/**
 * DocumentNavigator Widget
 *
 * Substack-style floating document navigation widget that displays a hierarchical
 * table of contents based on document headings. Supports smooth scrolling,
 * scroll spy, expand/collapse, and responsive behavior.
 */
import { UIWidget } from '../base/UIWidget.js';

export class DocumentNavigator extends UIWidget {
    constructor(options = {}) {
        super(options);

        // Navigation state
        this.isCollapsed = this.config.collapsed;
        this.currentSection = null;
        this.headings = [];
        this.navigationTree = [];

        // Scroll spy state
        this.scrollSpyEnabled = this.config.enableScrollSpy;
        this.scrollThrottle = null;

        // Event bindings
        this.boundScrollHandler = this.handleScroll.bind(this);
        this.boundResizeHandler = this.handleResize.bind(this);

        // Initialize responsive behavior
        this.mediaQuery = window.matchMedia('(max-width: 768px)');
    }

    getDefaultConfig() {
        return {
            ...super.getDefaultConfig(),
            position: 'left',           // 'left' or 'right'
            collapsed: true,            // Start collapsed
            autoHide: true,             // Hide on mobile
            maxHeadingLevel: 3,         // H1, H2, H3
            enableScrollSpy: true,      // Highlight current section
            smoothScroll: true,         // Smooth scroll behavior
            animationDuration: 300,     // Animation timing
            minHeadings: 2,            // Min headings to show navigator
            theme: 'default',          // Theme support

            // Styling options
            width: '280px',
            collapsedWidth: '40px',
            offset: { top: '80px', side: '20px' },

            // Accessibility
            enableKeyboard: true,
            ariaLabel: 'Document Navigation'
        };
    }

    async initialize() {
        await super.initialize();

        // Extract headings from container
        this.extractHeadings();
        this.buildNavigationTree();

        // Set up event listeners
        if (this.scrollSpyEnabled) {
            window.addEventListener('scroll', this.boundScrollHandler, { passive: true });
        }

        if (this.config.autoHide) {
            window.addEventListener('resize', this.boundResizeHandler);
            this.handleResize(); // Initial check
        }

        return this;
    }

    async render() {
        if (this.isRendered) {
            return this.element;
        }

        // Check if we have enough headings
        if (this.headings.length < this.config.minHeadings) {
            this.isRendered = true;
            return null; // Don't render if too few headings
        }

        // Create main container
        this.element = this.createElement('nav', {
            className: 'document-navigator markitect-widget',
            attributes: {
                'aria-label': this.config.ariaLabel,
                'role': 'navigation'
            },
            style: this.getNavigatorStyle()
        });

        // Apply CSS classes
        this.applyCSSClasses();
        this.addClass('theme-' + this.theme);
        this.addClass('position-' + this.config.position);

        // Create toggle button (always visible)
        this.createToggleButton();

        // Create navigation list (hidden when collapsed)
        this.createNavigationList();

        // Set initial visibility state
        if (this.isCollapsed) {
            await this.collapse({ immediate: true });
        } else {
            await this.expand({ immediate: true });
        }

        // Append to container
        this.container.appendChild(this.element);

        // Initialize scroll spy
        if (this.scrollSpyEnabled) {
            this.updateCurrentSection();
        }

        this.isRendered = true;
        this.emit('rendered');

        return this.element;
    }

    createToggleButton() {
        this.toggleButton = this.createElement('button', {
            className: 'navigator-toggle',
            attributes: {
                'type': 'button',
                'aria-label': this.isCollapsed ? 'Expand navigation' : 'Collapse navigation',
                'aria-expanded': !this.isCollapsed
            },
            innerHTML: this.getToggleIcon(),
            style: this.getToggleStyle()
        });

        // Toggle on click
        this.toggleButton.addEventListener('click', async () => {
            await this.toggle();
        });

