document.addEventListener('DOMContentLoaded', function() {
    const mainContent = document.getElementById('main-content');
    const appName = document.querySelector('.navbar-brand').textContent;

    // --- Helper Functions ---
    function setPageTitle(title) {
        document.title = `${appName} - ${title}`;
    }

    function showLoading() {
        mainContent.innerHTML = '<div class="text-center p-5"><div class="spinner-border text-primary" role="status"><span class="visually-hidden">Loading...</span></div></div>';
    }

    // Function to fetch content and update the main view
    function fetchContent(path, pushState = true) {
        showLoading();
        
        // Determine the API endpoint based on the path
        let apiPath = '';
        let pageTitle = '';
        let routePath = path;

        if (path === '/' || path === '/overview') {
            apiPath = '/api/items';
            pageTitle = 'Overview';
            routePath = '/';
        } else if (path === '/categories') {
            apiPath = '/api/categories';
            pageTitle = 'Categories';
        } else if (path === '/parts') {
            apiPath = '/api/parts';
            pageTitle = 'Parts';
        } else {
            // Fallback
            apiPath = '/api/items';
            pageTitle = 'Overview';
            routePath = '/';
        }

        fetch(apiPath)
            .then(response => {
                if (!response.ok) {
                    throw new Error(`HTTP error! status: ${response.status}`);
                }
                return response.text();
            })
            .then(html => {
                mainContent.innerHTML = html;
                if (pushState) {
                    history.pushState({ html: html, path: routePath }, '', routePath);
                }
                setPageTitle(pageTitle);
                updateActiveLink(routePath);
                // Re-initialize any scripts specific to the loaded content
                initPageSpecificScripts();
            })
            .catch(error => {
                console.error('Error fetching content:', error);
                mainContent.innerHTML = `<div class="alert alert-danger">${error.message}</div>`;
            });
    }

    // Update active class on sidebar links
    function updateActiveLink(path) {
        document.querySelectorAll('.nav-link[data-route]').forEach(link => {
            link.classList.remove('active');
            if (link.getAttribute('data-route') === path) {
                link.classList.add('active');
            }
        });
    }

    // Handle browser back/forward buttons
    window.onpopstate = function(event) {
        if (event.state && event.state.html) {
            mainContent.innerHTML = event.state.html;
            setPageTitle(event.state.path.substring(1) || 'Home');
            updateActiveLink(event.state.path);
            initPageSpecificScripts();
        } else {
            // If no state, force a full load of the current path
            fetchContent(window.location.pathname, false);
        }
    };

    // --- Event Listeners ---

    // Navigation links (Navbar and Sidebar)
    document.body.addEventListener('click', function(e) {
        const link = e.target.closest('a[data-route]');
        if (link) {
            e.preventDefault();
            const route = link.getAttribute('data-route');
            fetchContent(route);
        }
    });

    // Initial page load
    const initialPath = window.location.pathname === '/' ? '/items' : window.location.pathname;
    fetchContent(initialPath, false);

    // Page-specific scripts (e.g., form submissions)
    function initPageSpecificScripts() {
        // Overview page: filter form
        const filterForm = document.getElementById('filterForm');
        if (filterForm) {
            filterForm.addEventListener('submit', handleFilter);
        }

        // Overview page: edit/delete buttons
        document.querySelectorAll('.edit-btn').forEach(btn => {
            btn.addEventListener('click', handleEditItem);
        });
        document.querySelectorAll('.delete-btn').forEach(btn => {
            btn.addEventListener('click', handleDeleteItem);
        });

        // Parts page: add item form
        const addItemForm = document.getElementById('addItemForm');
        if (addItemForm) {
            addItemForm.addEventListener('submit', handleAddItem);
        }

        // Categories page: add category form
        const addCategoryForm = document.getElementById('addCategoryForm');
        if (addCategoryForm) {
            addCategoryForm.addEventListener('submit', handleAddCategory);
        }

        // Overview page: save edit item
        const saveEditItemBtn = document.getElementById('saveEditItemBtn');
        if (saveEditItemBtn) {
            saveEditItemBtn.addEventListener('click', handleSaveEditItem);
        }

