local Subject = require "rx.subjects.subject"
local Observer = require "rx.observer"
local util = require "rx.util"

--- @class ReplaySubject
-- @description A Subject that provides new Subscribers with some or all of the most recently
-- produced values upon subscription.
local ReplaySubject = setmetatable({}, Subject)
ReplaySubject.__index = ReplaySubject
ReplaySubject.__tostring = util.constant("ReplaySubject")

--- Creates a new ReplaySubject.
-- @arg {number=} bufferSize - The number of values to send to new subscribers. If nil, an infinite
--                             buffer is used (note that this could lead to memory issues).
-- @returns {ReplaySubject}
function ReplaySubject.create(n)
    local self = {
        observers = {},
        stopped = false,
        buffer = {},
        bufferSize = n,
    }

    return setmetatable(self, ReplaySubject)
end

--- Creates a new Observer and attaches it to the ReplaySubject. Immediately broadcasts the most
-- contents of the buffer to the Observer.
-- @arg {function} onNext - Called when the ReplaySubject produces a value.
-- @arg {function} onError - Called when the ReplaySubject terminates due to an error.
-- @arg {function} onCompleted - Called when the ReplaySubject completes normally.
function ReplaySubject:subscribe(onNext, onError, onCompleted)
    local observer

    if util.isa(onNext, Observer) then
        observer = onNext
    else
        observer = Observer.create(onNext, onError, onCompleted)
    end

    local subscription = Subject.subscribe(self, observer)

    for i = 1, #self.buffer do
        observer:onNext(util.unpack(self.buffer[i]))
    end

    return subscription
end

--- Pushes zero or more values to the ReplaySubject. They will be broadcasted to all Observers.
-- @arg {*...} values
function ReplaySubject:onNext(...)
    table.insert(self.buffer, util.pack(...))
    if self.bufferSize and #self.buffer > self.bufferSize then
        table.remove(self.buffer, 1)
    end

    return Subject.onNext(self, ...)
end

ReplaySubject.__call = ReplaySubject.onNext

return ReplaySubject
