"""RFC 4180-ish CSV parser + writer with correct handling of quoted fields."""
from __future__ import annotations


def parse_csv(text, delimiter=",", quotechar='"'):
    if text.startswith("\ufeff"):
        text = text[1:]
    rows = []
    field = []
    row = []
    i = 0
    n = len(text)
    in_quotes = False
    at_field_start = True

    def flush_field():
        nonlocal field, row, at_field_start
        row.append("".join(field))
        field = []
        at_field_start = True

    def flush_row():
        nonlocal row, at_field_start
        rows.append(row)
        row = []
        at_field_start = True

    if text == "":
        return rows
    while i < n:
        c = text[i]
        if in_quotes:
            if c == quotechar:
                if i + 1 < n and text[i + 1] == quotechar:
                    field.append(quotechar)
                    i += 2
                else:
                    in_quotes = False
                    i += 1
            else:
                field.append(c)
                i += 1
        else:
            if c == quotechar and at_field_start:
                in_quotes = True
                at_field_start = False
                i += 1
            elif c == delimiter:
                flush_field()
                i += 1
            elif c == "\r":
                flush_field()
                flush_row()
                if i + 1 < n and text[i + 1] == "\n":
                    i += 2
                else:
                    i += 1
                at_field_start = True
            elif c == "\n":
                flush_field()
                flush_row()
                i += 1
                at_field_start = True
            else:
                field.append(c)
                at_field_start = False
                i += 1
    if field or row or not at_field_start:
        if not at_field_start or field:
            flush_field()
        if row:
            flush_row()
    return rows


def _needs_quoting(field, delimiter, quotechar, lineterminator):
    if quotechar in field or delimiter in field:
        return True
    if "\n" in field or "\r" in field:
        return True
    if field != field.strip(" "):
        return True
    return False


def write(rows, delimiter=",", quotechar='"', lineterminator="\r\n"):
    out = []
    for row in rows:
        fields = []
        for f in row:
            f = "" if f is None else str(f)
            if _needs_quoting(f, delimiter, quotechar, lineterminator):
                f = quotechar + f.replace(quotechar, quotechar + quotechar) + quotechar
            fields.append(f)
        out.append(delimiter.join(fields))
    return lineterminator.join(out) + (lineterminator if rows else "")


def dumps(rows, **kw):
    return write(rows, **kw)


def loads(text, **kw):
    return parse_csv(text, **kw)