# This file is a part of Julia. License is MIT: http://julialang.org/license

## array.jl: Dense arrays

typealias Vector{T} Array{T,1}
typealias Matrix{T} Array{T,2}
typealias VecOrMat{T} Union{Vector{T}, Matrix{T}}

typealias DenseVector{T} DenseArray{T,1}
typealias DenseMatrix{T} DenseArray{T,2}
typealias DenseVecOrMat{T} Union{DenseVector{T}, DenseMatrix{T}}

call{T}(::Type{Vector{T}}, m::Integer) = Array{T}(m)
call{T}(::Type{Vector{T}}) = Array{T}(0)
call(::Type{Vector}, m::Integer) = Array{Any}(m)
call(::Type{Vector}) = Array{Any}(0)

call{T}(::Type{Matrix{T}}, m::Integer, n::Integer) = Array{T}(m, n)
call{T}(::Type{Matrix{T}}) = Array{T}(0, 0)
call(::Type{Matrix}, m::Integer, n::Integer) = Array{Any}(m, n)
call(::Type{Matrix}) = Array{Any}(0, 0)

## Basic functions ##

# convert Arrays to pointer arrays for ccall
function call{P<:Ptr,T<:Ptr}(::Type{Ref{P}}, a::Array{T}) # Ref{P<:Ptr}(a::Array{T<:Ptr})
    return RefArray(a) # effectively a no-op
end
function call{P<:Ptr,T}(::Type{Ref{P}}, a::Array{T}) # Ref{P<:Ptr}(a::Array)
    if (!isbits(T) && T <: eltype(P))
        # this Array already has the right memory layout for the requested Ref
        return RefArray(a,1,false) # root something, so that this function is type-stable
    else
        ptrs = Array(P, length(a)+1)
        roots = Array(Any, length(a))
        for i = 1:length(a)
            root = cconvert(P, a[i])
            ptrs[i] = unsafe_convert(P, root)::P
            roots[i] = root
        end
        ptrs[length(a)+1] = C_NULL
        return RefArray(ptrs,1,roots)
    end
end
cconvert{P<:Ptr,T<:Ptr}(::Union{Type{Ptr{P}},Type{Ref{P}}}, a::Array{T}) = a
cconvert{P<:Ptr}(::Union{Type{Ptr{P}},Type{Ref{P}}}, a::Array) = Ref{P}(a)

size(a::Array, d) = arraysize(a, d)
size(a::Vector) = (arraysize(a,1),)
size(a::Matrix) = (arraysize(a,1), arraysize(a,2))
size{_}(a::Array{_,3}) = (arraysize(a,1), arraysize(a,2), arraysize(a,3))
size{_}(a::Array{_,4}) = (arraysize(a,1), arraysize(a,2), arraysize(a,3), arraysize(a,4))
asize_from(a::Array, n) = n > ndims(a) ? () : (arraysize(a,n), asize_from(a, n+1)...)
size{_,N}(a::Array{_,N}) = asize_from(a, 1)::NTuple{N,Int}

length(a::Array) = arraylen(a)
elsize{T}(a::Array{T}) = isbits(T) ? sizeof(T) : sizeof(Ptr)
sizeof(a::Array) = elsize(a) * length(a)

strides{T}(a::Array{T,1}) = (1,)
strides{T}(a::Array{T,2}) = (1, size(a,1))
strides{T}(a::Array{T,3}) = (1, size(a,1), size(a,1)*size(a,2))

function isassigned{T}(a::Array{T}, i::Int...)
    ii = sub2ind(size(a), i...)
    1 <= ii <= length(a) || return false
    ccall(:jl_array_isassigned, Cint, (Any, UInt), a, ii-1) == 1
end

