import { unified } from 'unified';
import { visit } from 'unist-util-visit';
import remarkParse from 'remark-parse';
import remarkGfm from 'remark-gfm';
import remarkRehype from 'remark-rehype';
import remarkBreaks from 'remark-breaks';
import remarkMath from 'remark-math';
import rehypeKatex from 'rehype-katex';

function remarkSplitBlocks() {
    return (tree: any) => {
        visit(tree, 'paragraph', (node, index, parent) => {
            if (parent == null || index == null) {
                return;
            }

            const breakIndex = node.children.findIndex((child: any) => child.type === 'break');

            if (breakIndex === -1) {
                return;
            }

            const beforeBreak = node.children.slice(0, breakIndex);
            const afterBreak = node.children.slice(breakIndex + 1);

            // Keep content before the break in the current paragraph.
            node.children = beforeBreak;

            // Insert content after the break as the next sibling of this
            // paragraph in its actual parent (root, listItem, blockquote, etc.).
            // Previously this only spliced into tree.children and dropped
            // nested content when the parent wasn't a direct root child.
            if (afterBreak.length > 0) {
                const newParagraph = {
                    type: 'paragraph',
                    children: afterBreak,
                };

                parent.children.splice(index + 1, 0, newParagraph);

                // Continue at the newly inserted paragraph so further
                // hard breaks inside it are split as well.
                return index + 1;
            }
        });
    };
}

export default defineNuxtPlugin((nuxtApp) => {
    const remark =
        unified()
            .use(remarkParse)
            .use(remarkGfm)
            .use(remarkMath)
            .use(remarkBreaks)
            .use(remarkSplitBlocks)
            .use(remarkRehype, { allowDangerousHtml: true })
            .use(rehypeKatex, { output: 'mathml' });

    return {
        provide: {
            remark,
        }
    }
})