
r"""
CSV parsing and writing.

This module provides classes that assist in the reading and writing
of Comma Separated Value (CSV) files, and implements the interface
described by PEP 305.  Although many CSV files are simple to parse,
the format is not formally defined by a stable specification and
is subtle enough that parsing lines of a CSV file with something
like line.split(",") is bound to fail.  The module supports three
basic APIs: reading, writing, and registration of dialects.


DIALECT REGISTRATION:

Readers and writers support a dialect argument, which is a convenient
handle on a group of settings.  When the dialect argument is a string,
it identifies one of the dialects previously registered with the module.
If it is a class or instance, the attributes of the argument are used as
the settings for the reader or writer:

    class excel:
        delimiter = ','
        quotechar = '"'
        escapechar = None
        doublequote = True
        skipinitialspace = False
        lineterminator = '\r\n'
        quoting = QUOTE_MINIMAL

SETTINGS:

    * quotechar - specifies a one-character string to use as the
        quoting character.  It defaults to '"'.
    * delimiter - specifies a one-character string to use as the
        field separator.  It defaults to ','.
    * skipinitialspace - specifies how to interpret spaces which
        immediately follow a delimiter.  It defaults to False, which
        means that spaces immediately following a delimiter is part
        of the following field.
    * lineterminator - specifies the character sequence which should
        terminate rows.
    * quoting - controls when quotes should be generated by the writer.
        It can take on any of the following module constants:

        csv.QUOTE_MINIMAL means only when required, for example, when a
            field contains either the quotechar or the delimiter
        csv.QUOTE_ALL means that quotes are always placed around fields.
        csv.QUOTE_NONNUMERIC means that quotes are always placed around
            fields which do not parse as integers or floating-point
            numbers.
        csv.QUOTE_STRINGS means that quotes are always placed around
            fields which are strings.  Note that the Python value None
            is not a string.
        csv.QUOTE_NOTNULL means that quotes are only placed around fields
            that are not the Python value None.
        csv.QUOTE_NONE means that quotes are never placed around fields.
    * escapechar - specifies a one-character string used to escape
        the delimiter when quoting is set to QUOTE_NONE.
    * doublequote - controls the handling of quotes inside fields.  When
        True, two consecutive quotes are interpreted as one during read,
        and when writing, each quote character embedded in the data is
        written as two quotes
"""

import types
from _csv import Error, writer, reader, register_dialect, \
                 unregister_dialect, get_dialect, list_dialects, \
                 field_size_limit, \
                 QUOTE_MINIMAL, QUOTE_ALL, QUOTE_NONNUMERIC, QUOTE_NONE, \
                 QUOTE_STRINGS, QUOTE_NOTNULL
from _csv import Dialect as _Dialect

from io import StringIO

__all__ = ["QUOTE_MINIMAL", "QUOTE_ALL", "QUOTE_NONNUMERIC", "QUOTE_NONE",
           "QUOTE_STRINGS", "QUOTE_NOTNULL",
           "Error", "Dialect", "excel", "excel_tab",
           "field_size_limit", "reader", "writer",
           "register_dialect", "get_dialect", "list_dialects", "Sniffer",
           "unregister_dialect", "DictReader", "DictWriter",
           "unix_dialect"]


_dialect_attributes = frozenset({
    'delimiter', 'quotechar', 'escapechar', 'doublequote',
    'skipinitialspace', 'lineterminator', 'quoting', 'strict',
})

class Dialect:
    """Describe a CSV dialect.

    This must be subclassed (see csv.excel).  Valid attributes are:
    delimiter, quotechar, escapechar, doublequote, skipinitialspace,
    lineterminator, quoting.

