<template>
  <div ref="scrollContainer">
    <slot />
    <div ref="sentinel" style="height: 1px"></div>
  </div>
</template>

<script lang="ts">
import { Component, Emit, Prop, Vue } from "vue-facing-decorator";

@Component
export default class InfiniteScroll extends Vue {
  @Prop({ default: 100 })
  readonly distance!: number;
  private observer!: IntersectionObserver;
  private isInitialized = false;

  mounted() {
    this.$nextTick(() => {
      this.isInitialized = true;
      console.log("onMounted");
      const options = {
        root: this.$refs.scrollContainer as HTMLElement,
        rootMargin: `0px 0px ${this.distance}px 0px`,
        threshold: 1.0,
      };
      this.observer = new IntersectionObserver(
        (entries) => this.handleIntersection(entries),
        options
      );
      this.observer.observe(this.$refs.sentinel as HTMLElement);
    });
  }

  beforeUnmount() {
    this.observer.disconnect();
  }

  @Emit("reached-bottom")
  handleIntersection(entries: IntersectionObserverEntry[]) {
    console.log("handleIntersection");
    if (!this.isInitialized) {
      return false;
    }
    const entry = entries[0];
    if (entry.isIntersecting && entry.intersectionRatio > 0) {
      return true;
    }
    return false;
  }
}
</script>

<!-- Add "scoped" attribute to limit CSS to this component only -->
<style scoped></style>
