const fs = require("fs/promises");
const YAML = require("yaml");

const FRONTMATTER_PATTERN = /^---\n([\s\S]*?)\n---\n?/;

async function readFrontmatter(filePath) {
    const raw = await fs.readFile(filePath, "utf8");
    const match = raw.match(FRONTMATTER_PATTERN);

    if (!match) return null;

    const frontmatterText = match[1];
    const doc = YAML.parseDocument(frontmatterText);

    if (doc.errors.length) {
        const [error] = doc.errors;
        throw new Error(`Invalid frontmatter in ${filePath}: ${error.message}`);
    }

    const body = raw.slice(match[0].length);

    return { doc, body, frontmatterText };
}

async function writeFrontmatter(filePath, doc, body) {
    const serialized = doc.toString().trimEnd();
    const nextContent = `---\n${serialized}\n---\n${body}`;

    await fs.writeFile(filePath, nextContent, "utf8");
}

function extractRawDate(frontmatterText) {
    const match = frontmatterText.match(/^date:\s*(.+)$/m);
    return match ? match[1].trim() : null;
}

module.exports = {
    extractRawDate,
    readFrontmatter,
    writeFrontmatter,
};