"""
Helper routines for generating gpu kernels for nvcc.

"""


def nvcc_kernel(name, params, body):
    """
    Return the c code of a kernel function.

    Parameters
    ----------
    params
        The parameters to the function as one or more strings.
    body
        The [nested] list of statements for the body of the
        function. These will be separated by ';' characters.

    """
    paramstr = ', '.join(params)

    def flatbody():
        for b in body:
            if isinstance(b, (list, tuple)):
                for bb in b:
                    yield bb
            else:
                yield b
    bodystr = ';\n'.join(flatbody())
    return """__global__ void %(name)s (%(paramstr)s)
    {
        %(bodystr)s;
    }
    """ % locals()


def code_version(version):
    """
    Decorator to support version-based cache mechanism.

    """
    if not isinstance(version, tuple):
        raise TypeError('version must be tuple', version)

    def deco(f):
        f.code_version = version
        return f
    return deco

UNVERSIONED = ()


@code_version((1,))
def inline_reduce(N, buf, pos, count, manner_fn):
    """
    Return C++ code for a function that reduces a contiguous buffer.

    Parameters
    ----------
    N
        Length of the buffer.
    buf
        Buffer pointer.
    pos
        Index of executing thread.
    count
        Number of executing threads.
    manner_fn
        A function that accepts strings of arguments a
        and b, and returns c code for their reduction. (Example:
        return "%(a)s + %(b)s" for a sum reduction).

    :postcondition:
    This function leaves the answer in position 0 of the buffer. The
    rest of the buffer is trashed by this function.

    Notes
    ----- 
    buf should be in gpu shared memory, we access it many times.

    """
    loop_line = manner_fn("%s[%s]" % (buf, pos), "%s[i]" % (buf))
    r_16 = manner_fn("%s[%s]" % (buf, pos), "%s[%s+16]" % (buf, pos))
    r_8 = manner_fn("%s[%s]" % (buf, pos), "%s[%s+8]" % (buf, pos))
    r_4 = manner_fn("%s[%s]" % (buf, pos), "%s[%s+4]" % (buf, pos))
    r_2 = manner_fn("%s[%s]" % (buf, pos), "%s[%s+2]" % (buf, pos))
    r_1 = manner_fn("%s[%s]" % (buf, pos), "%s[%s+1]" % (buf, pos))

    return """
    {
        // This function trashes buf[1..warpSize],
        // leaving the reduction result in buf[0].

        if (%(pos)s < warpSize)
        {
            for (int i = %(pos)s + warpSize; i < %(N)s; i += warpSize)
            {
                %(buf)s[%(pos)s] = %(loop_line)s;
            }
            if (%(pos)s < 16)
            {
                //reduce so that %(pos)s 0 has the sum of everything
                if(%(pos)s + 16 < %(N)s)
                    %(buf)s[%(pos)s] = %(r_16)s;
                if(%(pos)s + 8 < %(N)s)
                    %(buf)s[%(pos)s] = %(r_8)s;
                if(%(pos)s + 4 < %(N)s)
                    %(buf)s[%(pos)s] = %(r_4)s;
                if(%(pos)s + 2 < %(N)s)
                    %(buf)s[%(pos)s] = %(r_2)s;
                if(%(pos)s + 1 < %(N)s)
                    %(buf)s[%(pos)s] = %(r_1)s;
            }
        }
    }
    """ % locals()


@code_version(inline_reduce.code_version)
def inline_reduce_max(N, buf, pos, count):
    return inline_reduce(N, buf, pos, count,
                         lambda a, b: "max(%s, %s)" % (a, b))


@code_version(inline_reduce.code_version)
def inline_reduce_sum(N, buf, pos, count):
    return inline_reduce(N, buf, pos, count,
                         lambda a, b: "%s + %s" % (a, b))


@code_version(inline_reduce.code_version)
def inline_reduce_min(N, buf, pos, count):
    return inline_reduce(N, buf, pos, count,
                         lambda a, b: "min(%s, %s)" % (a, b))


@code_version(inline_reduce.code_version)
def inline_reduce_prod(N, buf, pos, count):
    return inline_reduce(N, buf, pos, count,
                         lambda a, b: "%s * %s" % (a, b))


@code_version((2,) + inline_reduce_max.code_version +
              inline_reduce_sum.code_version)
def inline_softmax(N, buf, buf2, threadPos, threadCount):
    """

    Parameters
    ----------
    N
        Length of the buffer.
    threadPos
        Index of executing thread.
    threadCount
        Number of executing threads.

