const fs = require('fs');
const path = require('path');
const matter = require('gray-matter');

const postsDir = path.resolve(__dirname, '../content/post');

function formatDate(date) {
    if (!date) return null;
    const d = new Date(date);
    if (isNaN(d.getTime())) return null;
    const year = d.getFullYear();
    const month = String(d.getMonth() + 1).padStart(2, '0');
    const day = String(d.getDate()).padStart(2, '0');
    return `${year}${month}${day}`;
}

function traverseDir(dir) {
    const files = fs.readdirSync(dir);
    files.forEach(file => {
        const filePath = path.join(dir, file);
        const stat = fs.statSync(filePath);
        if (stat.isDirectory()) {
            traverseDir(filePath);
        } else if (file.endsWith('.md')) {
            processFile(filePath);
        }
    });
}

function processFile(filePath) {
    try {
        const fileContent = fs.readFileSync(filePath, 'utf8');
        const parsed = matter(fileContent);
        
        // Check if slug is already in target format (YYYYMMDDHHmm)
        // Or if it matches YYYYMMDD (old format we are migrating to)
        if (parsed.data.slug && /^\d{8,12}$/.test(String(parsed.data.slug))) {
            // console.log(`Skipping ${filePath}: Slug already formatted (${parsed.data.slug})`);
            return;
        }

        const dateSlug = formatDate(parsed.data.date);
        if (!dateSlug) {
            console.warn(`Skipping ${filePath}: No valid date found`);
            return;
        }

        // Update slug
        // Note: gray-matter might reformat the front matter slightly
        // We preserve existing data but update slug
        parsed.data.slug = dateSlug;

        // Convert back to string
        // Hugo front matter usually uses '---' delimiters
        // gray-matter defaults to '---'
        // We need to be careful about date formatting in output, 
        // but gray-matter usually handles Date objects by converting to ISO string
        
        // Force date to be string if it was parsed as Date object to avoid format changes?
        // Actually, Hugo likes ISO dates, so Date object to ISO string is fine.
        
        const newContent = matter.stringify(parsed.content, parsed.data);
        
        // fs.writeFileSync(filePath, newContent);
        // console.log(`Updated ${filePath}: slug set to ${dateSlug}`);
        
        // Wait, gray-matter stringify might change the order or format of other fields.
        // A safer approach is regex replacement if we only want to change slug.
        // But regex is brittle.
        // Let's stick to gray-matter but be careful.
        // Actually, let's use a custom replacement to be safe and preserve comments/formatting.
        
        let lines = fileContent.split('\n');
        let inFrontMatter = false;
        let slugFound = false;
        let dateFound = false;
        let newLines = [];
        let fmEndIndex = -1;

        for (let i = 0; i < lines.length; i++) {
            const line = lines[i];
            if (line.trim() === '---') {
                if (!inFrontMatter) {
                    inFrontMatter = true;
                } else {
                    inFrontMatter = false;
                    fmEndIndex = i;
                }
                newLines.push(line);
                continue;
            }

            if (inFrontMatter) {
                if (line.trim().startsWith('slug:')) {
                    newLines.push(`slug: ${dateSlug}`);
                    slugFound = true;
                } else if (line.trim().startsWith('date:')) {
                    newLines.push(line);
                    dateFound = true;
                } else {
                    newLines.push(line);
                }
            } else {
                newLines.push(line);
            }
        }

        if (!slugFound && fmEndIndex !== -1) {
            // Insert slug before the end of front matter
            // Find the last non-empty line before ---
            newLines.splice(fmEndIndex, 0, `slug: ${dateSlug}`);
        }

        fs.writeFileSync(filePath, newLines.join('\n'));
        console.log(`Updated ${filePath}: slug set to ${dateSlug}`);

    } catch (e) {
        console.error(`Error processing ${filePath}:`, e);
    }
}

console.log('Starting slug migration...');
traverseDir(postsDir);
console.log('Migration complete.');