        // Categories page: save edit category
        const saveEditBtn = document.getElementById('saveEditCategoryBtn');
        if (saveEditBtn) {
            saveEditBtn.addEventListener('click', handleSaveEditCategory);
        }

        // Categories page: edit/delete buttons
        document.querySelectorAll('.edit-category-btn').forEach(btn => {
            btn.addEventListener('click', handleEditCategory);
        });
        document.querySelectorAll('.delete-category-btn').forEach(btn => {
            btn.addEventListener('click', handleDeleteCategory);
        });
    }

    // Handler functions
    function handleAddItem(e) {
        e.preventDefault();
        const formData = new FormData(this);
        fetch('/api/items', {
            method: 'POST',
            body: formData
        })
        .then(response => response.json())
        .then(data => {
            if (data.success) {
                fetchContent('/', false); // Go to overview to see the new part
            } else {
                alert(data.error || 'Error adding part');
            }
        })
        .catch(error => {
            console.error('Error:', error);
            alert('Error adding part');
        });
    }

    function handleAddCategoryFromItem() {
        const name = document.getElementById('new_category_name').value.trim();
        if (!name) return;
        const formData = new FormData();
        formData.append('category_name', name);
        fetch('/api/categories', {
            method: 'POST',
            body: formData
        })
        .then(response => response.json())
        .then(data => {
            if (data.success) {
                const select = document.getElementById('category_id');
                const option = new Option(name, data.id);
                select.appendChild(option);
                select.value = data.id;
                document.getElementById('new_category_name').value = '';
                document.getElementById('addCategoryForm').classList.add('hidden');
            } else {
                alert(data.error || 'Error adding category');
            }
        })
        .catch(error => {
            console.error('Error:', error);
            alert('Error adding category');
        });
    }

    function handleFilter(e) {
        e.preventDefault();
        const search = document.getElementById('search').value;
        const categoryId = document.getElementById('category_filter').value;
        let url = '/api/items?';
        if (search) url += 'search=' + encodeURIComponent(search) + '&';
        if (categoryId) url += 'category_id=' + categoryId;
        fetch(url)
        .then(response => response.text())
        .then(html => {
            document.getElementById('itemsList').outerHTML = html.match(/<ul[^>]*id="itemsList"[^>]*>[\s\S]*?<\/ul>/)[0];
            initPageSpecificScripts(); // Re-init for new buttons
        })
        .catch(error => {
            console.error('Error:', error);
        });
    }

    function handleEditItem() {
        const id = this.getAttribute('data-id');
        // Fetch current item data
        fetch('/api/items/' + id)
        .then(response => response.json())
        .then(data => {
            if (data) {
                document.getElementById('edit_item_id').value = data.id;
                document.getElementById('edit_item_name').value = data.name;
                document.getElementById('edit_item_description').value = data.description || '';
                document.getElementById('edit_location').value = data.location || '';
                // Populate category select
                const categorySelect = document.getElementById('edit_item_category_id');
                categorySelect.innerHTML = '<option value="">-- Select Category --</option>';
                fetch('/api/categories/list')
                .then(resp => resp.json())
                .then(categories => {
                    categories.forEach(cat => {
                        const option = document.createElement('option');
                        option.value = cat.id;
                        option.textContent = cat.path;
                        categorySelect.appendChild(option);
                    });
                    categorySelect.value = data.category_id || '';
                    const modal = new bootstrap.Modal(document.getElementById('editItemModal'));
                    modal.show();
                });
            } else {
                alert('Part not found');
            }
        })
        .catch(error => {
            console.error('Error:', error);
            alert('Error fetching part');
        });
    }

    function handleDeleteItem() {
        const id = this.getAttribute('data-id');
        if (confirm(window.translations.deletePartConfirm)) {
            fetch('/api/items/' + id, {
                method: 'DELETE'
            })
            .then(response => response.json())
            .then(data => {
                if (data.success) {
                    this.closest('li').remove();
                } else {
                    alert(data.error || 'Error deleting part');
                }
            })
            .catch(error => {
                console.error('Error:', error);
                alert('Error deleting part');
            });
        }
    }

