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

struct Set{T} <: AbstractSet{T}
    dict::Dict{T,Nothing}

    Set{T}() where {T} = new(Dict{T,Nothing}())
    Set{T}(s::Set{T}) where {T} = new(Dict{T,Nothing}(s.dict))
end

Set{T}(itr) where {T} = union!(Set{T}(), itr)
Set() = Set{Any}()


"""
    Set([itr])

Construct a [`Set`](@ref) of the values generated by the given iterable object, or an
empty set. Should be used instead of [`BitSet`](@ref) for sparse integer sets, or
for sets of arbitrary objects.
"""
Set(itr) = _Set(itr, IteratorEltype(itr))

_Set(itr, ::HasEltype) = Set{eltype(itr)}(itr)

function _Set(itr, ::EltypeUnknown)
    T = @default_eltype(itr)
    (isconcretetype(T) || T === Union{}) || return grow_to!(Set{T}(), itr)
    return Set{T}(itr)
end

empty(s::AbstractSet{T}, ::Type{U}=T) where {T,U} = Set{U}()

# return an empty set with eltype T, which is mutable (can be grown)
# by default, a Set is returned
emptymutable(s::AbstractSet{T}, ::Type{U}=T) where {T,U} = Set{U}()

_similar_for(c::AbstractSet, ::Type{T}, itr, isz) where {T} = empty(c, T)

function show(io::IO, s::Set)
    print(io, "Set(")
    show_vector(io, s)
    print(io, ')')
end

isempty(s::Set) = isempty(s.dict)
length(s::Set)  = length(s.dict)
in(x, s::Set) = haskey(s.dict, x)
push!(s::Set, x) = (s.dict[x] = nothing; s)
pop!(s::Set, x) = (pop!(s.dict, x); x)
pop!(s::Set, x, default) = (x in s ? pop!(s, x) : default)

function pop!(s::Set)
    isempty(s) && throw(ArgumentError("set must be non-empty"))
    return pop!(s.dict)[1]
end

delete!(s::Set, x) = (delete!(s.dict, x); s)

copy(s::Set) = copymutable(s)

# Set is the default mutable fall-back
copymutable(s::AbstractSet{T}) where {T} = Set{T}(s)

sizehint!(s::Set, newsz) = (sizehint!(s.dict, newsz); s)
empty!(s::Set) = (empty!(s.dict); s)
rehash!(s::Set) = (rehash!(s.dict); s)

iterate(s::Set, i...)       = iterate(KeySet(s.dict), i...)

# In case the size(s) is smaller than size(t) its more efficient to iterate through
# elements of s instead and only delete the ones also contained in t.
# The threshold for this decision boils down to a tradeoff between
# size(s) * cost(in() + delete!()) ≶ size(t) * cost(delete!())
# Empirical observations on Ints point towards a threshold of 0.8.
# To be on the safe side (e.g. cost(in) >>> cost(delete!) ) a
# conservative threshold of 0.5 was chosen.
function setdiff!(s::Set, t::Set)
    if 2 * length(s) < length(t)
        for x in s
            x in t && delete!(s, x)
        end
    else
        for x in t
            delete!(s, x)
        end
    end
    return s
end

"""
    unique(itr)

Return an array containing only the unique elements of collection `itr`,
as determined by [`isequal`](@ref), in the order that the first of each
set of equivalent elements originally appears. The element type of the
input is preserved.

