using DataStructures

"""

Maintains a rolling window of the last `window_size` values

using an efficient circular buffer with O(1) push and pop operations.

# Arguments

- `window_size::Int`: The size of the window to maintain.

- `copy::Bool=false`: If `true`, the result will be a copy of the data as `Vector{In}`,

otherwise it will be a `view` into the underlying buffer.

The implementation is based on [DataStructures.jl](https://juliacollections.github.io/DataStructures.jl/latest/)'s [CircularBuffer](https://juliacollections.github.io/DataStructures.jl/latest/circ_buffer/).

Note that the returned value is a view into the buffer, so it is not a copy of the data,

hence the result should not be modified or stored for later use.

If temporary storage of the result or modification of the values is needed, a copy should be made.

"""

mutable struct WindowBuffer{T,copy} <: StreamOperation

const buffer::CircularBuffer{T}

const copy::Bool

WindowBuffer{T}(

window_size::Int

;

copy::Bool=false

) where {T} = begin

buffer = CircularBuffer{T}(window_size)

new{T,copy}(buffer, copy)

end

end

@inline function (op::WindowBuffer{T})(executor, value::T) where {T}

# automatically handles overwriting in a circular manner

push!(op.buffer, value)

nothing

end

@inline is_valid(op::WindowBuffer) = isfull(op.buffer)

@inline function get_state(op::WindowBuffer{T,false}) where {T}

view(op.buffer, :)

end

@inline function get_state(op::WindowBuffer{T,true}) where {T}

collect(op.buffer)

end

@inline Base.empty!(op::WindowBuffer) = empty!(op.buffer)

@inline Base.length(op::WindowBuffer) = length(op.buffer)