        // Keyboard support
        if (this.config.enableKeyboard) {
            this.toggleButton.addEventListener('keydown', this.handleKeyboard.bind(this));
        }

        this.element.appendChild(this.toggleButton);
    }

    createNavigationList() {
        this.navigationList = this.createElement('div', {
            className: 'navigator-list',
            style: this.getListStyle()
        });

        if (this.headings.length === 0) {
            this.createEmptyState();
        } else {
            this.populateNavigationList();
        }

        this.element.appendChild(this.navigationList);
    }

    createEmptyState() {
        const emptyMessage = this.createElement('div', {
            className: 'navigator-empty',
            textContent: 'No headings found',
            style: {
                padding: '1rem',
                textAlign: 'center',
                color: '#666',
                fontStyle: 'italic'
            }
        });

        this.navigationList.appendChild(emptyMessage);
    }

    populateNavigationList() {
        // Create header
        const header = this.createElement('div', {
            className: 'navigator-header',
            innerHTML: `
                <h3>Contents</h3>
                <button class="navigator-close" aria-label="Close navigation">✕</button>
            `,
            style: {
                display: 'flex',
                justifyContent: 'space-between',
                alignItems: 'center',
                padding: '1rem 1rem 0.5rem',
                borderBottom: '1px solid #eee',
                marginBottom: '0.5rem'
            }
        });

        // Close button functionality
        const closeButton = header.querySelector('.navigator-close');
        closeButton.addEventListener('click', async () => {
            await this.collapse();
        });

        this.navigationList.appendChild(header);

        // Create navigation items
        const navContainer = this.createElement('div', {
            className: 'navigator-items',
            style: {
                maxHeight: '70vh',
                overflowY: 'auto',
                padding: '0 0.5rem 1rem'
            }
        });

        this.renderNavigationTree(navContainer, this.navigationTree);
        this.navigationList.appendChild(navContainer);
    }

    renderNavigationTree(container, items, level = 0) {
        items.forEach(item => {
            const navItem = this.createElement('div', {
                className: `navigator-item level-${level}`,
                style: {
                    marginLeft: `${level * 1}rem`,
                    marginBottom: '0.25rem'
                }
            });

            // Create clickable link
            const link = this.createElement('a', {
                className: 'navigator-link',
                textContent: item.text,
                attributes: {
                    'href': `#${item.id}`,
                    'data-target': item.id,
                    'data-level': item.level,
                    'role': 'button',
                    'tabindex': '0'
                },
                style: {
                    display: 'block',
                    padding: '0.5rem 0.75rem',
                    textDecoration: 'none',
                    color: '#333',
                    borderRadius: '4px',
                    fontSize: level === 0 ? '0.9rem' : '0.8rem',
                    fontWeight: level === 0 ? '600' : '400',
                    transition: 'all 0.2s ease',
                    cursor: 'pointer'
                }
            });

            // Hover effects
            link.addEventListener('mouseenter', () => {
                link.style.backgroundColor = '#f0f0f0';
            });

            link.addEventListener('mouseleave', () => {
                if (!link.classList.contains('active')) {
                    link.style.backgroundColor = '';
                }
            });

            // Click navigation
            link.addEventListener('click', (e) => {
                e.preventDefault();
                this.navigateToHeading(item.id);
            });

            navItem.appendChild(link);

            // Render children recursively
            if (item.children && item.children.length > 0) {
                this.renderNavigationTree(navItem, item.children, level + 1);
            }

            container.appendChild(navItem);
        });
    }

    extractHeadings() {
        const headingSelectors = [];
        for (let i = 1; i <= this.config.maxHeadingLevel; i++) {
            headingSelectors.push(`h${i}`);
        }

        const headingElements = this.container.querySelectorAll(headingSelectors.join(', '));

        this.headings = Array.from(headingElements).map((heading, index) => {
            // Ensure heading has an ID
            if (!heading.id) {
                heading.id = `heading-${index + 1}`;
            }

            return {
                element: heading,
                id: heading.id,
                text: heading.textContent.trim(),
                level: parseInt(heading.tagName.substring(1)),
                offset: heading.offsetTop
            };
        });

        return this.headings;
    }

    buildNavigationTree() {
        this.navigationTree = [];
        const stack = [];

        this.headings.forEach(heading => {
            const item = {
                ...heading,
                children: []
            };