    :Precondition: buf and buf2 contain two identical copies of the input
        to softmax
    :Postcondition: buf contains the softmax, buf2 contains un-normalized
        softmax

    Notes
    -----
    buf and buf2 should be in gpu shared memory, we access it many times.

    We use __i as an int variable in a loop.

    """
    return [
            # get max of buf (trashing all but buf[0])
            inline_reduce_max(N, buf, threadPos, threadCount),
            '__syncthreads()',
            'float row_max = ' + buf + '[0]',
            '__syncthreads()',
            'for(int __i=' + threadPos + '; __i<' + N +
                  '; __i+=' + threadCount + '){',
                buf + '[__i] = exp(' + buf2 + '[__i] - row_max)',
                buf2 + '[__i] = ' + buf + '[__i]',
            '}',
            '__syncthreads()',
            inline_reduce_sum(N, buf, threadPos, threadCount),
            '__syncthreads()',
            'float row_sum = ' + buf + '[0]',
            '__syncthreads()',
            # divide each exp() result by the sum to complete the job.
            'for(int __i=' + threadPos + '; __i<' + N +
                  '; __i+=' + threadCount + '){',
                buf + '[__i] = ' + buf2 + '[__i] / row_sum',
            '}',
            '__syncthreads()',
            ]


@code_version((1,))
def inline_reduce_fixed_shared(N, buf, x, stride_x, pos, count,
                               manner_fn, manner_init,
                               b='', stride_b=''):
    """
    Return C++ code for a function that reduces a contiguous buffer.

    Parameters
    ----------
    N
        Length of the buffer.
    buf
        Buffer pointer of size warpSize * sizeof(float).
    pos
        Index of executing thread.
    count
        Number of executing threads.
    b
        Optional, pointer to the bias.
    stride_b
        Optional, the stride of b if b is provided.
    manner_fn
        A function that accepts strings of arguments a
        and b, and returns c code for their reduction. (Example:
        return "%(a)s + %(b)s" for a sum reduction).
    manner_init
        A function that accepts strings of arguments a
        and return c code for its initialization.

    :postcondition:
    This function leaves the answer in position 0 of the buffer. The
    rest of the buffer is trashed by this function.

    Notes
    -----
    buf should be in gpu shared memory, we access it many times.

    """
    if b:
        init = manner_init("%(x)s[%(pos)s * %(stride_x)s] +"
                           " %(b)s[%(pos)s * %(stride_b)s]" % locals())
        loop_line = manner_fn("red",
                              manner_init("%(x)s[i * %(stride_x)s] + "
                                          "%(b)s[i * %(stride_b)s]" %
                                          locals()))
    else:
        init = manner_init("%(x)s[%(pos)s * %(stride_x)s]" % locals())
        loop_line = manner_fn("red", manner_init("%(x)s[i * %(stride_x)s]" %
                                                 locals()))
    loop_line2 = manner_fn("%s[%s]" % (buf, pos),
                          "%s[i]" % buf)
    r_16 = manner_fn("%s[%s]" % (buf, pos), "%s[%s+16]" % (buf, pos))
    r_8 = manner_fn("%s[%s]" % (buf, pos), "%s[%s+8]" % (buf, pos))
    r_4 = manner_fn("%s[%s]" % (buf, pos), "%s[%s+4]" % (buf, pos))
    r_2 = manner_fn("%s[%s]" % (buf, pos), "%s[%s+2]" % (buf, pos))
    r_1 = manner_fn("%s[%s]" % (buf, pos), "%s[%s+1]" % (buf, pos))

