// Wandelt Markdown in Pango-Markup für St.Label um.
// Unterstützt: Überschriften, Fett, Kursiv, Durchgestrichen, Code (inline und Block),
// Listen, Checkboxen, Zitate, Links, Trennlinien.

const CODE_BG = '#2b2b2b';
const LINK_COLOR = '#8ab4f8';
const QUOTE_COLOR = '#b0b0b0';
// Platzhalter für herausgenommene Code-Spans (Private-Use-Zeichen, kommt in Text nicht vor).
const HOLE = '';

export function escapeMarkup(text) {
    return text.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
}

function inline(text) {
    // Inline-Code zuerst herausnehmen, damit Sternchen darin unberührt bleiben.
    const codes = [];
    let out = escapeMarkup(text).replace(/`([^`]+)`/g, (_, code) => {
        codes.push(`<span font_family="monospace" background="${CODE_BG}">${code}</span>`);
        return `${HOLE}${codes.length - 1}${HOLE}`;
    });
    out = out
        .replace(/!\[([^\]]*)\]\([^)]*\)/g, '[Bild: $1]')
        .replace(/\[([^\]]+)\]\([^)]*\)/g, `<u><span foreground="${LINK_COLOR}">$1</span></u>`)
        .replace(/\[\[([^\]]+)\]\]/g, `<u><span foreground="${LINK_COLOR}">$1</span></u>`)
        .replace(/\*\*(.+?)\*\*/g, '<b>$1</b>')
        .replace(/__(.+?)__/g, '<b>$1</b>')
        .replace(/~~(.+?)~~/g, '<s>$1</s>')
        .replace(/(^|[^*\w])\*([^*\s](?:[^*]*[^*\s])?)\*(?!\w)/g, '$1<i>$2</i>')
        .replace(/(^|[^_\w])_([^_\s](?:[^_]*[^_\s])?)_(?!\w)/g, '$1<i>$2</i>');
    return out.replace(new RegExp(`${HOLE}(\\d+)${HOLE}`, 'g'), (_, i) => codes[Number(i)]);
}

// Absolute Punktgrößen: Schlüsselwörter wie xx-large skalieren im ClutterText den ganzen Text.
const HEADING_SIZE = ['18pt', '15pt', '12.5pt', '11pt', '11pt', '11pt'];

export function renderMarkdown(text) {
    const lines = text.replace(/\r\n/g, '\n').split('\n');
    const out = [];
    let inCode = false;

    for (const line of lines) {
        if (/^\s*```/.test(line)) {
            inCode = !inCode;
            continue;
        }
        if (inCode) {
            out.push(`<span font_family="monospace" background="${CODE_BG}">${escapeMarkup(line) || ' '}</span>`);
            continue;
        }

        let match;
        if ((match = line.match(/^(#{1,6})\s+(.*)$/))) {
            const level = match[1].length;
            out.push(`<span size="${HEADING_SIZE[level - 1]}" weight="bold">${inline(match[2])}</span>`);
        } else if (/^\s*([-*_])(\s*\1){2,}\s*$/.test(line)) {
            out.push('<span foreground="#666666">────────────────────────────</span>');
        } else if ((match = line.match(/^(\s*)[-*+]\s+\[([ xX])\]\s+(.*)$/))) {
            const box = match[2] === ' ' ? '☐' : '☑';
            const body = match[2] === ' ' ? inline(match[3]) : `<span foreground="#888888"><s>${inline(match[3])}</s></span>`;
            out.push(`${indent(match[1])}${box}  ${body}`);
        } else if ((match = line.match(/^(\s*)[-*+]\s+(.*)$/))) {
            out.push(`${indent(match[1])}•  ${inline(match[2])}`);
        } else if ((match = line.match(/^(\s*)(\d+)[.)]\s+(.*)$/))) {
            out.push(`${indent(match[1])}${match[2]}.  ${inline(match[3])}`);
        } else if ((match = line.match(/^>\s?(.*)$/))) {
            out.push(`<span foreground="${QUOTE_COLOR}">▎ <i>${inline(match[1])}</i></span>`);
        } else {
            out.push(inline(line));
        }
    }
    return out.join('\n');
}

// Verschachtelte Listen: je 2 Leerzeichen oder 1 Tab eine Ebene tiefer.
function indent(spaces) {
    const level = spaces.replace(/\t/g, '  ').length / 2;
    return '    '.repeat(Math.floor(level) + 1);
}