/**
 * GoingsOn - Pagination Manager
 * Generic pagination handling for lists.
 * Replaces duplicate pagination code in tasks.js and emails.js.
 */

class PaginationManager {
    /**
     * Create a pagination manager.
     * @param {string} type - Item type identifier (used for DOM element IDs)
     * @param {number} itemsPerPage - Number of items per page
     */
    constructor(type, itemsPerPage = 25) {
        this.type = type;
        this.itemsPerPage = itemsPerPage;
        this.currentPage = 1;
        this.totalItems = 0;
    }

    /**
     * Navigate to a page.
     * @param {'prev'|'next'|number} direction - Direction or page number
     * @returns {number} The new current page
     */
    goToPage(direction) {
        const maxPage = this.getMaxPage();

        if (direction === 'prev') {
            this.currentPage = Math.max(1, this.currentPage - 1);
        } else if (direction === 'next') {
            this.currentPage = Math.min(maxPage, this.currentPage + 1);
        } else if (typeof direction === 'number') {
            this.currentPage = Math.max(1, Math.min(maxPage, direction));
        }

        return this.currentPage;
    }

    /**
     * Get the current page number.
     * @returns {number}
     */
    getCurrentPage() {
        return this.currentPage;
    }

    /**
     * Get the maximum page number.
     * @returns {number}
     */
    getMaxPage() {
        return Math.max(1, Math.ceil(this.totalItems / this.itemsPerPage));
    }

    /**
     * Set the total number of items and validate current page.
     * @param {number} total - Total number of items
     */
    setTotalItems(total) {
        this.totalItems = total;
        // Validate current page
        const maxPage = this.getMaxPage();
        if (this.currentPage > maxPage) {
            this.currentPage = maxPage;
        }
        if (this.currentPage < 1) {
            this.currentPage = 1;
        }
    }

    /**
     * Reset pagination to first page.
     */
    reset() {
        this.currentPage = 1;
    }

    /**
     * Get the offset for the current page (for backend pagination).
     * @returns {number} The number of items to skip
     */
    getOffset() {
        return (this.currentPage - 1) * this.itemsPerPage;
    }

    /**
     * Get a paginated slice of items (for client-side pagination).
     * @param {Array} items - All items
     * @returns {Array} Paginated items
     */
    paginate(items) {
        const start = this.getOffset();
        return items.slice(start, start + this.itemsPerPage);
    }

    /**
     * Update the pagination UI elements.
     */
    updateUI() {
        const container = document.getElementById(`${this.type}-pagination`);
        const prevBtn = document.getElementById(`${this.type}-prev-page`);
        const nextBtn = document.getElementById(`${this.type}-next-page`);
        const pageInfo = document.getElementById(`${this.type}-page-info`);

        if (!container) return;

        // Show/hide pagination
        if (this.totalItems <= this.itemsPerPage) {
            container.style.display = 'none';
            return;
        }

        container.style.display = 'flex';

        const maxPage = this.getMaxPage();

        // Update buttons
        if (prevBtn) prevBtn.disabled = this.currentPage <= 1;
        if (nextBtn) nextBtn.disabled = this.currentPage >= maxPage;

        // Update page info
        if (pageInfo) {
            const start = (this.currentPage - 1) * this.itemsPerPage + 1;
            const end = Math.min(this.currentPage * this.itemsPerPage, this.totalItems);
            pageInfo.textContent = `${start}-${end} of ${this.totalItems} (Page ${this.currentPage}/${maxPage})`;
        }
    }

    /**
     * Get pagination info for display.
     * @returns {Object} Pagination info
     */
    getInfo() {
        const maxPage = this.getMaxPage();
        const start = (this.currentPage - 1) * this.itemsPerPage + 1;
        const end = Math.min(this.currentPage * this.itemsPerPage, this.totalItems);

        return {
            currentPage: this.currentPage,
            maxPage,
            start,
            end,
            total: this.totalItems,
            hasPrev: this.currentPage > 1,
            hasNext: this.currentPage < maxPage
        };
    }
}

// ============ Populate GoingsOn Namespace ============

if (window.GoingsOn) {
    GoingsOn.PaginationManager = PaginationManager;
}