/**
 * Initializes tab navigation with chevron-based overflow scrolling.
 *
 * Markup (author writes):
 *   <div data-tabs>
 *     <div class="app-tabs-nav">
 *       <button data-tab="system" data-tab-default>System</button>
 *       ...
 *     </div>
 *     <div data-tab-panel="system">...</div>
 *   </div>
 *
 * JS wraps the nav in `.app-tabs-nav-wrap` and injects chevron buttons when
 * the strip overflows. No-JS fallback: native horizontal scrollbar stays.
 */
export function initTabs(root = document) {
  const containers = root.querySelectorAll('[data-tabs]');
  const instances = [];

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

    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');
        tab.setAttribute('tabindex', isActive ? '0' : '-1');
      });

      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
        }
      }
    };

    // ----------------------------------------------------------------
    //  ARIA: role, aria-controls, aria-labelledby (WAI-ARIA Tabs pattern)
    // ----------------------------------------------------------------
    const nav = container.querySelector('.app-tabs-nav');
    const tabIdPrefix = container.id || `tabs-${Math.random().toString(36).slice(2, 8)}`;

    tabs.forEach(tab => {
      const tabName = tab.dataset.tab;
      const tabId = `${tabIdPrefix}-tab-${tabName}`;
      const panelId = `${tabIdPrefix}-panel-${tabName}`;
      tab.setAttribute('role', 'tab');
      tab.id = tabId;
      tab.setAttribute('aria-controls', panelId);
      tab.addEventListener('click', (e) => {
        e.preventDefault();
        activateTab(tab.dataset.tab);
        // Scroll the active tab into view within the nav strip
        scrollTabIntoView(tab);
      });
    });

    panels.forEach(panel => {
      const panelName = panel.dataset.tabPanel;
      const panelId = `${tabIdPrefix}-panel-${panelName}`;
      const tabId = `${tabIdPrefix}-tab-${panelName}`;
      panel.setAttribute('role', 'tabpanel');
      panel.id = panelId;
      panel.setAttribute('aria-labelledby', tabId);
    });

    if (nav) {
      nav.setAttribute('role', 'tablist');
    }

    // ----------------------------------------------------------------
    //  Arrow-key navigation (WAI-ARIA Tabs pattern)
    // ----------------------------------------------------------------
    if (nav) {
      nav.addEventListener('keydown', (e) => {
        const currentIndex = tabs.indexOf(e.target);
        if (currentIndex === -1) {return;}

        let nextIndex = -1;
        if (e.key === 'ArrowRight') {
          nextIndex = (currentIndex + 1) % tabs.length;
        } else if (e.key === 'ArrowLeft') {
          nextIndex = (currentIndex - 1 + tabs.length) % tabs.length;
        } else if (e.key === 'Home') {
          nextIndex = 0;
        } else if (e.key === 'End') {
          nextIndex = tabs.length - 1;
        }

        if (nextIndex >= 0) {
          e.preventDefault();
          tabs[nextIndex].focus();
          activateTab(tabs[nextIndex].dataset.tab);
          scrollTabIntoView(tabs[nextIndex]);
        }
      });
    }

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

    // ----------------------------------------------------------------
    //  Chevron overflow scrolling
    // ----------------------------------------------------------------
    /** @param {HTMLElement} tabEl */
    function scrollTabIntoView(tabEl) {
      if (!nav) {return;}
      tabEl.scrollIntoView({ block: 'nearest', inline: 'nearest', behavior: 'smooth' });
    }

    if (nav) {
      initChevronScroll(nav);

      // Once the first tab is activated, ensure it's visible
      const activeBtn = nav.querySelector('.is-active');
      if (activeBtn) {
        // Defer so layout has settled
        requestAnimationFrame(() => scrollTabIntoView(activeBtn));
      }
    }

