bramw_baserow/web-frontend/modules/core/components/Dropdown.vue

<template>
  <div class="dropdown">
    <a class="dropdown__selected" @click="show()">
      <template v-if="hasValue()">
        <i
          v-if="selectedIcon"
          class="dropdown__selected-icon fas"
          :class="'fa-' + selectedIcon"
        ></i>
        {{ selectedName }}
      </template>
      <template v-if="!hasValue()">
        Make a choice
      </template>
      <i class="dropdown__toggle-icon fas fa-caret-down"></i>
    </a>
    <div class="dropdown__items" :class="{ hidden: !open }">
      <div v-if="showSearch" class="select__search">
        <i class="select__search-icon fas fa-search"></i>
        <input
          ref="search"
          v-model="query"
          type="text"
          class="select__search-input"
          :placeholder="searchText"
          @keyup="search(query)"
        />
      </div>
      <ul ref="items" class="select__items">
        <slot></slot>
      </ul>
    </div>
  </div>
</template>

<script>
import { isElement } from '@baserow/modules/core/utils/dom'

// @TODO focus on tab
export default {
  name: 'Dropdown',
  props: {
    value: {
      type: [String, Number, Boolean, Object],
      required: false,
      default: null,
    },
    searchText: {
      type: String,
      required: false,
      default: 'Search',
    },
    showSearch: {
      type: Boolean,
      required: false,
      default: true,
    },
  },
  data() {
    return {
      loaded: false,
      open: false,
      name: null,
      icon: null,
      query: '',
      hover: null,
    }
  },
  computed: {
    selectedName() {
      return this.getSelectedProperty(this.value, 'name')
    },
    selectedIcon() {
      return this.getSelectedProperty(this.value, 'icon')
    },
  },
  watch: {
    value() {
      this.$nextTick(() => {
        // When the value changes we want to forcefully reload the selectName and
        // selectedIcon a little bit later because the children might have changed.
        this.forceRefreshSelectedValue()
      })
    },
  },
  mounted() {
    // When the component is mounted we want to forcefully reload the selectedName and
    // selectedIcon.
    this.forceRefreshSelectedValue()
  },
  methods: {
    /**
     * Returns true if there is a value.
     * @return {boolean}
     */
    hasValue() {
      return this.value === 0 ? true : !!this.value
    },
    /**
     * Shows the lists of choices, so a user can change the value.
     */
    show() {
      this.open = true
      this.hover = this.value
      this.$emit('show')

      this.$nextTick(() => {
        // We have to wait for the input to be visible before we can focus.
        this.showSearch && this.$refs.search.focus()

        // Scroll to the selected child.
        this.$children.forEach((child) => {
          if (child.value === this.value) {
            this.$refs.items.scrollTop =
              child.$el.offsetTop -
              child.$el.clientHeight -
              Math.round(this.$refs.items.clientHeight / 2)
          }
        })
      })

      // If the user clicks outside the dropdown while the list of choices of open we
      // have to hide them.
      this.$el.clickOutsideEvent = (event) => {
        if (
          // Check if the context menu is still open
          this.open &&
          // If the click was outside the context element because we want to ignore
          // clicks inside it.
          !isElement(this.$el, event.target)
        ) {
          this.hide()
        }
      }
      document.body.addEventListener('click', this.$el.clickOutsideEvent)

      this.$el.keydownEvent = (event) => {
        if (
          // Check if the context menu is still open
          this.open &&
          // Check if the user has hit either of the keys we care about. If not,
          // ignore.
          (event.code === 'ArrowUp' || event.code === 'ArrowDown')
        ) {
          // Prevent scrolling up and down while pressing the up and down key.
          event.stopPropagation()
          event.preventDefault()
          this.handleUpAndDownArrowPress(event)
        }
        // Allow the Enter key to select the value that is currently being hovered
        // over.
        if (this.open && event.code === 'Enter') {
          // Prevent submitting the whole form when pressing the enter key while the
          // dropdown is open.
          event.preventDefault()
          this.select(this.hover)
        }
      }
      document.body.addEventListener('keydown', this.$el.keydownEvent)
    },
    /**
     * Hides the list of choices
     */
    hide() {
      this.open = false
      this.$emit('hide')

