/**
 * Initializes tab navigation
 * Usage:
 * - Tab buttons: <button data-tab="system">System</button>
 * - Tab panels: <div data-tab-panel="system">...</div>
 * - Container: <div data-tabs>...</div>
 * - URL param: ?tab=system
 */
export function initTabs(root = document) {
  const containers = root.querySelectorAll('[data-tabs]');

  containers.forEach((container) => {
    if (container.dataset.tabsBound === '1') {return;}
    container.dataset.tabsBound = '1';
    container.dataset.tabsReady = '0';

    const tabs = Array.from(container.querySelectorAll('[data-tab]'));
    const panels = Array.from(container.querySelectorAll('[data-tab-panel]'));

    if (!tabs.length || !panels.length) {return;}

    const storageKey = container.dataset.tabsStorageKey || (container.id ? `tabs:${container.id}` : null);
    const urlParamName = container.dataset.tabsParam || 'tab';

    // Helper to get URL parameter
    const getUrlParam = (name) => {
      const params = new URLSearchParams(window.location.search);
      return params.get(name);
    };

    // Helper to set URL parameter
    const setUrlParam = (name, value) => {
      const url = new URL(window.location);
      url.searchParams.set(name, value);
      window.history.replaceState({}, '', url);
    };

    // Get initial active tab from URL param, localStorage, or data-tab-default
    let activeTab = null;
    const urlTab = getUrlParam(urlParamName);
    if (urlTab && panels.some(p => p.dataset.tabPanel === urlTab)) {
      activeTab = urlTab;
    } else if (storageKey) {
      try {
        const stored = localStorage.getItem(storageKey);
        if (stored && panels.some(p => p.dataset.tabPanel === stored)) {
          activeTab = stored;
        }
      } catch (e) {
        // localStorage not available
      }
    }
    if (!activeTab) {
      const defaultTab = container.querySelector('[data-tab-default]');
      activeTab = defaultTab?.dataset.tab || tabs[0]?.dataset.tab;
    }

    const activateTab = (tabName) => {
      tabs.forEach(tab => {
        const isActive = tab.dataset.tab === tabName;
        tab.classList.toggle('is-active', isActive);
        tab.setAttribute('aria-selected', isActive ? 'true' : 'false');
      });

      panels.forEach(panel => {
        const isVisible = panel.dataset.tabPanel === tabName;
        panel.hidden = !isVisible;
        panel.setAttribute('aria-hidden', isVisible ? 'false' : 'true');
      });

      // Update URL parameter
      setUrlParam(urlParamName, tabName);

      // Save to localStorage
      if (storageKey) {
        try {
          localStorage.setItem(storageKey, tabName);
        } catch (e) {
          // localStorage not available
        }
      }
    };

    // Initialize tabs
    tabs.forEach(tab => {
      tab.setAttribute('role', 'tab');
      tab.addEventListener('click', (e) => {
        e.preventDefault();
        activateTab(tab.dataset.tab);
      });
    });

    panels.forEach(panel => {
      panel.setAttribute('role', 'tabpanel');
    });

    container.setAttribute('role', 'tablist');

    // Activate initial tab
    if (activeTab) {
      activateTab(activeTab);
    }
    container.dataset.tabsReady = '1';

    // --- Form validation awareness ---
    const form = container.closest('form');
    if (form) {
      const inputSelector = 'input,select,textarea';
      const formId = form.id;

      const belongsToForm = (field) => {
        const f = field.getAttribute('form');
        if (!f) return true;       // kein form-Attr → gehört zum Ancestor-Form
        if (!formId) return false; // Feld hat form-Attr, unser Form hat keine ID
        return f === formId;
      };

      const clearInvalidMarkers = () => {
        tabs.forEach(tab => tab.classList.remove('has-invalid'));
      };

      const findInvalidPanels = () => {
        clearInvalidMarkers();
        let firstInvalidTab = null;

        panels.forEach(panel => {
          const fields = panel.querySelectorAll(inputSelector);
          const hasInvalid = Array.from(fields).some(f => belongsToForm(f) && !f.disabled && !f.checkValidity());
          if (hasInvalid) {
            const tabName = panel.dataset.tabPanel;
            const tab = tabs.find(t => t.dataset.tab === tabName);
            if (tab) {
              tab.classList.add('has-invalid');
            }
            if (!firstInvalidTab) {
              firstInvalidTab = tabName;
            }
          }
        });

        return firstInvalidTab;
      };

      // Intercept submit buttons — both inside the form and external ones linked via form="id".
      // We use document-level click (capture) so we catch ALL submit triggers before native validation.
      document.addEventListener('click', (e) => {
        const btn = e.target.closest('button, [type="submit"]');
        if (!btn) {return;}

        // Check if this button submits OUR form
        const btnFormAttr = btn.getAttribute('form');
        const isInternalSubmit = !btnFormAttr && form.contains(btn) && (btn.type === 'submit' || (!btn.type && btn.tagName === 'BUTTON'));
        const isExternalSubmit = btnFormAttr && formId && btnFormAttr === formId && btn.type === 'submit';
        if (!isInternalSubmit && !isExternalSubmit) {return;}

        const firstInvalidTab = findInvalidPanels();
        if (!firstInvalidTab) {return;}

        // Active panel already shows the first invalid tab — let native validation handle it
        const activePanel = panels.find(p => !p.hidden);
        const needsTabSwitch = activePanel?.dataset.tabPanel !== firstInvalidTab;

        // Open any closed <details> ancestors of invalid fields so the browser can focus them
        const invalidFields = form.querySelectorAll(inputSelector);
        for (const field of invalidFields) {
          if (!belongsToForm(field) || field.disabled || field.checkValidity()) {continue;}
          let el = field.parentElement;
          while (el && el !== form) {
            if (el.tagName === 'DETAILS' && !el.open) {
              el.open = true;
            }
            el = el.parentElement;
          }
        }

        if (!needsTabSwitch) {return;}

        // Prevent native submit so the browser doesn't try to focus a hidden field
        e.preventDefault();
        activateTab(firstInvalidTab);

        requestAnimationFrame(() => {
          form.reportValidity();
        });
      }, true);

      form.addEventListener('input', (e) => {
        const panel = e.target.closest('[data-tab-panel]');
        if (!panel) {return;}
        const tabName = panel.dataset.tabPanel;
        const tab = tabs.find(t => t.dataset.tab === tabName);
        if (!tab) {return;}
        const fields = panel.querySelectorAll(inputSelector);
        if (Array.from(fields).every(f => !belongsToForm(f) || f.disabled || f.checkValidity())) {
          tab.classList.remove('has-invalid');
        }
      });

      form.addEventListener('change', (e) => {
        const panel = e.target.closest('[data-tab-panel]');
        if (!panel) {return;}
        const tabName = panel.dataset.tabPanel;
        const tab = tabs.find(t => t.dataset.tab === tabName);
        if (!tab) {return;}
        const fields = panel.querySelectorAll(inputSelector);
        if (Array.from(fields).every(f => !belongsToForm(f) || f.disabled || f.checkValidity())) {
          tab.classList.remove('has-invalid');
        }
      });
    }

    // Listen for popstate (back/forward navigation)
    window.addEventListener('popstate', () => {
      const newTab = getUrlParam(urlParamName);
      if (newTab && panels.some(p => p.dataset.tabPanel === newTab)) {
        activateTab(newTab);
      }
    });
  });
}

// Auto-initialize on load
if (document.readyState === 'loading') {
  document.addEventListener('DOMContentLoaded', () => initTabs());
} else {
  initTabs();
}