import cython
from cython import Py_ssize_t
import numpy as np

cimport numpy as cnp
from numpy cimport (
    int64_t,
    intp_t,
    ndarray,
    uint64_t,
)

cnp.import_array()

from pandas._libs.algos import groupsort_indexer

from pandas._libs.dtypes cimport (
    numeric_object_t,
    numeric_t,
)


@cython.wraparound(False)
@cython.boundscheck(False)
def inner_join(const intp_t[:] left, const intp_t[:] right,
               Py_ssize_t max_groups):
    cdef:
        Py_ssize_t i, j, k, count = 0
        intp_t[::1] left_sorter, right_sorter
        intp_t[::1] left_count, right_count
        intp_t[::1] left_indexer, right_indexer
        intp_t lc, rc
        Py_ssize_t left_pos = 0, right_pos = 0, position = 0
        Py_ssize_t offset

    left_sorter, left_count = groupsort_indexer(left, max_groups)
    right_sorter, right_count = groupsort_indexer(right, max_groups)

    with nogil:
        # First pass, determine size of result set, do not use the NA group
        for i in range(1, max_groups + 1):
            lc = left_count[i]
            rc = right_count[i]

            if rc > 0 and lc > 0:
                count += lc * rc

    left_indexer = np.empty(count, dtype=np.intp)
    right_indexer = np.empty(count, dtype=np.intp)

    with nogil:
        # exclude the NA group
        left_pos = left_count[0]
        right_pos = right_count[0]
        for i in range(1, max_groups + 1):
            lc = left_count[i]
            rc = right_count[i]

            if rc > 0 and lc > 0:
                for j in range(lc):
                    offset = position + j * rc
                    for k in range(rc):
                        left_indexer[offset + k] = left_pos + j
                        right_indexer[offset + k] = right_pos + k
                position += lc * rc
            left_pos += lc
            right_pos += rc

        # Will overwrite left/right indexer with the result
        _get_result_indexer(left_sorter, left_indexer)
        _get_result_indexer(right_sorter, right_indexer)

    return np.asarray(left_indexer), np.asarray(right_indexer)


@cython.wraparound(False)
@cython.boundscheck(False)
def left_outer_join(const intp_t[:] left, const intp_t[:] right,
                    Py_ssize_t max_groups, bint sort=True):
    cdef:
        Py_ssize_t i, j, k, count = 0
        ndarray[intp_t] rev
        intp_t[::1] left_count, right_count
        intp_t[::1] left_sorter, right_sorter
        intp_t[::1] left_indexer, right_indexer
        intp_t lc, rc
        Py_ssize_t left_pos = 0, right_pos = 0, position = 0
        Py_ssize_t offset

    left_sorter, left_count = groupsort_indexer(left, max_groups)
    right_sorter, right_count = groupsort_indexer(right, max_groups)

    with nogil:
        # First pass, determine size of result set, do not use the NA group
        for i in range(1, max_groups + 1):
            if right_count[i] > 0:
                count += left_count[i] * right_count[i]
            else:
                count += left_count[i]

    left_indexer = np.empty(count, dtype=np.intp)
    right_indexer = np.empty(count, dtype=np.intp)

    with nogil:
        # exclude the NA group
        left_pos = left_count[0]
        right_pos = right_count[0]
        for i in range(1, max_groups + 1):
            lc = left_count[i]
            rc = right_count[i]

            if rc == 0:
                for j in range(lc):
                    left_indexer[position + j] = left_pos + j
                    right_indexer[position + j] = -1
                position += lc
            else:
                for j in range(lc):
                    offset = position + j * rc
                    for k in range(rc):
                        left_indexer[offset + k] = left_pos + j
                        right_indexer[offset + k] = right_pos + k
                position += lc * rc
            left_pos += lc
            right_pos += rc