## copy ##

function unsafe_copy!{T}(dest::Ptr{T}, src::Ptr{T}, n)
    ccall(:memmove, Ptr{Void}, (Ptr{Void}, Ptr{Void}, UInt),
          dest, src, n*sizeof(T))
    return dest
end

function unsafe_copy!{T}(dest::Array{T}, doffs, src::Array{T}, soffs, n)
    if isbits(T)
        unsafe_copy!(pointer(dest, doffs), pointer(src, soffs), n)
    else
        for i=0:n-1
            @inbounds arrayset(dest, src[i+soffs], i+doffs)
        end
    end
    return dest
end

function copy!{T}(dest::Array{T}, doffs::Integer, src::Array{T}, soffs::Integer, n::Integer)
    n == 0 && return dest
    if n < 0 || soffs < 1 || doffs < 1 || soffs+n-1 > length(src) || doffs+n-1 > length(dest)
        throw(BoundsError())
    end
    unsafe_copy!(dest, doffs, src, soffs, n)
end

copy!{T}(dest::Array{T}, src::Array{T}) = copy!(dest, 1, src, 1, length(src))

function copy(a::Array)
    b = similar(a)
    ccall(:memcpy, Ptr{Void}, (Ptr{Void}, Ptr{Void}, UInt), b, a, sizeof(a))
    return b
end

function reinterpret{T,S}(::Type{T}, a::Array{S,1})
    nel = Int(div(length(a)*sizeof(S),sizeof(T)))
    # TODO: maybe check that remainder is zero?
    return reinterpret(T, a, (nel,))
end

function reinterpret{T,S}(::Type{T}, a::Array{S})
    if sizeof(S) != sizeof(T)
        throw(ArgumentError("result shape not specified"))
    end
    reinterpret(T, a, size(a))
end

function reinterpret{T,S,N}(::Type{T}, a::Array{S}, dims::NTuple{N,Int})
    if !isbits(T)
        throw(ArgumentError("cannot reinterpret Array{$(S)} to ::Type{Array{$(T)}}, type $(T) is not a bitstype"))
    end
    if !isbits(S)
        throw(ArgumentError("cannot reinterpret Array{$(S)} to ::Type{Array{$(T)}}, type $(S) is not a bitstype"))
    end
    nel = div(length(a)*sizeof(S),sizeof(T))
    if prod(dims) != nel
        throw(DimensionMismatch("new dimensions $(dims) must be consistent with array size $(nel)"))
    end
    ccall(:jl_reshape_array, Array{T,N}, (Any, Any, Any), Array{T,N}, a, dims)
end

# reshaping to same # of dimensions
function reshape{T,N}(a::Array{T,N}, dims::NTuple{N,Int})
    if prod(dims) != length(a)
        throw(DimensionMismatch("new dimensions $(dims) must be consistent with array size $(length(a))"))
    end
    if dims == size(a)
        return a
    end
    ccall(:jl_reshape_array, Array{T,N}, (Any, Any, Any), Array{T,N}, a, dims)
end

# reshaping to different # of dimensions
function reshape{T,N}(a::Array{T}, dims::NTuple{N,Int})
    if prod(dims) != length(a)
        throw(DimensionMismatch("new dimensions $(dims) must be consistent with array size $(length(a))"))
    end
    ccall(:jl_reshape_array, Array{T,N}, (Any, Any, Any), Array{T,N}, a, dims)
end

## Constructors ##

similar(a::Array, T, dims::Dims)      = Array(T, dims)
similar{T}(a::Array{T,1})             = Array(T, size(a,1))
similar{T}(a::Array{T,2})             = Array(T, size(a,1), size(a,2))
similar{T}(a::Array{T,1}, dims::Dims) = Array(T, dims)
similar{T}(a::Array{T,1}, m::Int)     = Array(T, m)
similar{T}(a::Array{T,1}, S)          = Array(S, size(a,1))
similar{T}(a::Array{T,2}, dims::Dims) = Array(T, dims)
similar{T}(a::Array{T,2}, m::Int)     = Array(T, m)
similar{T}(a::Array{T,2}, S)          = Array(S, size(a,1), size(a,2))