# Examples
```jldoctest
julia> unique([1, 2, 6, 2])
3-element Array{Int64,1}:
 1
 2
 6

julia> unique(Real[1, 1.0, 2])
2-element Array{Real,1}:
 1
 2
```
"""
function unique(itr)
    T = @default_eltype(itr)
    out = Vector{T}()
    seen = Set{T}()
    y = iterate(itr)
    y === nothing && return out
    x, i = y
    if !isconcretetype(T) && IteratorEltype(itr) == EltypeUnknown()
        S = typeof(x)
        return _unique_from(itr, S[x], Set{S}((x,)), i)
    end
    push!(seen, x)
    push!(out, x)
    return unique_from(itr, out, seen, i)
end

_unique_from(itr, out, seen, i) = unique_from(itr, out, seen, i)
@inline function unique_from(itr, out::Vector{T}, seen, i) where T
    while true
        y = iterate(itr, i)
        y === nothing && break
        x, i = y
        S = typeof(x)
        if !(S === T || S <: T)
            R = promote_typejoin(S, T)
            seenR = convert(Set{R}, seen)
            outR = convert(Vector{R}, out)
            if !in(x, seenR)
                push!(seenR, x)
                push!(outR, x)
            end
            return _unique_from(itr, outR, seenR, i)
        end
        if !in(x, seen)
            push!(seen, x)
            push!(out, x)
        end
    end
    return out
end

"""
    unique(f, itr)

Returns an array containing one value from `itr` for each unique value produced by `f`
applied to elements of `itr`.

# Examples
```jldoctest
julia> unique(x -> x^2, [1, -1, 3, -3, 4])
3-element Array{Int64,1}:
 1
 3
 4
```
"""
function unique(f, C)
    out = Vector{eltype(C)}()

    s = iterate(C)
    if s === nothing
        return out
    end
    (x, i) = s
    y = f(x)
    seen = Set{typeof(y)}()
    push!(seen, y)
    push!(out, x)

    return _unique!(f, out, C, seen, i)
end

function _unique!(f, out::AbstractVector, C, seen::Set, i)
    s = iterate(C, i)
    while s !== nothing
        (x, i) = s
        y = f(x)
        if y ∉ seen
            push!(out, x)
            if y isa eltype(seen)
                push!(seen, y)
            else
                seen2 = convert(Set{promote_typejoin(eltype(seen), typeof(y))}, seen)
                push!(seen2, y)
                return _unique!(f, out, C, seen2, i)
            end
        end
        s = iterate(C, i)
    end

    return out
end

"""
    unique!(f, A::AbstractVector)

Selects one value from `A` for each unique value produced by `f` applied to
elements of `A` , then return the modified A.

!!! compat "Julia 1.1"
    This method is available as of Julia 1.1.

# Examples
```jldoctest
julia> unique!(x -> x^2, [1, -1, 3, -3, 4])
3-element Array{Int64,1}:
 1
 3
 4

julia> unique!(n -> n%3, [5, 1, 8, 9, 3, 4, 10, 7, 2, 6])
3-element Array{Int64,1}:
 5
 1
 9

julia> unique!(iseven, [2, 3, 5, 7, 9])
2-element Array{Int64,1}:
 2
 3
```
"""
function unique!(f, A::AbstractVector)
    if length(A) <= 1
        return A
    end

    i = firstindex(A)
    x = @inbounds A[i]
    y = f(x)
    seen = Set{typeof(y)}()
    push!(seen, y)
    return _unique!(f, A, seen, i, i+1)
end

function _unique!(f, A::AbstractVector, seen::Set, current::Integer, i::Integer)
    while i <= lastindex(A)
        x = @inbounds A[i]
        y = f(x)
        if y ∉ seen
            current += 1
            @inbounds A[current] = x
            if y isa eltype(seen)
                push!(seen, y)
            else
                seen2 = convert(Set{promote_typejoin(eltype(seen), typeof(y))}, seen)
                push!(seen2, y)
                return _unique!(f, A, seen2, current, i+1)
            end
        end
        i += 1
    end
    return resize!(A, current - firstindex(A) + 1)
end


# If A is not grouped, then we will need to keep track of all of the elements that we have
# seen so far.
_unique!(A::AbstractVector) = unique!(identity, A::AbstractVector)