      // Make sure that all the items are visible the next time we open the dropdown.
      this.query = ''
      this.search(this.query)

      document.body.removeEventListener('click', this.$el.clickOutsideEvent)
      document.body.removeEventListener('keydown', this.$el.keydownEvent)
    },
    /**
     * Selects a new value which will also be
     */
    select(value) {
      this.$emit('input', value)
      this.$emit('change', value)
      this.hide()
    },
    /**
     * If not empty it will only show children that contain the given query.
     */
    search(query) {
      this.$children.forEach((item) => {
        item.search(query)
      })
    },
    /**
     * Loops over all children to see if any of the values match with given value. If
     * so the requested property of the child is returned
     */
    getSelectedProperty(value, property) {
      for (const i in this.$children) {
        const item = this.$children[i]
        if (item.value === value) {
          return item[property]
        }
      }
      return ''
    },
    /**
     * A nasty hack, but in some cases the $children have not yet been loaded when the
     * `selectName` and `selectIcon` are computed. This would result in an empty
     * initial value of the Dropdown because the correct value can't be extracted from
     * the DropdownItem. With this hack we force the computed properties to recompute
     * when the component is mounted. At this moment the $children have been added.
     */
    forceRefreshSelectedValue() {
      this._computedWatchers.selectedName.run()
      this._computedWatchers.selectedIcon.run()
      this.$forceUpdate()
    },
    /**
     * Method that is called when the arrow up or arrow down key is pressed. Based on
     * the index of the current child, the next child enabled child is set as hover.
     */
    handleUpAndDownArrowPress(event) {
      const children = this.$children.filter(
        (child) => !child.disabled && child.isVisible(this.query)
      )

      let index = children.findIndex((item) => item.value === this.hover)
      index = event.code === 'ArrowUp' ? index - 1 : index + 1

      // Check if the new index is within the allowed range.
      if (index < 0 || index > children.length - 1) {
        return
      }

      const next = children[index]
      this.hover = next.value
      this.$refs.items.scrollTop = this.getScrollTopAmountForNextChild(next)
    },
    /**
     * When scrolling up and down between options with the keyboard, this
     * method calculates the expected behavior to the user considering
     * disabled items that need to be skipped and a limited dropdown
     * window in which to scroll
     */
    getScrollTopAmountForNextChild(itemToScrollTo) {
      // If the element to scroll to is below the current dropdown's
      // bottom scroll position, then scroll so that the item to scroll to
      // is the last viewable item in the dropdown window.
      if (
        itemToScrollTo.$el.offsetTop >
        this.$refs.items.scrollTop + this.$refs.items.clientHeight
      ) {
        return (
          itemToScrollTo.$el.offsetTop -
          itemToScrollTo.$el.clientHeight -
          (this.$refs.items.clientHeight - itemToScrollTo.$el.clientHeight)
        )
      }

      // If the element to scroll to is above our current scroll position
      // in the window, we need to scroll to the item and position it as
      // the top item in the scroll window.
      if (
        itemToScrollTo.$el.offsetTop <
        this.$refs.items.scrollTop + this.$refs.items.offsetTop
      ) {
        // To figure out how much to scroll, we need the top and bottom
        // margin of the element we're scrolling to
        const style =
          itemToScrollTo.$el.currentStyle ||
          window.getComputedStyle(itemToScrollTo.$el)
        return (
          itemToScrollTo.$el.offsetTop -
          this.$refs.search.clientHeight -
          (parseInt(style.marginTop) + parseInt(style.marginBottom))
        )
      }

      return this.$refs.items.scrollTop
    },
  },
}
</script>