# T[x...] constructs Array{T,1}
function getindex(T::Type, vals...)
    a = Array(T,length(vals))
    @inbounds for i = 1:length(vals)
        a[i] = vals[i]
    end
    return a
end

function getindex(::Type{Any}, vals::ANY...)
    a = Array(Any,length(vals))
    @inbounds for i = 1:length(vals)
        a[i] = vals[i]
    end
    return a
end

function fill!(a::Union{Array{UInt8}, Array{Int8}}, x::Integer)
    ccall(:memset, Ptr{Void}, (Ptr{Void}, Cint, Csize_t), a, x, length(a))
    return a
end

function fill!{T<:Union{Integer,AbstractFloat}}(a::Array{T}, x)
    # note: checking bit pattern
    xT = convert(T,x)
    if isbits(T) && nfields(T)==0 &&
        ((sizeof(T)==1 && reinterpret(UInt8, xT) == 0) ||
         (sizeof(T)==2 && reinterpret(UInt16, xT) == 0) ||
         (sizeof(T)==4 && reinterpret(UInt32, xT) == 0) ||
         (sizeof(T)==8 && reinterpret(UInt64, xT) == 0))
        ccall(:memset, Ptr{Void}, (Ptr{Void}, Cint, Csize_t),
              a, 0, length(a)*sizeof(T))
    else
        for i in eachindex(a)
            @inbounds a[i] = xT
        end
    end
    return a
end

fill(v, dims::Dims)       = fill!(Array(typeof(v), dims), v)
fill(v, dims::Integer...) = fill!(Array(typeof(v), dims...), v)

cell(dims::Integer...)   = Array(Any, dims...)
cell(dims::Tuple{Vararg{Integer}}) = Array(Any, convert(Tuple{Vararg{Int}}, dims))

for (fname, felt) in ((:zeros,:zero), (:ones,:one))
    @eval begin
        ($fname)(T::Type, dims...)       = fill!(Array(T, dims...), ($felt)(T))
        ($fname)(dims...)                = fill!(Array(Float64, dims...), ($felt)(Float64))
        ($fname){T}(A::AbstractArray{T}) = fill!(similar(A), ($felt)(T))
    end
end

function eye(T::Type, m::Integer, n::Integer)
    a = zeros(T,m,n)
    for i = 1:min(m,n)
        a[i,i] = one(T)
    end
    return a
end
eye(m::Integer, n::Integer) = eye(Float64, m, n)
eye(T::Type, n::Integer) = eye(T, n, n)
eye(n::Integer) = eye(Float64, n)
eye{T}(x::AbstractMatrix{T}) = eye(T, size(x, 1), size(x, 2))

function one{T}(x::AbstractMatrix{T})
    m,n = size(x)
    m==n || throw(DimensionMismatch("multiplicative identity defined only for square matrices"))
    eye(T, m)
end

## Conversions ##

convert{T,n}(::Type{Array{T}}, x::Array{T,n}) = x
convert{T,n}(::Type{Array{T,n}}, x::Array{T,n}) = x

convert{T,n,S}(::Type{Array{T}}, x::AbstractArray{S,n}) = convert(Array{T,n}, x)
convert{T,n,S}(::Type{Array{T,n}}, x::AbstractArray{S,n}) = copy!(Array(T, size(x)), x)

promote_rule{T,n,S}(::Type{Array{T,n}}, ::Type{Array{S,n}}) = Array{promote_type(T,S),n}

"""
    collect(element_type, collection)

Return an array of type `Array{element_type,1}` of all items in a collection.
"""
function collect{T}(::Type{T}, itr)
    if applicable(length, itr)
        # when length() isn't defined this branch might pollute the
        # type of the other.
        a = Array(T,length(itr)::Integer)
        i = 0
        for x in itr
            a[i+=1] = x
        end
    else
        a = Array(T,0)
        for x in itr
            push!(a,x)
        end
    end
    return a
end

"""
    collect(collection)

Return an array of all items in a collection. For associative collections, returns Pair{KeyType, ValType}.
"""
collect(itr) = collect(eltype(itr), itr)

## Iteration ##
start(A::Array) = 1
next(a::Array,i) = (a[i],i+1)
done(a::Array,i) = i == length(a)+1

## Indexing: getindex ##

# This is more complicated than it needs to be in order to get Win64 through bootstrap
getindex(A::Array, i1::Real) = arrayref(A, to_index(i1))
getindex(A::Array, i1::Real, i2::Real, I::Real...) = arrayref(A, to_index(i1), to_index(i2), to_indexes(I...)...)

unsafe_getindex(A::Array, i1::Real, I::Real...) = @inbounds return arrayref(A, to_index(i1), to_indexes(I...)...)

