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"""Iterator (quasi)affine mapping patterns."""

from enum import IntEnum

import tvm_ffi

from tvm.ir import PrimExpr
from tvm.runtime import Object

from . import _ffi_api


@tvm_ffi.register_object("arith.IterMapExpr")
class IterMapExpr(PrimExpr):
    """Base class of all IterMap expressions."""


@tvm_ffi.register_object("arith.IterMark")
class IterMark(Object):
    """Mark the source as an iterator in [0, extent).

    Parameters
    ----------
    source : PrimExpr.
        The source expression.

    extent : PrimExpr
        The extent of the iterator.
    """

    def __init__(self, source, extent):
        self.__init_handle_by_constructor__(_ffi_api.IterMark, source, extent)


@tvm_ffi.register_object("arith.IterSplitExpr")
class IterSplitExpr(IterMapExpr):
    """Split of an iterator.

    result = floormod(floordiv(source, lower_factor), extent) * scale

    Parameters
    ----------
    source : IterMark
        The source marked iterator.

    lower_factor : PrimExpr
        The lower factor to split the domain.

    extent : PrimExpr
        The extent of the split.

    scale : PrimExpr
        Additional scale to the split.
    """

    def __init__(self, source, lower_factor, extent, scale):
        self.__init_handle_by_constructor__(
            _ffi_api.IterSplitExpr, source, lower_factor, extent, scale
        )


@tvm_ffi.register_object("arith.IterSumExpr")
class IterSumExpr(IterMapExpr):
    """Fuse multiple iterators by summing them with scaling.

    result = sum(args) + base

    Parameters
    ----------
    args : List[IterSplitExpr]
        The input to the sum expression.

    base : PrimExpr
        The base offset.
    """

    def __init__(self, args, base):
        self.__init_handle_by_constructor__(_ffi_api.IterSumExpr, args, base)


@tvm_ffi.register_object("arith.IterMapResult")
class IterMapResult(Object):
    """Result of iter map detection."""


class IterMapLevel(IntEnum):
    """Possible kinds of iter mapping check level."""

    Bijective = 0
    Surjective = 1
    NoCheck = 3

    @staticmethod
    def from_str(name: str):
        """Helper to create level enum from string"""
        if name is None:
            return IterMapLevel.NoCheck
        name = name.lower()
        if name == "bijective":
            check_level = IterMapLevel.Bijective
        elif name == "surjective":
            check_level = IterMapLevel.Surjective
        elif name == "nocheck":
            check_level = IterMapLevel.NoCheck
        else:
            raise ValueError(f"Unknown check level {name}")
        return check_level


def detect_iter_map(
    indices,
    input_iters,
    predicate=True,
    check_level=IterMapLevel.Surjective,
    simplify_trivial_iterators=True,
):
    """Detect if indices can be written as mapped iters from input iters

    Parameters
    ----------
    indices : List[PrimExpr]
        The input indices

    input_iters : Map[tvm.tirx.Var, Range]
        The domain of each input iterators.

    predicate : PrimExpr
        The predicate constraints on the input iterators

    check_level : Union[str, IterMapLevel]
        Checking level of iteration mapping

    simplify_trivial_iterators: bool
        If true, iterators with extent of 1 will be replaced with a
        constant value.

    Returns
    -------
    results : IterMapResult
        The iter map matching result.
        The result's .indices is empty array if no match can be found.

    """
    if isinstance(check_level, str):
        check_level = IterMapLevel.from_str(check_level)
    elif check_level is None:
        check_level = IterMapLevel.NoCheck
    return _ffi_api.DetectIterMap(
        indices, input_iters, predicate, check_level, simplify_trivial_iterators
    )


def normalize_to_iter_sum(index, input_iters):
    """Normalize expr to iter sum.

    The normalized result ensures that
    each scale is in the form of (symbol_prod) * cscale
    It will also sort in desc order by cscale then len(symbol_prod).

    Parameters
    ----------
    index : PrimExpr
        The input index

    input_iters : Map[tvm.tirx.Var, Range]
        The domain of each input iterators.

    Returns
    -------
    iter_sum: IterSumExpr
        The result iter sum

    Note
    ----
    This function does best effort detection, so some undetected
    part can go into iter_sum.base

    This function is useful to decide the stride multiplier and
    division factor in buffer access patterns.
    """
    return _ffi_api.NormalizeToIterSum(index, input_iters)


def iter_map_simplify(
    indices,
    input_iters,
    predicate=True,
    check_level=IterMapLevel.Surjective,
    simplify_trivial_iterators=True,
):
    """Simplify the indices using iter map detection.