        # Will overwrite left/right indexer with the result
        _get_result_indexer(left_sorter, left_indexer)
        _get_result_indexer(right_sorter, right_indexer)

    if not sort:  # if not asked to sort, revert to original order
        if len(left) == len(left_indexer):
            # no multiple matches for any row on the left
            # this is a short-cut to avoid groupsort_indexer
            # otherwise, the `else` path also works in this case
            rev = np.empty(len(left), dtype=np.intp)
            rev.put(np.asarray(left_sorter), np.arange(len(left)))
        else:
            rev, _ = groupsort_indexer(left_indexer, len(left))

        return np.asarray(left_indexer).take(rev), np.asarray(right_indexer).take(rev)
    else:
        return np.asarray(left_indexer), np.asarray(right_indexer)


@cython.wraparound(False)
@cython.boundscheck(False)
def full_outer_join(const intp_t[:] left, const intp_t[:] right,
                    Py_ssize_t max_groups):
    cdef:
        Py_ssize_t i, j, k, count = 0
        intp_t[::1] left_sorter, right_sorter
        intp_t[::1] left_count, right_count
        intp_t[::1] left_indexer, right_indexer
        intp_t lc, rc
        intp_t left_pos = 0, right_pos = 0
        Py_ssize_t offset, position = 0

    left_sorter, left_count = groupsort_indexer(left, max_groups)
    right_sorter, right_count = groupsort_indexer(right, max_groups)

    with nogil:
        # First pass, determine size of result set, do not use the NA group
        for i in range(1, max_groups + 1):
            lc = left_count[i]
            rc = right_count[i]

            if rc > 0 and lc > 0:
                count += lc * rc
            else:
                count += lc + rc

    left_indexer = np.empty(count, dtype=np.intp)
    right_indexer = np.empty(count, dtype=np.intp)

    with nogil:
        # exclude the NA group
        left_pos = left_count[0]
        right_pos = right_count[0]
        for i in range(1, max_groups + 1):
            lc = left_count[i]
            rc = right_count[i]

            if rc == 0:
                for j in range(lc):
                    left_indexer[position + j] = left_pos + j
                    right_indexer[position + j] = -1
                position += lc
            elif lc == 0:
                for j in range(rc):
                    left_indexer[position + j] = -1
                    right_indexer[position + j] = right_pos + j
                position += rc
            else:
                for j in range(lc):
                    offset = position + j * rc
                    for k in range(rc):
                        left_indexer[offset + k] = left_pos + j
                        right_indexer[offset + k] = right_pos + k
                position += lc * rc
            left_pos += lc
            right_pos += rc

        # Will overwrite left/right indexer with the result
        _get_result_indexer(left_sorter, left_indexer)
        _get_result_indexer(right_sorter, right_indexer)

    return np.asarray(left_indexer), np.asarray(right_indexer)


@cython.wraparound(False)
@cython.boundscheck(False)
cdef void _get_result_indexer(intp_t[::1] sorter, intp_t[::1] indexer) nogil:
    """NOTE: overwrites indexer with the result to avoid allocating another array"""
    cdef:
        Py_ssize_t i, n, idx

    if len(sorter) > 0:
        # cython-only equivalent to
        #  `res = algos.take_nd(sorter, indexer, fill_value=-1)`
        n = indexer.shape[0]
        for i in range(n):
            idx = indexer[i]
            if idx == -1:
                indexer[i] = -1
            else:
                indexer[i] = sorter[idx]
    else:
        # length-0 case
        indexer[:] = -1


def ffill_indexer(const intp_t[:] indexer) -> np.ndarray:
    cdef:
        Py_ssize_t i, n = len(indexer)
        ndarray[intp_t] result
        intp_t val, last_obs

    result = np.empty(n, dtype=np.intp)
    last_obs = -1

    for i in range(n):
        val = indexer[i]
        if val == -1:
            result[i] = last_obs
        else:
            result[i] = val
            last_obs = val

    return result


# ----------------------------------------------------------------------
# left_join_indexer, inner_join_indexer, outer_join_indexer
# ----------------------------------------------------------------------

