def create_catalog_html(datasets, username=None):
    """Creates HTML string for the dataset catalog with improved card design."""
    if not datasets:
        return """
        <div class="empty-state">
            <div class="empty-state-icon">📦</div>
            <div class="empty-state-title">No datasets available</div>
            <div class="empty-state-text">Check back soon for new data products.</div>
        </div>
        """

    cards_html = ""
    for i, dataset in enumerate(datasets):
        dataset_id = dataset.get('dataset_id', '')
        display_name = dataset.get('display_name', dataset_id)
        description = dataset.get('description', 'No description available.')

        # Determine pricing display
        plans = dataset.get("plans", [])
        is_free = False
        price = "10"
        trial_days = 1

        if plans:
            plan = plans[0]
            price_id = plan.get("stripe_price_id", "")
            if price_id in ["free", "0", 0]:
                is_free = True
                trial_days = plan.get("access_duration_days", 1)
            else:
                price = plan.get("price", "10")

        # Price badge
        if is_free:
            trial_text = "24h" if trial_days == 1 else f"{trial_days}-day"
            price_badge = f'<span class="catalog-price-badge free">{trial_text} Free Trial</span>'
        else:
            price_badge = f'<span class="catalog-price-badge paid">${price}<span class="period">/mo</span></span>'

        # Action area - only show hint when not logged in
        if not username:
            action_html = '''
            <div class="catalog-card-action">
                <span class="action-hint login-required">Sign in to subscribe</span>
            </div>
            '''
        else:
            action_html = ''

        cards_html += f"""
        <div class="catalog-card" data-dataset-id="{dataset_id}">
            <div class="catalog-card-header">
                <div class="catalog-card-icon">📊</div>
                <div class="catalog-card-title-area">
                    <h3 class="catalog-card-title">{display_name}</h3>
                    <span class="catalog-card-id">{dataset_id}</span>
                </div>
            </div>
            <p class="catalog-card-description">{description}</p>
            <div class="catalog-card-footer">
                {price_badge}
                {action_html}
            </div>
        </div>
        """

    # Wrap in container with improved styles
    html = f"""
    <div class="catalog-container">
        {cards_html}
    </div>
    <style>
        .catalog-container {{
            display: flex;
            flex-direction: column;
            gap: 1rem;
            padding: 0.5rem 0;
        }}

        .catalog-card {{
            background: var(--bg-card, #1c1c1e);
            border: 1px solid var(--border-color, rgba(255,255,255,0.08));
            border-radius: 16px;
            padding: 1.25rem 1.5rem;
            transition: all 0.2s ease;
            position: relative;
        }}

        .catalog-card:hover {{
            border-color: var(--border-color-strong, rgba(255,255,255,0.15));
            transform: translateY(-2px);
            box-shadow: 0 8px 25px rgba(0,0,0,0.15);
        }}

        .catalog-card-header {{
            display: flex;
            align-items: flex-start;
            gap: 1rem;
            margin-bottom: 0.75rem;
        }}

        .catalog-card-icon {{
            font-size: 2rem;
            line-height: 1;
            flex-shrink: 0;
        }}

        .catalog-card-title-area {{
            flex: 1;
            min-width: 0;
        }}

        .catalog-card-title {{
            font-size: 1.125rem;
            font-weight: 600;
            color: var(--text-primary, #f5f5f7);
            margin: 0 0 0.25rem 0;
            line-height: 1.3;
        }}

        .catalog-card-id {{
            font-size: 0.75rem;
            color: var(--text-tertiary, #6e6e73);
            font-family: 'SF Mono', Monaco, monospace;
            background: var(--bg-tertiary, rgba(255,255,255,0.05));
            padding: 0.125rem 0.5rem;
            border-radius: 4px;
            display: inline-block;
        }}

        .catalog-card-description {{
            font-size: 0.875rem;
            color: var(--text-secondary, #a1a1a6);
            line-height: 1.5;
            margin: 0 0 1rem 0;
        }}

        .catalog-card-footer {{
            display: flex;
            align-items: center;
            justify-content: space-between;
            flex-wrap: wrap;
            gap: 0.75rem;
            padding-top: 0.75rem;
            border-top: 1px solid var(--border-color, rgba(255,255,255,0.06));
        }}

        .catalog-price-badge {{
            font-size: 1rem;
            font-weight: 600;
            padding: 0.375rem 0.875rem;
            border-radius: 20px;
            display: inline-flex;
            align-items: baseline;
            gap: 0.125rem;
        }}

        .catalog-price-badge.free {{
            background: rgba(52, 199, 89, 0.15);
            color: #34c759;
        }}

        .catalog-price-badge.paid {{
            background: var(--bg-tertiary, rgba(255,255,255,0.05));
            color: var(--text-primary, #f5f5f7);
        }}

        .catalog-price-badge .period {{
            font-size: 0.75rem;
            font-weight: 400;
            color: var(--text-tertiary, #6e6e73);
        }}

        .catalog-card-action {{
            display: flex;
            align-items: center;
        }}

        .action-hint {{
            font-size: 0.8125rem;
            color: var(--text-tertiary, #6e6e73);
        }}

        .action-hint.login-required {{
            font-style: italic;
            color: var(--text-tertiary, #6e6e73);
        }}

        @media (max-width: 640px) {{
            .catalog-card-footer {{
                flex-direction: column;
                align-items: flex-start;
            }}
        }}
    </style>
    """

    return html


def get_dataset_choices(datasets, username=None):
    """Returns list of (label, dataset_id) tuples for dropdown."""
    if not datasets or not username:
        return []

    choices = []
    for dataset in datasets:
        plans = dataset.get("plans", [])
        if plans:
            plan = plans[0]
            price_id = plan.get("stripe_price_id", "")
            if price_id in ["free", "0", 0]:
                trial_days = plan.get("access_duration_days", 1)
                trial_text = "24h" if trial_days == 1 else f"{trial_days}-day"
                label = f"{dataset.get('display_name', dataset.get('dataset_id'))} ({trial_text} Trial)"
            else:
                price = plan.get("price", "10")
                label = f"{dataset.get('display_name', dataset.get('dataset_id'))} (${price}/mo)"
            choices.append((label, dataset.get('dataset_id')))

    return choices