import os
import pypandoc
import re

root = ""

# Compiles a single slide by splitting it up into single metadata and data
# attributes, loading them into the corresponding template, and returning the
# result.
def compile_slide(slide, root_directory):
    global root
    root = root_directory
    slide = slide.strip()
    slide_metadata = get_slide_metadata(slide)
    slide_data = get_slide_data(slide)
    slide = get_slide_layout(slide_metadata['layout'])

    if 'todo' in slide_data.keys():
        # TODO: Move the css into a global onpoint.css file
        slide = '<aside class="todo" style="position:absolute; z-index:100; display:block; background:rgba(255,0,0,.8); top:0; right:0; max-width:20%; margin:.5em; padding:.5em; border-radius:1em; font-family:sans-serif; font-size: .8em;">@todo</aside>' + slide

    for key, value in slide_data.items():
        placeholder = '@' + key
        filler = convert_slide_content(value)

        # very unelegant attempt at inline elements
        inline_key = '@' + key + '(inline)'
        if inline_key in slide:
            slide = slide.replace(
                inline_key,
                re.sub(r"<p>(.+)</p>", r"\1", filler)
            )

        elif '@' + key in slide:
            slide = slide.replace(placeholder, filler)


    return slide

# Parses the metadata passage of a given slide and returns the metadata as a
# dictionary. For some items, default values are used if the slide does not
# contain them.
def get_slide_metadata(slide):
    metadata = { 'layout': 'default' }
    metadata_attributes = re.search('^@slide\((.+)\)', slide.splitlines()[0])
    if metadata_attributes:
        metadata_attributes = metadata_attributes.group(1).split(' ')
        for attribute in metadata_attributes:
            metadata[attribute.split('=')[0]] = attribute.split('=')[1]
    return metadata

# Parses the data part of a given slide and returns dictionary of field names
# and corresponding raw values.
def get_slide_data(slide):
    if slide.startswith('@slide'):
        slide = slide[slide.find('\n')+1:] # cut off @slide declaration
    slide_data = slide.strip().split('\n\n@')
    slide_data = { item.split()[0].strip('@') : "\n".join(item.splitlines()[1:]) for item in slide_data }
    return slide_data

# Reads the layout file for a given layout name and returns its content as a
# string.
def get_slide_layout(layout_name):
    global root
    try:
        return open(os.path.join(root, 'layouts/' + layout_name + '.html'), 'r', encoding='utf8').read()
    except FileNotFoundError:
        raise Exception('Layout ' + layout_name + ' not found!')

# Calls the pandoc converter to convert a given Markdown string to HTML.
# Returns an HTML string.
def convert_slide_content(content):
    filters = []
    pdoc_args = [
        '--mathjax' # Preparing formulas
    ]
    return pypandoc.convert_text(
        content, 'html',
        format='md',
        extra_args=pdoc_args,
        filters=filters)