Obsidian Computer

-- VARIABLES --
bRunning = true -- Whether or not the program is running.
tConnectedTurtles = {}
---------------

-- Locates and opens any modem that exists on this computer.
-- Throws an error if no modem exists.
function openExistantModem()
    local tSides = rs.getSides()

    for nSideIndex, sSide in ipairs(tSides) do
        if peripheral.isPresent(sSide) and peripheral.getType(sSide) == "modem" then
            rednet.open(sSide)
            return
        end
    end

    error("No modem found.")
end

-- SETUP:
--  Each turtle will have a chest behind them and a stack of redstone.
--  There will be three blocks in front of them, where the obsidian will be.

-- Opens or closes the pistons, depending on their current state.
-- CLOSED: Lava will be contained.
-- OPENED: Lave will be lose, generating obsidian.
function togglePistons()
    -- If the redstone is activated, then the pistons are closed, open them.
    if rs.getInput("right") then
        rs.setOutput("back", false)
    -- If the redstone is not activated, then the pistons are open, close them.
    else
        rs.setOutput("back", true)
    end
end


-- Checks if all of the coneected turtles have the proper materials
-- to perform another collection cycle.
function turtlesHaveProperMaterials()
    for nTurtleIndex, nTurtleID in ipairs(tConnectedTurtles) do
        -- Send a message to the turtle asking if it is ready for another cycle.
        rednet.send(nTurtleID, "READY_FOR_CYCLE?")
        -- Wait for a response from the turtle with a timeout of 3 seconds.
        local nSender, sMessage = rednet.receive(3)
        -- If the message received is nil because the timeout triggered, stop the loop and return false.
        if not sMessage then
            return false
        end
    end

    -- If the loop completed without returning, then the turtles are ready to complete another colleciton cycle.
    return true
end

-- Sends all of the proper messages to the turtles, telling them
-- to begin the collection of the obsiian that was just generated.
function startObsidianCollection_withTurtles()
    -- Before we begin the collection, make sure all of the turtles have
    -- the proper materials for another cycle.
    -- PROPER MATERIALS:
    -- 3 redstone.
    if turtlesHaveProperMaterials() then
        for nTurtleIndex, nTurtleID in ipairs(tConnectedTurtles) do
            rednet.send(nTurtleID, "BEGIN_COLLECTION")
        end

        return true
    else
        bRunning = false
        return false
    end
end

-- Sends acknowledgements to all of the turtles so that they will stop sending confirmations,
-- in the case of a failure during the collection process.
function sendEmergencyAcknowledgements()
    for nTurtleIndex, nTurtleID in ipairs(tConnectedTurtles) do
        rednet.send(nTurtleID, "COMPLETION_ACKNOWLEDGED")
    end
end

-- Waits for the confirmation message from all turtles, then closes the pistons.
-- ASSUMES THAT THE PISTONS ARE OPEN!
-- Turtles perform their collection routine, then send confirmation messages
-- back to this computer. This computer will send an acknowledgement back to
-- the turtles, then the turtles will await another collection request. TURTLES
-- WILL CONTINUE SENDING CONFIRMATIONS UNTIL ACKNOWLEDGED!!!
function waitForCollectionCompletion()
    for nTurtleID, nTurtleID in ipairs(tConnectedTurtles) do
        local nSender, sMessage = rednet.receive(8)


        -- If the message received was not from a turtle, and was about a completed collection, close the pistons.
        if sMessage ~= "COLLECTION_COMPLETE" then
            togglePistons()
            sendEmergencyAcknowledgements() -- Send out acknowledgements just so that the turtles will stop sending confirmations.

            bRunning = false
            return false
        -- If the message was a completion confirmation, acknowledge it so we can listen for other confirmations.
        else
            rednet.send(nSender, "COMPLETION_ACKNOWLEDGED")
        end
    end

    -- Now that all of the turtles have sent a confirmation message, close the pistons.
    togglePistons()
    return true
end

-- Incorporates all above methods into one collection cycle.
function collectionCycle()
    if startObsidianCollection_withTurtles() then
        if waitForCollectionCompletion() then
            return true
        else
            return false
        end
    else
        return false
    end
end

-- The main loop of the program.
print("Cycling started...")
openExistantModem()
while bRunning do
    local sInput = read()

    if sInput == "start" then
        if not collectionCycle() then
            print("Cycle failure.")
        end
    end
end