import { Plugin, loadMathJax, finishRenderMath, renderMath } from 'obsidian';

function convertLink(link : HTMLElement) {
    const linkText = link.textContent?.trim();

    if (linkText?.contains('$')) {
        
        // Each section of text between unescaped $ signs
        // Fallback to empty list if null, as this happens when input is empty
        const sections = mathSplit(linkText);

        let isMath = false;
        link.innerText = '';

        for (let i = 0; i < sections.length; i++) {
            if (isMath) {
                link.createSpan().replaceWith(renderMath(sections[i], false));
            } else {
                link.createSpan().innerText += sections[i];
            }

            isMath = !isMath;
        }

        finishRenderMath();
    }
}

// Splits at math delimeters, handling escapes properly
// Returns an array of alternating normal text and math text
function mathSplit(input : string) : string[]  {
    let output = [''];

    let backslashes = 0;

    for (let i = 0; i < input.length; i++) {
        let curr = input[i];
            
        if (curr == '\\') {
            backslashes++;
        }
        else {
            for (let j = 0; j < Math.ceil(backslashes / 2); j++) {
                output[output.length - 1] = output[output.length - 1] + "\\";
            }

            if (curr == '$' && backslashes % 2 == 0) {
                output.push('');
            }
            else {
                output[output.length - 1] = output[output.length - 1] + curr;
            }

            backslashes = 0;
        }
    }

    return output;
}

export default class MathJaxWikiLinks extends Plugin {
    async onload() {
        await loadMathJax();

        this.registerMarkdownPostProcessor((element, context) => {
            element.querySelectorAll('.internal-link').forEach(convertLink);
        });
    }
}