# Joins on ordered, unique indices

# right might contain non-unique values

@cython.wraparound(False)
@cython.boundscheck(False)
def left_join_indexer_unique(
    ndarray[numeric_object_t] left,
    ndarray[numeric_object_t] right
):
    """
    Both left and right are strictly monotonic increasing.
    """
    cdef:
        Py_ssize_t i, j, nleft, nright
        ndarray[intp_t] indexer
        numeric_object_t lval, rval

    i = 0
    j = 0
    nleft = len(left)
    nright = len(right)

    indexer = np.empty(nleft, dtype=np.intp)
    while True:
        if i == nleft:
            break

        if j == nright:
            indexer[i] = -1
            i += 1
            continue

        rval = right[j]

        while i < nleft - 1 and left[i] == rval:
            indexer[i] = j
            i += 1

        if left[i] == right[j]:
            indexer[i] = j
            i += 1
            while i < nleft - 1 and left[i] == rval:
                indexer[i] = j
                i += 1
            j += 1
        elif left[i] > rval:
            indexer[i] = -1
            j += 1
        else:
            indexer[i] = -1
            i += 1
    return indexer


@cython.wraparound(False)
@cython.boundscheck(False)
def left_join_indexer(ndarray[numeric_object_t] left, ndarray[numeric_object_t] right):
    """
    Two-pass algorithm for monotonic indexes. Handles many-to-one merges.

    Both left and right are monotonic increasing, but at least one of them
    is non-unique (if both were unique we'd use left_join_indexer_unique).
    """
    cdef:
        Py_ssize_t i, j, k, nright, nleft, count
        numeric_object_t lval, rval
        ndarray[intp_t] lindexer, rindexer
        ndarray[numeric_object_t] result

    nleft = len(left)
    nright = len(right)

    # First pass is to find the size 'count' of our output indexers.
    i = 0
    j = 0
    count = 0
    if nleft > 0:
        while i < nleft:
            if j == nright:
                count += nleft - i
                break

            lval = left[i]
            rval = right[j]

            if lval == rval:
                # This block is identical across
                #  left_join_indexer, inner_join_indexer, outer_join_indexer
                count += 1
                if i < nleft - 1:
                    if j < nright - 1 and right[j + 1] == rval:
                        j += 1
                    else:
                        i += 1
                        if left[i] != rval:
                            j += 1
                elif j < nright - 1:
                    j += 1
                    if lval != right[j]:
                        i += 1
                else:
                    # end of the road
                    break
            elif lval < rval:
                count += 1
                i += 1
            else:
                j += 1

    # do it again now that result size is known

    lindexer = np.empty(count, dtype=np.intp)
    rindexer = np.empty(count, dtype=np.intp)
    result = np.empty(count, dtype=left.dtype)

    i = 0
    j = 0
    count = 0
    if nleft > 0:
        while i < nleft:
            if j == nright:
                while i < nleft:
                    lindexer[count] = i
                    rindexer[count] = -1
                    result[count] = left[i]
                    i += 1
                    count += 1
                break

            lval = left[i]
            rval = right[j]

            if lval == rval:
                lindexer[count] = i
                rindexer[count] = j
                result[count] = lval
                count += 1
                if i < nleft - 1:
                    if j < nright - 1 and right[j + 1] == rval:
                        j += 1
                    else:
                        i += 1
                        if left[i] != rval:
                            j += 1
                elif j < nright - 1:
                    j += 1
                    if lval != right[j]:
                        i += 1
                else:
                    # end of the road
                    break
            elif lval < rval:
                # i.e. lval not in right; we keep for left_join_indexer
                lindexer[count] = i
                rindexer[count] = -1
                result[count] = lval
                count += 1
                i += 1
            else:
                # i.e. rval not in left; we discard for left_join_indexer
                j += 1

    return result, lindexer, rindexer


@cython.wraparound(False)
@cython.boundscheck(False)
def inner_join_indexer(ndarray[numeric_object_t] left, ndarray[numeric_object_t] right):
    """
    Two-pass algorithm for monotonic indexes. Handles many-to-one merges.