    """
    _name = ""
    _valid = False
    # placeholders
    delimiter = None
    quotechar = None
    escapechar = None
    doublequote = None
    skipinitialspace = None
    lineterminator = None
    quoting = None

    def __init__(self):
        if self.__class__ != Dialect:
            self._valid = True
        self._validate()

    def _validate(self):
        try:
            _Dialect(self)
        except TypeError as e:
            # Re-raise to get a traceback showing more user code.
            raise Error(str(e)) from None

    def __replace__(self, /, **changes):
        unexpected = changes.keys() - _dialect_attributes
        if unexpected:
            raise TypeError(f'__replace__() got an unexpected keyword '
                            f'argument {min(unexpected)!r}')
        new = object.__new__(self.__class__)
        new.__dict__.update(self.__dict__)
        new.__dict__.update(changes)
        new._validate()
        return new

class excel(Dialect):
    """Describe the usual properties of Excel-generated CSV files."""
    delimiter = ','
    quotechar = '"'
    doublequote = True
    skipinitialspace = False
    lineterminator = '\r\n'
    quoting = QUOTE_MINIMAL
register_dialect("excel", excel)

class excel_tab(excel):
    """Describe the usual properties of Excel-generated TAB-delimited files."""
    delimiter = '\t'
register_dialect("excel-tab", excel_tab)

class unix_dialect(Dialect):
    """Describe the usual properties of Unix-generated CSV files."""
    delimiter = ','
    quotechar = '"'
    doublequote = True
    skipinitialspace = False
    lineterminator = '\n'
    quoting = QUOTE_ALL
register_dialect("unix", unix_dialect)


class DictReader:
    def __init__(self, f, fieldnames=None, restkey=None, restval=None,
                 dialect="excel", *args, **kwds):
        if fieldnames is not None and iter(fieldnames) is fieldnames:
            fieldnames = list(fieldnames)
        self._fieldnames = fieldnames   # list of keys for the dict
        self.restkey = restkey          # key to catch long rows
        self.restval = restval          # default value for short rows
        self.reader = reader(f, dialect, *args, **kwds)
        self.dialect = dialect
        self.line_num = 0

    def __iter__(self):
        return self

    @property
    def fieldnames(self):
        if self._fieldnames is None:
            try:
                self._fieldnames = next(self.reader)
            except StopIteration:
                pass
        self.line_num = self.reader.line_num
        return self._fieldnames

    @fieldnames.setter
    def fieldnames(self, value):
        self._fieldnames = value

    def __next__(self):
        if self.line_num == 0:
            # Used only for its side effect.
            self.fieldnames
        row = next(self.reader)
        self.line_num = self.reader.line_num

        # unlike the basic reader, we prefer not to return blanks,
        # because we will typically wind up with a dict full of None
        # values
        while row == []:
            row = next(self.reader)
        d = dict(zip(self.fieldnames, row))
        lf = len(self.fieldnames)
        lr = len(row)
        if lf < lr:
            d[self.restkey] = row[lf:]
        elif lf > lr:
            for key in self.fieldnames[lr:]:
                d[key] = self.restval
        return d

    __class_getitem__ = classmethod(types.GenericAlias)


class DictWriter:
    def __init__(self, f, fieldnames, restval="", extrasaction="raise",
                 dialect="excel", *args, **kwds):
        if fieldnames is not None and iter(fieldnames) is fieldnames:
            fieldnames = list(fieldnames)
        self.fieldnames = fieldnames    # list of keys for the dict
        self.restval = restval          # for writing short dicts
        extrasaction = extrasaction.lower()
        if extrasaction not in ("raise", "ignore"):
            raise ValueError("extrasaction (%s) must be 'raise' or 'ignore'"
                             % extrasaction)
        self.extrasaction = extrasaction
        self.writer = writer(f, dialect, *args, **kwds)

    def writeheader(self):
        header = dict(zip(self.fieldnames, self.fieldnames))
        return self.writerow(header)

    def _dict_to_list(self, rowdict):
        if self.extrasaction == "raise":
            wrong_fields = rowdict.keys() - self.fieldnames
            if wrong_fields:
                raise ValueError("dict contains fields not in fieldnames: "
                                 + ", ".join([repr(x) for x in wrong_fields]))
        return (rowdict.get(key, self.restval) for key in self.fieldnames)

    def writerow(self, rowdict):
        return self.writer.writerow(self._dict_to_list(rowdict))

    def writerows(self, rowdicts):
        return self.writer.writerows(map(self._dict_to_list, rowdicts))

