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

export function checkStructure(tree: Root): LintResult[] {
  const results: LintResult[] = [];

  // Collect all headers
  const headers: { depth: number; text: string; line: number }[] = [];

  visit(tree, 'heading', (node: any) => {
    const text = node.children.map((c: any) => c.value).join('');
    headers.push({
      depth: node.depth,
      text: text,
      line: node.position?.start.line || 0
    });
  });

  // Rule 4: "### 学習目標" exists
  const goalsHeaderIndex = headers.findIndex(h => h.depth === 3 && h.text === '学習目標');
  if (goalsHeaderIndex === -1) {
    results.push({ ruleId: '4', message: 'Missing "### 学習目標" section' });
  }

  // Rule 6: "## まとめ" exists at the end
  // It should be the *last* H2 header, or at least exist as an H2.
  const summaryHeaderIndex = headers.findIndex(h => h.depth === 2 && h.text === 'まとめ');

  if (summaryHeaderIndex === -1) {
    results.push({ ruleId: '6', message: 'Missing "## まとめ" section' });
  } else {
    // Check if it's the last H2?
    // The rule says "最後に `## まとめ` がある" (Summary is at the end).
    // We can check if there are any H2s after it.
    const h2sAfterSummary = headers.slice(summaryHeaderIndex + 1).filter(h => h.depth === 2);
    if (h2sAfterSummary.length > 0) {
      results.push({ ruleId: '6', message: '"## まとめ" must be the last H2 section' });
    }
  }

  // Rule 5: Learning items are H2 (`##`)
  // Basically, checks that other main sections are H2.
  // And "### 学習目標" is an exception (H3).
  // This rule is a bit broad. It probably implies that the main content structure should use H2 for items.
  // If we identify "Learning Items" as sections between Goals and Summary.

  if (goalsHeaderIndex !== -1 && summaryHeaderIndex !== -1) {
    if (goalsHeaderIndex > summaryHeaderIndex) {
      results.push({ ruleId: '3', message: 'Structure invalid: "学習目標" appears after "まとめ"' });
    } else {
      // Check items between goals and summary
      // They should be H2?
      // Actually, "Overview" is before Goals.
      // Goals (H3) -> Items (H2) -> Summary (H2).
      // If there is an H2 *before* Goals, that might be "Overview"??
      // But Overview usually doesn't have a header in the description: "2. その章の概要文章".
      // So no header for Overview.

      // Check for any H2 between start and Goals?
      // If strict, maybe no H2 allowed before Goals?
      const h2BeforeGoals = headers.filter(h => h.depth === 2 && headers.indexOf(h) < goalsHeaderIndex);
      if (h2BeforeGoals.length > 0) {
        // Maybe warning? Or maybe strict.
        // The rule says "Overview -> Goals". If Overview has H2, it's fine?
        // But "学習項目はすべて `##` のH2見出し" implies H2s are Learning Items.
        // If Overview is H2, is it a Learning Item? No.
        // Let's assume Overview text has NO header.
        // So any H2 before Goals is suspicious if Goals is H3.
        // But wait, H1 is title.
        // Let's assume NO H2 before Goals.

        // results.push({ ruleId: '3', message: 'Found H2 section before "### 学習目標". Overview should not have a header or check structure.' });
      }

      // Check sections between Goals (H3) and Summary (H2)
      // We expect H2s here.
      // We can iterate headers between goalsHeaderIndex and summaryHeaderIndex
      for (let i = goalsHeaderIndex + 1; i < summaryHeaderIndex; i++) {
        const h = headers[i];
        // If it's a main section, it should be H2.
        // Subsections (H3, H4) are allowed inside items.
        // But we shouldn't have H1.
        if (h.depth === 1) {
          results.push({ ruleId: '5', message: 'H1 header found within content. Only one H1 (Title) allowed (handled by frontmatter usually, or top level).' });
        }
        // If we see H2, it's a learning item. Good.
      }
    }
  }

  return results;
}