import { LintResult } from '../linter.js';
import { Root } from 'mdast';
import { visit } from 'unist-util-visit';

export function checkToc(tree: Root): LintResult[] {
  const results: LintResult[] = [];
  let frontmatterNodeIndex = -1;
  let tocFound = false;
  let tocImmediatelyAfter = false;

  // Find frontmatter index
  visit(tree, 'yaml', (node, index) => {
    if (frontmatterNodeIndex === -1 && typeof index === 'number') {
      frontmatterNodeIndex = index;
    }
  });

  if (frontmatterNodeIndex !== -1) {
    // Check nodes after frontmatter
    // We expect the next *meaningful* node to be the TOC. 
    // Sometimes there might be empty text nodes or whitespace, but remark usually handles blocks.
    // However, if there are blank lines, they might just be ignored in AST structure or appear as distinct nodes depending on config.
    // With remark-parse, usually the next block-level node is what we care about.

    const children = tree.children;
    // Look at the node immediately following YAML
    // But be careful about index bounds
    if (frontmatterNodeIndex + 1 < children.length) {
      const nextNode = children[frontmatterNodeIndex + 1];

      // Check if it matches {{ toc }}
      // Usually parsed as a paragraph containing text "{{ toc }}"
      if (nextNode.type === 'paragraph') {
        const textContent = nextNode.children.map(c => (c as any).value).join('');
        if (textContent.trim() === '{{ toc }}') {
          tocImmediatelyAfter = true;
        }
      }
    }
  }

  // If frontmatter exists, we expect TOC after it.
  // If frontmatter is missing, Rule 1 catches it, but if we found FM, we check TOC.
  if (frontmatterNodeIndex !== -1 && !tocImmediatelyAfter) {
    results.push({ ruleId: '2', message: '{{ toc }} must be placed immediately after frontmatter' });
  }

  return results;
}