    function handleAddCategory() {
        const formData = new FormData(this);
        fetch('/api/categories', {
            method: 'POST',
            body: formData
        })
        .then(response => response.json())
        .then(data => {
            if (data.success) {
                fetchContent('/categories', false);
            } else {
                alert(data.error || 'Error adding category');
            }
        })
        .catch(error => {
            console.error('Error:', error);
            alert('Error adding category');
        });
    }

    function handleSaveEditItem() {
        const id = document.getElementById('edit_item_id').value;
        const name = document.getElementById('edit_item_name').value.trim();
        const description = document.getElementById('edit_item_description').value;
        const categoryId = document.getElementById('edit_item_category_id').value;
        const location = document.getElementById('edit_location').value.trim();
        const imageFile = document.getElementById('edit_image').files[0];

        if (!name) {
            alert('Part name is required');
            return;
        }

        const formData = new FormData();
        formData.append('item_name', name);
        formData.append('item_description', description);
        formData.append('category_id', categoryId || '');
        formData.append('location', location);
        if (imageFile) {
            formData.append('image', imageFile);
        }

        fetch('/api/items/' + id, {
            method: 'PUT',
            body: formData
        })
        .then(response => response.json())
        .then(data => {
            if (data.success) {
                bootstrap.Modal.getInstance(document.getElementById('editItemModal')).hide();
                fetchContent('/', false); // Reload overview
            } else {
                alert(data.error || 'Error updating part');
            }
        })
        .catch(error => {
            console.error('Error:', error);
            alert('Error updating part');
        });
    }

    function handleSaveEditCategory() {
        const id = document.getElementById('edit_category_id').value;
        const name = document.getElementById('edit_category_name').value.trim();
        const parentId = document.getElementById('edit_parent_category_id').value;

        if (!name) {
            alert('Category name is required');
            return;
        }

        const data = {
            category_name: name,
            parent_category_id: parentId || null
        };

        fetch('/api/categories/' + id, {
            method: 'PUT',
            headers: {
                'Content-Type': 'application/json'
            },
            body: JSON.stringify(data)
        })
        .then(response => response.json())
        .then(data => {
            if (data.success) {
                bootstrap.Modal.getInstance(document.getElementById('editCategoryModal')).hide();
                fetchContent('/categories', false);
            } else {
                alert(data.error || 'Error updating category');
            }
        })
        .catch(error => {
            console.error('Error:', error);
            alert('Error updating category');
        });
    }

    function handleEditCategory() {
        const id = this.getAttribute('data-id');
        // Fetch current category data
        fetch('/api/categories/' + id)
        .then(response => {
            if (!response.ok) {
                throw new Error('HTTP ' + response.status + ': ' + response.statusText);
            }
            return response.json();
        })
        .then(data => {
            if (data && !data.error) {
                document.getElementById('edit_category_id').value = data.id;
                document.getElementById('edit_category_name').value = data.name;
                // Populate parent select, excluding current category
                const parentSelect = document.getElementById('edit_parent_category_id');
                parentSelect.innerHTML = '<option value="">-- No Parent --</option>';
                fetch('/api/categories/list')
                .then(resp => resp.json())
                .then(categories => {
                    categories.forEach(cat => {
                        if (cat.id != data.id) {
                            const option = document.createElement('option');
                            option.value = cat.id;
                            option.textContent = cat.path;
                            parentSelect.appendChild(option);
                        }
                    });
                    parentSelect.value = data.parent_id || '';
                    const modal = new bootstrap.Modal(document.getElementById('editCategoryModal'));
                    modal.show();
                });
            } else {
                alert(data.error || 'Category not found');
            }
        })
        .catch(error => {
            console.error('Error:', error);
            alert('Error fetching category: ' + error.message);
        });
    }

    function handleDeleteCategory() {
        const id = this.getAttribute('data-id');
        if (confirm(window.translations.deleteCategoryConfirm)) {
            fetch('/api/categories/' + id, {
                method: 'DELETE'
            })
            .then(response => response.json())
            .then(data => {
                if (data.success) {
                    this.closest('li').remove();
                } else {
                    alert(data.error || 'Error deleting category');
                }
            })
            .catch(error => {
                console.error('Error:', error);
                alert('Error deleting category');
            });
        }
    }
});