import React, { useState } from 'react'

const baseClass = 'BusyIndicator-'+Math.random().toString(36).slice(2)

// Add busy indicator stylesheet
var style = document.createElement('style');
style.type = 'text/css';
style.innerHTML = `
.${baseClass} {
  position: fixed;
  height: 3px;
  width: 100%;
  top: 0;
  left: 0;
  z-index: 1000;
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.2) inset;
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform ease-in 300ms, opacity ease-in 300ms;
  transition-delay: 0;
  opacity: 0;
}
.${baseClass}.active {
  animation: ${baseClass} 2s cubic-bezier(.4,.45,.6,.55) infinite;
  animation-fill-mode: forwards;
  opacity: 1;
}

@keyframes ${baseClass} {
  0% {
    transform: scaleX(0);
  }
  10% {
    transform: scaleX(0.3);
  }
  50% {
    transform: scaleX(0.7);
  }
  90% {
    transform: scaleX(0.8);
  }
  100% {
    transform: scaleX(1);
  }
}`;
document.getElementsByTagName('head')[0].appendChild(style);


interface BusyIndicatorProps extends React.HTMLAttributes<any> {
  color?: string
  delayMs?: number
  isBusy?: boolean
}

export default function BusyIndicator({ className, color, active, isBusy, delayMs, style, ...props }) {
  let [hasRendered, setHasRendered] = useState(false)
  let isActive = active || isBusy

  // Prevent the `active` class from being applied on the first render,
  // to allow the CSS animation's delay prop to work even if `isActive`
  // is true when the component is mounted.
  if (!hasRendered) {
    isActive = false
    setTimeout(() => setHasRendered(true))
  }

  // Only add the `active` class to this element while the
  // next page is loading, triggering a CSS animation to
  // show or hide the loading bar.
  return React.createElement('div', {
    ...props,
    className: `${baseClass} ${isActive ? 'active' : ''} ${className || ''}`,
    style: {
      backgroundColor: color,

      ...(isActive ? {
        transitionDelay: (delayMs || 0)+'ms',
      } : {}),

      ...style
    }
  })
}

(BusyIndicator as any).defaultProps = {
  color: '#F54391',
  delayMs: 333,
}