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import type { Expression, Super } from 'estree';
import Slugger from 'github-slugger';
import type { MdxTextExpression } from 'mdast-util-mdx-expression';
import type { Node } from 'unist';
import { visit } from 'unist-util-visit';
import { InvalidAstroDataError, safelyGetAstroData } from './frontmatter-injection.js';
import type { MarkdownAstroData, MarkdownHeading, MarkdownVFile, RehypePlugin } from './types.js';
const rawNodeTypes = new Set(['text', 'raw', 'mdxTextExpression']);
const codeTagNames = new Set(['code', 'pre']);
export function rehypeHeadingIds(): ReturnType<RehypePlugin> {
return function (tree, file: MarkdownVFile) {
const headings: MarkdownHeading[] = [];
const slugger = new Slugger();
const isMDX = isMDXFile(file);
const astroData = safelyGetAstroData(file.data);
visit(tree, (node) => {
if (node.type !== 'element') return;
const { tagName } = node;
if (tagName[0] !== 'h') return;
const [, level] = tagName.match(/h([0-6])/) ?? [];
if (!level) return;
const depth = Number.parseInt(level);
let text = '';
visit(node, (child, __, parent) => {
if (child.type === 'element' || parent == null) {
return;
}
if (child.type === 'raw') {
if (child.value.match(/^\n?<.*>\n?$/)) {
return;
}
}
if (rawNodeTypes.has(child.type)) {
if (isMDX || codeTagNames.has(parent.tagName)) {
let value = child.value;
if (isMdxTextExpression(child) && !(astroData instanceof InvalidAstroDataError)) {
const frontmatterPath = getMdxFrontmatterVariablePath(child);
if (Array.isArray(frontmatterPath) && frontmatterPath.length > 0) {
const frontmatterValue = getMdxFrontmatterVariableValue(astroData, frontmatterPath);
if (typeof frontmatterValue === 'string') {
value = frontmatterValue;
}
}
}
text += value;
} else {
text += child.value.replace(/\{/g, '${');
}
}
});
node.properties = node.properties || {};
if (typeof node.properties.id !== 'string') {
let slug = slugger.slug(text);
if (slug.endsWith('-')) slug = slug.slice(0, -1);
node.properties.id = slug;
}
headings.push({ depth, slug: node.properties.id, text });
});
file.data.__astroHeadings = headings;
};
}
function isMDXFile(file: MarkdownVFile) {
return Boolean(file.history[0]?.endsWith('.mdx'));
}
/**
* Check if an ESTree entry is `frontmatter.*.VARIABLE`.
* If it is, return the variable path (i.e. `["*", ..., "VARIABLE"]`) minus the `frontmatter` prefix.
*/
function getMdxFrontmatterVariablePath(node: MdxTextExpression): string[] | Error {
if (!node.data?.estree || node.data.estree.body.length !== 1) return new Error();
const statement = node.data.estree.body[0];
// Check for "[ANYTHING].[ANYTHING]".
if (statement?.type !== 'ExpressionStatement' || statement.expression.type !== 'MemberExpression')
return new Error();
let expression: Expression | Super = statement.expression;
const expressionPath: string[] = [];
// Traverse the expression, collecting the variable path.
while (
expression.type === 'MemberExpression' &&
expression.property.type === (expression.computed ? 'Literal' : 'Identifier')
) {
expressionPath.push(
expression.property.type === 'Literal'
? String(expression.property.value)
: expression.property.name
);
expression = expression.object;
}
// Check for "frontmatter.[ANYTHING]".
if (expression.type !== 'Identifier' || expression.name !== 'frontmatter') return new Error();
return expressionPath.reverse();
}
function getMdxFrontmatterVariableValue(astroData: MarkdownAstroData, path: string[]) {
let value: MdxFrontmatterVariableValue = astroData.frontmatter;
for (const key of path) {
if (!value[key]) return undefined;
value = value[key];
}
return value;
}
function isMdxTextExpression(node: Node): node is MdxTextExpression {
return node.type === 'mdxTextExpression';
}
type MdxFrontmatterVariableValue =
MarkdownAstroData['frontmatter'][keyof MarkdownAstroData['frontmatter']];
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