import fs from 'fs';
import path from 'path';
import { fileURLToPath } from 'url';

const __dirname = path.dirname(fileURLToPath(import.meta.url));

/**
 * 미리보기 이미지 저장 디렉터리
 * @returns {string}
 */
export function getPreviewsDir() {
    const dir = process.env.PREVIEWS_PATH || path.join(__dirname, '..', '..', 'data', 'previews');
    if (!fs.existsSync(dir)) {
        fs.mkdirSync(dir, { recursive: true });
    }
    return dir;
}

/**
 * base64 data URL을 PNG 파일로 저장
 * @param {string} shareCode
 * @param {string} dataUrl
 * @returns {string} 파일명
 */
export function savePreviewImage(shareCode, dataUrl) {
    if (!dataUrl || !dataUrl.startsWith('data:image')) {
        return null;
    }
    const base64 = dataUrl.replace(/^data:image\/\w+;base64,/, '');
    const fileName = `${shareCode}.png`;
    fs.writeFileSync(path.join(getPreviewsDir(), fileName), Buffer.from(base64, 'base64'));
    return fileName;
}

/**
 * @param {string} shareCode
 * @returns {string|null}
 */
export function getPreviewFilePath(shareCode) {
    const filePath = path.join(getPreviewsDir(), `${shareCode}.png`);
    return fs.existsSync(filePath) ? filePath : null;
}

/**
 * @param {string} shareCode
 * @param {string|null} [previewImageRecord] DB preview_image 컬럼
 * @returns {string|null}
 */
export function getPreviewUrl(shareCode, previewImageRecord = null) {
    const hasFile = Boolean(getPreviewFilePath(shareCode));
    if (hasFile || previewImageRecord) {
        return `/api/v1/decks/${shareCode}/preview`;
    }
    return null;
}

/**
 * 공유 코드에 연결된 미리보기 파일 삭제
 * @param {string} shareCode
 * @returns {boolean}
 */
export function deletePreviewImage(shareCode) {
    const filePath = path.join(getPreviewsDir(), `${shareCode}.png`);
    if (!fs.existsSync(filePath)) return false;
    try {
        fs.unlinkSync(filePath);
        return true;
    } catch (err) {
        console.warn(`[preview] 삭제 실패: ${filePath}`, err);
        return false;
    }
}

/**
 * DB에서 참조하지 않는 미리보기 파일 목록
 * @param {Iterable<string>} referencedShareCodes
 * @returns {Array<{fileName: string, size: number, modifiedAt: string}>}
 */
export function listOrphanPreviewImages(referencedShareCodes) {
    const referenced = new Set([...referencedShareCodes].map((code) => `${code}.png`));
    return fs
        .readdirSync(getPreviewsDir(), { withFileTypes: true })
        .filter((entry) => entry.isFile() && entry.name.toLowerCase().endsWith('.png'))
        .filter((entry) => !referenced.has(entry.name))
        .map((entry) => {
            const stat = fs.statSync(path.join(getPreviewsDir(), entry.name));
            return {
                fileName: entry.name,
                size: stat.size,
                modifiedAt: stat.mtime.toISOString(),
            };
        })
        .sort((a, b) => b.modifiedAt.localeCompare(a.modifiedAt));
}

/**
 * 미참조 미리보기 파일 일괄 삭제
 * @param {Iterable<string>} referencedShareCodes
 * @returns {{deletedCount: number, deletedBytes: number}}
 */
export function deleteOrphanPreviewImages(referencedShareCodes) {
    const orphans = listOrphanPreviewImages(referencedShareCodes);
    let deletedBytes = 0;

    orphans.forEach((file) => {
        fs.unlinkSync(path.join(getPreviewsDir(), file.fileName));
        deletedBytes += file.size;
    });

    return { deletedCount: orphans.length, deletedBytes };
}