    __class_getitem__ = classmethod(types.GenericAlias)


class Sniffer:
    '''
    "Sniffs" the format of a CSV file (i.e. delimiter, quotechar)
    Returns a Dialect object.
    '''
    # Characters which can be guessed as a delimiter if the delimiters
    # argument is not specified.
    _delimiter_candidates = [c for c in map(chr, range(128))
                             if not c.isalnum()]

    def __init__(self):
        # in case there is more than one possible delimiter
        self.preferred = [',', '\t', ';', ' ', ':']


    def sniff(self, sample, delimiters=None):
        """
        Analyze the sample and return a Dialect subclass reflecting the
        parameters found.  If the optional delimiters parameter is
        given, it is interpreted as a string containing possible valid
        delimiter characters.  Raises Error if the dialect cannot be
        determined.

        The dialect is guessed by parsing the sample with every
        plausible combination of delimiter, quotechar and escapechar,
        and choosing the combination which splits the sample into rows
        with the most consistent number of fields.

        A large sample is parsed incrementally: first only its
        beginning, then, after eliminating the combinations which are
        clearly worse than the leader, a several times larger part,
        and so on.

        If several combinations fit the sample equally well, the
        delimiters listed in the preferred attribute are preferred, in
        that order, no matter how many times each of them occurs.
        """
        import re
        from collections import defaultdict

        if self._parses_as_single_column(sample):
            # There is no delimiter to find; any combination could
            # only find a bogus one inside the quoted fields.
            raise Error("Could not determine delimiter")

        chars = set(sample)
        if delimiters is None:
            delimiters = self._delimiter_candidates
        delimiters = [d for d in delimiters
                      if d in chars and d not in '\r\n"\'\\']
        # Combinations to try, numbered by preference for breaking
        # ties.  The unquoted combinations are parsed from the start;
        # the rest stay dormant until the quote character occurs at
        # the start of a field (see _split_dormant).
        groups = defaultdict(list)
        order = 0
        # Only '\\' is tried as an escape character: others are not
        # seen in the wild.
        for escapechar in ('', '\\') if '\\' in chars else ('',):
            for quotechar in '"', "'", '':
                if quotechar and quotechar not in chars:
                    continue
                for delimiter in delimiters:
                    groups[quotechar].append(
                        (order, delimiter, quotechar, escapechar))
                    order += 1
        active = groups.pop('', [])
        # Only non-empty groups were created; a plain dict cannot
        # grow one by accident.
        dormant = dict(groups)

        # The initial window should cover the minimal number of rows
        # required for elimination (see _eliminate_worse) at a typical
        # line length, so that the first round can already eliminate.
        window = 2000
        # A line with its line break: '\r', '\n' or '\r\n' (the
        # reader treats other line boundary characters as ordinary
        # data, but does not support a bare '\r' inside a chunk).
        # The \z alternative produces one final empty match.
        line_re = re.compile(r'[^\r\n]*(?:\r\n|[\r\n]|\z)')
        parsed = []
        lines = []
        first_round = True
        while active or dormant:
            end = min(window, len(sample))
            part = sample[:end]
            lines = line_re.findall(part)
            del lines[-1]
            cut = not part.endswith(('\r', '\n'))
            for quotechar in list(dormant):
                activated, still = self._split_dormant(
                    part, quotechar, dormant[quotechar])
                active += activated
                if still:
                    dormant[quotechar] = still
                else:
                    del dormant[quotechar]
            parsed = [(combo, self._try_dialect(lines, cut, *combo[1:]))
                      for combo in active]
            if end == len(sample):
                break
            active = self._eliminate_worse(parsed, not first_round)
            first_round = False
            if len(active) <= 3:
                # Quoted data most often leaves three survivors: the
                # true dialect, its equally consistent unquoted shadow,
                # and one accident.  Parsing the whole sample with them
                # is cheaper than another elimination round.
                window = len(sample)
            else:
                # Too small a factor would increase the total
                # re-parsing cost, too large -- the cost of the next
                # round if this one did not eliminate enough.
                window *= 4

