local Observable = require "rx.observable"
local Observer = require "rx.observer"
local Subscription = require "rx.subscription"
local util = require "rx.util"

--- @class Subject
-- @description Subjects function both as an Observer and as an Observable. Subjects inherit all
-- Observable functions, including subscribe. Values can also be pushed to the Subject, which will
-- be broadcasted to any subscribed Observers.
local Subject = setmetatable({}, Observable)
Subject.__index = Subject
Subject.__tostring = util.constant("Subject")

--- Creates a new Subject.
-- @returns {Subject}
function Subject.create()
    local self = {
        observers = {},
        stopped = false,
    }

    return setmetatable(self, Subject)
end

--- Creates a new Observer and attaches it to the Subject.
-- @arg {function|table} onNext|observer - A function called when the Subject produces a value or
--                                         an existing Observer to attach to the Subject.
-- @arg {function} onError - Called when the Subject terminates due to an error.
-- @arg {function} onCompleted - Called when the Subject completes normally.
function Subject:subscribe(onNext, onError, onCompleted)
    local observer

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

    table.insert(self.observers, observer)

    return Subscription.create(function()
        for i = 1, #self.observers do
            if self.observers[i] == observer then
                table.remove(self.observers, i)
                return
            end
        end
    end)
end

--- Pushes zero or more values to the Subject. They will be broadcasted to all Observers.
-- @arg {*...} values
function Subject:onNext(...)
    if not self.stopped then
        for i = #self.observers, 1, -1 do
            self.observers[i]:onNext(...)
        end
    end
end

--- Signal to all Observers that an error has occurred.
-- @arg {string=} message - A string describing what went wrong.
function Subject:onError(message)
    if not self.stopped then
        for i = #self.observers, 1, -1 do
            self.observers[i]:onError(message)
        end

        self.stopped = true
    end
end

--- Signal to all Observers that the Subject will not produce any more values.
function Subject:onCompleted()
    if not self.stopped then
        for i = #self.observers, 1, -1 do
            self.observers[i]:onCompleted()
        end

        self.stopped = true
    end
end

Subject.__call = Subject.onNext

return Subject
