export function scanForProblems(context, logError, options) {
  for (const img of context.querySelectorAll('img')) {
    if (!img.hasAttribute('alt')) {
      logError(new ImageWithoutAltAttributeError(img))
    }
  }

  for (const a of context.querySelectorAll('a')) {
    if (a.hasAttribute('name') || elementIsHidden(a)) {
      continue
    }
    if (a.getAttribute('href') == null && a.getAttribute('role') !== 'button') {
      logError(new LinkWithoutLabelOrRoleError(a))
    } else if (!accessibleText(a)) {
      logError(new ElementWithoutLabelError(a))
    }
  }

  for (const button of context.querySelectorAll('button')) {
    if (!elementIsHidden(button) && !accessibleText(button)) {
      logError(new ButtonWithoutLabelError(button))
    }
  }

  for (const label of context.querySelectorAll('label')) {
    // In case label.control isn't supported by browser, find the control manually (IE)
    const control = label.control || document.getElementById(label.getAttribute('for')) || label.querySelector('input')

    if (!control && !elementIsHidden(label)) {
      logError(new LabelMissingControlError(label))
    }
  }

  for (const input of context.querySelectorAll('input[type=text], input[type=url], input[type=search], input[type=number], textarea')) {
    // In case input.labels isn't supported by browser, find the control manually (IE)
    const inputLabel = input.labels ? input.labels[0] : input.closest('label') || document.querySelector(`label[for="${input.id}"]`)
    if (!inputLabel && !elementIsHidden(input) && !input.hasAttribute('aria-label')) {
      logError(new InputMissingLabelError(input))
    }
  }
  if (options && options['ariaPairs']) {
    for (const selector in options['ariaPairs']) {
      const ARIAAttrsRequired =  options['ariaPairs'][selector]
      for (const target of context.querySelectorAll(selector)) {
        const missingAttrs = []

        for (const attr of ARIAAttrsRequired) {
          if (!target.hasAttribute(attr)) missingAttrs.push(attr)
        }

        if (missingAttrs.length > 0) {
          logError(new ARIAAttributeMissingError(target, missingAttrs.join(', ')))
        }
      }
    }
  }
}

function errorSubclass(fn) {
  fn.prototype = new Error()
  fn.prototype.constructor = fn
}

function ImageWithoutAltAttributeError(element) {
  this.name = 'ImageWithoutAltAttributeError'
  this.stack = new Error().stack
  this.element = element
  this.message = `Missing alt attribute on ${inspect(element)}`
}
errorSubclass(ImageWithoutAltAttributeError)

function ElementWithoutLabelError(element) {
  this.name = 'ElementWithoutLabelError'
  this.stack = new Error().stack
  this.element = element
  this.message = `Missing text, title, or aria-label attribute on ${inspect(element)}`
}
errorSubclass(ElementWithoutLabelError)

function LinkWithoutLabelOrRoleError(element) {
  this.name = 'LinkWithoutLabelOrRoleError'
  this.stack = new Error().stack
  this.element = element
  this.message = `Missing href or role=button on ${inspect(element)}`
}
errorSubclass(LinkWithoutLabelOrRoleError)

function LabelMissingControlError(element) {
  this.name = 'LabelMissingControlError'
  this.stack = new Error().stack
  this.element = element
  this.message = `Label missing control on ${inspect(element)}`
}
errorSubclass(LabelMissingControlError)

function InputMissingLabelError(element) {
  this.name = 'InputMissingLabelError'
  this.stack = new Error().stack
  this.element = element
  this.message = `Missing label for or aria-label attribute on ${inspect(element)}`
}
errorSubclass(InputMissingLabelError)

function ButtonWithoutLabelError(element) {
  this.name = 'ButtonWithoutLabelError'
  this.stack = new Error().stack
  this.element = element
  this.message = `Missing text or aria-label attribute on ${inspect(element)}`
}
errorSubclass(ButtonWithoutLabelError)

function ARIAAttributeMissingError(element, attr) {
  this.name = 'ARIAAttributeMissingError'
  this.stack = new Error().stack
  this.element = element
  this.message = `Missing ${attr} attribute on ${inspect(element)}`
}
errorSubclass(ARIAAttributeMissingError)

function elementIsHidden(element) {
  return element.closest('[aria-hidden="true"], [hidden], [style*="display: none"]') != null
}

function isText(value) {
  return typeof value === 'string' && !!value.trim()
}

// Public: Check if an element has text visible by sight or screen reader.
//
// Examples
//
//   <img alt="github" src="github.png">
//   # => true
//
//   <span aria-label="Open"></span>
//   # => true
//
//   <button></button>
//   # => false
//
// Returns String text.
function accessibleText(node) {
  switch (node.nodeType) {
    case Node.ELEMENT_NODE:
      if (isText(node.getAttribute('alt')) || isText(node.getAttribute('aria-label')) || isText(node.getAttribute('title'))) return true
      for (let i = 0; i < node.childNodes.length; i++) {
        if (accessibleText(node.childNodes[i])) return true
      }
      break
    case Node.TEXT_NODE:
      return isText(node.data)
  }
}

function inspect(element) {
  let tagHTML = element.outerHTML
  if (element.innerHTML) tagHTML = tagHTML.replace(element.innerHTML, '...')

  const parents = []
  while (element) {
    if (element.nodeName === 'BODY') break
    parents.push(selectors(element))
    // Stop traversing when we hit an ID
    if (element.id) break
    element = element.parentNode
  }
  return `"${parents.reverse().join(' > ')}". \n\n${tagHTML}`
}

function selectors(element) {
  const components = [element.nodeName.toLowerCase()]
  if (element.id) components.push(`#${element.id}`)
  if (element.classList) {
    for (const name of element.classList) {
      if (name.match(/^js-/)) components.push(`.${name}`)
    }
  }

  return components.join('')
}