/**
 * ============================================================
 * 파일: assets/css/datalab/skeleton_loader.css
 * ============================================================
 * 목적: 통계 데이터 로딩 중 Skeleton UI 스타일
 *
 * 기능:
 * 1. 로딩 애니메이션: pulse 애니메이션으로 "로딩 중" 시각화
 * 2. 반응형 디자인: 다양한 크기의 통계 카드 지원
 * 3. 부드러운 전환: 로딩 완료 시 페이드 아웃
 *
 * 사용 예시:
 * ```html
 * <div class="stat-card skeleton-loading">
 *     <div class="skeleton-overlay">
 *         <div class="skeleton-header"></div>
 *         <div class="skeleton-chart"></div>
 *     </div>
 * </div>
 * ```
 *
 * 개선 사항:
 * - 기존: 탭 클릭 후 2-5초 동안 아무것도 표시 안 함
 * - 개선: 로딩 중임을 명확하게 표시하여 사용자 체감 개선
 * ============================================================
 */

/* ============================================================
   1. Skeleton 기본 스타일
   ============================================================ */

.skeleton-loading {
    position: relative;
    overflow: hidden;
}

.skeleton-overlay {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: #fff;
    z-index: 10;
    border-radius: 4px;
}

/* ============================================================
   2. Skeleton 요소별 스타일
   ============================================================ */

.skeleton-header {
    height: 20px;
    background: linear-gradient(
        90deg,
        #f0f0f0 25%,
        #e0e0e0 50%,
        #f0f0f0 75%
    );
    background-size: 200% 100%;
    margin-bottom: 16px;
    border-radius: 4px;
    animation: skeleton-loading 1.5s infinite;
}

.skeleton-chart {
    height: 250px;
    background: linear-gradient(
        90deg,
        #f0f0f0 25%,
        #e0e0e0 50%,
        #f0f0f0 75%
    );
    background-size: 200% 100%;
    border-radius: 4px;
    animation: skeleton-loading 1.5s infinite;
}

/* 작은 차트용 skeleton */
.skeleton-overlay.small .skeleton-chart {
    height: 150px;
}

/* 큰 차트용 skeleton */
.skeleton-overlay.large .skeleton-chart {
    height: 400px;
}

/* ============================================================
   3. Skeleton 로딩 애니메이션
   ============================================================ */

@keyframes skeleton-loading {
    0% {
        background-position: 200% 0;
    }
    100% {
        background-position: -200% 0;
    }
}

/* 펄스(pulse) 애니메이션 (대체 방식) */
@keyframes skeleton-pulse {
    0%, 100% {
        opacity: 0.6;
    }
    50% {
        opacity: 1;
    }
}

.skeleton-pulse {
    animation: skeleton-pulse 1.5s ease-in-out infinite;
}

/* ============================================================
   4. 로딩 상태 표시
   ============================================================ */

.stats-loading-indicator {
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 20px;
    color: #999;
    font-size: 14px;
}

.stats-loading-indicator::before {
    content: '';
    width: 12px;
    height: 12px;
    border: 2px solid #f3f3f3;
    border-top: 2px solid #183EA0;
    border-radius: 50%;
    animation: spin 1s linear infinite;
    margin-right: 8px;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* ============================================================
   5. 로딩 진행률 표시
   ============================================================ */

.stats-progress-bar {
    height: 4px;
    background: #f0f0f0;
    border-radius: 2px;
    overflow: hidden;
    margin: 16px 0;
}

.stats-progress-bar-fill {
    height: 100%;
    background: linear-gradient(90deg, #183EA0, #1e5fbf);
    border-radius: 2px;
    animation: progress-fill 2s ease-in-out infinite;
}

@keyframes progress-fill {
    0% {
        width: 0%;
    }
    50% {
        width: 70%;
    }
    100% {
        width: 100%;
    }
}

/* ============================================================
   6. 페이드 아웃 애니메이션
   ============================================================ */

.skeleton-fade-out {
    animation: skeleton-fade-out 0.3s ease-out forwards;
}

@keyframes skeleton-fade-out {
    from {
        opacity: 1;
        visibility: visible;
    }
    to {
        opacity: 0;
        visibility: hidden;
    }
}

/* ============================================================
   7. 에러 상태
   ============================================================ */

.stats-error-message {
    padding: 16px;
    background: #fff3cd;
    border: 1px solid #ffc107;
    border-radius: 4px;
    margin-bottom: 16px;
    color: #856404;
}

.stats-error-message p {
    margin: 0 0 8px 0;
    font-weight: 500;
}

.stats-error-message small {
    display: block;
    margin-top: 4px;
    opacity: 0.8;
}

/* ============================================================
   8. 모바일 최적화
   ============================================================ */

@media (max-width: 768px) {
    .skeleton-header {
        height: 18px;
        margin-bottom: 12px;
    }

    .skeleton-chart {
        height: 200px;
    }

    .skeleton-overlay.small .skeleton-chart {
        height: 120px;
    }

    .skeleton-overlay.large .skeleton-chart {
        height: 300px;
    }
}

/* ============================================================
   9. 다크모드 지원 (필요시)
   ============================================================ */

@media (prefers-color-scheme: dark) {
    .skeleton-header,
    .skeleton-chart {
        background: linear-gradient(
            90deg,
            #2a2a2a 25%,
            #333 50%,
            #2a2a2a 75%
        );
    }

    .skeleton-overlay {
        background: #1a1a1a;
    }
}

/* ============================================================
   10. 성능 최적화 (GPU 가속)
   ============================================================ */

.skeleton-loading {
    will-change: opacity;
    transform: translateZ(0);
    backface-visibility: hidden;
}

.skeleton-overlay {
    will-change: opacity;
}