Location System - find your enemy's computers

-- Location System
-- by MysticT

local tLocations = {}
local tKnownLocations = {}
local bDebug = false

-- Helper functions

local function clear()
term.clear()
term.setCursorPos(1, 1)
end

local function table_size(t)
local i = 0
for _,_ in pairs(t) do
i = i + 1
end
return i
end

local function connect()
print("Starting location system...")
print("Connecting to rednet...")
for _,s in ipairs(rs.getSides()) do
if peripheral.isPresent(s) and peripheral.getType(s) == "modem" then
rednet.open(s)
return true
end
end
print("No modem found")
print("Aborting")
return false
end

local function _print(...)
if bDebug then
print(...)
end
end

local function vector_equal(v1, v2)
return v1.x == v2.x and v1.y == v2.y and v1.z == v2.z
end

-- Load/Save functions

local function save()
_print("Saving locations...")
local file = fs.open("locations.dat", "w")
if file then
for id, loc in pairs(tKnownLocations) do
file.writeLine(tostring(id)..": "..tostring(loc.x)..", "..tostring(loc.y)..", "..tostring(loc.z))
end
file.close()
_print("Locations saved")
return true
end
_print("Error saving locations")
return false
end

local function load()
_print("Loading locations")
local file = fs.open("locations.dat", "r")
if file then
local i = 0
local sLine = file.readLine()
while sLine do
local sId, sX, sY, sZ = string.match(sLine, "(%d+): (%-?%d+), (%-?%d+), (%-?%d+)")
local id, x, y, z = tonumber(sId), tonumber(sX), tonumber(sY), tonumber(sZ)
if id and x and y and z then
tKnownLocations[id] = vector.new(x, y, z)
i = i + 1
end
sLine = file.readLine()
end
file.close()
_print(n, " locations loaded")
return true, i
end
_print("Error loading locations")
return false
end

-- Location functions

local function trilaterate(A, B, C)
local a2b = B.position - A.position
local a2c = C.position - A.position
if math.abs( a2b:normalize():dot( a2c:normalize() ) ) > 0.999 then
return nil
end
local d = a2b:length()
local ex = a2b:normalize( )
local i = ex:dot( a2c )
local ey = (a2c - (ex * i)):normalize()
local j = ey:dot( a2c )
local ez = ex:cross( ey )
local r1 = A.distance
local r2 = B.distance
local r3 = C.distance
local x = (r1*r1 - r2*r2 + d*d) / (2*d)
local y = (r1*r1 - r3*r3 - x*x + (x-i)*(x-i) + j*j) / (2*j)
local result = A.position + (ex * x) + (ey * y)
local zSquared = r1*r1 - x*x - y*y
if zSquared > 0 then
local z = math.sqrt(zSquared)
local result1 = result + (ez * z)
local result2 = result - (ez * z)
local rounded1, rounded2 = result1:round(), result2:round()
if rounded1.x ~= rounded2.x or rounded1.y ~= rounded2.y or rounded1.z ~= rounded2.z then
return result1, result2
else
return rounded1
end
end
return result:round()
end

local function narrow(p1, p2, fix)
local dist1 = math.abs((p1 - fix.position):length() - fix.distance)
local dist2 = math.abs((p2 - fix.position):length() - fix.distance)
if math.abs(dist1 - dist2) < 0.05 then
return p1, p2
elseif dist1 < dist2 then
return p1:round()
else
return p2:round()
end
end

function locate(id)
local tFixes = {}
local p1, p2
for _,t in pairs(tLocations[id]) do
table.insert(tFixes, { ["position"] = vector.new(t.x, t.y, t.z), ["distance"] = t.d })
end
local i = 3
while (p1 == nil or p2 ~= nil) and i <= #tFixes do
if not p1 then
p1, p2 = trilaterate(tFixes[1], tFixes[2], tFixes[i])
else
p1, p2 = narrow(p1, p2, tFixes[i])
end
i = i + 1
end
if p1 and p2 then
_print("Ambiguous position")
_print("Could be "..p1.x..","..p1.y..","..p1.z.." or "..p2.x..","..p2.y..","..p2.z)
elseif p1 then
if not tKnownLocations[id] or not vector_equal(tKnownLocations[id], p1) then
print("Location added:")
print(id, ": ", p1)
tKnownLocations[id] = p1
save()
end
else
_print("Couldn't determine location for ", id)
end
end

local function addLocation(id, t)
if not tLocations[t.id] then
tLocations[t.id] = {}
end
local tLoc = {}
tLoc.x = t.x
tLoc.y = t.y
tLoc.z = t.z
tLoc.d = t.d
tLocations[t.id][id] = tLoc
if table_size(tLocations[t.id]) >= 3 then
_print("Trying to locate #", t.id)
locate(t.id)
end
end

-- Event handlers

local function handle_message(id, msg)
local st = string.match(msg, "<LOCATION> (.+)")
if st then
local t = textutils.unserialize(st)
if t and type(t) == "table" then
_print("Location received from ", id, ":")
_print(t.id, ": ", "(", t.x, ", ", t.y, ", ", t.z, ", ", t.d, ")")
addLocation(id, t)
end
end
end

local function handle_char(c)
c = string.lower(c)
if c == "l" then
print("Locations:")
for id, loc in pairs(tKnownLocations) do
print(id, ": ", loc)
end
elseif c == "c" then
clear()
end
end

-- Start program

local function printUsage()
local sName = fs.getName(shell.getRunningProgram())
print("Usage:")
print(sName, " receive [debug]")
print(sName, " host id x y z")
end

local tArgs = {...}
local sAction = tArgs[1]
if not sAction then
printUsage()
return
end

if sAction == "receive" then
if #tArgs > 1 then
if string.lower(tArgs[2]) == "debug" then
bDebug = true
else
printUsage()
return
end
end
clear()
if not connect() then
return
end
local ok, n = load()
if ok then
print("Loaded ", n, " locations")
end
print("Waiting for messages...")
print("Press l to list located computers")
print("Press c to clear the screen")
while true do
local evt, arg1, arg2 = os.pullEvent()
if evt == "rednet_message" then
handle_message(arg1, arg2)
elseif evt == "char" then
handle_char(arg1)
end
end
elseif sAction == "host" then
local nMasterID = tonumber(tArgs[2])
local tLoc = {}
tLoc.x = tonumber(tArgs[3])
tLoc.y = tonumber(tArgs[4])
tLoc.z = tonumber(tArgs[5])
if not nMasterID or not tLoc.x or not tLoc.y or not tLoc.z then
printUsage()
return
end
clear()
if not connect() then
return
end
print("Waiting for messages...")
while true do
local id, msg, dist = rednet.receive()
print("Message received from ", id, " at ", dist, " meters.")
tLoc.id = id
tLoc.d = dist
rednet.send(nMasterID, "<LOCATION> "..textutils.serialize(tLoc))
end
else
printUsage()
end