import fs from 'fs';
import type MarkdownIt from 'markdown-it';
import type { RuleBlock } from 'markdown-it/lib/parser_block';

export const snippetPlugin = (md: MarkdownIt, root: string) => {
  const parser: RuleBlock = (state, startLine, _endLine, silent) => {
    const CH = '<'.charCodeAt(0);
    const pos = state.bMarks[startLine] + state.tShift[startLine];
    const max = state.eMarks[startLine];

    // if it's indented more than 3 spaces, it should be a code block
    if (state.sCount[startLine] - state.blkIndent >= 4) {
      return false;
    }

    for (let i = 0; i < 3; ++i) {
      const ch = state.src.charCodeAt(pos + i);
      if (ch !== CH || pos + i >= max) return false;
    }

    if (silent) {
      return true;
    }

    const start = pos + 3;
    const end = state.skipSpacesBack(max, pos);
    const rawPath = state.src.slice(start, end)?.trim().replace(/^@/, root);
    const filename = rawPath.split(/{/).shift()?.trim();
    const content = fs.existsSync(filename)
      ? fs.readFileSync(filename).toString()
      : 'Not found: ' + filename;
    const meta = rawPath.replace(filename, '');

    state.line = startLine + 1;

    const token = state.push('fence', 'code', 0);
    token.info = filename.split('.').pop() + meta;
    token.content = content;
    token.markup = '```';
    token.map = [startLine, startLine + 1];

    return true;
  };

  md.block.ruler.before('fence', 'snippet', parser);
};