# Django 4.2.11 documentation

# Source code for django.db.models.functions.window

    from django.db.models.expressions import Func
    from django.db.models.fields import FloatField, IntegerField

    __all__ = [
        "CumeDist",
        "DenseRank",
        "FirstValue",
        "Lag",
        "LastValue",
        "Lead",
        "NthValue",
        "Ntile",
        "PercentRank",
        "Rank",
        "RowNumber",
    ]

    class CumeDist(Func):
        function = "CUME_DIST"
        output_field = FloatField()
        window_compatible = True

    class DenseRank(Func):
        function = "DENSE_RANK"
        output_field = IntegerField()
        window_compatible = True

    class FirstValue(Func):
        arity = 1
        function = "FIRST_VALUE"
        window_compatible = True

    class LagLeadFunction(Func):
        window_compatible = True

        def __init__(self, expression, offset=1, default=None, **extra):
            if expression is None:
                raise ValueError(
                    "%s requires a non-null source expression." % self.__class__.__name__
                )
            if offset is None or offset <= 0:
                raise ValueError(
                    "%s requires a positive integer for the offset."
                    % self.__class__.__name__
                )
            args = (expression, offset)
            if default is not None:
                args += (default,)
            super().__init__(*args, **extra)

        def _resolve_output_field(self):
            sources = self.get_source_expressions()
            return sources[0].output_field

    class Lag(LagLeadFunction):
        function = "LAG"

    class LastValue(Func):
        arity = 1
        function = "LAST_VALUE"
        window_compatible = True

    class Lead(LagLeadFunction):
        function = "LEAD"

    class NthValue(Func):
        function = "NTH_VALUE"
        window_compatible = True

        def __init__(self, expression, nth=1, **extra):
            if expression is None:
                raise ValueError(
                    "%s requires a non-null source expression." % self.__class__.__name__
                )
            if nth is None or nth <= 0:
                raise ValueError(
                    "%s requires a positive integer as for nth." % self.__class__.__name__
                )
            super().__init__(expression, nth, **extra)

        def _resolve_output_field(self):
            sources = self.get_source_expressions()
            return sources[0].output_field

    class Ntile(Func):
        function = "NTILE"
        output_field = IntegerField()
        window_compatible = True

        def __init__(self, num_buckets=1, **extra):
            if num_buckets <= 0:
                raise ValueError("num_buckets must be greater than 0.")
            super().__init__(num_buckets, **extra)

    class PercentRank(Func):
        function = "PERCENT_RANK"
        output_field = FloatField()
        window_compatible = True

    class Rank(Func):
        function = "RANK"
        output_field = IntegerField()
        window_compatible = True

    class RowNumber(Func):
        function = "ROW_NUMBER"
        output_field = IntegerField()
        window_compatible = True