function pgsh(ev) {
  var self = this

  /**
   * Terminal UI/Shell Entry Point
   */
  ev.on('cmd_entered', function(input) {
    var args = input.trim().split(' ')
    // Use the first argument as a command, or the value of `active`.
    var command = self.active ? self.active : args.shift()
    if (command in self.commands) {
      self[command](args)
    } else if (command) {
      show(command + ' not found')
    }
  })

  /**
   * Key functions
   */
  ev.on('mount', function() {
    document.getElementById(ev.id).onkeydown = function(e) {
      var code = e.keyCode || e.which
      // Tab for file path completion.
      if (code == 9) {
        var input = ev.tags['command-line'].refs.command.value.trim().split(' ')
        var command = input.shift()
        if (['cat', 'cd', 'ls'].indexOf(command) != -1) {
          var args = input.join(' ').trim()
          var isFile = (command == 'cat') ? true : false;
          var path = completePath(args, isFile)
          if (path) { ev.trigger('cmd_set', command + ' ' + path) }
        }
        e.preventDefault()
      }
    }
  })

  /**
   * Variables and Setup
   */
  var getHome = function() { return self.su_active ? '/root' : '/home/pgs' }
  this.cwd = getHome()
  var getPrompt = function() {
    if (self.su_active) {
      return '' +
      '<span style="color:#dc322f">root </span>' +
      '<span style="color:#b58900">' + self.cwd + ' </span>' +
      '<span style="color:#268bd2">% </span>'
    }
    return '' +
      '<span style="color:#d33682">pgs </span>' +
      '<span style="color:#b58900">' + self.cwd + ' </span>' +
      '<span style="color:#2aa198">$ </span>'
  }
  this.prompt = getPrompt()
  this.welcome = '' +
    'Linux parsleygardens.net 3.4.5-6-7-i286 #8 PGS Vimputer' +
    '3.4.56-7 i286\n\n' +
    '~ Welcome to Parsley Gardens! ~\n' +
    '"He maketh me to lie down in green pa..."\n\n' +
    'Type `<strong>help</strong>` for list of commands\n\n'
  this.tree = pgfs

  /**
   * Commands
   */
  this.commands = {
    'about':    { order: 1, help: 'Author Information' },
    'cat':      { order: 2, help: 'Con(cat)enate the contents of a file' },
    'cd':       { order: 2, help: 'Change folder/directory' },
    'clear':    { order: 2, help: 'Clears the screen' },
    'exit':     { order: 2, help: 'Leave the current context' },
    'hello':    { order: 2, help: 'Say hello to the computer\nUsage: hello [name]' },
    'help':     { order: 1, help: 'List commands or view information for one\nUsage: help [command]' },
    'ls':       { order: 2, help: 'List folder contents' },
    'pwd':      { order: 2, help: 'Show the current working directory' },
    'search':   { order: 2, help: 'Search the Web (with a Duck)\nUsage: search [query]' },
    'su':       { order: 2, help: 'Gain Phenomenal Cosmic Power' },
    'version':  { order: 1, help: 'Display shell information' }
  }
  this.about = function(args) { self.cat(['/home/pgs/about.md']) }
  this.cat = function(args) {
    var arg = args.join(' ').trim()
    var path = resolveAbsPath(arg)
    if (pathExists(path, true)) {
      var content = getContents(path)
      if (path.search('.md|.sh') != -1) {
        content = hljs.highlightAuto(content).value
      }
      show('\n' + content + '\n\n')
    } else {
      show("cat: " + arg + ": no such file")
    }
  }
  this.cd = function(args) {
    var arg = args.join(' ').trim()
    arg = arg ? arg : getHome()
    var path = resolveAbsPath(arg)
    if (pathExists(path)) {
      self.cwd = path
      ev.trigger('prompt_set', getPrompt())
    } else {
      show("cd: " + arg + ": no such directory")
    }
  }
  this.clear = function(args) { ev.trigger('disp_clear') }
  this.exit = function(args) {
    if (self.su_active) {
      self.su_active = false
      ev.trigger('prompt_set', getPrompt())
      return
    }
    show('Close browser window to exit')
  }
  this.hello = function(args) {
    address = args.join(' ').trim()
    if (address.length == 0) {
      show('Hello to you too')
    } else if (address == 'pgsh') {
      show('Hello human')
    } else {
      show('My name is not "' + address + '"')
    }
  }
  this.help = function(args) {
    command = args.join(' ').trim()
    if (command in self.commands) {
      show(self.commands[command].help)
    } else if (command) {
      show('No information for: ' + command)
    } else {
      var main = []
      var other = []
      for (var name in self.commands) {
        if (self.commands[name].order == 1) {
          main.push(name)
        } else {
          other.push(name)
        }
      }
      show('\nAvailable commands:\n\n' +
           '* ' + main.sort().join(' ') + '\n\n' +
           '* ' + other.sort().join(' ') + '\n\n' +
           '`help [command]` for more information.')
    }
  }
  this.ls = function(args) {
    var arg = args.join(' ').trim()
    var folder = arg || self.cwd
    var path = resolveAbsPath(folder)
    if (pathExists(path)) {
      var contents = getContents(path)
      var dstat = 'drwxr-xr-x <span style="color:#268bd2">'
      var fstat = '-rw-r--r-- '
      var items = []
      for (var item in contents) {
        var prefix = (typeof contents[item] === 'string') ? fstat : dstat
        var suffix = (typeof contents[item] === 'string') ? '' : '</span>'
        items.push(prefix + item + suffix)
      }
      items.unshift(dstat + '..</span>')
      items.unshift('total ' + items.length)
      show(items.join('\n'))
    } else {
      show("ls: " + args + ": no such directory")
    }
  }
  this.pwd = function(args) { show(self.cwd) }
  this.search = function(args) {
    if (!args.join(' ').trim()) { return show(self.commands.search.help) }
    ev.trigger('prompt_hide')
    show('Searching for "' + args.join(' ') + '" in new window...')
    setTimeout(function() {
      window.open('https://duckduckgo.com/?q=' + args.join('+'), '_blank')
      ev.trigger('prompt_show')
    }, 1000)
  }
  this.su = function(args) {
    if (self.su_active !== true) {
      self.su_active = true
      if (!self.su_warned) {
        self.su_warned = true
        show('\n\n' +
             'We trust you have received the usual lecture from the ' +
             'local System Administrator.\n' +
             'It usually boils down to these three things:\n\n' +
             '    #1) Respect the privacy of others.\n' +
             '    #2) Think before you type.\n' +
             '    #3) With great power comes great\n\n')
      }
      ev.trigger('prompt_set', getPrompt())
    }
  }
  this.version = function(args) {
    show('Parsley Gardens Shell (pgsh) 1.2.0\nBuilt with: ' +
         '<a target="_blank" href="http://riot.js.org">Riot</a> ' +
         '<a target="_blank" href="https://skeleton-framework.github.io">Skeleton</a> ' +
         '<a target="_blank" href="https://highlightjs.org">highlight.js</a>')
  }