            // Find correct parent based on heading level
            while (stack.length > 0 && stack[stack.length - 1].level >= heading.level) {
                stack.pop();
            }

            if (stack.length === 0) {
                // Top level item
                this.navigationTree.push(item);
            } else {
                // Child item
                stack[stack.length - 1].children.push(item);
            }

            stack.push(item);
        });

        return this.navigationTree;
    }

    async toggle(options = {}) {
        return this.isCollapsed ? this.expand(options) : this.collapse(options);
    }

    async expand(options = {}) {
        if (!this.isCollapsed) {
            return this;
        }

        this.isCollapsed = false;

        if (this.toggleButton) {
            this.toggleButton.setAttribute('aria-expanded', 'true');
            this.toggleButton.setAttribute('aria-label', 'Collapse navigation');
            this.toggleButton.innerHTML = this.getToggleIcon();
        }

        if (this.navigationList) {
            if (this.enableAnimations && !options.immediate) {
                await this.animateExpand();
            } else {
                this.navigationList.style.display = '';
                this.element.style.width = this.config.width;
            }
        }

        this.emit('toggle', { expanded: true });
        return this;
    }

    async collapse(options = {}) {
        if (this.isCollapsed) {
            return this;
        }

        this.isCollapsed = true;

        if (this.toggleButton) {
            this.toggleButton.setAttribute('aria-expanded', 'false');
            this.toggleButton.setAttribute('aria-label', 'Expand navigation');
            this.toggleButton.innerHTML = this.getToggleIcon();
        }

        if (this.navigationList) {
            if (this.enableAnimations && !options.immediate) {
                await this.animateCollapse();
            } else {
                this.navigationList.style.display = 'none';
                this.element.style.width = this.config.collapsedWidth;
            }
        }

        this.emit('toggle', { expanded: false });
        return this;
    }

    async animateExpand() {
        return new Promise(resolve => {
            this.navigationList.style.opacity = '0';
            this.navigationList.style.display = '';

            // Animate width and opacity
            this.element.style.transition = `width ${this.animationDuration}ms ease-in-out`;
            this.navigationList.style.transition = `opacity ${this.animationDuration}ms ease-in-out`;

            // Force reflow
            this.element.offsetWidth;

            this.element.style.width = this.config.width;
            this.navigationList.style.opacity = '1';

            setTimeout(() => {
                this.element.style.transition = '';
                this.navigationList.style.transition = '';
                resolve();
            }, this.animationDuration);
        });
    }

    async animateCollapse() {
        return new Promise(resolve => {
            this.element.style.transition = `width ${this.animationDuration}ms ease-in-out`;
            this.navigationList.style.transition = `opacity ${this.animationDuration}ms ease-in-out`;

            this.navigationList.style.opacity = '0';
            this.element.style.width = this.config.collapsedWidth;

            setTimeout(() => {
                this.navigationList.style.display = 'none';
                this.element.style.transition = '';
                this.navigationList.style.transition = '';
                resolve();
            }, this.animationDuration);
        });
    }

    navigateToHeading(headingId) {
        const targetElement = document.getElementById(headingId);
        if (!targetElement) {
            console.warn(`Heading with ID '${headingId}' not found`);
            return;
        }

        // Update active navigation item
        this.setActiveItem(headingId);

        // Scroll to target
        if (this.config.smoothScroll) {
            targetElement.scrollIntoView({
                behavior: 'smooth',
                block: 'start',
                inline: 'nearest'
            });
        } else {
            targetElement.scrollIntoView();
        }

        // Emit navigation event
        this.emit('navigate', { target: headingId, element: targetElement });