        best = None
        best_score = None
        for combo, rows in sorted(parsed):
            if rows is None:
                continue
            _, delimiter, quotechar, escapechar = combo
            nfields, share = self._modal_share(rows)
            if nfields < 2:
                # The delimiter does not delimit anything.
                continue
            try:
                preference = -self.preferred.index(delimiter)
            except ValueError:
                preference = -len(self.preferred)
            # A successful quoted parse is direct evidence; the preferred
            # delimiters list is only a nudge.
            score = (share, len(rows), bool(quotechar), preference)
            if best_score is None or score > best_score:
                best_score = score
                best = combo[1:]

        if best is None:
            raise Error("Could not determine delimiter")
        delimiter, quotechar, escapechar = best
        doublequote = self._detect_doublequote(lines, *best)
        skipinitialspace = self._detect_skipinitialspace(lines, *best,
                                                         doublequote)

        class dialect(Dialect):
            _name = "sniffed"
            quoting = QUOTE_MINIMAL

        dialect.lineterminator = self._detect_lineterminator(lines)
        dialect.delimiter = delimiter
        # _csv.reader won't accept a quotechar of ''
        dialect.quotechar = quotechar or '"'
        dialect.escapechar = escapechar or None
        dialect.doublequote = doublequote
        dialect.skipinitialspace = skipinitialspace

        return dialect

    def _parses_as_single_column(self, sample):
        """
        True if the whole sample parses as a single column of quoted
        fields (the last one may be cut off in the middle), so there
        is no delimiter to find.
        """
        import re

        for q in '"', "'":
            if q in sample:
                row_re = (fr' *+{q}(?:[^{q}]|{q}{q})*+'
                          fr'(?:{q} *+(?:[\r\n]++|\z)|\z)')
                if re.fullmatch(fr'(?:{row_re})++', sample):
                    return True
        return False

    def _split_dormant(self, part, quotechar, combos):
        """
        Split the dormant combinations into those ready for trial
        parsing and the rest.

        A combination is ready when its quote character occurs in
        *part* at the start of a field, i.e. at the start of a line or
        after its delimiter; until then parsing would not differ from
        the unquoted variant.  Spaces before the quote are allowed even
        for the space delimiter: a false activation only costs a trial
        parse.
        """
        import re

        remaining = {combo[1] for combo in combos}
        found = set()
        pos = 0
        while remaining:
            # Include only the delimiters not found yet, so that the
            # search skips over the found ones; the compiled patterns
            # come from the re cache.
            cls = re.escape(''.join(sorted(remaining)))
            m = re.compile(fr'(?:^|([\r\n{cls}]))'
                           fr' *{quotechar}').search(part, pos)
            if m is None:
                break
            pre = m[1]
            if pre is None or pre in '\r\n':
                # A quote at the start of a line starts a field for
                # every delimiter.
                found |= remaining
                break
            found.add(pre)
            remaining.discard(pre)
            pos = m.end()
        activated = [combo for combo in combos if combo[1] in found]
        still_dormant = [combo for combo in combos if combo[1] not in found]
        return activated, still_dormant

