import os
import re
from typing import List, Match
from xml.etree.ElementTree import Element

from markdown import Extension, Markdown
from markdown.blockparser import BlockParser
from markdown.blockprocessors import BlockProcessor

from zerver.lib.exceptions import InvalidMarkdownIncludeStatementError
from zerver.lib.markdown.priorities import BLOCK_PROCESSOR_PRIORITIES


class IncludeExtension(Extension):
    def __init__(self, base_path: str) -> None:
        super().__init__()
        self.base_path = base_path

    def extendMarkdown(self, md: Markdown) -> None:
        md.parser.blockprocessors.register(
            IncludeBlockProcessor(md.parser, self.base_path),
            "include",
            BLOCK_PROCESSOR_PRIORITIES["include"],
        )


class IncludeBlockProcessor(BlockProcessor):
    RE = re.compile(r"^ {,3}\{!([^!]+)!\} *$", re.M)

    def __init__(self, parser: BlockParser, base_path: str) -> None:
        super().__init__(parser)
        self.base_path = base_path

    def test(self, parent: Element, block: str) -> bool:
        return bool(self.RE.search(block))

    def expand_include(self, m: Match[str]) -> str:
        try:
            with open(os.path.normpath(os.path.join(self.base_path, m[1]))) as f:
                lines = f.read().splitlines()
        except OSError as e:
            raise InvalidMarkdownIncludeStatementError(m[0].strip()) from e

        for prep in self.parser.md.preprocessors:
            lines = prep.run(lines)

        return "\n".join(lines)

    def run(self, parent: Element, blocks: List[str]) -> None:
        self.parser.state.set("include")
        self.parser.parseChunk(parent, self.RE.sub(self.expand_include, blocks.pop(0)))
        self.parser.state.reset()


def makeExtension(base_path: str) -> IncludeExtension:
    return IncludeExtension(base_path=base_path)