import requests
import json


class JForm:
    """Retrieves results from one jForm questionnaire.

    In this context, "JForm" refers to this class, and "jForm", the online service also known as
    SJTU Questionnaires, hosted on https://wj.sjtu.edu.cn/.

    JImbrella's database relies on JForm to sync its database against jForm's.

    Each JForm object requires a checkpoint file in which to store the id of the latest answer
    sheet it has read. Each time the API detects the presence of new answer sheets, the file will
    be overwritten.
    """

    def __init__(self, name: str, url: str, checkpoint_fp: str):
        self._name = name  # internal identifier
        self.url = url
        self._checkpoint_fp = checkpoint_fp

    def _get(self, page=1) -> dict:
        """Internal method to HTTP GET the API in JSON format."""
        resp = requests.get(
            self.url,
            params={
                "params": json.dumps(
                    {
                        "current": page,
                        "pageSize": 100,
                    }
                ),
                "sort": json.dumps({"id": "desc"}),
            },
        )
        return resp

    def _read_checkpoint(self) -> int:
        """Read checkpoint file and returns contents. No safeguards."""
        try:
            with open(self._checkpoint_fp) as f:
                checkpoint = f.read()
                f.close()
                return int(checkpoint)
        except FileNotFoundError:
            return 0

    def _write_checkpoint(self, checkpoint: int) -> None:
        """Write into checkpoint file."""
        try:
            with open(self._checkpoint_fp, "x") as f:
                f.write(str(checkpoint))
                f.close()
        except FileExistsError:
            with open(self._checkpoint_fp, "w") as f:
                f.write(str(checkpoint))
                f.close()

    def get_unread(self) -> list:
        """Get unread answers to required fields as a list of dicts, most recent last."""
        checkpoint = self._read_checkpoint()
        unread = []
        latest_id = 0
        page = 1
        found_read = False
        while not found_read:
            try:
                resp = self._get(page=page)
            except:
                break  # quietly abort
            if resp.status_code != 200:
                break

            sheets = resp.json()["data"]["rows"]
            if not latest_id:
                # the first page of sheets we have retrieved this run.
                # on this page, the first answer sheet is the latest.
                # update checkpoint. next time, stop before this id.
                latest_id = sheets[0]["id"]
                self._write_checkpoint(latest_id)

            if not sheets:
                # somehow jForm doesn't respond with a 404
                # when we exceed the total pages of a questionnaire
                # instead it just returns 200 along with an empty data field
                break
            for sheet in sheets:
                if sheet["id"] <= checkpoint:
                    # is checkpoint or earlier than checkpoint
                    found_read = True
                    break
                ans = sheet["answers"]
                unread.append(
                    {
                        "name": ans[0]["answer"],
                        "id": ans[1]["answer"],
                        "phone": ans[2]["answer"],
                        "key": ans[3]["answer"],
                    }
                )
            page += 1

        return unread