assert = require 'assert'
fs     = require 'fs'
path   = require 'path'
vm     = require 'vm'
Module = require 'module'


# Loader injects several hooks into the standard Module loader so that conventions can specify their
# custom behavior.
#
# It focuses entirely on sandboxed module loads to promote best practices, and to reduce complexity.
class Loader extends Module
  constructor: (componentName, autorequireParent, convention) ->
    super componentName

    @convention        = convention
    @autorequireParent = autorequireParent

  # Load a module and return its exports.
  @loadModule: (componentName, modulePath, autorequireParent, convention) ->
    loader = new this(componentName, autorequireParent, convention)
    loader.load(modulePath)

    loader.exports

  # Unfortunately, Node's
  # [`Module prototype`](https://github.com/joyent/node/blob/master/lib/module.js) doesn't break
  # `_compile` into meaningful chunks, so we're stuck re-implementing parts of it in order to inject
  # our hooks.
  #
  # Our re-implementation stops at the end of the sandboxed module section of `_compile` - right at
  # the end of the `if (Module._contextLoad)` conditional in the Node source.
  _compile: (content, filename) ->
    throw new Error 'Compiling a root module is not supported by autorequire.' if @id == '.'

    content = @_cleanContent content
    sandbox = @_buildSandbox filename

    sandbox = @convention.modifySandbox sandbox, this if @convention.modifySandbox
    content = @convention.modifySource  content, this if @convention.modifySource

    vm.runInContext content, sandbox, filename, true

    @sandbox = sandbox
    @exports = @convention.modifyExports @exports, this if @convention.modifyExports

  # ## Compatibility Helpers

  # Overrides the built in load so that we can perform extension-specific behavior.
  #
  # Any extension handlers specified via `_extensions` will override those defined on
  # `require.extensions`.
  load: (filename) ->
    assert.ok not @loaded

    @filename = filename
    @paths    = Module._nodeModulePaths path.dirname filename

    extension = path.extname filename
    extension = '.js' if not Module._extensions[extension]

    (@_extensions[extension] || Module._extensions[extension])(this, filename)

    @loaded = true

  # ## Extension Specific Helpers

  _extensions:
    # We want to load coffeescript sources without its scope wrapper - we're already evaluating them
    # within a sandboxed context, so they won't leak into the global context.
    #
    # This allows conventions to defined properties out of the module's global context w/o having to
    # resort to module.exports.
    '.coffee': (module, filename) ->
      content = require('coffee-script').compile fs.readFileSync(filename, 'utf8'),
        filename: filename, bare: true
      module._compile content, filename

version = (parseInt(v) for v in process.version.match(/v(\d+)\.(\d+)\.(\d+)/)[1..3])

# Include behavior appropriate for the current version of Node.
behavior =
  if      version[1] == 8 and version[2] >= 0  then require './loader_behavior/v0.6.10'
  else if version[1] == 7 and version[2] >= 2  then require './loader_behavior/v0.6.10'
  else if version[1] == 7 and version[2] >= 0  then require './loader_behavior/v0.5.2'
  else if version[1] == 6 and version[2] >= 10 then require './loader_behavior/v0.6.10'
  else if version[1] == 6 and version[2] >= 0  then require './loader_behavior/v0.5.2'
  else if version[1] == 5 and version[2] >= 2  then require './loader_behavior/v0.5.2'
  else if version[1] == 5 and version[2] >= 1  then require './loader_behavior/v0.5.1'
  else if version[1] == 5 and version[2] >= 0  then require './loader_behavior/v0.4.0'
  else if version[1] == 4 and version[2] >= 0  then require './loader_behavior/v0.4.0'
  else throw new Error "No autorequire.Loader behavior defined for node #{process.version}"

for k, v of behavior
  Loader::[k] = v

module.exports = Loader