lightning comms

local sensor = peripheral.find "manipulator"

local function bitpack(a, b, c, d)
    return bit.bor(bit.blshift(a, 6), bit.blshift(b, 4), bit.blshift(c, 2), d)
end

local function bitunpack(x)
    return bit.brshift(bit.band(x, 192), 6), bit.brshift(bit.band(x, 48), 4), bit.band(bit.brshift(x, 12), 2), bit.band(x, 3)
end

local function has_struck()
    for _, x in pairs(sensor.sense()) do
        if x.displayName == "item.tile.wood.oak" then return false end
    end
    return true
end

local function ticks()
    return os.time() * 1000
end

local function syncto(interval)
    local t_now = ticks()
    local x = interval - t_now % interval
    if x > 0 then sleep(x * 0.05) end
end

local function instantiate_creeper()
    commands.execAsync [[kill @e[type=item,r=3] ]]
    commands.execAsync [[summon item ~ ~1 ~ {Item:{id:"minecraft:planks",Count:1}}]]
    sleep()
end

local function cause_lightning()
    for i = 1, 10 do commands.execAsync "summon lightning_bolt 27387 50 -86351" end
end

local function recv()
    syncto(20)
    instantiate_creeper()
    -- receive preamble
    sleep(0.05)
    if not has_struck() then return false end
    syncto(3)
    if not has_struck() then return false end
    syncto(5)
    if not has_struck() then return false end
    print "Preamble acquired."
    local q = {}
    while true do
        syncto(20)
        instantiate_creeper()
        sleep(0.1)
        local ctr = 0
        while true do
            if has_struck() then break end
            sleep()
            if ctr > 50 then return end
            ctr = ctr + 1
        end
        local delay = ticks() % 20
        print("delay", math.floor(delay / 3))
        table.insert(q, math.floor(delay / 3))
    end
    local out = ""
    for i = 1, #q, 4 do
        table.insert(string.byte(bitpack(q[i], q[i+1], q[i+2], q[i+3])))
    end
    return out
end

local function send(x)
    syncto(20)
    sleep(0.05)
    cause_lightning()
    syncto(3)
    cause_lightning()
    syncto(5)
    cause_lightning()
    local pkt = {string.byte(x, 1, #x)}
    local rawpkt = {}
    for _, v in pairs(pkt) do
        local a, b, c, d = bitunpack(v)
        table.insert(rawpkt, a)
        table.insert(rawpkt, b)
        table.insert(rawpkt, c)
        table.insert(rawpkt, d)
    end
    for _, v in pairs(rawpkt) do
        syncto(20)
        sleep(0.15 * v + 0.1)
        print("TX", ticks(), v)
        cause_lightning()
    end
end

if ... == "send" then
    send "Test.."
else
    while true do print(recv()) end
end