from datetime import datetime

from sqlalchemy import desc

from crc import db, session
from crc.api.common import ApiError

from crc.models.approval import ApprovalModel, ApprovalStatus, ApprovalFile, Approval
from crc.models.study import StudyModel
from crc.models.workflow import WorkflowModel
from crc.services.file_service import FileService


class ApprovalService(object):
    """Provides common tools for working with an Approval"""

    @staticmethod
    def __one_approval_from_study(study, approver_uid = None):
        """Returns one approval, with all additional approvals as 'related_approvals',
        the main approval can be pinned to an approver with an optional argument.
        Will return null if no approvals exist on the study."""
        main_approval = None
        related_approvals = []
        approvals = db.session.query(ApprovalModel).filter(ApprovalModel.study_id == study.id).all()
        for approval_model in approvals:
            if approval_model.approver_uid == approver_uid:
                main_approval = Approval.from_model(approval_model)
            else:
                related_approvals.append(Approval.from_model(approval_model))
        if not main_approval and len(related_approvals) > 0:
            main_approval = related_approvals[0]
            related_approvals = related_approvals[1:]
        if len(related_approvals) > 0:
            main_approval.related_approvals = related_approvals
        return main_approval

    @staticmethod
    def get_approvals_per_user(approver_uid):
        """Returns a list of approval objects (not db models) for the given
         approver. """
        studies = db.session.query(StudyModel).join(ApprovalModel).\
            filter(ApprovalModel.approver_uid == approver_uid).all()
        approvals = []
        for study in studies:
            approval = ApprovalService.__one_approval_from_study(study, approver_uid)
            if approval:
                approvals.append(approval)
        return approvals

    @staticmethod
    def get_all_approvals():
        """Returns a list of all approval objects (not db models), one record
        per study, with any associated approvals grouped under the first approval."""
        studies = db.session.query(StudyModel).all()
        approvals = []
        for study in studies:
            approval = ApprovalService.__one_approval_from_study(study)
            if approval:
                approvals.append(approval)
        return approvals

    @staticmethod
    def get_approvals_for_study(study_id):
        """Returns an array of Approval objects for the study, it does not
         compute the related approvals."""
        db_approvals = session.query(ApprovalModel).filter_by(study_id=study_id).all()
        return [Approval.from_model(approval_model) for approval_model in db_approvals]


    @staticmethod
    def update_approval(approval_id, approver_uid, status):
        """Update a specific approval"""
        db_approval = session.query(ApprovalModel).get(approval_id)
        if db_approval:
            db_approval.status = status
            session.add(db_approval)
            session.commit()
        # TODO: Log update action by approver_uid - maybe ?
        return db_approval

    @staticmethod
    def add_approval(study_id, workflow_id, approver_uid):
        """we might have multiple approvals for a workflow, so I would expect this
            method to get called multiple times for the same workflow.  This will
            only add a new approval if no approval already exists for the approver_uid,
            unless the workflow has changed, at which point, it will CANCEL any
            pending approvals and create a new approval for the latest version
            of the workflow."""

        # Find any existing approvals for this workflow and approver.
        latest_approval_request = db.session.query(ApprovalModel). \
            filter(ApprovalModel.workflow_id == workflow_id). \
            filter(ApprovalModel.approver_uid == approver_uid). \
            order_by(desc(ApprovalModel.version)).first()

        # Construct as hash of the latest files to see if things have changed since
        # the last approval.
        workflow = db.session.query(WorkflowModel).filter(WorkflowModel.id == workflow_id).first()
        workflow_data_files = FileService.get_workflow_data_files(workflow_id)
        current_data_file_ids = list(data_file.id for data_file in workflow_data_files)

        if len(current_data_file_ids) == 0:
            raise ApiError("invalid_workflow_approval", "You can't create an approval for a workflow that has"
                                                        "no files to approve in it.")

        # If an existing approval request exists and no changes were made, do nothing.
        # If there is an existing approval request for a previous version of the workflow
        # then add a new request, and cancel any waiting/pending requests.
        if latest_approval_request:
            request_file_ids = list(file.file_data_id for file in latest_approval_request.approval_files)
            current_data_file_ids.sort()
            request_file_ids.sort()
            if current_data_file_ids == request_file_ids:
                return  # This approval already exists.
            else:
                latest_approval_request.status = ApprovalStatus.CANCELED.value
                db.session.add(latest_approval_request)
                version = latest_approval_request.version + 1
        else:
            version = 1

        model = ApprovalModel(study_id=study_id, workflow_id=workflow_id,
                              approver_uid=approver_uid, status=ApprovalStatus.PENDING.value,
                              message="", date_created=datetime.now(),
                              version=version)
        approval_files = ApprovalService._create_approval_files(workflow_data_files, model)
        db.session.add(model)
        db.session.add_all(approval_files)
        db.session.commit()

    @staticmethod
    def _create_approval_files(workflow_data_files, approval):
        """Currently based exclusively on the status of files associated with a workflow."""
        file_approval_models = []
        for file_data in workflow_data_files:
            file_approval_models.append(ApprovalFile(file_data_id=file_data.id,
                                                     approval=approval))
        return file_approval_models