    Both left and right are monotonic increasing but not necessarily unique.
    """
    cdef:
        Py_ssize_t i, j, k, nright, nleft, count
        numeric_object_t lval, rval
        ndarray[intp_t] lindexer, rindexer
        ndarray[numeric_object_t] result

    nleft = len(left)
    nright = len(right)

    # First pass is to find the size 'count' of our output indexers.
    i = 0
    j = 0
    count = 0
    if nleft > 0 and nright > 0:
        while True:
            if i == nleft:
                break
            if j == nright:
                break

            lval = left[i]
            rval = right[j]
            if lval == rval:
                count += 1
                if i < nleft - 1:
                    if j < nright - 1 and right[j + 1] == rval:
                        j += 1
                    else:
                        i += 1
                        if left[i] != rval:
                            j += 1
                elif j < nright - 1:
                    j += 1
                    if lval != right[j]:
                        i += 1
                else:
                    # end of the road
                    break
            elif lval < rval:
                # i.e. lval not in right; we discard for inner_indexer
                i += 1
            else:
                # i.e. rval not in left; we discard for inner_indexer
                j += 1

    # do it again now that result size is known

    lindexer = np.empty(count, dtype=np.intp)
    rindexer = np.empty(count, dtype=np.intp)
    result = np.empty(count, dtype=left.dtype)

    i = 0
    j = 0
    count = 0
    if nleft > 0 and nright > 0:
        while True:
            if i == nleft:
                break
            if j == nright:
                break

            lval = left[i]
            rval = right[j]
            if lval == rval:
                lindexer[count] = i
                rindexer[count] = j
                result[count] = lval
                count += 1
                if i < nleft - 1:
                    if j < nright - 1 and right[j + 1] == rval:
                        j += 1
                    else:
                        i += 1
                        if left[i] != rval:
                            j += 1
                elif j < nright - 1:
                    j += 1
                    if lval != right[j]:
                        i += 1
                else:
                    # end of the road
                    break
            elif lval < rval:
                # i.e. lval not in right; we discard for inner_indexer
                i += 1
            else:
                # i.e. rval not in left; we discard for inner_indexer
                j += 1

    return result, lindexer, rindexer


@cython.wraparound(False)
@cython.boundscheck(False)
def outer_join_indexer(ndarray[numeric_object_t] left, ndarray[numeric_object_t] right):
    """
    Both left and right are monotonic increasing but not necessarily unique.
    """
    cdef:
        Py_ssize_t i, j, nright, nleft, count
        numeric_object_t lval, rval
        ndarray[intp_t] lindexer, rindexer
        ndarray[numeric_object_t] result

    nleft = len(left)
    nright = len(right)

    # First pass is to find the size 'count' of our output indexers.
    # count will be length of left plus the number of elements of right not in
    # left (counting duplicates)
    i = 0
    j = 0
    count = 0
    if nleft == 0:
        count = nright
    elif nright == 0:
        count = nleft
    else:
        while True:
            if i == nleft:
                count += nright - j
                break
            if j == nright:
                count += nleft - i
                break

            lval = left[i]
            rval = right[j]
            if lval == rval:
                count += 1
                if i < nleft - 1:
                    if j < nright - 1 and right[j + 1] == rval:
                        j += 1
                    else:
                        i += 1
                        if left[i] != rval:
                            j += 1
                elif j < nright - 1:
                    j += 1
                    if lval != right[j]:
                        i += 1
                else:
                    # end of the road
                    break
            elif lval < rval:
                count += 1
                i += 1
            else:
                count += 1
                j += 1

    lindexer = np.empty(count, dtype=np.intp)
    rindexer = np.empty(count, dtype=np.intp)
    result = np.empty(count, dtype=left.dtype)