# Faster contiguous indexing using copy! for UnitRange and Colon
getindex(A::Array, I::UnitRange{Int}) = (checkbounds(A, I); unsafe_getindex(A, I))
function unsafe_getindex(A::Array, I::UnitRange{Int})
    lI = length(I)
    X = similar(A, lI)
    if lI > 0
        unsafe_copy!(X, 1, A, first(I), lI)
    end
    return X
end
getindex(A::Array, c::Colon) = unsafe_getindex(A, c)
function unsafe_getindex(A::Array, ::Colon)
    lI = length(A)
    X = similar(A, lI)
    if lI > 0
        unsafe_copy!(X, 1, A, 1, lI)
    end
    return X
end

# This is redundant with the abstract fallbacks, but needed for bootstrap
function getindex{T<:Real}(A::Array, I::Range{T})
    return [ A[to_index(i)] for i in I ]
end

## Indexing: setindex! ##
setindex!{T}(A::Array{T}, x, i1::Real) = arrayset(A, convert(T,x)::T, to_index(i1))
setindex!{T}(A::Array{T}, x, i1::Real, i2::Real, I::Real...) = arrayset(A, convert(T,x)::T, to_index(i1), to_index(i2), to_indexes(I...)...)

# Type inference is confused by `@inbounds return ...` and introduces a
# !ispointerfree local variable and a GC frame
unsafe_setindex!{T}(A::Array{T}, x, i1::Real, I::Real...) =
    (@inbounds arrayset(A, convert(T,x)::T, to_index(i1), to_indexes(I...)...); A)

# These are redundant with the abstract fallbacks but needed for bootstrap
function setindex!(A::Array, x, I::AbstractVector{Int})
    is(A, I) && (I = copy(I))
    for i in I
        A[i] = x
    end
    return A
end
function setindex!(A::Array, X::AbstractArray, I::AbstractVector{Int})
    setindex_shape_check(X, length(I))
    count = 1
    if is(X,A)
        X = copy(X)
        is(I,A) && (I = X::typeof(I))
    elseif is(I,A)
        I = copy(I)
    end
    for i in I
        A[i] = X[count]
        count += 1
    end
    return A
end

# Faster contiguous setindex! with copy!
setindex!{T}(A::Array{T}, X::Array{T}, I::UnitRange{Int}) = (checkbounds(A, I); unsafe_setindex!(A, X, I))
function unsafe_setindex!{T}(A::Array{T}, X::Array{T}, I::UnitRange{Int})
    lI = length(I)
    setindex_shape_check(X, lI)
    if lI > 0
        unsafe_copy!(A, first(I), X, 1, lI)
    end
    return A
end
setindex!{T}(A::Array{T}, X::Array{T}, c::Colon) = unsafe_setindex!(A, X, c)
function unsafe_setindex!{T}(A::Array{T}, X::Array{T}, ::Colon)
    lI = length(A)
    setindex_shape_check(X, lI)
    if lI > 0
        unsafe_copy!(A, 1, X, 1, lI)
    end
    return A
end

# efficiently grow an array

function _growat!(a::Vector, i::Integer, delta::Integer)
    n = length(a)
    if i < div(n,2)
        _growat_beg!(a, i, delta)
    else
        _growat_end!(a, i, delta)
    end
    return a
end

function _growat_beg!(a::Vector, i::Integer, delta::Integer)
    ccall(:jl_array_grow_beg, Void, (Any, UInt), a, delta)
    if i > 1
        ccall(:memmove, Ptr{Void}, (Ptr{Void}, Ptr{Void}, Csize_t),
              pointer(a, 1), pointer(a, 1+delta), (i-1)*elsize(a))
    end
    return a
end

function _growat_end!(a::Vector, i::Integer, delta::Integer)
    ccall(:jl_array_grow_end, Void, (Any, UInt), a, delta)
    n = length(a)
    if n >= i+delta
        ccall(:memmove, Ptr{Void}, (Ptr{Void}, Ptr{Void}, Csize_t),
              pointer(a, i+delta), pointer(a, i), (n-i-delta+1)*elsize(a))
    end
    return a
end

