endernet

--To use in your program, the following lines must be added.
--os.loadAPI("endernet")
--os.pullEvent = endernet.middle
--os.pullEventRaw = endernet.middleRaw
--
--This API exposes the following methods (NOTE: all topics MUST begin with "/", otherwise they will be dropped with 404 error code)
--send(string topic, string message) --Sends a message to the specified topic --Returns maximum number of possibly connected clients (Not all that useful, but can be informative)
--subscribe(string topic) --Subscribes to a topic in order to receive messages from it --Returns nil
--assert(string topic) --Asserts a topic, renewing a request in case its connection is dropped
--unsubscribe(string topic) --Unsubscribes from a topic --Returns nil
--receive() --Receives message from any of the subscribed topics --Returns topic, message
--middle(event) --Meant to replace os.pullEvent, and handles http events in order to keep them alive
--middleRaw(event) --Same as above, for os.pullEventRaw

--Define global api modifications to help later
function table.contains(table, element)
    for _, value in pairs(table) do
        if value == element then
            return true
        end
    end
    return false
end

--Define local variables
local subdTopics = {}
local baseUrl = "https://ccnet.herokuapp.com"
local sendUrl = "/send"
local query = "/query"
local dataToSend = "?message="

--Define functions
function send(topic,message) --Sends a message to a topic
    local hhandle = http.get(baseUrl..sendUrl..topic..dataToSend..textutils.urlEncode(message))
    return tonumber(hhandle.readAll())
end

function subscribe(topic) --Subscribes to a topic
    if not table.contains(subdTopics,topic) then
        table.insert(subdTopics,topic)
        http.request(baseUrl..query..topic)
    end
end

function assert(topic) --Asserts a topic, renewing it's connection in case it dropped
    http.request(baseUrl..query..topic)
end

function unsubscribe(topic) --Unsubscribes from a topic
    for k,v in pairs(subdTopics) do
        if v==topic then
            table.remove(subdTopics,k)
        end
    end
end

function receive() --Returns topic, message
    local event = {middle("endernet_receive")}
    return event[2],event[3]
end

function middle(eventName) --os.pullEvent = endernet.middle
    --Define variables that I'd prefer not to leak out but are evaluated later
    local event
    local topic
    local message

    --Yield should work, because if it's overwritten, the computer won't work
    event = {coroutine.yield()}
    if event[1]=="terminate" then
        error("Terminated")
    end

    --Parse the event
    if event[1]=="http_success" then
        topic = string.gsub(event[2],baseUrl..query,"")
        if table.contains(subdTopics,topic) then
            http.request(event[2])
        end
        if eventName==nil or eventName=="endernet_receive" then
            if string.find(event[2],baseUrl..query)~=nil then
                message = event[3].readAll()
                return "endernet_receive",topic,message
            else
                return table.unpack(event)
            end
        else
            return middle(eventName)
        end
    elseif event[1]=="http_failure" then
        if table.contains(subdTopics,string.gsub(event[2],baseUrl..query,"")) then
            http.request(event[2])
        end
        return middle(eventName)
    else
        if eventName==nil or event[1]==eventName then
            return table.unpack(event)
        else
            return middle(eventName)
        end
    end

end

function middleRaw(eventName) --os.pullEvent = endernet.middle
    --Define variables that I'd prefer not to leak out but are evaluated later
    local event
    local topic
    local message

    --Yield should work, because if it's overwritten, the computer won't work
    event = {coroutine.yield()}

    --Parse the event
    if event[1]=="http_success" then
        topic = string.gsub(event[2],baseUrl..query,"")
        if table.contains(subdTopics,topic) then
            http.request(event[2])
        end
        if eventName==nil or eventName=="endernet_receive" then
            if string.find(event[2],baseUrl..query)~=nil then
                message = event[3].readAll()
                return "endernet_receive",topic,message
            else
                return table.unpack(event)
            end
        else
            return middle(eventName)
        end
    elseif event[1]=="http_failure" then
        if table.contains(subdTopics,string.gsub(event[2],baseUrl..query,"")) then
            http.request(event[2])
        end
        return middle(eventName)
    else
        if eventName==nil or event[1]==eventName then
            return table.unpack(event)
        else
            return middle(eventName)
        end
    end

end