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

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

                node.children = beforeBreak;

                const newParagraph = {
                    type: 'paragraph',
                    children: afterBreak,
                };

                let rootChildIndex = -1;
                if (parent.type === 'root') {
                    rootChildIndex = index!;
                } else {
                    rootChildIndex = tree.children.findIndex((child: any) =>
                        child === parent || (child.children && child.children.includes(node))
                    );

                    if (rootChildIndex === -1) {
                        rootChildIndex = tree.children.indexOf(parent);
                    }
                }

                if (rootChildIndex !== -1) {
                    tree.children.splice(rootChildIndex + 1, 0, newParagraph);
                }

                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,
        }
    }
})