# If A is grouped, so that each unique element is in a contiguous group, then we only
# need to keep track of one element at a time. We replace the elements of A with the
# unique elements that we see in the order that we see them. Once we have iterated
# through A, we resize A based on the number of unique elements that we see.
function _groupedunique!(A::AbstractVector)
    isempty(A) && return A
    idxs = eachindex(A)
    y = first(A)
    # We always keep the first element
    it = iterate(idxs, iterate(idxs)[2])
    count = 1
    for x in Iterators.drop(A, 1)
        if !isequal(x, y)
            y = A[it[1]] = x
            count += 1
            it = iterate(idxs, it[2])
        end
    end
    resize!(A, count)
end

"""
    unique!(A::AbstractVector)

Remove duplicate items as determined by [`isequal`](@ref), then return the modified `A`.
`unique!` will return the elements of `A` in the order that they occur. If you do not care
about the order of the returned data, then calling `(sort!(A); unique!(A))` will be much
more efficient as long as the elements of `A` can be sorted.

# Examples
```jldoctest
julia> unique!([1, 1, 1])
1-element Array{Int64,1}:
 1

julia> A = [7, 3, 2, 3, 7, 5];

julia> unique!(A)
4-element Array{Int64,1}:
 7
 3
 2
 5

julia> B = [7, 6, 42, 6, 7, 42];

julia> sort!(B);  # unique! is able to process sorted data much more efficiently.

julia> unique!(B)
3-element Array{Int64,1}:
  6
  7
 42
```
"""
function unique!(A::Union{AbstractVector{<:Real}, AbstractVector{<:AbstractString},
                          AbstractVector{<:Symbol}})
    if isempty(A)
        return A
    elseif issorted(A) || issorted(A, rev=true)
        return _groupedunique!(A)
    else
        return _unique!(A)
    end
end
# issorted fails for some element types, so the method above has to be restricted to
# elements with isless/< defined.
function unique!(A)
    if isempty(A)
        return A
    else
        return _unique!(A)
    end
end

"""
    allunique(itr) -> Bool

Return `true` if all values from `itr` are distinct when compared with [`isequal`](@ref).

# Examples
```jldoctest
julia> a = [1; 2; 3]
3-element Array{Int64,1}:
 1
 2
 3

julia> allunique([a, a])
false
```
"""
function allunique(C)
    seen = Set{eltype(C)}()
    for x in C
        if in(x, seen)
            return false
        else
            push!(seen, x)
        end
    end
    true
end

allunique(::Set) = true

allunique(r::AbstractRange{T}) where {T} = (step(r) != zero(T)) || (length(r) <= 1)
allunique(r::StepRange{T,S}) where {T,S} = (step(r) != zero(S)) || (length(r) <= 1)

filter!(f, s::Set) = unsafe_filter!(f, s)

const hashs_seed = UInt === UInt64 ? 0x852ada37cfe8e0ce : 0xcfe8e0ce
function hash(s::AbstractSet, h::UInt)
    hv = hashs_seed
    for x in s
        hv ⊻= hash(x)
    end
    hash(hv, h)
end

convert(::Type{T}, s::T) where {T<:AbstractSet} = s
convert(::Type{T}, s::AbstractSet) where {T<:AbstractSet} = T(s)


## replace/replace! ##

function check_count(count::Integer)
    count < 0 && throw(DomainError(count, "`count` must not be negative (got $count)"))
    return min(count, typemax(Int)) % Int
end

# TODO: use copy!, which is currently unavailable from here since it is defined in Future
_copy_oftype(x, ::Type{T}) where {T} = copyto!(similar(x, T), x)
# TODO: use similar() once deprecation is removed and it preserves keys
_copy_oftype(x::AbstractDict, ::Type{T}) where {T} = merge!(empty(x, T), x)
_copy_oftype(x::AbstractSet, ::Type{T}) where {T} = union!(empty(x, T), x)