    Parameters
    ----------
    indices : List[PrimExpr]
        The input indices

    input_iters : Map[tvm.tirx.Var, Range]
        The domain of each input iterators.

    predicate : PrimExpr
        The predicate constraints on the input iterators

    check_level : Union[str, IterMapLevel]
        Checking level of iteration mapping

    simplify_trivial_iterators: bool
        If true, iterators with extent of 1 will be replaced with a
        constant value.

    Returns
    -------
    results : IterMapResult
        The iter map matching result.
        The result's .indices is empty array if no match can be found.

    """
    if isinstance(check_level, str):
        check_level = IterMapLevel.from_str(check_level)
    elif check_level is None:
        check_level = IterMapLevel.NoCheck
    return _ffi_api.IterMapSimplify(
        indices, input_iters, predicate, check_level, simplify_trivial_iterators
    )


def normalize_iter_map_to_expr(expr):
    """Given an IterMapExpr, transform it to normal PrimExpr

    Parameters
    ----------
    expr : IterMapExpr
        the input IterMapExpr

    Returns
    -------
    result : PrimExpr
        the corresponding normal PrimExpr
    """
    return _ffi_api.NormalizeIterMapToExpr(expr)


def subspace_divide(
    bindings,
    input_iters,
    sub_iters,
    predicate=True,
    check_level=IterMapLevel.Surjective,
    simplify_trivial_iterators=True,
):
    """Detect if bindings can be written as
    ``[a_0*e_0 + b_0 + c_0, a_1*e_1 + b_1, ..., a_n*e_n + b_n]``

    where::

        a = some-quasi-affine-iter-map(input_iters set_minus sub_iters)
        b = some-quasi-affine-iter-map(sub_iters)
        c is constant symbols
        e is the extent of b

    For example::

        z*12 + y*3 + x + c = (z*4+y)*3 + x
        bindings = [z*12 + y*3 + x + c]
        input_iters = [z, y, x]
        sub_iter = [x]
        Then the result will be [a, b] where
        a = [z*4 + y]
        b = [x]

    Parameters
    ----------
    bindings : List[PrimExpr]
        The input bindings

    input_iters : Map[tvm.tirx.Var, Range]
        The domain of input iterator, which is the basis of the whole space

    sub_iters : Array[tvm.tirx.Var]
        The subset of input_iters, which is the basis of the subspace

    predicate : PrimExpr
        The predicate constraints on the input iterators

    check_level : Union[str, IterMapLevel]
        Checking level of iteration mapping

    simplify_trivial_iterators: bool
        If true, iterators with extent of 1 will be replaced with a
        constant value.

    Returns
    -------
    results : List[List[PrimExpr]]
        The result list has length ``len(bindings) + 1``.

        - ``[0, len(bindings))``: The iter map matching result.
          The inner list is of length 2. The first expr is the basis
          of the quotient space. The second expr is the basis of the subspace.
        - ``len(bindings)``: the predicate of outer space and inner space.
        - Empty array if no match can be found.
    """
    if isinstance(check_level, str):
        check_level = IterMapLevel.from_str(check_level)
    return _ffi_api.SubspaceDivide(
        bindings, input_iters, sub_iters, predicate, check_level, simplify_trivial_iterators
    )


def inverse_affine_iter_map(iter_map, outputs):
    """Apply the inverse of the affine transformation to the outputs.
    Similar to the back-propagation, starting from the outputs, it visits the DAG of the expressions
    in reverse topology order and applies the inverse of the affine transformation until it reaches
    the input. The affine iter map is required to be bijective.

    For example, iter_map = [l0 // 16, l0 % 16], outputs = [output_0, output_1],
    the affine transformation specified by `iter_map` will be applied to `outputs` and the result
    will be {l0: ((output_0*16) + output_1)}.

    See also :any:`detect_iter_map`.

    Parameters
    ----------
    iter_map : List[IterSumExpr]
        The bijective affine iter map.
    outputs : List[PrimExpr]
        The outputs of the affine transformation.

    Returns
    -------
    results : Map[tvm.tirx.Var, PrimExpr]
        The map from the input to the transformed result.
    """
    return _ffi_api.InverseAffineIterMap(iter_map, outputs)
