import csv
import datetime
import decimal
import io
import logging
import typing
import urllib.parse
from collections.abc import Callable, Iterable, Mapping, Sequence
from decimal import Decimal
from pathlib import Path

from frozendict import frozendict

from . import data

logger = logging.getLogger(__name__)

CSV_DIALECT = 'one_true_dialect'
csv.register_dialect(CSV_DIALECT, lineterminator='\n', skipinitialspace=True)

T = typing.TypeVar('T')


def try_value(fn: Callable[[str], T], s: str) -> T | None:
    try:
        return fn(s)
    except (ValueError, decimal.InvalidOperation):
        return None


def csv_str_to_value(
    s: str,
) -> (
    str
    | Decimal
    | datetime.date
    | datetime.datetime
    | urllib.parse.ParseResult
    | bool
    | None
):
    s = s.strip()
    if len(s) == 0:
        return None
    if (v_decimal := try_value(Decimal, s)) is not None:
        return v_decimal
    if (v_date := try_value(datetime.date.fromisoformat, s)) is not None:
        return v_date
    if (v_datetime := try_value(datetime.datetime.fromisoformat, s)) is not None:
        return v_datetime
    if s.startswith(('http://', 'https://')):
        return urllib.parse.urlparse(s)
    if s.lower() == 'false':
        return False
    if s.lower() == 'true':
        return True
    if s.lower() == 'none':
        return None
    return s


def csv_safe_value(v: object) -> str:
    if isinstance(v, urllib.parse.ParseResult):
        return v.geturl()
    if isinstance(v, datetime.datetime):
        assert v.tzinfo is not None, v
    return str(v)


def equals_without_fields(
    a: Mapping[str, object],
    b: Mapping[str, object],
    fields: Iterable[str] = frozenset(),
) -> bool:
    a = dict(a)
    b = dict(b)

    for f in fields:
        del a[f], b[f]

    return frozendict(a) == frozendict(b)


def deduplicate_by_ignoring_certain_fields(
    dicts: list[dict],
    deduplicate_ignore_columns: Iterable[str],
) -> list[dict]:
    """Removes duplicates that occur when ignoring certain columns.

    Output order is stable.
    """
    to_remove = set()
    for idx1, first in enumerate(dicts):
        for idx2, second in enumerate(dicts[idx1 + 1 :], idx1 + 1):
            if equals_without_fields(first, second, deduplicate_ignore_columns):
                to_remove.add(idx2)
            del idx2, second
        del idx1, first

    to_remove = sorted(to_remove)
    while to_remove:
        del dicts[to_remove.pop()]

    return dicts


def deduplicate_dicts(
    dicts: Sequence[dict[str,typing.Any] | frozendict[str,typing.Any]],
    deduplicate_mode: data.DeduplicateMode,
    deduplicate_ignore_columns: list[str],
) -> tuple[Sequence[dict[str,typing.Any]], list[str]]:
    assert isinstance(deduplicate_ignore_columns, list), deduplicate_ignore_columns

    fieldnames = []
    for d in dicts:
        for k in d.keys():
            if k not in fieldnames:
                fieldnames.append(k)
            del k
        del d

    if deduplicate_mode == data.DeduplicateMode.ONLY_LATEST:
        while len(dicts) >= 2 and equals_without_fields(
            dicts[-1],
            dicts[-2],
            deduplicate_ignore_columns,
        ):
            del dicts[-1]
    elif deduplicate_mode == data.DeduplicateMode.BY_ALL_COLUMNS:
        dicts = deduplicate_by_ignoring_certain_fields(
            dicts,
            deduplicate_ignore_columns,
        )
    elif deduplicate_mode != data.DeduplicateMode.NONE:
        dicts = set(dicts)

    dicts = sorted(dicts, key=lambda d: tuple(str(d.get(fn, '')) for fn in fieldnames))
    return dicts, fieldnames


def normalize_dict(d: dict[str,typing.Any]) -> frozendict[str,typing.Any]:
    return frozendict(
        {k: csv_str_to_value(str(v)) for k, v in d.items() if csv_str_to_value(str(v)) is not None},
    )


def load_csv_file(csv_file: Path) -> list[frozendict]:
    dicts: list[frozendict] = []
    with open(csv_file) as csvfile:
        reader = csv.DictReader(csvfile, dialect=CSV_DIALECT)
        for row in reader:
            for k in list(row.keys()):
                orig = row[k]
                row[k] = csv_str_to_value(orig)
                if row[k] is None:
                    del row[k]
                del k, orig
            dicts.append(frozendict(row))
            del row
        del csvfile
    return dicts


def extend_csv_file(
    csv_file: Path,
    new_dicts: list[dict],
    deduplicate_mode: data.DeduplicateMode,
    deduplicate_ignore_columns: list[str],
) -> dict:
    assert isinstance(deduplicate_ignore_columns, list), deduplicate_ignore_columns

    try:
        dicts = load_csv_file(csv_file)
    except FileNotFoundError as e:
        logger.info('Creating file: %s', csv_file)
        dicts = []

    original_num_dicts = len(dicts)
    dicts += [normalize_dict(d) for d in new_dicts]
    del new_dicts

    dicts, fieldnames = deduplicate_dicts(
        dicts,
        deduplicate_mode,
        deduplicate_ignore_columns,
    )

    csvfile_in_memory = io.StringIO()
    writer = csv.DictWriter(
        csvfile_in_memory,
        fieldnames=fieldnames,
        dialect=CSV_DIALECT,
    )
    writer.writeheader()
    for d in dicts:
        writable_d = {k:csv_safe_value(v) for k,v in d.items()}
        writer.writerow(writable_d)
        del d, writable_d
    output_csv = csvfile_in_memory.getvalue()
    del writer, csvfile_in_memory

    csv_file.parent.mkdir(parents=True, exist_ok=True)
    with open(csv_file, 'w') as csvfile:
        csvfile.write(output_csv)
        del csvfile
    logger.info(
        'Extended CSV "%s" from %d to %d lines',
        csv_file,
        original_num_dicts,
        len(dicts),
    )

    return {
        'extended': original_num_dicts != len(dicts),
        'input_lines': original_num_dicts,
        'output_lines': len(dicts),
        'dicts': dicts,
    }