/**
 * TT-Core Infinite Scroll Composable (Vue 3)
 * Provides infinite scrolling functionality
 */

/**
 * Create an infinite scroll composable
 * @param {Ref} items - Reactive reference to items array
 * @param {Object} options - Scroll options
 * @returns {Object} - Composable with visible items and methods
 */
export function useInfiniteScroll(items, options = {}) {
    const { ref, computed, onMounted, onBeforeUnmount, onUpdated } = Vue;

    const visibleCount = ref(options.initialCount || 50);
    const incrementBy = options.incrementBy || 50;
    const sentinelRef = ref(null);
    let scrollObserver = null;

    const visibleItems = computed(() => {
        return items.value.slice(0, visibleCount.value);
    });

    const hasMore = computed(() => {
        return visibleCount.value < items.value.length;
    });

    const loadMore = () => {
        if (hasMore.value) {
            visibleCount.value += incrementBy;
        }
    };

    const resetVisibleCount = () => {
        visibleCount.value = options.initialCount || 50;
    };

    const setupScrollObserver = () => {
        scrollObserver = new IntersectionObserver(
            ([entry]) => {
                if (entry && entry.isIntersecting) {
                    loadMore();
                }
            },
            {
                root: options.root || null,
                threshold: 0.1
            }
        );

        if (sentinelRef.value) {
            scrollObserver.observe(sentinelRef.value);
        }
    };

    onMounted(() => {
        setupScrollObserver();
    });

    onBeforeUnmount(() => {
        if (scrollObserver) {
            scrollObserver.disconnect();
            scrollObserver = null;
        }
    });

    onUpdated(() => {
        // Reconnect observer when DOM updates
        if (scrollObserver && sentinelRef.value) {
            scrollObserver.disconnect();
            scrollObserver.observe(sentinelRef.value);
        }
    });

    return {
        sentinelRef,
        visibleItems,
        visibleCount,
        hasMore,
        loadMore,
        resetVisibleCount
    };
}

/**
 * Create an infinite scroll mixin (backward compatibility)
 * @param {Object} options - Scroll options
 * @returns {Object} - Vue mixin
 */
export function createInfiniteScrollMixin(options = {}) {
    return {
        data() {
            return {
                visibleCount: options.initialCount || 50,
                incrementBy: options.incrementBy || 50,
                scrollObserver: null
            };
        },
        computed: {
            visibleItems() {
                const items = this[options.itemsKey || 'items'] || [];
                return items.slice(0, this.visibleCount);
            }
        },
        mounted() {
            this.setupScrollObserver();
        },
        beforeUnmount() {
            if (this.scrollObserver) {
                this.scrollObserver.disconnect();
                this.scrollObserver = null;
            }
        },
        updated() {
            // Reconnect observer when DOM updates
            if (this.scrollObserver && this.$refs.sentinel) {
                this.scrollObserver.disconnect();
                this.scrollObserver.observe(this.$refs.sentinel);
            }
        },
        methods: {
            setupScrollObserver() {
                this.scrollObserver = new IntersectionObserver(
                    ([entry]) => {
                        if (entry && entry.isIntersecting) {
                            this.loadMore();
                        }
                    },
                    {
                        root: this.$refs.tableWrap || null,
                        threshold: 0.1
                    }
                );

                if (this.$refs.sentinel) {
                    this.scrollObserver.observe(this.$refs.sentinel);
                }
            },
            loadMore() {
                const items = this[options.itemsKey || 'items'] || [];
                if (this.visibleCount < items.length) {
                    this.visibleCount += this.incrementBy;
                }
            },
            resetVisibleCount() {
                this.visibleCount = options.initialCount || 50;
            }
        }
    };
}