const MOBILE_POINTER_QUERY = '(pointer: coarse)';
const KEYBOARD_OPEN_THRESHOLD_PX = 96;
const MIN_LAYOUT_VIEWPORT_HEIGHT_PX = 320;

const LAYOUT_HEIGHT_VAR = '--platform-layout-viewport-height';
const KEYBOARD_FOCUS_OFFSET_VAR = '--platform-keyboard-focus-offset';
const KEYBOARD_INSET_VAR = '--platform-keyboard-inset-bottom';
const KEYBOARD_EXPOSED_FILL_VAR = '--platform-keyboard-exposed-fill';
const KEYBOARD_EXPOSED_FILL_FALLBACK =
  'linear-gradient(180deg, #fffdf9 0%, #fdf9f5 54%, #f8efe7 100%)';

type KeyboardFocusShiftInput = {
  layoutHeight: number;
  visualTop: number;
  visualHeight: number;
  hasEditableTarget: boolean;
  threshold?: number;
};

function readVisualViewport() {
  return typeof window !== 'undefined' ? window.visualViewport : undefined;
}

export function resolveMobileKeyboardExposedFill() {
  if (typeof window === 'undefined' || typeof document === 'undefined') {
    return KEYBOARD_EXPOSED_FILL_FALLBACK;
  }

  const platformShell = document.querySelector('.platform-viewport-shell');
  if (!(platformShell instanceof HTMLElement)) {
    return KEYBOARD_EXPOSED_FILL_FALLBACK;
  }

  const platformFill = window
    .getComputedStyle(platformShell)
    .getPropertyValue('--platform-body-fill')
    .trim();
  return platformFill || KEYBOARD_EXPOSED_FILL_FALLBACK;
}

function readLayoutViewportHeight() {
  if (typeof window === 'undefined' || typeof document === 'undefined') {
    return MIN_LAYOUT_VIEWPORT_HEIGHT_PX;
  }

  const visualViewport = readVisualViewport();
  return Math.max(
    window.innerHeight || 0,
    document.documentElement.clientHeight || 0,
    visualViewport?.height ?? 0,
    MIN_LAYOUT_VIEWPORT_HEIGHT_PX,
  );
}

function shouldHandleMobileKeyboardFocus() {
  if (typeof window === 'undefined' || typeof navigator === 'undefined') {
    return false;
  }

  return (
    navigator.maxTouchPoints > 0 ||
    window.matchMedia(MOBILE_POINTER_QUERY).matches
  );
}

function isDisabledEditableControl(element: HTMLElement) {
  return (
    'disabled' in element &&
    Boolean((element as HTMLInputElement | HTMLTextAreaElement).disabled)
  );
}

function isReadOnlyEditableControl(element: HTMLElement) {
  return (
    'readOnly' in element &&
    Boolean((element as HTMLInputElement | HTMLTextAreaElement).readOnly)
  );
}

/**
 * 中文注释：只把会唤起移动端输入法的控件纳入键盘聚焦处理。
 * 文件、滑块、复选框等输入控件不需要挪动画布。
 */
export function isEditableKeyboardTarget(
  element: Element | null,
): element is HTMLElement {
  if (
    typeof HTMLElement === 'undefined' ||
    !(element instanceof HTMLElement)
  ) {
    return false;
  }

  if (element.isContentEditable) {
    return true;
  }

  if (isDisabledEditableControl(element) || isReadOnlyEditableControl(element)) {
    return false;
  }

  if (element instanceof HTMLTextAreaElement) {
    return true;
  }

  if (!(element instanceof HTMLInputElement)) {
    return false;
  }

  const inputType = (element.type || 'text').toLowerCase();
  return !new Set([
    'button',
    'checkbox',
    'color',
    'file',
    'hidden',
    'image',
    'radio',
    'range',
    'reset',
    'submit',
  ]).has(inputType);
}

export function resolveMobileKeyboardState({
  layoutHeight,
  visualTop,
  visualHeight,
  hasEditableTarget,
  threshold = KEYBOARD_OPEN_THRESHOLD_PX,
}: KeyboardFocusShiftInput) {
  const visualBottom = visualTop + visualHeight;
  const insetBottom = Math.max(0, Math.round(layoutHeight - visualBottom));
  const isOpen =
    hasEditableTarget && layoutHeight - visualHeight > threshold;

