1 files changed, 104 insertions, 0 deletions
diff --git a/ui/app/components/unit-input/unit-input.component.js b/ui/app/components/unit-input/unit-input.component.js
new file mode 100644
index 000000000..f1ebf4d77
--- /dev/null
+++ b/ui/app/components/unit-input/unit-input.component.js
@@ -0,0 +1,104 @@
+import React, { PureComponent } from 'react'
+import PropTypes from 'prop-types'
+import classnames from 'classnames'
+import { removeLeadingZeroes } from '../send/send.utils'
+
+/**
+ * Component that attaches a suffix or unit of measurement trailing user input, ex. 'ETH'. Also
+ * allows rendering a child component underneath the input to, for example, display conversions of
+ * the shown suffix.
+ */
+export default class UnitInput extends PureComponent {
+  static propTypes = {
+    children: PropTypes.node,
+    error: PropTypes.bool,
+    onBlur: PropTypes.func,
+    onChange: PropTypes.func,
+    placeholder: PropTypes.string,
+    suffix: PropTypes.string,
+    value: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
+  }
+
+  static defaultProps = {
+    placeholder: '0',
+  }
+
+  constructor (props) {
+    super(props)
+
+    this.state = {
+      value: props.value || '',
+    }
+  }
+
+  componentDidUpdate (prevProps) {
+    const { value: prevPropsValue } = prevProps
+    const { value: propsValue } = this.props
+    const { value: stateValue } = this.state
+
+    if (prevPropsValue !== propsValue && propsValue !== stateValue) {
+      this.setState({ value: propsValue })
+    }
+  }
+
+  handleFocus = () => {
+    this.unitInput.focus()
+  }
+
+  handleChange = event => {
+    const { value: userInput } = event.target
+    let value = userInput
+
+    if (userInput.length && userInput.length > 1) {
+      value = removeLeadingZeroes(userInput)
+    }
+
+    this.setState({ value })
+    this.props.onChange(value)
+  }
+
+  handleBlur = event => {
+    const { onBlur } = this.props
+    typeof onBlur === 'function' && onBlur(this.state.value)
+  }
+
+  getInputWidth (value) {
+    const valueString = String(value)
+    const valueLength = valueString.length || 1
+    const decimalPointDeficit = valueString.match(/\./) ? -0.5 : 0
+    return (valueLength + decimalPointDeficit + 0.75) + 'ch'
+  }
+
+  render () {
+    const { error, placeholder, suffix, children } = this.props
+    const { value } = this.state
+
+    return (
+      <div
+        className={classnames('unit-input', { 'unit-input--error': error })}
+        onClick={this.handleFocus}
+      >
+        <div className="unit-input__input-container">
+          <input
+            type="number"
+            className="unit-input__input"
+            value={value}
+            placeholder={placeholder}
+            onChange={this.handleChange}
+            onBlur={this.handleBlur}
+            style={{ width: this.getInputWidth(value) }}
+            ref={ref => { this.unitInput = ref }}
+          />
+          {
+            suffix && (
+              <div className="unit-input__suffix">
+                { suffix }
+              </div>
+            )
+          }
+        </div>
+        { children }
+      </div>
+    )
+  }
+}