import xml.etree.ElementTree as ElementTree

from SpiffWorkflow.bpmn.BpmnScriptEngine import BpmnScriptEngine
from SpiffWorkflow.bpmn.serializer.CompactWorkflowSerializer import CompactWorkflowSerializer
from SpiffWorkflow.bpmn.workflow import BpmnWorkflow
from SpiffWorkflow.camunda.parser.CamundaParser import CamundaParser

from crc import db
from crc.models.file import FileDataModel, FileModel
from crc.models.workflow import WorkflowStatus


class CustomBpmnScriptEngine(BpmnScriptEngine):
    """This is a custom script processor that can be easily injected into Spiff Workflow.
    Rather than execute arbitrary code, this assumes the script references a fully qualified python class
    such as myapp.RandomFact. """

    def execute(self, task, script, **kwargs):
        """
        Assume that the script read in from the BPMN file is a fully qualified python class. Instantiate
        that class, pass in any data available to the current task so that it might act on it.
        Assume that the class implements the "do_task" method.

        This allows us to reference custom code from the BPMN diagram.
        """
        module_name = "crc." + script
        class_name = module_name.split(".")[-1]
        mod = __import__(module_name, fromlist=[class_name])
        klass = getattr(mod, class_name)
        klass().do_task(task.data)


class WorkflowProcessor:

    _script_engine = CustomBpmnScriptEngine()
    _serializer = CompactWorkflowSerializer()

    def __init__(self, workflow_spec_id, bpmn_json):
        self.bpmn_workflow = self._serializer.deserialize_workflow(bpmn_json, self.get_spec(workflow_spec_id))
        self.bpmn_workflow.script_engine = self._script_engine

    @staticmethod
    def get_spec(workflow_spec_id):
        file_data_models = db.session.query(FileDataModel) \
            .join(FileModel) \
            .filter(FileModel.workflow_spec_id == workflow_spec_id).all()
        parser = CamundaParser()
        for file_data in file_data_models:
            bpmn = ElementTree.fromstring(file_data.data)
            process_id = WorkflowProcessor.__get_process_id(bpmn)
            parser.add_bpmn_xml(bpmn, filename=file_data.file_model.name)
        return parser.get_spec(process_id)

    @classmethod
    def create(cls, workflow_spec_id):
        parser = CamundaParser()
        spec = WorkflowProcessor.get_spec(workflow_spec_id)

        bpmn_workflow = BpmnWorkflow(spec, script_engine=cls._script_engine)
        bpmn_workflow.do_engine_steps()
        json = cls._serializer.serialize_workflow(bpmn_workflow)
        processor = cls(workflow_spec_id, json)
        return processor

    def get_status(self):
        if self.bpmn_workflow.is_completed():
            return WorkflowStatus.complete
        user_tasks = self.bpmn_workflow.get_ready_user_tasks()
        if len(user_tasks) > 0:
            return WorkflowStatus.user_input_required
        else:
            return WorkflowStatus.waiting

    def do_engine_steps(self):
        self.bpmn_workflow.do_engine_steps()

    def serialize(self):
        return self._serializer.serialize_workflow(self.bpmn_workflow)

    def next_user_tasks(self):
        return self.bpmn_workflow.get_ready_user_tasks()

    def complete_task(self, task):
        self.bpmn_workflow.complete_task_from_id(task.id)

    def get_data(self):
        return self.bpmn_workflow.data

    def get_ready_user_tasks(self):
        return self.bpmn_workflow.get_ready_user_tasks()


    @staticmethod
    def __get_process_id(et_root):
        process_elements = []
        for child in et_root:
            if child.tag.endswith('process') and child.attrib.get('isExecutable', False):
                process_elements.append(child)

        if len(process_elements) == 0:
            raise Exception('No executable process tag found')

        if len(process_elements) > 1:
            raise Exception('Multiple executable processes tags found')

        return process_elements[0].attrib['id']