import csv
import os
from .lockfile import Lockfile
from .utils import identity


class CsvTable:
    def __init__(self, path, schema: list):
        """A generic CSV table of data, and basic I/O operations.

        The first column should be unique. If so, it can be used to index rows, a feature of
        method `_find`.

        Arguments:
        - path      | file path for table.
        - schema    | list of dicts, each for a datum field (column).
                    | each dict contains the following keys:
                    | "name": what the column will be called in the dict that `_read` returns.
                    | "serializer": function to be applied to the datum when being written.
                    | "deserializer": same as above except it is when datum is being read.
                    | the latter two are optional, and when they are not specified, the default is
                    | the identity function, i.e. f such that f(x) = x for any x.
        """
        self.path = path
        for col in schema:
            for func in ("serializer", "deserializer"):
                if func not in col or col[func] is None:
                    col[func] = identity

        # schema: column number -> name and (de)serialization functions
        # reverse_schema: name -> column number
        self.schema = schema
        self.reverse_schema = {schema[i]["name"]: i for i in range(len(schema))}
        self.lockfile = Lockfile(self.path)
        # Create file if it does not yet exist
        try:
            f = open(self.path, "x")
            f.close()
        except FileExistsError:
            pass

    def _read(self) -> list:
        """Deserialize table."""
        with open(self.path) as f:
            reader = csv.reader(f)
            rows = []
            # `rows` is a list of 2-tuples
            for row in reader:
                # for each tuple (k, v) in `rows`,
                # it will be unzipped into a dict key-value pair
                rows.append(
                    dict(
                        [
                            (sch["name"], sch["deserializer"](datum))
                            for sch, datum in zip(self.schema, row)
                        ]
                    )
                )
            f.close()
            return rows

    def _write(self, rows: list) -> None:
        """Serialize table. When a failure occurs, abort and recover data."""
        # make backup in memory
        with open(self.path) as f:
            backup = f.read()
            f.close()

        self.lockfile.lock()

        f = open(self.path, "w")
        try:
            writer = csv.writer(f)
            for row in rows:
                writer.writerow([row[col["name"]] for col in self.schema])
        except Exception as e:
            # failure occurred on write
            # abort write, and write back contents as they were before
            # TODO: keep log
            f.close()
            f = open(self.path, "w")
            f.write(backup)
            raise e
        finally:
            f.close()

        self.lockfile.unlock()

    def _append(self, row) -> list:
        """Append one row, and return the entire updated table."""
        rows = self._read()
        rows.append(row)
        self._write(rows)
        return rows

    def _update(self, update: dict) -> list:
        """Update one row, and return the entire updated table."""
        rows = self._read()
        index_column = self.schema[0]["name"]
        for idx, row in enumerate(rows):
            if row[index_column] == update[index_column]:
                rows[idx] = update
                self._write(rows)
                return rows