/* @flow */

const fnExpRE = /^\s*([\w$_]+|\([^)]*?\))\s*=>|^function\s*\(/

const simplePathRE = /^\s*[A-Za-z_$][\w$]*(?:\.[A-Za-z_$][\w$]*|\['.*?']|\[".*?"]|\[\d+]|\[[A-Za-z_$][\w$]*])*\s*$/

// keyCode aliases

const keyCodes = {

  esc: 27,

  tab: 9,

  enter: 13,

  space: 32,

  up: 38,

  left: 37,

  right: 39,

  down: 40,

  'delete': [8, 46]

}

const modifierCode = {

  stop: '$event.stopPropagation();',

  prevent: '$event.preventDefault();',

  self: 'if($event.target !== $event.currentTarget)return;'

}

const isMouseEventRE = /^mouse|^pointer|^(click|dblclick|contextmenu|wheel)$/

const mouseEventModifierCode = {

  ctrl: 'if(!$event.ctrlKey)return;',

  shift: 'if(!$event.shiftKey)return;',

  alt: 'if(!$event.altKey)return;',

  meta: 'if(!$event.metaKey)return;'

}

export function genHandlers (events: ASTElementHandlers, native?: boolean): string {

  let res = native ? 'nativeOn:{' : 'on:{'

  for (const name in events) {

    res += `"${name}":${genHandler(name, events[name])},`

  }

  return res.slice(0, -1) + '}'

}

function genHandler (

  name: string,

  handler: ASTElementHandler | Array<ASTElementHandler>

): string {

  if (!handler) {

    return 'function(){}'

  } else if (Array.isArray(handler)) {

    return `[${handler.map(handler => genHandler(name, handler)).join(',')}]`

  } else if (!handler.modifiers) {

    return fnExpRE.test(handler.value) || simplePathRE.test(handler.value)

      ? handler.value

      : `function($event){${handler.value}}`

  } else {

    let code = ''

    const keys = []

    const isMouseEvnet = isMouseEventRE.test(name)

    for (const key in handler.modifiers) {

      if (modifierCode[key]) {

        code += modifierCode[key]

      } else if (isMouseEvnet && mouseEventModifierCode[key]) {

        code += mouseEventModifierCode[key]

      } else {

        keys.push(key)

      }

    }

    if (keys.length) {

      code = genKeyFilter(keys) + code

    }

    const handlerCode = simplePathRE.test(handler.value)

      ? handler.value + '($event)'

      : handler.value

    return 'function($event){' + code + handlerCode + '}'

  }

}

function genKeyFilter (keys: Array<string>): string {

  const code = keys.length === 1

    ? normalizeKeyCode(keys[0])

    : Array.prototype.concat.apply([], keys.map(normalizeKeyCode))

  if (Array.isArray(code)) {

    return `if(${code.map(c => `$event.keyCode!==${c}`).join('&&')})return;`

  } else {

    return `if($event.keyCode!==${code})return;`

  }

}

function normalizeKeyCode (key) {

  return (

    parseInt(key, 10) || // number keyCode

    keyCodes[key] || // built-in alias

    `_k(${JSON.stringify(key)})` // custom alias

  )

}