# efficiently delete part of an array

function _deleteat!(a::Vector, i::Integer, delta::Integer)
    n = length(a)
    last = i+delta-1
    if i-1 < n-last
        _deleteat_beg!(a, i, delta)
    else
        _deleteat_end!(a, i, delta)
    end
    return a
end

function _deleteat_beg!(a::Vector, i::Integer, delta::Integer)
    if i > 1
        ccall(:memmove, Ptr{Void}, (Ptr{Void}, Ptr{Void}, Csize_t),
              pointer(a, 1+delta), pointer(a, 1), (i-1)*elsize(a))
    end
    ccall(:jl_array_del_beg, Void, (Any, UInt), a, delta)
    return a
end

function _deleteat_end!(a::Vector, i::Integer, delta::Integer)
    n = length(a)
    if n >= i+delta
        ccall(:memmove, Ptr{Void}, (Ptr{Void}, Ptr{Void}, Csize_t),
              pointer(a, i), pointer(a, i+delta), (n-i-delta+1)*elsize(a))
    end
    ccall(:jl_array_del_end, Void, (Any, UInt), a, delta)
    return a
end

## Dequeue functionality ##

function push!{T}(a::Array{T,1}, item)
    # convert first so we don't grow the array if the assignment won't work
    itemT = convert(T, item)
    ccall(:jl_array_grow_end, Void, (Any, UInt), a, 1)
    a[end] = itemT
    return a
end

function push!(a::Array{Any,1}, item::ANY)
    ccall(:jl_array_grow_end, Void, (Any, UInt), a, 1)
    arrayset(a, item, length(a))
    return a
end

function append!{T}(a::Array{T,1}, items::AbstractVector)
    n = length(items)
    ccall(:jl_array_grow_end, Void, (Any, UInt), a, n)
    copy!(a, length(a)-n+1, items, 1, n)
    return a
end

function prepend!{T}(a::Array{T,1}, items::AbstractVector)
    n = length(items)
    ccall(:jl_array_grow_beg, Void, (Any, UInt), a, n)
    if a === items
        copy!(a, 1, items, n+1, n)
    else
        copy!(a, 1, items, 1, n)
    end
    return a
end

function resize!(a::Vector, nl::Integer)
    l = length(a)
    if nl > l
        ccall(:jl_array_grow_end, Void, (Any, UInt), a, nl-l)
    else
        if nl < 0
            throw(ArgumentError("new length must be ≥ 0"))
        end
        ccall(:jl_array_del_end, Void, (Any, UInt), a, l-nl)
    end
    return a
end

function sizehint!(a::Vector, sz::Integer)
    ccall(:jl_array_sizehint, Void, (Any, UInt), a, sz)
    a
end

function pop!(a::Vector)
    if isempty(a)
        throw(ArgumentError("array must be non-empty"))
    end
    item = a[end]
    ccall(:jl_array_del_end, Void, (Any, UInt), a, 1)
    return item
end

function unshift!{T}(a::Array{T,1}, item)
    item = convert(T, item)
    ccall(:jl_array_grow_beg, Void, (Any, UInt), a, 1)
    a[1] = item
    return a
end

function shift!(a::Vector)
    if isempty(a)
        throw(ArgumentError("array must be non-empty"))
    end
    item = a[1]
    ccall(:jl_array_del_beg, Void, (Any, UInt), a, 1)
    return item
end

function insert!{T}(a::Array{T,1}, i::Integer, item)
    if !(1 <= i <= length(a)+1)
        throw(BoundsError())
    end
    if i == length(a)+1
        return push!(a, item)
    end
    item = convert(T, item)
    _growat!(a, i, 1)
    a[i] = item
    return a
end

function deleteat!(a::Vector, i::Integer)
    if !(1 <= i <= length(a))
        throw(BoundsError())
    end
    return _deleteat!(a, i, 1)
end