    # do it again, but populate the indexers / result

    i = 0
    j = 0
    count = 0
    if nleft == 0:
        for j in range(nright):
            lindexer[j] = -1
            rindexer[j] = j
            result[j] = right[j]
    elif nright == 0:
        for i in range(nleft):
            lindexer[i] = i
            rindexer[i] = -1
            result[i] = left[i]
    else:
        while True:
            if i == nleft:
                while j < nright:
                    lindexer[count] = -1
                    rindexer[count] = j
                    result[count] = right[j]
                    count += 1
                    j += 1
                break
            if j == nright:
                while i < nleft:
                    lindexer[count] = i
                    rindexer[count] = -1
                    result[count] = left[i]
                    count += 1
                    i += 1
                break

            lval = left[i]
            rval = right[j]

            if lval == rval:
                lindexer[count] = i
                rindexer[count] = j
                result[count] = lval
                count += 1
                if i < nleft - 1:
                    if j < nright - 1 and right[j + 1] == rval:
                        j += 1
                    else:
                        i += 1
                        if left[i] != rval:
                            j += 1
                elif j < nright - 1:
                    j += 1
                    if lval != right[j]:
                        i += 1
                else:
                    # end of the road
                    break
            elif lval < rval:
                # i.e. lval not in right; we keep for outer_join_indexer
                lindexer[count] = i
                rindexer[count] = -1
                result[count] = lval
                count += 1
                i += 1
            else:
                # i.e. rval not in left; we keep for outer_join_indexer
                lindexer[count] = -1
                rindexer[count] = j
                result[count] = rval
                count += 1
                j += 1

    return result, lindexer, rindexer


# ----------------------------------------------------------------------
# asof_join_by
# ----------------------------------------------------------------------

from pandas._libs.hashtable cimport (
    HashTable,
    Int64HashTable,
    PyObjectHashTable,
    UInt64HashTable,
)

ctypedef fused by_t:
    object
    int64_t
    uint64_t


def asof_join_backward_on_X_by_Y(numeric_t[:] left_values,
                                 numeric_t[:] right_values,
                                 by_t[:] left_by_values,
                                 by_t[:] right_by_values,
                                 bint allow_exact_matches=True,
                                 tolerance=None):

    cdef:
        Py_ssize_t left_pos, right_pos, left_size, right_size, found_right_pos
        ndarray[intp_t] left_indexer, right_indexer
        bint has_tolerance = False
        numeric_t tolerance_ = 0
        numeric_t diff = 0
        HashTable hash_table
        by_t by_value

    # if we are using tolerance, set our objects
    if tolerance is not None:
        has_tolerance = True
        tolerance_ = tolerance

    left_size = len(left_values)
    right_size = len(right_values)

    left_indexer = np.empty(left_size, dtype=np.intp)
    right_indexer = np.empty(left_size, dtype=np.intp)

    if by_t is object:
        hash_table = PyObjectHashTable(right_size)
    elif by_t is int64_t:
        hash_table = Int64HashTable(right_size)
    elif by_t is uint64_t:
        hash_table = UInt64HashTable(right_size)

    right_pos = 0
    for left_pos in range(left_size):
        # restart right_pos if it went negative in a previous iteration
        if right_pos < 0:
            right_pos = 0

        # find last position in right whose value is less than left's
        if allow_exact_matches:
            while (right_pos < right_size and
                   right_values[right_pos] <= left_values[left_pos]):
                hash_table.set_item(right_by_values[right_pos], right_pos)
                right_pos += 1
        else:
            while (right_pos < right_size and
                   right_values[right_pos] < left_values[left_pos]):
                hash_table.set_item(right_by_values[right_pos], right_pos)
                right_pos += 1
        right_pos -= 1

        # save positions as the desired index
        by_value = left_by_values[left_pos]
        found_right_pos = (hash_table.get_item(by_value)
                           if by_value in hash_table else -1)
        left_indexer[left_pos] = left_pos
        right_indexer[left_pos] = found_right_pos

        # if needed, verify that tolerance is met
        if has_tolerance and found_right_pos != -1:
            diff = left_values[left_pos] - right_values[found_right_pos]
            if diff > tolerance_:
                right_indexer[left_pos] = -1

    return left_indexer, right_indexer


def asof_join_forward_on_X_by_Y(numeric_t[:] left_values,
                                numeric_t[:] right_values,
                                by_t[:] left_by_values,
                                by_t[:] right_by_values,
                                bint allow_exact_matches=1,
                                tolerance=None):

    cdef:
        Py_ssize_t left_pos, right_pos, left_size, right_size, found_right_pos
        ndarray[intp_t] left_indexer, right_indexer
        bint has_tolerance = False
        numeric_t tolerance_ = 0
        numeric_t diff = 0
        HashTable hash_table
        by_t by_value