    def _make_reader(self, lines, delimiter, quotechar, escapechar,
                     doublequote=True, skipinitialspace=None):
        """
        Create a reader for trial parsing.  quotechar '' means no
        quoting and escapechar '' means no escape character.
        """
        if skipinitialspace is None:
            # Be lenient to spaces after a delimiter, unless the
            # delimiter is a space itself.
            skipinitialspace = delimiter != ' '
        return reader(lines, delimiter=delimiter,
                      quotechar=quotechar or '"',
                      quoting=QUOTE_MINIMAL if quotechar else QUOTE_NONE,
                      escapechar=escapechar or None,
                      doublequote=doublequote,
                      skipinitialspace=skipinitialspace,
                      strict=True)

    def _try_dialect(self, lines, cut, delimiter, quotechar, escapechar):
        """
        Parse the sample, pre-split into *lines*, and return the list
        of the number of fields in every parsed row, or None if not a
        single row was parsed.

        If the sample cannot be parsed to the end (for example it is
        cut off in the middle of a quoted field, or the combination
        does not fit the sample), the rows parsed so far are counted.
        The last row is not counted if *cut* is true: the sample can
        be cut off in the middle of it.
        """
        rows = []
        try:
            rows.extend(map(len, self._make_reader(lines, delimiter,
                                                   quotechar, escapechar)))
        except Error:
            # The row which failed to parse is not counted.
            pass
        else:
            if cut and len(rows) > 1:
                rows.pop()
        if 0 in rows:
            # Blank lines produce empty rows.
            rows = [nfields for nfields in rows if nfields]
        return rows or None

    def _eliminate_worse(self, parsed, judge_hopeless):
        """
        Return the combinations from *parsed* (a list of (combination,
        rows) pairs) without those which are clearly worse than the
        leader.  Combinations with too few parsed rows (e.g. if the
        parsed part ends in the middle of a large quoted field) are
        not judged yet.

        If *judge_hopeless* is false, keep the combinations whose
        delimiter does not delimit anything.  Unlike the comparison
        with the leader, which self-normalizes when the parsed part is
        not representative, this verdict is absolute and irreversible,
        so it is not trusted to the first part, which covers the least
        representative beginning of the sample (titles, headers,
        preamble).
        """
        # Judging a combination by fewer rows is too noisy.
        min_rows = 16
        hopeless = set()
        scores = {}
        for combo, rows in parsed:
            if rows is not None and len(rows) >= min_rows:
                nfields, share = self._modal_share(rows)
                if nfields < 2:
                    if judge_hopeless:
                        hopeless.add(combo)
                else:
                    scores[combo] = share
        threshold = max(scores.values(), default=0.0) - 0.1
        return [combo for combo, _ in parsed
                if combo not in hopeless
                and scores.get(combo, threshold) >= threshold]

    def _modal_share(self, rows):
        """
        The most common number of fields in a row and its share of all
        rows.  Prefer the smaller number of fields in the case of a
        tie: a candidate delimiter which delimits only half of the rows
        is not convincing.
        """
        from collections import Counter

        counts = Counter(rows)
        nfields = max(counts, key=lambda n: (counts[n], -n))
        return nfields, counts[nfields] / len(rows)

    def _detect_doublequote(self, lines, delimiter, quotechar, escapechar):
        """
        True if a doubled quote character represents a single quote
        character in the sample: interpreting it so changes the result
        of parsing.
        """
        if not quotechar or not any(quotechar * 2 in line
                                    for line in lines):
            return False
        readers = [self._make_reader(
                lines, delimiter, quotechar, escapechar,
                doublequote=doublequote)
            for doublequote in (False, True)]
        while True:
            rows = []
            for rdr in readers:
                try:
                    rows.append(next(rdr))
                except (StopIteration, Error):
                    # Ending cleanly and failing are equivalent here:
                    # after equal rows both readers are at the same
                    # position, so they cannot end for different
                    # reasons.
                    rows.append(None)
            if rows[0] != rows[1]:
                return True
            if rows == [None, None]:
                return False

