<template>
  <a-tooltip
    :trigger="['focus']"
    placement="topLeft"
    overlayClassName="numeric-input"
  >
    <span slot="title" v-if="value" class="numeric-input-title">
      {{value !== '-' ? formatNumber(value) : '-'}}
    </span>
    <template slot="title" v-else>
      Input a number
    </template>
    <a-input
      :value="value"
      @change="onChange"
      @blur="onBlur"
      placeholder="Input a number"
      maxLength="25"
      style="width: 120px"
    />
  </a-tooltip>
</template>
<script>
function formatNumber (value) {
  value += ''
  const list = value.split('.')
  const prefix = list[0].charAt(0) === '-' ? '-' : ''
  let num = prefix ? list[0].slice(1) : list[0]
  let result = ''
  while (num.length > 3) {
    result = `,${num.slice(-3)}${result}`
    num = num.slice(0, num.length - 3)
  }
  if (num) {
    result = num + result
  }
  return `${prefix}${result}${list[1] ? `.${list[1]}` : ''}`
}

export default {
  data () {
    this.formatNumber = formatNumber
    return {
      value: '',
    }
  },
  methods: {
    onChange (e) {
      const { value } = e.target
      const reg = /^-?(0|[1-9][0-9]*)(\.[0-9]*)?$/
      if ((!isNaN(value) && reg.test(value)) || value === '' || value === '-') {
        this.value = value
      }
    },
    // '.' at the end or only '-' in the input box.
    onBlur () {
      const { value, onChange } = this
      if (value.charAt(value.length - 1) === '.' || value === '-') {
        onChange({ value: value.slice(0, -1) })
      }
    },
  },
}
</script>
<style>
/* to prevent the arrow overflow the popup container,
or the height is not enough when content is empty */
.numeric-input .ant-tooltip-inner {
  min-width: 32px;
  min-height: 37px;
}

.numeric-input .numeric-input-title {
  font-size: 14px;
}
</style>