_copy_oftype(x::AbstractArray{T}, ::Type{T}) where {T} = copy(x)
_copy_oftype(x::AbstractDict{K,V}, ::Type{Pair{K,V}}) where {K,V} = copy(x)
_copy_oftype(x::AbstractSet{T}, ::Type{T}) where {T} = copy(x)

_similar_or_copy(x::Any) = similar(x)
_similar_or_copy(x::Any, ::Type{T}) where {T} = similar(x, T)
# Make a copy on construction since it is faster than inserting elements separately
_similar_or_copy(x::Union{AbstractDict,AbstractSet}) = copy(x)
_similar_or_copy(x::Union{AbstractDict,AbstractSet}, ::Type{T}) where {T} = _copy_oftype(x, T)

# to make replace/replace! work for a new container type Cont, only
# _replace!(new::Callable, res::Cont, A::Cont, count::Int)
# has to be implemented

"""
    replace!(A, old_new::Pair...; [count::Integer])

For each pair `old=>new` in `old_new`, replace all occurrences
of `old` in collection `A` by `new`.
Equality is determined using [`isequal`](@ref).
If `count` is specified, then replace at most `count` occurrences in total.
See also [`replace`](@ref replace(A, old_new::Pair...)).

# Examples
```jldoctest
julia> replace!([1, 2, 1, 3], 1=>0, 2=>4, count=2)
4-element Array{Int64,1}:
 0
 4
 1
 3

julia> replace!(Set([1, 2, 3]), 1=>0)
Set([0, 2, 3])
```
"""
replace!(A, old_new::Pair...; count::Integer=typemax(Int)) =
    replace_pairs!(A, A, check_count(count), old_new)

function replace_pairs!(res, A, count::Int, old_new::Tuple{Vararg{Pair}})
    @inline function new(x)
        for o_n in old_new
            isequal(first(o_n), x) && return last(o_n)
        end
        return x # no replace
    end
    _replace!(new, res, A, count)
end

"""
    replace!(new::Function, A; [count::Integer])

Replace each element `x` in collection `A` by `new(x)`.
If `count` is specified, then replace at most `count` values in total
(replacements being defined as `new(x) !== x`).

# Examples
```jldoctest
julia> replace!(x -> isodd(x) ? 2x : x, [1, 2, 3, 4])
4-element Array{Int64,1}:
 2
 2
 6
 4

julia> replace!(Dict(1=>2, 3=>4)) do kv
           first(kv) < 3 ? first(kv)=>3 : kv
       end
Dict{Int64,Int64} with 2 entries:
  3 => 4
  1 => 3

julia> replace!(x->2x, Set([3, 6]))
Set([6, 12])
```
"""
replace!(new::Callable, A; count::Integer=typemax(Int)) =
    _replace!(new, A, A, check_count(count))

"""
    replace(A, old_new::Pair...; [count::Integer])

Return a copy of collection `A` where, for each pair `old=>new` in `old_new`,
all occurrences of `old` are replaced by `new`.
Equality is determined using [`isequal`](@ref).
If `count` is specified, then replace at most `count` occurrences in total.

The element type of the result is chosen using promotion (see [`promote_type`](@ref))
based on the element type of `A` and on the types of the `new` values in pairs.
If `count` is omitted and the element type of `A` is a `Union`, the element type
of the result will not include singleton types which are replaced with values of
a different type: for example, `Union{T,Missing}` will become `T` if `missing` is
replaced.

See also [`replace!`](@ref).