  /**
   * Helper Functions
   */
  var show = function(text) { ev.trigger('disp_add', text) }
  var set = function(text) { ev.trigger('disp_set', text) }

  // Calculate a destination's path with respect to the current folder.
  var resolveAbsPath = function(dest) {
    var parts = dest.trim().split('/')
    var absolute = dest.substring(0, 1) == '/' || self.cwd == '/'
    var path = absolute ? [''] : self.cwd.split('/')
    parts.forEach(function(part) {
      if (part == '..' && path.length > 1) { path.pop() }
      if (part != '..' && part) { path.push(part) }
    })
    return (path.length > 1) ? path.join('/') : '/'
  }

  // Check if a path exists in the tree.
  var pathExists = function(path, isFile) {
    // Old way of defining default values, for Safari.
    var isFile = (typeof isFile !== 'undefined') ? isFile : false;
    var parts = path.trim().split('/')
    var fname = isFile ? parts.pop() : ''
    var tree = self.tree
    for (var i = 0; i < parts.length; i++) {
      var part = parts[i]
      if (!part) {
        continue
      }
      if (!(tree.hasOwnProperty(part) && typeof tree[part] === 'object')) {
        return false
      }
      tree = tree[part]
    }
    if (isFile && !(tree.hasOwnProperty(fname) && typeof tree[fname] === 'string')) {
      return false
    }
    return true
  }

  // Return the contents of a given path.
  var getContents = function(path) {
    var parts = path.trim().split('/')
    var tree = self.tree
    parts.forEach(function(part) {
      if (part) { tree = tree[part] }
    })
    // Sort JS object. Not a great way, but more compatible.
    if (typeof tree === 'object') {
      var keys = []
      for (key in tree) {
        keys.push(key)
      }
      keys.sort()
      var temp = {}
      keys.forEach(function(key) {
        temp[key] = tree[key]
      })
      tree = temp
    }
    return tree
  }

  // Complete a given file path string based on the current tree.
  var completePath = function(input, isFile) {
    // Extract file fragment and get actual path.
    var slash = input.lastIndexOf('/') + 1
    var frag = input.substring(slash)
    var base = input.substring(0, slash)
    var path = resolveAbsPath(base)
    // Complete fragments.
    if (pathExists(path)) {
      var contents = getContents(path)
      var found = ''
      for (var name in contents) {
        if (!isFile && typeof contents[name] === 'string') { continue }
        if (!frag) { found = name; break }
        if (name.indexOf(frag) == 0) { found = name; break }
      }
      var end = (typeof contents[found] === 'object') ? '/' : ''
      return base + found + end
    }
    return ''
  }
}