    def _detect_skipinitialspace(self, lines, delimiter, quotechar,
                                 escapechar, doublequote):
        """
        Detect whether the spaces following a delimiter are a part of
        the format or of the data.
        """
        results = []
        for skipinitialspace in False, True:
            rows = []
            try:
                rows.extend(self._make_reader(
                    lines, delimiter, quotechar, escapechar,
                    doublequote=doublequote,
                    skipinitialspace=skipinitialspace))
            except Error:
                # Keep the rows parsed before the error.
                pass
            results.append([row for row in rows if row])
        if results[0] == results[1]:
            return False  # No evidence.
        counts = [[len(row) for row in rows] for rows in results]
        if counts[0] != counts[1]:
            # Prefer the more consistent row widths.
            return len(set(counts[1])) <= len(set(counts[0]))
        # Only some spaces are stripped.  A field differs only if
        # a space was skipped at its start, which tells the padding
        # apart from the spaces inside quoted or escaped fields.
        if not all(kept_field != skipped_field
                   for kept_row, skipped_row in zip(*results)
                   for kept_field, skipped_field in zip(kept_row[1:],
                                                        skipped_row[1:])):
            return False
        # The first field of a row is commonly not padded ('a, b, c'),
        # so the first fields need only agree with each other.
        first = [kept_row[0] != skipped_row[0]
                 for kept_row, skipped_row in zip(*results)]
        return all(first) or not any(first)

    def _detect_lineterminator(self, lines):
        """
        Detect the line terminator by majority vote among the line
        endings.  A line break inside a quoted field is counted too,
        but it takes more of them than of the real ones to win the
        vote.  A tie is broken in the order '\\r\\n', '\\n', '\\r',
        so a sample without a complete line gives '\\r\\n'.
        """
        counts = dict.fromkeys(('\r\n', '\n', '\r'), 0)
        for line in lines:
            for lineterminator in counts:
                if line.endswith(lineterminator):
                    counts[lineterminator] += 1
                    break
        # max() returns the first of equal candidates, and dict
        # preserves the insertion order.
        return max(counts, key=counts.get)

    def has_header(self, sample):
        # Creates a dictionary of types of data in each column. If any
        # column is of a single type (say, integers), *except* for the first
        # row, then the first row is presumed to be labels. If the type
        # can't be determined, it is assumed to be a string in which case
        # the length of the string is the determining factor: if all of the
        # rows except for the first are the same length, it's a header.
        # Finally, a 'vote' is taken at the end for each column, adding or
        # subtracting from the likelihood of the first row being a header.

        rdr = reader(StringIO(sample), self.sniff(sample))

        header = next(rdr) # assume first row is header

        columns = len(header)
        columnTypes = {}
        for i in range(columns): columnTypes[i] = None

        checked = 0
        for row in rdr:
            # arbitrary number of rows to check, to keep it sane
            if checked > 20:
                break
            checked += 1

            if len(row) != columns:
                continue # skip rows that have irregular number of columns

            for col in list(columnTypes.keys()):
                thisType = complex
                try:
                    thisType(row[col])
                except (ValueError, OverflowError):
                    # fallback to length of string
                    thisType = len(row[col])

                if thisType != columnTypes[col]:
                    if columnTypes[col] is None: # add new column type
                        columnTypes[col] = thisType
                    else:
                        # type is inconsistent, remove column from
                        # consideration
                        del columnTypes[col]

        # finally, compare results against first row and "vote"
        # on whether it's a header
        hasHeader = 0
        for col, colType in columnTypes.items():
            if isinstance(colType, int): # it's a length
                if len(header[col]) != colType:
                    hasHeader += 1
                else:
                    hasHeader -= 1
            else: # attempt typecast
                try:
                    colType(header[col])
                except (ValueError, TypeError):
                    hasHeader += 1
                else:
                    hasHeader -= 1

        return hasHeader > 0


def __getattr__(name):
    if name == "__version__":
        from warnings import _deprecated

        _deprecated("__version__", remove=(3, 20))
        return "1.0"  # Do not change
    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")