# Examples
```jldoctest
julia> replace([1, 2, 1, 3], 1=>0, 2=>4, count=2)
4-element Array{Int64,1}:
 0
 4
 1
 3

julia> replace([1, missing], missing=>0)
2-element Array{Int64,1}:
 1
 0
```
"""
function replace(A, old_new::Pair...; count::Union{Integer,Nothing}=nothing)
    V = promote_valuetype(old_new...)
    if count isa Nothing
        T = promote_type(subtract_singletontype(eltype(A), old_new...), V)
        replace_pairs!(_similar_or_copy(A, T), A, typemax(Int), old_new)
    else
        U = promote_type(eltype(A), V)
        replace_pairs!(_similar_or_copy(A, U), A, check_count(count), old_new)
    end
end

promote_valuetype(x::Pair{K, V}) where {K, V} = V
promote_valuetype(x::Pair{K, V}, y::Pair...) where {K, V} =
    promote_type(V, promote_valuetype(y...))

# Subtract singleton types which are going to be replaced
@pure issingletontype(T::DataType) = isdefined(T, :instance)
issingletontype(::Type) = false
function subtract_singletontype(::Type{T}, x::Pair{K}) where {T, K}
    if issingletontype(K)
        Core.Compiler.typesubtract(T, K)
    else
        T
    end
end
subtract_singletontype(::Type{T}, x::Pair{K}, y::Pair...) where {T, K} =
    subtract_singletontype(subtract_singletontype(T, y...), x)

"""
    replace(new::Function, A; [count::Integer])

Return a copy of `A` where each value `x` in `A` is replaced by `new(x)`
If `count` is specified, then replace at most `count` values in total
(replacements being defined as `new(x) !== x`).

# Examples
```jldoctest
julia> replace(x -> isodd(x) ? 2x : x, [1, 2, 3, 4])
4-element Array{Int64,1}:
 2
 2
 6
 4

julia> replace(Dict(1=>2, 3=>4)) do kv
           first(kv) < 3 ? first(kv)=>3 : kv
       end
Dict{Int64,Int64} with 2 entries:
  3 => 4
  1 => 3
```
"""
replace(new::Callable, A; count::Integer=typemax(Int)) =
    _replace!(new, _similar_or_copy(A), A, check_count(count))

# Handle ambiguities
replace!(a::Callable, b::Pair; count::Integer=-1) = throw(MethodError(replace!, (a, b)))
replace!(a::Callable, b::Pair, c::Pair; count::Integer=-1) = throw(MethodError(replace!, (a, b, c)))
replace(a::Callable, b::Pair; count::Integer=-1) = throw(MethodError(replace, (a, b)))
replace(a::Callable, b::Pair, c::Pair; count::Integer=-1) = throw(MethodError(replace, (a, b, c)))
replace(a::AbstractString, b::Pair, c::Pair) = throw(MethodError(replace, (a, b, c)))

### replace! for AbstractDict/AbstractSet

askey(k, ::AbstractDict) = k.first
askey(k, ::AbstractSet) = k

function _replace!(new::Callable, res::T, A::T,
                   count::Int) where T<:Union{AbstractDict,AbstractSet}
    c = 0
    if res === A # cannot replace elements while iterating over A
        repl = Pair{eltype(A),eltype(A)}[]
        for x in A
            y = new(x)
            if x !== y
                push!(repl, x => y)
                c += 1
            end
            c == count && break
        end
        for oldnew in repl
            pop!(res, askey(first(oldnew), res))
        end
        for oldnew in repl
            push!(res, last(oldnew))
        end
    else
        for x in A
            y = new(x)
            if x !== y
                pop!(res, askey(x, res))
                push!(res, y)
                c += 1
            end
            c == count && break
        end
    end
    res
end

### replace! for AbstractArray

function _replace!(new::Callable, res::AbstractArray, A::AbstractArray, count::Int)
    c = 0
    if count >= length(A) # simpler loop allows for SIMD
        for i in eachindex(A)
            @inbounds Ai = A[i]
            y = new(Ai)
            @inbounds res[i] = y
        end
    else
        for i in eachindex(A)
            @inbounds Ai = A[i]
            if c < count
                y = new(Ai)
                @inbounds res[i] = y
                c += (Ai !== y)
            else
                @inbounds res[i] = Ai
            end
        end
    end
    res
end
