_verbose('executing: %s' % cmd)
    if os.system(cmd):
        raise EApp('failed command: %s' % cmd)


def latex2img(infile, outfile, imgfmt, dpi, modified):
    '''
    Convert LaTeX input file infile to image file named outfile.
    '''
    outfile = os.path.abspath(outfile)
    outdir = os.path.dirname(outfile)
    if not os.path.isdir(outdir):
        raise EApp('directory does not exist: %s' % outdir)
    texfile = tempfile.mktemp(suffix='.tex', dir=os.path.dirname(outfile))
    basefile = os.path.splitext(texfile)[0]
    dvifile = basefile + '.dvi'
    temps = [basefile + ext for ext in ('.tex', '.dvi', '.aux', '.log')]
    skip = False
    if infile == '-':
        tex = sys.stdin.read()
        if modified:
            checksum = md5((tex + imgfmt + str(dpi)).encode('utf-8')).digest()
            md5_file = os.path.splitext(outfile)[0] + '.md5'
            if os.path.isfile(md5_file) and os.path.isfile(outfile) and \
                    checksum == read_file(md5_file, 'rb'):
                skip = True
    else:
        if not os.path.isfile(infile):
            raise EApp('input file does not exist: %s' % infile)
        tex = read_file(infile)
        if modified and os.path.isfile(outfile) and \
                os.path.getmtime(infile) <= os.path.getmtime(outfile):
            skip = True
    if skip:
        print_verbose('skipped: no change: %s' % outfile)
        return
    tex = '%s\n%s\n%s\n' % (TEX_HEADER, tex.strip(), TEX_FOOTER)
    print_verbose('tex:\n%s' % tex)
    write_file(texfile, tex)
    saved_pwd = os.getcwd()
    os.chdir(outdir)
    try:
        # Compile LaTeX document to DVI file.
        run('latex %s' % texfile)
        if imgfmt == 'svg':
            # Convert DVI file to SVG.
            cmd = 'dvisvgm'
            cmd += ' --no-fonts'
            cmd += ' --scale=1.4'
            cmd += ' --exact'
            cmd += ' -o "%s" "%s"' % (outfile, dvifile)
        else:
            # Convert DVI file to PNG.
            cmd = 'dvipng'
            if dpi:
                cmd += ' -D %s' % dpi
            cmd += ' -T tight -x 1000 -z 9 -bg Transparent --truecolor'
            cmd += ' -o "%s" "%s" ' % (outfile, dvifile)
        run(cmd)
    finally:
        os.chdir(saved_pwd)
        for f in temps:
            if os.path.isfile(f):
                print_verbose('deleting: %s' % f)
                os.remove(f)
    if 'md5_file' in locals():
        print_verbose('writing: %s' % md5_file)
        write_file(md5_file, checksum, 'wb')


def usage(msg=''):
    if msg:
        print_stderr(msg)
    print_stderr(
        '\n'
        'usage:\n'
        '    latex2img [options] INFILE\n'
        '\n'
        'options:\n'
        '    -D DPI\n'
        '    -o OUTFILE\n'
        '    -f FORMAT\n'
        '    -m\n'
        '    -v\n'
        '    --help\n'
        '    --version'
    )


def main():
    # Process command line options.
    global verbose
    dpi = None
    outfile = None
    imgfmt = 'png'
    modified = False
    import getopt
    opts, args = getopt.getopt(sys.argv[1:], 'D:o:mhvf:', ['help', 'version'])
    for o, v in opts:
        if o in ('--help', '-h'):
            print(__doc__)
            sys.exit(0)
        if o == '--version':
            print(('latex2img version %s' % (VERSION,)))
            sys.exit(0)
        if o == '-D':
            dpi = v
        if o == '-o':
            outfile = v
        if o == '-m':
            modified = True
        if o == '-v':
            verbose = True
        if o == '-f':
            imgfmt = v
    if len(args) != 1:
        usage()
        sys.exit(1)
    infile = args[0]
    if dpi and not dpi.isdigit():
        usage('invalid DPI')
        sys.exit(1)
    if imgfmt not in {'png', 'svg'}:
        usage('Invalid image format. Valid values are "png" or "svg".')
        sys.exit(1)
    if outfile is None:
        if infile == '-':
            usage('OUTFILE must be specified')
            sys.exit(1)
        outfile = os.path.splitext(infile)[0] + '.' + imgfmt
    # Do the work.
    latex2img(infile, outfile, imgfmt, dpi, modified)
    # Print something to suppress asciidoc 'no output from filter' warnings.
    if infile == '-':
        sys.stdout.write(' ')


if __name__ == "__main__":
    try:
        main()
    except SystemExit:
        raise
    except KeyboardInterrupt:
        sys.exit(1)
    except Exception as e:
        print_stderr("%s: %s" % (os.path.basename(sys.argv[0]), str(e)))
        sys.exit(1)
