"""
This file contains POST routes methods.
"""
import bottle
import json
from sqlalchemy.exc import IntegrityError

import database
import tools
from reference_fetcher import arxiv


def create_paper(db):
    """
    Create a new resource identified by its DOI or arXiv eprint id.

    .. code-block:: bash

        POST /papers
        Content-Type: application/vnd.api+json
        Accept: application/vnd.api+json

        {
            "data": {
                "doi": "10.1126/science.1252319",
                // OR
                "arxiv_id": "1401.2910"
            }
        }


    .. code-block:: json

        {
            "data": {
                {
                    "type": "papers",
                    "id": 1,
                    "attributes": {
                        "doi": "10.1126/science.1252319",
                        "arxiv_id": "1401.2910"
                    },
                    "links": {
                        "self": "/papers/1"
                    },
                    "relationships": {
                        TODO
                    }
                }
            }
        }

    :param db: A database session, injected by the ``Bottle`` plugin.
    :returns: An ``HTTPResponse``.
    """
    data = json.loads(bottle.request.body.read().decode("utf-8"))
    # Validate the request
    if("data" not in data or
       "type" not in data["data"] or
       data["data"]["type"] != "papers" or
       ("doi" not in data["data"] and "arxiv_id" not in data["data"])):
        return bottle.HTTPError(403, "Forbidden")

    data = data["data"]

    if "doi" in data:
        paper = create_by_doi(data["doi"], db)
    elif "arxiv_id" in data:
        paper = create_by_arxiv(data["arxiv"], db)

    if paper is None:
        return bottle.HTTPError(409, "Conflict")

    # Return the resource
    response = {
        "data": paper.json_api_repr()
    }
    # TODO: Return a 202 as the resource has been accepted but is not yet
    # processed, especially since its relationships have not yet been fetched.
    headers = {"Location": "/papers/%d" % (paper.id,)}
    return tools.APIResponse(status=202,
                             body=tools.pretty_json(response),
                             headers=headers)


def create_by_doi(doi, db):
    """
    Create a new resource identified by its DOI, if it does not exist.

    :param doi: The DOI of the paper.
    :param db: A database session.
    :returns: ``None`` if insertion failed, the ``Paper`` object otherwise.
    """
    paper = database.Paper(doi=doi)

    # Try to fetch an arXiv id
    arxiv_id = arxiv.get_arxiv_eprint_from_doi(doi)
    if arxiv_id:
        paper.arxiv_id = arxiv_id

    # Add it to the database
    try:
        db.add(paper)
        db.flush()
    except IntegrityError:
        # Unique constraint violation, paper already exists
        db.rollback()
        return None

    # Return the paper
    return paper


def create_by_arxiv(arxiv, db):
    """
    Create a new resource identified by its arXiv eprint ID, if it does not
    exist.

    :param arxiv: The arXiv eprint ID.
    :param db: A database session.
    :returns: ``None`` if insertion failed, the ``Paper`` object otherwise.
    """
    paper = database.Paper(arxiv_id=arxiv)

    # Try to fetch an arXiv id
    doi = arxiv.get_doi(arxiv)
    if doi:
        paper.doi = doi

    # Add it to the database
    try:
        db.add(paper)
        db.flush()
    except IntegrityError:
        # Unique constraint violation, paper already exists
        db.rollback()
        return None

    # Return the paper
    return paper


def update_relationships(id, name, db):
    """
    Update the relationships associated to a given paper.

    :param id: The id of the paper to update relationships.
    :param name: The name of the relationship to update.
    :param db: A database session, passed by Bottle plugin.
    :returns: No content. 204 on success, 403 on error.
    """
    data = json.loads(bottle.request.body.read().decode("utf-8"))
    # Validate the request
    if "data" not in data:
        return bottle.HTTPError(403, "Forbidden")
    # Filter data, invalid entries are ignored
    data = [i for i in data["data"]
            if "type" in i and i["type"] == name and "id" in i]
    # Complete replacement (data == []) is forbidden
    if len(data) == 0:
        return bottle.HTTPError(403, "Forbidden")
    # Update all the relationships
    for i in data:
        updated = update_relationship_backend(id, i["id"], name, db)
        if updated is None:
            # An error occurred => 403
            return bottle.HTTPError(403, "Forbidden")
    # Return an empty 204 on success
    return tools.APIResponse(status=204, body="")


def update_relationship_backend(left_id, right_id, name, db):
    """
    Backend method to update a single relationship between two papers.

    :param left_id: ID of the paper on the left of the relationship.
    :param right_id: ID of the paper on the right of the relationship.
    :param name: Name of the relationship between the two papers.
    :param db: A database session.
    :returns: The updated left paper on success, ``None`` otherwise.
    """
    # Load necessary resources
    left_paper = db.query(database.Paper).filter_by(id=left_id).first()
    right_paper = db.query(database.Paper).filter_by(id=right_id).first()
    if left_paper is None or right_paper is None:
        # Abort
        return None
    relationship = db.query(database.Relationship).filter_by(name=name).first()
    if relationship is None:
        relationship = database.Relationship(name=name)
        db.add(relationship)
        db.flush()
    # Update the relationship
    a = database.Association(relationship_id=relationship.id)
    a.right_paper = right_paper
    left_paper.related.append(a)
    try:
        db.add(a)
        db.add(left_paper)
    except IntegrityError:
        # Unique constraint violation, relationship already exists
        db.rollback()
        return None
    return left_paper