import { Rule } from './rule-interface';
/**
* MD001: Heading levels should only increment by one level at a time
*
* This rule is triggered when you skip heading levels in a markdown document, for example:
*
* # Heading 1
* ### Heading 3
*
* This rule requires that heading levels only increment by one level at a time.
*/
export const name = 'MD001';
export const description = 'Heading levels should only increment by one level at a time';
/**
* Fixes markdown content to ensure heading levels only increment by one level at a time
* @param lines Array of string lines to fix
* @returns Fixed lines array with proper heading level increments
*/
export function fix(lines: string[]): string[] {
if (lines.length === 0) return lines;
const result = [...lines];
let previousLevel = 0;
// Helper to extract heading level from a line
function getHeadingLevel(line: string): number {
const match = line.match(/^(#{1,6})(?:\s|$)/);
return match ? match[1].length : 0;
}
// Helper to change a heading's level
function changeHeadingLevel(line: string, newLevel: number): string {
// ATX heading (# style)
if (/^#{1,6}\s/.test(line)) {
const content = line.replace(/^#{1,6}\s+/, '');
return '#'.repeat(newLevel) + ' ' + content;
}
// Closed ATX heading (# style #)
else if (/^#{1,6}\s.*\s+#{1,6}$/.test(line)) {
const content = line.replace(/^#{1,6}\s+/, '').replace(/\s+#{1,6}$/, '');
return '#'.repeat(newLevel) + ' ' + content + ' ' + '#'.repeat(newLevel);
}
// If we can't determine the heading style, return original line
return line;
}
// Scan through each line to find headings and fix levels
for (let i = 0; i < lines.length; i++) {
const line = lines[i];
const level = getHeadingLevel(line);
// Skip non-heading lines
if (level === 0) {
continue;
}
// For the first heading, just set the previous level
if (previousLevel === 0) {
previousLevel = level;
continue;
}
// If we skip levels (e.g., from h1 to h3), fix it
if (level > previousLevel + 1) {
// Change to one level deeper than previous
const newLevel = previousLevel + 1;
result[i] = changeHeadingLevel(line, newLevel);
previousLevel = newLevel;
} else {
// If no issues, update previous level
previousLevel = level;
}
}
return result;
}
/**
* Rule implementation for MD001
*/
export const rule: Rule = {
name,
description,
fix
};
export default rule;