function deleteat!{T<:Integer}(a::Vector, r::UnitRange{T})
    n = length(a)
    isempty(r) && return a
    f = first(r)
    l = last(r)
    if !(1 <= f && l <= n)
        throw(BoundsError())
    end
    return _deleteat!(a, f, length(r))
end

function deleteat!(a::Vector, inds)
    n = length(a)
    s = start(inds)
    done(inds, s) && return a
    (p, s) = next(inds, s)
    q = p+1
    while !done(inds, s)
        (i,s) = next(inds, s)
        if !(q <= i <= n)
            if i < q
                throw(ArgumentError("indices must be unique and sorted"))
            else
                throw(BoundsError())
            end
        end
        while q < i
            @inbounds a[p] = a[q]
            p += 1; q += 1
        end
        q = i+1
    end
    while q <= n
        @inbounds a[p] = a[q]
        p += 1; q += 1
    end
    ccall(:jl_array_del_end, Void, (Any, UInt), a, n-p+1)
    return a
end

const _default_splice = []

function splice!(a::Vector, i::Integer, ins=_default_splice)
    v = a[i]
    m = length(ins)
    if m == 0
        _deleteat!(a, i, 1)
    elseif m == 1
        a[i] = ins[1]
    else
        _growat!(a, i, m-1)
        k = 1
        for x in ins
            a[i+k-1] = x
            k += 1
        end
    end
    return v
end

function splice!{T<:Integer}(a::Vector, r::UnitRange{T}, ins=_default_splice)
    v = a[r]
    m = length(ins)
    if m == 0
        deleteat!(a, r)
        return v
    end

    n = length(a)
    f = first(r)
    l = last(r)
    d = length(r)

    if m < d
        delta = d - m
        if f-1 < n-l
            _deleteat_beg!(a, f, delta)
        else
            _deleteat_end!(a, l-delta+1, delta)
        end
    elseif m > d
        delta = m - d
        if f-1 < n-l
            _growat_beg!(a, f, delta)
        else
            _growat_end!(a, l+1, delta)
        end
    end

    k = 1
    for x in ins
        a[f+k-1] = x
        k += 1
    end
    return v
end

function empty!(a::Vector)
    ccall(:jl_array_del_end, Void, (Any, UInt), a, length(a))
    return a
end

# use memcmp for lexcmp on byte arrays
function lexcmp(a::Array{UInt8,1}, b::Array{UInt8,1})
    c = ccall(:memcmp, Int32, (Ptr{UInt8}, Ptr{UInt8}, UInt),
              a, b, min(length(a),length(b)))
    c < 0 ? -1 : c > 0 ? +1 : cmp(length(a),length(b))
end

# note: probably should be StridedVector or AbstractVector
function reverse(A::AbstractVector, s=1, n=length(A))
    B = similar(A)
    for i = 1:s-1
        B[i] = A[i]
    end
    for i = s:n
        B[i] = A[n+s-i]
    end
    for i = n+1:length(A)
        B[i] = A[i]
    end
    B
end
reverseind(a::AbstractVector, i::Integer) = length(a) + 1 - i

reverse(v::StridedVector) = (n=length(v); [ v[n-i+1] for i=1:n ])
reverse(v::StridedVector, s, n=length(v)) = reverse!(copy(v), s, n)
function reverse!(v::StridedVector, s=1, n=length(v))
    if n <= s  # empty case; ok
    elseif !(1 ≤ s ≤ endof(v))
        throw(BoundsError(v, s))
    elseif !(1 ≤ n ≤ endof(v))
        throw(BoundsError(v, n))
    end
    r = n
    @inbounds for i in s:div(s+n-1, 2)
        v[i], v[r] = v[r], v[i]
        r -= 1
    end
    v
end

function vcat{T}(arrays::Vector{T}...)
    n = 0
    for a in arrays
        n += length(a)
    end
    arr = Array(T, n)
    ptr = pointer(arr)
    offset = 0
    if isbits(T)
        elsz = sizeof(T)
    else
        elsz = div(WORD_SIZE,8)
    end
    for a in arrays
        nba = length(a)*elsz
        ccall(:memcpy, Ptr{Void}, (Ptr{Void}, Ptr{Void}, UInt),
              ptr+offset, a, nba)
        offset += nba
    end
    return arr
end

function hcat{T}(V::Vector{T}...)
    height = length(V[1])
    for j = 2:length(V)
        if length(V[j]) != height
            throw(DimensionMismatch("vectors must have same lengths"))
        end
    end
    [ V[j][i]::T for i=1:length(V[1]), j=1:length(V) ]
end


