"""An extension to capture amsmath latex environments."""
import re

from markdown_it import MarkdownIt
from markdown_it.common.utils import escapeHtml
from markdown_it.rules_block import StateBlock

# Taken from amsmath version 2.1
# http://anorien.csc.warwick.ac.uk/mirrors/CTAN/macros/latex/required/amsmath/amsldoc.pdf
ENVIRONMENTS = [
    # 3.2 single equation with an automatically gen-erated number
    "equation",
    # 3.3 variation equation, used for equations that don’t fit on a single line
    "multline",
    # 3.5 a group of consecutive equations when there is no alignment desired among them
    "gather",
    # 3.6 Used for two or more equations when vertical alignment is desired
    "align",
    # allows the horizontal space between equationsto be explicitly specified.
    "alignat",
    # stretches the space betweenthe equation columns to the maximum possible width
    "flalign",
    # 4.1 The pmatrix, bmatrix, Bmatrix, vmatrix and Vmatrix have (respectively)
    # (),[],{},||,and ‖‖ delimiters built in.
    "matrix",
    "pmatrix",
    "bmatrix",
    "Bmatrix",
    "vmatrix",
    "Vmatrix",
    # eqnarray is another math environment, it is not part of amsmath,
    # and note that it is better to use align or equation+split instead
    "eqnarray",
]
# other "non-top-level" environments:

# 3.4 the split environment is for single equations that are too long to fit on one line
# and hence must be split into multiple lines,
# it is intended for use only inside some other displayed equation structure,
# usually an equation, align, or gather environment

# 3.7 variants gathered, aligned,and alignedat are provided
# whose total width is the actual width of the contents;
# thus they can be used as a component in a containing expression

RE_OPEN = re.compile(r"\\begin\{(" + "|".join(ENVIRONMENTS) + r")([\*]?)\}")


def amsmath_plugin(md: MarkdownIt):
    """Parses TeX math equations, without any surrounding delimiters,
    only for top-level `amsmath <https://ctan.org/pkg/amsmath>`__ environments:

    .. code-block:: latex

        \\begin{gather*}
        a_1=b_1+c_1\\\\
        a_2=b_2+c_2-d_2+e_2
        \\end{gather*}

    """
    md.block.ruler.before(
        "blockquote",
        "amsmath",
        amsmath_block,
        {"alt": ["paragraph", "reference", "blockquote", "list", "footnote_def"]},
    )
    md.add_render_rule("amsmath", render_amsmath_block)


def match_environment(string):
    match_open = RE_OPEN.match(string)
    if not match_open:
        return None
    environment = match_open.group(1)
    numbered = match_open.group(2)
    match_close = re.search(
        r"\\end\{" + environment + numbered.replace("*", r"\*") + "\\}", string
    )
    if not match_close:
        return None
    return (environment, numbered, match_close.end())


def amsmath_block(state: StateBlock, startLine: int, endLine: int, silent: bool):

    # if it's indented more than 3 spaces, it should be a code block
    if state.sCount[startLine] - state.blkIndent >= 4:
        return False

    begin = state.bMarks[startLine] + state.tShift[startLine]

    outcome = match_environment(state.src[begin:])
    if not outcome:
        return False
    environment, numbered, endpos = outcome
    endpos += begin

    line = startLine
    while line < endLine:
        if endpos >= state.bMarks[line] and endpos <= state.eMarks[line]:
            # line for end of block math found ...
            state.line = line + 1
            break
        line += 1

    if not silent:
        token = state.push("amsmath", "math", 0)
        token.block = True
        token.content = state.src[begin:endpos]
        token.meta = {"environment": environment, "numbered": numbered}
        token.map = [startLine, line]

    return True


def render_amsmath_block(self, tokens, idx, options, env):
    token = tokens[idx]
    return (
        '<section class="amsmath">\n<eqn>\n'
        f"{escapeHtml(token.content)}\n</eqn>\n</section>\n"
    )
