import os
import sys

from MiscUtils.PropertiesObject import PropertiesObject


class PlugInError(Exception):
    """Plug-in error."""


class PlugIn(object):
    """Template for Webware Plug-ins.

    A plug-in is a software component that is loaded by WebKit in order to
    provide additional WebKit functionality without necessarily having to modify
    WebKit's source. The most infamous plug-in is PSP (Python Server Pages)
    which ships with Webware.

    Plug-ins often provide additional servlet factories, servlet subclasses,
    examples and documentation. Ultimately, it is the plug-in author's choice
    as to what to provide and in what manner.

    Instances of this class represent plug-ins which are ultimately Python
    packages (see the Python Tutorial, 6.4: "Packages" at
    http://docs.python.org/tut/node8.html#SECTION008400000000000000000).

    A plug-in must also be a Webware component which means that it will have
    a Properties.py file advertising its name, version, requirements, etc.
    You can ask a plug-in for its properties().

    The plug-in/package must have an __init__.py while must contain a function:
        def InstallInWebKit(appServer):
    This function is invoked to take whatever actions are needed to plug the
    new component into WebKit. See PSP for an example.

    If you ask an AppServer for its plugIns(), you will get a list of instances
    of this class.

    The path of the plug-in is added to sys.path, if it's not already there.
    This is convenient, but we may need a more sophisticated solution in the
    future to avoid name collisions between plug-ins.

    Note that this class is hardly ever subclassed. The software in the
    plug-in package is what provides new functionality and there is currently
    no way to tell AppServer to use custom subclasses of this class on a
    case-by-case basis (and so far there is currently no need).

    Instructions for invoking:
        p = PlugIn(self, '../Foo')  # 'self' is typically AppServer. It gets passed to InstallInWebKit()
        willNotLoadReason = plugIn.load()
        if willNotLoadReason:
            print '    Plug-in %s cannot be loaded because:\n    %s' % (path, willNotLoadReason)
            return None
        p.install()
        # Note that load() and install() could raise exceptions. You should expect this.
    """


    ## Init, load and install ##

    def __init__(self, appServer, path):
        """Initializes the plug-in with basic information.

        This lightweight constructor does not access the file system.
        """
        self._appServer = appServer
        self._path = path
        self._dir, self._name = os.path.split(path)
        self._cacheDir = os.path.join(
            self._appServer.application()._cacheDir, self._name)
        self._ver = '(unknown)'
        self._docs = self._docContext = None
        self._examplePages = self._examplePagesContext = None

    def load(self):
        """Loads the plug-in into memory, but does not yet install it.

        Will return None on success, otherwise a message (string) that says
        why the plug-in could not be loaded.
        """
        print 'Loading plug-in: %s at %s' % (self._name, self._path)

        assert os.path.exists(self._path)

        # Grab the Properties.py
        self._properties = PropertiesObject(self.serverSidePath('Properties.py'))
        if not self._properties['willRun']:
            return self._properties['willNotRunReason']

        # Update sys.path
        if not self._dir in sys.path:
            sys.path.append(self._dir)

        # Import the package
        self._module = __import__(self._name, globals(), [], [])

        # Inspect it and verify some required conventions
        if not hasattr(self._module, 'InstallInWebKit'):
            raise PlugInError(
                "Plug-in '%s' in '%s' has no InstallInWebKit() function."
                % (self._name, self._dir))

        # Give the module a pointer back to us
        setattr(self._module, 'plugIn', self)

        # Make a subdirectory for it in the Cache directory:
        if not os.path.exists(self._cacheDir):
            os.mkdir(self._cacheDir)

        self.setUpDocContext()
        self.setUpExamplePages()

    def setUpDocContext(self):
        """Add a context for the documentation."""
        app = self._appServer.application()
        if app.hasContext('Docs'):
            self._docs = self._properties.get('docs') or None
            if self.hasDocs():
                docsPath = self.serverSidePath('Docs')
                assert os.path.exists(docsPath), (
                    'Plug-in %s says it has documentation, '
                    'but there is no Docs/ subdir.' % self._name)
                if os.path.exists(os.path.join(docsPath, '__init__.py')):
                    ctxName = self._name + '/Docs'
                    if not app.hasContext(ctxName):
                        app.addContext(ctxName, docsPath)
                    self._docContext = ctxName
                else:
                    print ('Cannot create Docs context for plug-in %s'
                        ' (no __init__.py found).' % self._name)

    def setUpExamplePages(self):
        """Add a context for the examples."""
        app = self._appServer.application()
        if app.hasContext('Examples'):
            config = self._properties.get('WebKitConfig', {})
            self._examplePages = config.get('examplePages') or None
            if self.hasExamplePages():
                examplesPath = self.serverSidePath('Examples')
                assert os.path.exists(examplesPath), (
                    'Plug-in %s says it has example pages, '
                    'but there is no Examples/ subdir.' % self._name)
                if os.path.exists(os.path.join(examplesPath, '__init__.py')):
                    ctxName = self._name + '/Examples'
                    if not app.hasContext(ctxName):
                        app.addContext(ctxName, examplesPath)
                    self._examplePagesContext = ctxName
                else:
                    print ('Cannot create Examples context for plug-in %s'
                        ' (no __init__.py found).' % self._name)

    def docs(self):
        return self._docs

    def hasDocs(self):
        return self._docs is not None

    def docsContext(self):
        return self._docsContext

    def examplePages(self):
        return self._examplePages

    def hasExamplePages(self):
        return self._examplePages is not None

    def examplePagesContext(self):
        return self._examplePagesContext

    def install(self):
        """Install plug-in by invoking its required InstallInWebKit function."""
        self._module.InstallInWebKit(self._appServer)


    ## Access ##

    def name(self):
        """Return the name of the plug-in. Example: 'Foo'"""
        return self._name

    def directory(self):
        """Return the directory in which the plug-in resides. Example: '..'"""
        return self._dir

    def path(self):
        """Return the full path of the plug-in. Example: '../Foo'"""
        return self._path

    def serverSidePath(self, path=None):
        if path:
            return os.path.normpath(os.path.join(self._path, path))
        else:
            return self._path

    def module(self):
        """Return the Python module object of the plug-in."""
        return self._module

    def properties(self):
        """Return the properties.

        This is a dictionary-like object, of the plug-in which comes
        from its Properties.py file. See MiscUtils.PropertiesObject.py.
        """
        return self._properties