## find ##

# returns the index of the next non-zero element, or 0 if all zeros
function findnext(A, start::Integer)
    for i = start:length(A)
        if A[i] != 0
            return i
        end
    end
    return 0
end
findfirst(A) = findnext(A, 1)

# returns the index of the next matching element
function findnext(A, v, start::Integer)
    for i = start:length(A)
        if A[i] == v
            return i
        end
    end
    return 0
end
findfirst(A, v) = findnext(A, v, 1)

# returns the index of the next element for which the function returns true
function findnext(testf::Function, A, start::Integer)
    for i = start:length(A)
        if testf(A[i])
            return i
        end
    end
    return 0
end
findfirst(testf::Function, A) = findnext(testf, A, 1)

# returns the index of the previous non-zero element, or 0 if all zeros
function findprev(A, start)
    for i = start:-1:1
        A[i] != 0 && return i
    end
    0
end
findlast(A) = findprev(A, length(A))

# returns the index of the matching element, or 0 if no matching
function findprev(A, v, start)
    for i = start:-1:1
        A[i] == v && return i
    end
    0
end
findlast(A, v) = findprev(A, v, length(A))

# returns the index of the previous element for which the function returns true, or zero if it never does
function findprev(testf::Function, A, start)
    for i = start:-1:1
        testf(A[i]) && return i
    end
    0
end
findlast(testf::Function, A) = findprev(testf, A, length(A))

function find(testf::Function, A::AbstractArray)
    # use a dynamic-length array to store the indexes, then copy to a non-padded
    # array for the return
    tmpI = Array(Int, 0)
    for i = 1:length(A)
        if testf(A[i])
            push!(tmpI, i)
        end
    end
    I = Array(Int, length(tmpI))
    copy!(I, tmpI)
    I
end

function find(A::StridedArray)
    nnzA = countnz(A)
    I = similar(A, Int, nnzA)
    count = 1
    for i=1:length(A)
        if A[i] != 0
            I[count] = i
            count += 1
        end
    end
    return I
end

find(x::Number) = x == 0 ? Array(Int,0) : [1]
find(testf::Function, x::Number) = !testf(x) ? Array(Int,0) : [1]

findn(A::AbstractVector) = find(A)

function findn(A::StridedMatrix)
    nnzA = countnz(A)
    I = similar(A, Int, nnzA)
    J = similar(A, Int, nnzA)
    count = 1
    for j=1:size(A,2), i=1:size(A,1)
        if A[i,j] != 0
            I[count] = i
            J[count] = j
            count += 1
        end
    end
    return (I, J)
end

function findnz{T}(A::AbstractMatrix{T})
    nnzA = countnz(A)
    I = zeros(Int, nnzA)
    J = zeros(Int, nnzA)
    NZs = Array(T, nnzA)
    count = 1
    if nnzA > 0
        for j=1:size(A,2), i=1:size(A,1)
            Aij = A[i,j]
            if Aij != 0
                I[count] = i
                J[count] = j
                NZs[count] = Aij
                count += 1
            end
        end
    end
    return (I, J, NZs)
end

function findmax(a)
    if isempty(a)
        throw(ArgumentError("collection must be non-empty"))
    end
    s = start(a)
    mi = i = 1
    m, s = next(a, s)
    while !done(a, s)
        ai, s = next(a, s)
        i += 1
        if ai > m || m!=m
            m = ai
            mi = i
        end
    end
    return (m, mi)
end

function findmin(a)
    if isempty(a)
        throw(ArgumentError("collection must be non-empty"))
    end
    s = start(a)
    mi = i = 1
    m, s = next(a, s)
    while !done(a, s)
        ai, s = next(a, s)
        i += 1
        if ai < m || m!=m
            m = ai
            mi = i
        end
    end
    return (m, mi)
end

indmax(a) = findmax(a)[2]
indmin(a) = findmin(a)[2]

