// Mixins
import Measurable from '../../mixins/measurable'
import Toggleable from '../../mixins/toggleable'

// Directives
import intersect from '../../directives/intersect'

// Utilities
import mixins from '../../util/mixins'
import { getSlot } from '../../util/helpers'

// Types
import { VNode } from 'vue'
import { PropValidator } from 'vue/types/options'

export default mixins(
  Measurable,
  Toggleable
).extend({
  name: 'VLazy',

  directives: { intersect },

  props: {
    options: {
      type: Object,
      // For more information on types, navigate to:
      // https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API
      default: () => ({
        root: undefined,
        rootMargin: undefined,
        threshold: undefined,
      }),
    } as PropValidator<IntersectionObserverInit>,
    tag: {
      type: String,
      default: 'div',
    },
    transition: {
      type: String,
      default: 'fade-transition',
    },
  },

  computed: {
    styles (): object {
      return {
        ...this.measurableStyles,
      }
    },
  },

  methods: {
    genContent () {
      const children = this.isActive && getSlot(this)

      return this.transition
        ? this.$createElement('transition', {
          props: { name: this.transition },
        }, children)
        : children
    },
    onObserve (
      entries: IntersectionObserverEntry[],
      observer: IntersectionObserver,
      isIntersecting: boolean,
    ) {
      if (this.isActive) return

      this.isActive = isIntersecting
    },
  },

  render (h): VNode {
    return h(this.tag, {
      staticClass: 'v-lazy',
      attrs: this.$attrs,
      directives: [{
        name: 'intersect',
        value: {
          handler: this.onObserve,
          options: this.options,
        },
      }],
      on: this.$listeners,
      style: this.styles,
    }, [this.genContent()])
  },
})