  return {
    isOpen,
    insetBottom: isOpen ? insetBottom : 0,
  };
}

export function stabilizeMobileViewportKeyboardFocus() {
  if (
    typeof document === 'undefined' ||
    !shouldHandleMobileKeyboardFocus() ||
    document.documentElement.dataset.mobileViewportKeyboardFocus === 'true'
  ) {
    return;
  }

  document.documentElement.dataset.mobileViewportKeyboardFocus = 'true';

  const root = document.documentElement;
  const visualViewport = readVisualViewport();
  let stableLayoutHeight = readLayoutViewportHeight();
  let frameId = 0;

  const setLayoutHeight = (nextHeight: number) => {
    stableLayoutHeight = Math.max(
      MIN_LAYOUT_VIEWPORT_HEIGHT_PX,
      Math.round(nextHeight),
    );
    root.style.setProperty(LAYOUT_HEIGHT_VAR, `${stableLayoutHeight}px`);
  };

  const setKeyboardState = (isOpen: boolean, insetBottom = 0) => {
    if (isOpen) {
      root.style.setProperty(
        KEYBOARD_EXPOSED_FILL_VAR,
        resolveMobileKeyboardExposedFill(),
      );
      root.dataset.mobileKeyboardOpen = 'true';
    } else {
      delete root.dataset.mobileKeyboardOpen;
    }

    root.style.setProperty(
      KEYBOARD_INSET_VAR,
      `${Math.max(0, Math.round(insetBottom))}px`,
    );
  };

  const resetFocusShift = () => {
    root.style.setProperty(KEYBOARD_FOCUS_OFFSET_VAR, '0px');
  };

  const readActiveTarget = () =>
    isEditableKeyboardTarget(document.activeElement)
      ? document.activeElement
      : null;

  const syncKeyboardFocus = () => {
    const activeTarget = readActiveTarget();
    const viewport = readVisualViewport();
    const visualTop = viewport?.offsetTop ?? 0;
    const visualHeight = viewport?.height ?? window.innerHeight;
    const keyboardState = resolveMobileKeyboardState({
      layoutHeight: stableLayoutHeight,
      visualTop,
      visualHeight,
      hasEditableTarget: Boolean(activeTarget),
    });

    if (!keyboardState.isOpen || !activeTarget) {
      setKeyboardState(false);
      resetFocusShift();

      if (!activeTarget) {
        setLayoutHeight(readLayoutViewportHeight());
      }
      return;
    }

    // 中文注释：H5 浏览器和小程序 web-view 已会自行处理输入框可见性。
    // 这里只记录键盘状态、隐藏底部 dock，并给可能露出的宿主区域补浅色背景。
    setKeyboardState(true, keyboardState.insetBottom);
    resetFocusShift();
  };

  const scheduleSync = () => {
    if (frameId) {
      window.cancelAnimationFrame(frameId);
    }

    frameId = window.requestAnimationFrame(() => {
      frameId = 0;
      syncKeyboardFocus();
    });
  };

  const scheduleKeyboardAnimationSync = () => {
    scheduleSync();
    window.setTimeout(scheduleSync, 90);
    window.setTimeout(scheduleSync, 260);
  };

  setLayoutHeight(stableLayoutHeight);
  setKeyboardState(false);
  resetFocusShift();

  document.addEventListener('focusin', scheduleKeyboardAnimationSync, true);
  document.addEventListener('focusout', scheduleKeyboardAnimationSync, true);
  window.addEventListener('resize', scheduleKeyboardAnimationSync);
  window.addEventListener('orientationchange', () => {
    setKeyboardState(false);
    resetFocusShift();
    window.setTimeout(() => {
      setLayoutHeight(readLayoutViewportHeight());
      scheduleSync();
    }, 320);
  });
  visualViewport?.addEventListener('resize', scheduleKeyboardAnimationSync);
  visualViewport?.addEventListener('scroll', scheduleKeyboardAnimationSync);
}