# similar to Matlab's ismember
# returns a vector containing the highest index in b for each value in a that is a member of b
function indexin(a::AbstractArray, b::AbstractArray)
    bdict = Dict(zip(b, 1:length(b)))
    [get(bdict, i, 0) for i in a]
end

# findin (the index of intersection)
function findin(a, b::UnitRange)
    ind = Array(Int, 0)
    f = first(b)
    l = last(b)
    for i = 1:length(a)
        if f <= a[i] <= l
            push!(ind, i)
        end
    end
    ind
end

function findin(a, b)
    ind = Array(Int, 0)
    bset = Set(b)
    @inbounds for i = 1:length(a)
        a[i] in bset && push!(ind, i)
    end
    ind
end

# Copying subregions
function indcopy(sz::Dims, I::Vector)
    n = length(I)
    s = sz[n]
    for i = n+1:length(sz)
        s *= sz[i]
    end
    dst = eltype(I)[findin(I[i], i < n ? (1:sz[i]) : (1:s)) for i = 1:n]
    src = eltype(I)[I[i][findin(I[i], i < n ? (1:sz[i]) : (1:s))] for i = 1:n]
    dst, src
end

function indcopy(sz::Dims, I::Tuple{Vararg{RangeIndex}})
    n = length(I)
    s = sz[n]
    for i = n+1:length(sz)
        s *= sz[i]
    end
    dst::typeof(I) = ntuple(i-> findin(I[i], i < n ? (1:sz[i]) : (1:s)), n)::typeof(I)
    src::typeof(I) = ntuple(i-> I[i][findin(I[i], i < n ? (1:sz[i]) : (1:s))], n)::typeof(I)
    dst, src
end

## Filter ##

# given a function returning a boolean and an array, return matching elements
filter(f, As::AbstractArray) = As[map(f, As)::AbstractArray{Bool}]

function filter!(f, a::Vector)
    insrt = 1
    for curr = 1:length(a)
        if f(a[curr])
            a[insrt] = a[curr]
            insrt += 1
        end
    end
    deleteat!(a, insrt:length(a))
    return a
end

function filter(f, a::Vector)
    r = Array(eltype(a), 0)
    for i = 1:length(a)
        if f(a[i])
            push!(r, a[i])
        end
    end
    return r
end

# set-like operators for vectors
# These are moderately efficient, preserve order, and remove dupes.

function intersect(v1, vs...)
    ret = Array(eltype(v1),0)
    for v_elem in v1
        inall = true
        for i = 1:length(vs)
            if !in(v_elem, vs[i])
                inall=false; break
            end
        end
        if inall
            push!(ret, v_elem)
        end
    end
    ret
end

function union(vs...)
    ret = Array(promote_eltype(vs...),0)
    seen = Set()
    for v in vs
        for v_elem in v
            if !in(v_elem, seen)
                push!(ret, v_elem)
                push!(seen, v_elem)
            end
        end
    end
    ret
end
# setdiff only accepts two args
function setdiff(a, b)
    args_type = promote_type(eltype(a), eltype(b))
    bset = Set(b)
    ret = Array(args_type,0)
    seen = Set{eltype(a)}()
    for a_elem in a
        if !in(a_elem, seen) && !in(a_elem, bset)
            push!(ret, a_elem)
            push!(seen, a_elem)
        end
    end
    ret
end
# symdiff is associative, so a relatively clean
# way to implement this is by using setdiff and union, and
# recursing. Has the advantage of keeping order, too, but
# not as fast as other methods that make a single pass and
# store counts with a Dict.
symdiff(a) = a
symdiff(a, b) = union(setdiff(a,b), setdiff(b,a))
symdiff(a, b, rest...) = symdiff(a, symdiff(b, rest...))