        // Optionally collapse after navigation on mobile
        if (this.mediaQuery.matches && this.config.autoHide) {
            setTimeout(() => this.collapse(), 500);
        }
    }

    setActiveItem(headingId) {
        // Remove previous active state
        const previousActive = this.findElement('.navigator-link.active');
        if (previousActive) {
            previousActive.classList.remove('active');
            previousActive.style.backgroundColor = '';
        }

        // Set new active state
        const newActive = this.findElement(`[data-target="${headingId}"]`);
        if (newActive) {
            newActive.classList.add('active');
            newActive.style.backgroundColor = '#e3f2fd';
            newActive.style.color = '#1976d2';
        }

        this.currentSection = headingId;
    }

    handleScroll() {
        if (!this.scrollSpyEnabled || !this.isRendered) {
            return;
        }

        // Throttle scroll events
        if (this.scrollThrottle) {
            return;
        }

        this.scrollThrottle = setTimeout(() => {
            this.updateCurrentSection();
            this.scrollThrottle = null;
        }, 100);
    }

    updateCurrentSection() {
        const scrollPosition = window.pageYOffset + 100; // Offset for header
        let currentHeading = null;

        // Find the current heading based on scroll position
        for (let i = this.headings.length - 1; i >= 0; i--) {
            const heading = this.headings[i];
            if (heading.element.offsetTop <= scrollPosition) {
                currentHeading = heading;
                break;
            }
        }

        if (currentHeading && currentHeading.id !== this.currentSection) {
            this.setActiveItem(currentHeading.id);
        }
    }

    getCurrentSection() {
        return this.currentSection;
    }

    handleResize() {
        if (!this.config.autoHide) {
            return;
        }

        if (this.mediaQuery.matches) {
            // Mobile: hide navigator
            if (this.element) {
                this.element.style.display = 'none';
            }
        } else {
            // Desktop: show navigator
            if (this.element) {
                this.element.style.display = '';
            }
        }
    }

    handleKeyboard(event) {
        switch (event.key) {
            case 'Enter':
            case ' ':
                event.preventDefault();
                this.toggle();
                break;
            case 'Escape':
                event.preventDefault();
                this.collapse();
                break;
        }
    }

    getNavigatorStyle() {
        const baseStyle = {
            position: 'fixed',
            top: this.config.offset.top,
            zIndex: '1000',
            backgroundColor: 'rgba(255, 255, 255, 0.95)',
            border: '1px solid #e1e5e9',
            borderRadius: '8px',
            boxShadow: '0 2px 8px rgba(0, 0, 0, 0.15)',
            backdropFilter: 'blur(8px)',
            width: this.isCollapsed ? this.config.collapsedWidth : this.config.width,
            maxHeight: '80vh',
            overflow: 'hidden',
            transition: 'width 0.3s ease-in-out'
        };

        // Position-specific styling
        if (this.config.position === 'left') {
            baseStyle.left = this.config.offset.side;
        } else {
            baseStyle.right = this.config.offset.side;
        }

        return baseStyle;
    }

    getToggleStyle() {
        return {
            width: '100%',
            height: this.config.collapsedWidth,
            border: 'none',
            backgroundColor: 'transparent',
            cursor: 'pointer',
            display: 'flex',
            alignItems: 'center',
            justifyContent: 'center',
            fontSize: '16px',
            color: '#666',
            transition: 'color 0.2s ease'
        };
    }

    getListStyle() {
        return {
            display: this.isCollapsed ? 'none' : '',
            opacity: this.isCollapsed ? '0' : '1'
        };
    }

    getToggleIcon() {
        if (this.isCollapsed) {
            return this.config.position === 'left' ? '☰' : '☰';
        } else {
            return '✕';
        }
    }

    async destroy() {
        // Remove event listeners
        window.removeEventListener('scroll', this.boundScrollHandler);
        window.removeEventListener('resize', this.boundResizeHandler);

        // Clear throttle
        if (this.scrollThrottle) {
            clearTimeout(this.scrollThrottle);
        }

        await super.destroy();
    }
}