    # if we are using tolerance, set our objects
    if tolerance is not None:
        has_tolerance = True
        tolerance_ = tolerance

    left_size = len(left_values)
    right_size = len(right_values)

    left_indexer = np.empty(left_size, dtype=np.intp)
    right_indexer = np.empty(left_size, dtype=np.intp)

    if by_t is object:
        hash_table = PyObjectHashTable(right_size)
    elif by_t is int64_t:
        hash_table = Int64HashTable(right_size)
    elif by_t is uint64_t:
        hash_table = UInt64HashTable(right_size)

    right_pos = right_size - 1
    for left_pos in range(left_size - 1, -1, -1):
        # restart right_pos if it went over in a previous iteration
        if right_pos == right_size:
            right_pos = right_size - 1

        # find first position in right whose value is greater than left's
        if allow_exact_matches:
            while (right_pos >= 0 and
                   right_values[right_pos] >= left_values[left_pos]):
                hash_table.set_item(right_by_values[right_pos], right_pos)
                right_pos -= 1
        else:
            while (right_pos >= 0 and
                   right_values[right_pos] > left_values[left_pos]):
                hash_table.set_item(right_by_values[right_pos], right_pos)
                right_pos -= 1
        right_pos += 1

        # save positions as the desired index
        by_value = left_by_values[left_pos]
        found_right_pos = (hash_table.get_item(by_value)
                           if by_value in hash_table else -1)
        left_indexer[left_pos] = left_pos
        right_indexer[left_pos] = found_right_pos

        # if needed, verify that tolerance is met
        if has_tolerance and found_right_pos != -1:
            diff = right_values[found_right_pos] - left_values[left_pos]
            if diff > tolerance_:
                right_indexer[left_pos] = -1

    return left_indexer, right_indexer


def asof_join_nearest_on_X_by_Y(numeric_t[:] left_values,
                                numeric_t[:] right_values,
                                by_t[:] left_by_values,
                                by_t[:] right_by_values,
                                bint allow_exact_matches=True,
                                tolerance=None):

    cdef:
        Py_ssize_t left_size, right_size, i
        ndarray[intp_t] left_indexer, right_indexer, bli, bri, fli, fri
        numeric_t bdiff, fdiff

    left_size = len(left_values)
    right_size = len(right_values)

    left_indexer = np.empty(left_size, dtype=np.intp)
    right_indexer = np.empty(left_size, dtype=np.intp)

    # search both forward and backward
    bli, bri = asof_join_backward_on_X_by_Y(
        left_values,
        right_values,
        left_by_values,
        right_by_values,
        allow_exact_matches,
        tolerance,
    )
    fli, fri = asof_join_forward_on_X_by_Y(
        left_values,
        right_values,
        left_by_values,
        right_by_values,
        allow_exact_matches,
        tolerance,
    )

    for i in range(len(bri)):
        # choose timestamp from right with smaller difference
        if bri[i] != -1 and fri[i] != -1:
            bdiff = left_values[bli[i]] - right_values[bri[i]]
            fdiff = right_values[fri[i]] - left_values[fli[i]]
            right_indexer[i] = bri[i] if bdiff <= fdiff else fri[i]
        else:
            right_indexer[i] = bri[i] if bri[i] != -1 else fri[i]
        left_indexer[i] = bli[i]

    return left_indexer, right_indexer


# ----------------------------------------------------------------------
# asof_join
# ----------------------------------------------------------------------

def asof_join_backward(numeric_t[:] left_values,
                       numeric_t[:] right_values,
                       bint allow_exact_matches=True,
                       tolerance=None):

    cdef:
        Py_ssize_t left_pos, right_pos, left_size, right_size
        ndarray[intp_t] left_indexer, right_indexer
        bint has_tolerance = False
        numeric_t tolerance_ = 0
        numeric_t diff = 0

