/**
 * 下拉刷新通用工具 (BEXPullRefresh)
 *
 * 用法：
 *   var ptr = BEXPullRefresh.init(document.getElementById('myContainer'), {
 *     onRefresh: async function () { await fetchData(); },
 *     texts: { pull: '下拉刷新', release: '释放刷新', refreshing: '刷新中...' },
 *     threshold: 56
 *   });
 *
 *   // 手动销毁：ptr.destroy();
 *   // 销毁全部：BEXPullRefresh.destroyAll();
 */
(function () {
    'use strict';

    var instances = [];

    function PTRInstance(container, options) {
        var opts = options || {};
        var threshold = opts.threshold || 56;
        var onRefresh = opts.onRefresh || function () { return Promise.resolve(); };
        var texts = opts.texts || {
            pull: 'Pull to refresh',
            release: 'Release to refresh',
            refreshing: 'Refreshing...'
        };

        var state = { pulling: false, refreshing: false, startY: 0, currentY: 0 };
        var indicatorEl = null;
        var spinnerEl = null;
        var textEl = null;

        function buildDOM() {
            indicatorEl = document.createElement('div');
            indicatorEl.className = 'ptr-indicator';
            indicatorEl.innerHTML =
                '<div class="ptr-spinner"></div>' +
                '<span class="ptr-text">' + texts.pull + '</span>';

            var parent = container.parentNode;
            parent.insertBefore(indicatorEl, container);
            spinnerEl = indicatorEl.querySelector('.ptr-spinner');
            textEl = indicatorEl.querySelector('.ptr-text');

            container.classList.add('ptr-container');

            // 确保父级支持 absolute 定位
            if (parent !== document.body) {
                var parentPos = window.getComputedStyle(parent).position;
                if (parentPos === 'static') parent.style.position = 'relative';
            }
        }

        function getScrollTop() {
            return document.documentElement.scrollTop || document.body.scrollTop || 0;
        }

        function applyTransform(y, noTransition) {
            if (noTransition) container.classList.add('ptr-pulling');
            else container.classList.remove('ptr-pulling');
            container.style.transform = 'translateY(' + y + 'px)';
            // 指示器从 translateY(-100%) → 0%：y 0→threshold 时，百分比 -100→0
            var pullPercent = ((y / threshold) * 100 - 100).toFixed(1);
            indicatorEl.style.transform = 'translateY(' + pullPercent + '%)';
        }

        function setSpinnerOpacity(opacity) {
            spinnerEl.style.opacity = String(opacity);
        }

        function startRefresh() {
            state.refreshing = true;
            indicatorEl.classList.add('ptr-refreshing');
            applyTransform(threshold, false);
            setSpinnerOpacity(1);
            textEl.textContent = texts.refreshing;

            onRefresh().then(function () {
                finishRefresh();
            }).catch(function () {
                finishRefresh();
            });
        }

        function finishRefresh() {
            state.refreshing = false;
            indicatorEl.classList.remove('ptr-refreshing');
            container.classList.remove('ptr-pulling');
            container.style.transform = 'translateY(0)';
            indicatorEl.style.transform = 'translateY(-100%)';
            setSpinnerOpacity(0);
            textEl.textContent = texts.pull;
        }

        function onTouchStart(e) {
            if (state.refreshing) return;
            state.startY = e.touches[0].clientY;
            state.pulling = false;
        }

        function isDocumentScrollLocked() {
            var htmlStyle = window.getComputedStyle(document.documentElement);
            return htmlStyle.overflow === 'hidden' || htmlStyle.overflowY === 'hidden';
        }

        function onTouchMove(e) {
            if (state.refreshing || isDocumentScrollLocked()) return;
            var scrollTop = getScrollTop();
            if (scrollTop > 0) return;
            var deltaY = e.touches[0].clientY - state.startY;
            if (deltaY <= 0) return;
            state.pulling = true;
            state.currentY = Math.min(deltaY * 0.5, threshold * 1.5);
            applyTransform(state.currentY, true);
            setSpinnerOpacity(Math.min(state.currentY / threshold, 1));
            textEl.textContent = state.currentY >= threshold ? texts.release : texts.pull;
        }

        function onTouchEnd() {
            if (!state.pulling || state.refreshing) return;
            state.pulling = false;
            if (state.currentY >= threshold) {
                startRefresh();
            } else {
                applyTransform(0, false);
                setSpinnerOpacity(0);
                textEl.textContent = texts.pull;
            }
        }

        this.destroy = function () {
            document.removeEventListener('touchstart', onTouchStart);
            document.removeEventListener('touchmove', onTouchMove);
            document.removeEventListener('touchend', onTouchEnd);
            if (indicatorEl && indicatorEl.parentNode) {
                indicatorEl.parentNode.removeChild(indicatorEl);
            }
            container.classList.remove('ptr-container', 'ptr-pulling');
            container.style.transform = '';
            var idx = instances.indexOf(this);
            if (idx > -1) instances.splice(idx, 1);
        };

        buildDOM();
        document.addEventListener('touchstart', onTouchStart, { passive: true });
        document.addEventListener('touchmove', onTouchMove, { passive: true });
        document.addEventListener('touchend', onTouchEnd);

        instances.push(this);
    }

    window.BEXPullRefresh = {
        init: function (container, options) {
            if (!container) throw new Error('BEXPullRefresh.init: container is required');
            return new PTRInstance(container, options);
        },
        destroyAll: function () {
            while (instances.length) {
                instances[instances.length - 1].destroy();
            }
        }
    };
})();