    return """
    {
        // This function trashes buf[1..n_threads],
        // leaving the reduction result in buf[0].
        float red = %(init)s;
        #pragma unroll 16
        for (int i = %(pos)s + %(count)s; i<%(N)s; i += %(count)s){
          red = %(loop_line)s;
        }
        buf[%(pos)s] = red;
        __syncthreads();
        if (%(pos)s < warpSize)
        {
            for (int i = %(pos)s + warpSize; i < %(count)s; i += warpSize)
            {
                %(buf)s[%(pos)s] = %(loop_line2)s;
            }
            if (%(pos)s < 16)
            {
                //reduce so that %(pos)s 0 has the reduction of everything
                if(%(pos)s + 16 < %(N)s)
                    %(buf)s[%(pos)s] = %(r_16)s;
                if(%(pos)s + 8 < %(N)s)
                    %(buf)s[%(pos)s] = %(r_8)s;
                if(%(pos)s + 4 < %(N)s)
                    %(buf)s[%(pos)s] = %(r_4)s;
                if(%(pos)s + 2 < %(N)s)
                    %(buf)s[%(pos)s] = %(r_2)s;
                if(%(pos)s + 1 < %(N)s)
                    %(buf)s[%(pos)s] = %(r_1)s;
            }
        }
    }
    """ % locals()


@code_version(inline_reduce_fixed_shared.code_version)
def inline_reduce_fixed_shared_max(N, buf, x, stride_x, pos, count,
                                   b='', stride_b=''):
    return inline_reduce_fixed_shared(N, buf, x, stride_x, pos, count,
                                      lambda a, b: "max(%s, %s)" % (a, b),
                                      lambda a: a,
                                      b, stride_b)


@code_version((1,) + inline_reduce_max.code_version +
              inline_reduce_sum.code_version)
def inline_softmax_fixed_shared(N, buf, x, stride_x,
                                sm, sm_stride,
                                threadPos, threadCount,
                                b='', stride_b=''):
    """

    Parameters
    ----------
    N
        Length of the buffer, atleast waprSize(32).
    buf
        A shared memory buffer of size warpSize * sizeof(float).
    x
        A ptr to the gpu memory where the row is stored.
    stride_x
        The stride between each element in x.
    sm
        A ptr to the gpu memory to store the result.
    sm_stride
        The stride between each sm element.
    threadPos
        Index of executing thread.
    threadCount
        Number of executing threads.
    b
        Optional, pointer to the bias.
    stride_b
        Optional, the stride of b if b is provided.

    :Precondition: buf is empty
    :Postcondition: buf[0] contains the softmax,
        buf2 contains un-normalized softmax

    Notes
    -----
    buf should be in gpu shared memory, we access it many times.

    We use tx as an int variable in a loop.

    """
    ret = [
        # get max of buf (trashing all but buf[0])
        inline_reduce_fixed_shared_max(N, buf, x, stride_x,
                                       threadPos, threadCount, b, stride_b),
        '__syncthreads()',
        'float row_max = ' + buf + '[0]',
        '__syncthreads()',
        inline_reduce_fixed_shared(N, buf, x, stride_x, threadPos, threadCount,
                                   lambda a, b: "%s + %s" % (a, b),
                                   lambda a: "exp(%s - row_max)" % a,
                                   b, stride_b),
        '__syncthreads()',
        'float row_sum = ' + buf + '[0]',
        '__syncthreads()',
        "for (int tx = threadIdx.x; tx< N; tx += blockDim.x){",
        ]
    # This set all value correctly
    if b:
        ret += [
            "%(sm)s[tx * %(sm_stride)s] = "
            "  exp(%(x)s[tx * %(stride_x)s] +"
            "            %(b)s[tx * %(stride_b)s] - row_max)"
            " / row_sum" % locals()]
    else:
        ret += [
            "%(sm)s[tx * %(sm_stride)s] = "
            "exp(%(x)s[tx * %(stride_x)s] - row_max) / row_sum" % locals()]
    ret += [
        "}",
        '__syncthreads()',
    ]
    return ret