    # if we are using tolerance, set our objects
    if tolerance is not None:
        has_tolerance = True
        tolerance_ = tolerance

    left_size = len(left_values)
    right_size = len(right_values)

    left_indexer = np.empty(left_size, dtype=np.intp)
    right_indexer = np.empty(left_size, dtype=np.intp)

    right_pos = 0
    for left_pos in range(left_size):
        # restart right_pos if it went negative in a previous iteration
        if right_pos < 0:
            right_pos = 0

        # find last position in right whose value is less than left's
        if allow_exact_matches:
            while (right_pos < right_size and
                   right_values[right_pos] <= left_values[left_pos]):
                right_pos += 1
        else:
            while (right_pos < right_size and
                   right_values[right_pos] < left_values[left_pos]):
                right_pos += 1
        right_pos -= 1

        # save positions as the desired index
        left_indexer[left_pos] = left_pos
        right_indexer[left_pos] = right_pos

        # if needed, verify that tolerance is met
        if has_tolerance and right_pos != -1:
            diff = left_values[left_pos] - right_values[right_pos]
            if diff > tolerance_:
                right_indexer[left_pos] = -1

    return left_indexer, right_indexer


def asof_join_forward(numeric_t[:] left_values,
                      numeric_t[:] right_values,
                      bint allow_exact_matches=True,
                      tolerance=None):

    cdef:
        Py_ssize_t left_pos, right_pos, left_size, right_size
        ndarray[intp_t] left_indexer, right_indexer
        bint has_tolerance = False
        numeric_t tolerance_ = 0
        numeric_t diff = 0

    # if we are using tolerance, set our objects
    if tolerance is not None:
        has_tolerance = True
        tolerance_ = tolerance

    left_size = len(left_values)
    right_size = len(right_values)

    left_indexer = np.empty(left_size, dtype=np.intp)
    right_indexer = np.empty(left_size, dtype=np.intp)

    right_pos = right_size - 1
    for left_pos in range(left_size - 1, -1, -1):
        # restart right_pos if it went over in a previous iteration
        if right_pos == right_size:
            right_pos = right_size - 1

        # find first position in right whose value is greater than left's
        if allow_exact_matches:
            while (right_pos >= 0 and
                   right_values[right_pos] >= left_values[left_pos]):
                right_pos -= 1
        else:
            while (right_pos >= 0 and
                   right_values[right_pos] > left_values[left_pos]):
                right_pos -= 1
        right_pos += 1

        # save positions as the desired index
        left_indexer[left_pos] = left_pos
        right_indexer[left_pos] = (right_pos
                                   if right_pos != right_size else -1)

        # if needed, verify that tolerance is met
        if has_tolerance and right_pos != right_size:
            diff = right_values[right_pos] - left_values[left_pos]
            if diff > tolerance_:
                right_indexer[left_pos] = -1

    return left_indexer, right_indexer


def asof_join_nearest(numeric_t[:] left_values,
                      numeric_t[:] right_values,
                      bint allow_exact_matches=True,
                      tolerance=None):

    cdef:
        Py_ssize_t left_size, i
        ndarray[intp_t] left_indexer, right_indexer, bli, bri, fli, fri
        numeric_t bdiff, fdiff

    left_size = len(left_values)

    left_indexer = np.empty(left_size, dtype=np.intp)
    right_indexer = np.empty(left_size, dtype=np.intp)

    # search both forward and backward
    bli, bri = asof_join_backward(left_values, right_values,
                                  allow_exact_matches, tolerance)
    fli, fri = asof_join_forward(left_values, right_values,
                                 allow_exact_matches, tolerance)

    for i in range(len(bri)):
        # choose timestamp from right with smaller difference
        if bri[i] != -1 and fri[i] != -1:
            bdiff = left_values[bli[i]] - right_values[bri[i]]
            fdiff = right_values[fri[i]] - left_values[fli[i]]
            right_indexer[i] = bri[i] if bdiff <= fdiff else fri[i]
        else:
            right_indexer[i] = bri[i] if bri[i] != -1 else fri[i]
        left_indexer[i] = bli[i]

    return left_indexer, right_indexer