const FIRST_BUTTON_CLASS = 'erp-pagination-first';
const LAST_BUTTON_CLASS = 'erp-pagination-last';
const JUMP_BUTTON_CLASS = 'erp-pagination-jump';
const DEFAULT_PAGE_SIZE = 10;
const DEFAULT_PAGE_SIZES = [10, 20, 50, 100];
const PAGE_KEY_PATTERN = /(^page$|Page$|^page[A-Z])/;

const toNumber = value => {
  const number = Number(value);
  return Number.isFinite(number) ? number : 0;
};

const getNativeInputValueSetter = input => {
  const prototype = Object.getPrototypeOf(input);
  const descriptor = Object.getOwnPropertyDescriptor(prototype, 'value');
  return descriptor && descriptor.set;
};

const setInputValue = (input, value) => {
  const setter = getNativeInputValueSetter(input);
  if (setter) {
    setter.call(input, value);
  } else {
    input.value = value;
  }
  input.dispatchEvent(new Event('input', { bubbles: true }));
};

const getPaginationState = pagination => {
  const active = pagination.querySelector('.el-pager li.is-active');
  const jumpInput = pagination.querySelector('.el-pagination__editor input');
  const currentPage = toNumber(
    active && active.textContent ? active.textContent.trim() : jumpInput?.value
  );
  const pageCount = toNumber(jumpInput?.getAttribute('max'));
  return {
    currentPage: currentPage || 1,
    pageCount: pageCount || 1,
    jumpInput,
  };
};

const changePage = (pagination, page) => {
  const { currentPage, pageCount, jumpInput } = getPaginationState(pagination);
  const targetPage = Math.min(Math.max(toNumber(page), 1), pageCount);
  if (!targetPage || targetPage === currentPage) return;

  const targetPager = Array.from(pagination.querySelectorAll('.el-pager li.number')).find(
    item => toNumber(item.textContent && item.textContent.trim()) === targetPage
  );
  if (targetPager) {
    targetPager.click();
    return;
  }

  if (jumpInput) {
    setInputValue(jumpInput, targetPage);
    jumpInput.dispatchEvent(new Event('change', { bubbles: true }));
    jumpInput.dispatchEvent(new KeyboardEvent('keydown', { key: 'Enter', bubbles: true }));
  }
};

const createPaginationButton = (className, text, onClick) => {
  const button = document.createElement('button');
  button.type = 'button';
  button.className = `erp-pagination-button ${className}`;
  button.textContent = text;
  button.addEventListener('click', onClick);
  return button;
};

const setButtonDisabled = (button, disabled) => {
  if (!button || button.disabled === disabled) return;
  button.disabled = disabled;
};

const isPageConfig = value =>
  value &&
  typeof value === 'object' &&
  ('pageSize' in value || 'currentPage' in value || 'total' in value);

const normalizePageConfig = page => {
  if (!isPageConfig(page)) return;
  page.pageSize = DEFAULT_PAGE_SIZES.includes(toNumber(page.pageSize))
    ? toNumber(page.pageSize)
    : DEFAULT_PAGE_SIZE;
  page.pageSizes = DEFAULT_PAGE_SIZES;
};

const normalizeComponentPageConfigs = pagination => {
  let component = pagination.__vueParentComponent;
  while (component) {
    [component.data, component.setupState].forEach(state => {
      if (!state) return;
      Object.keys(state)
        .filter(key => PAGE_KEY_PATTERN.test(key))
        .forEach(key => normalizePageConfig(state[key]));
    });
    component = component.parent;
  }
};

const updatePaginationButtons = pagination => {
  const { currentPage, pageCount, jumpInput } = getPaginationState(pagination);
  const firstButton = pagination.querySelector(`.${FIRST_BUTTON_CLASS}`);
  const lastButton = pagination.querySelector(`.${LAST_BUTTON_CLASS}`);
  const jumpButton = pagination.querySelector(`.${JUMP_BUTTON_CLASS}`);

  setButtonDisabled(firstButton, currentPage <= 1);
  setButtonDisabled(lastButton, currentPage >= pageCount);
  setButtonDisabled(jumpButton, !jumpInput || jumpInput.disabled);
};

const enhancePagination = pagination => {
  const prevButton = pagination.querySelector('.btn-prev');
  const nextButton = pagination.querySelector('.btn-next');
  const jumpWrapper = pagination.querySelector('.el-pagination__jump');

  normalizeComponentPageConfigs(pagination);

  if (prevButton && !pagination.querySelector(`.${FIRST_BUTTON_CLASS}`)) {
    const firstButton = createPaginationButton(FIRST_BUTTON_CLASS, '首页', () => {
      changePage(pagination, 1);
    });
    prevButton.before(firstButton);
  }

  if (nextButton && !pagination.querySelector(`.${LAST_BUTTON_CLASS}`)) {
    const lastButton = createPaginationButton(LAST_BUTTON_CLASS, '尾页', () => {
      const { pageCount } = getPaginationState(pagination);
      changePage(pagination, pageCount);
    });
    nextButton.after(lastButton);
  }

  if (jumpWrapper && !pagination.querySelector(`.${JUMP_BUTTON_CLASS}`)) {
    const jumpButton = createPaginationButton(JUMP_BUTTON_CLASS, '跳转', () => {
      const { jumpInput } = getPaginationState(pagination);
      if (!jumpInput) return;
      changePage(pagination, jumpInput.value);
    });
    jumpWrapper.after(jumpButton);
  }

  updatePaginationButtons(pagination);
};

const enhanceAllPaginations = () => {
  document.querySelectorAll('.el-pagination').forEach(enhancePagination);
};

export const setupPaginationEnhancer = () => {
  if (typeof window === 'undefined' || typeof document === 'undefined') return;

  const scheduleEnhance = () => {
    window.requestAnimationFrame(enhanceAllPaginations);
  };

  scheduleEnhance();
  const observer = new MutationObserver(scheduleEnhance);
  observer.observe(document.body, {
    attributes: true,
    attributeFilter: ['class', 'disabled'],
    childList: true,
    subtree: true,
  });
};