    // --- 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.
      const onFormClickCapture = (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();
        });
      };

      const onFormInput = (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');
        }
      };

      document.addEventListener('click', onFormClickCapture, true);
      form.addEventListener('input', onFormInput);
      form.addEventListener('change', onFormInput);

      cleanupFns.push(() => {
        document.removeEventListener('click', onFormClickCapture, true);
        form.removeEventListener('input', onFormInput);
        form.removeEventListener('change', onFormInput);
      });
    }

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

    const destroy = () => {
      cleanupFns.forEach((fn) => fn());
      cleanupFns.length = 0;
      delete container.dataset.tabsBound;
      delete container.dataset.tabsReady;
    };

    container._tabsApi = { activateTab, destroy };
    instances.push(container._tabsApi);
  });

  return instances;
}

// ------------------------------------------------------------------
//  Chevron-scroll helper — wraps .app-tabs-nav in .app-tabs-nav-wrap
//  and injects ‹ / › buttons that appear only when the strip overflows.
// ------------------------------------------------------------------
const SCROLL_STEP = 160; // px per click
const SCROLL_THRESHOLD = 2; // tolerance for "at edge" detection

/** @param {HTMLElement} nav  The .app-tabs-nav element */
function initChevronScroll(nav) {
  // Wrap: nav → wrap > [chevronStart, nav, chevronEnd]
  const wrap = document.createElement('div');
  wrap.className = 'app-tabs-nav-wrap';
  nav.parentNode.insertBefore(wrap, nav);
  wrap.appendChild(nav);

  // Create chevron buttons
  const btnStart = createChevronBtn('start', 'bi-chevron-left');
  const btnEnd = createChevronBtn('end', 'bi-chevron-right');
  wrap.appendChild(btnStart);
  wrap.appendChild(btnEnd);

  // Scroll handlers
  btnStart.addEventListener('click', () => {
    nav.scrollBy({ left: -SCROLL_STEP, behavior: 'smooth' });
  });
  btnEnd.addEventListener('click', () => {
    nav.scrollBy({ left: SCROLL_STEP, behavior: 'smooth' });
  });

  // Continuous scroll on long-press
  addLongPress(btnStart, () => nav.scrollBy({ left: -SCROLL_STEP, behavior: 'smooth' }));
  addLongPress(btnEnd, () => nav.scrollBy({ left: SCROLL_STEP, behavior: 'smooth' }));

  // Observe overflow
  const update = () => {
    const hasOverflow = nav.scrollWidth > nav.clientWidth + SCROLL_THRESHOLD;
    wrap.classList.toggle('has-overflow', hasOverflow);

    if (hasOverflow) {
      const atStart = nav.scrollLeft <= SCROLL_THRESHOLD;
      const atEnd = nav.scrollLeft + nav.clientWidth >= nav.scrollWidth - SCROLL_THRESHOLD;
      btnStart.disabled = atStart;
      btnEnd.disabled = atEnd;
    }
  };

  nav.addEventListener('scroll', update, { passive: true });

  // ResizeObserver to detect container width changes
  if (typeof ResizeObserver !== 'undefined') {
    const ro = new ResizeObserver(update);
    ro.observe(nav);
  }

  // Initial check (deferred so layout is settled)
  requestAnimationFrame(update);
}

/** @returns {HTMLButtonElement} */
function createChevronBtn(direction, iconClass) {
  const btn = document.createElement('button');
  btn.type = 'button';
  btn.className = `app-tabs-chevron app-tabs-chevron--${direction}`;
  btn.setAttribute('aria-hidden', 'true');
  btn.setAttribute('tabindex', '-1');
  const icon = document.createElement('i');
  icon.className = `bi ${iconClass}`;
  icon.setAttribute('aria-hidden', 'true');
  btn.appendChild(icon);
  return btn;
}

/** Repeats callback while button is held down */
function addLongPress(btn, callback) {
  let interval = null;
  const start = () => { interval = setInterval(callback, 180); };
  const stop = () => { clearInterval(interval); interval = null; };
  btn.addEventListener('pointerdown', start);
  btn.addEventListener('pointerup', stop);
  btn.addEventListener('pointerleave', stop);
  btn.addEventListener('pointercancel', stop);
}

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