from the depths harpoon-ish guidance

-- guidance parameters --

local skimAlt = 10  -- ASL alt (m) for seaskimming portion
local cruiseThrust = 8500 -- thrust for sea skimming phase

local beginClimbPhase = 950 -- distance (m) to begin the pop-up for the top down attack
local climbAimHeight = 125 -- ASL alt (m) to aim during climb phase
local climbThrust = 11500 -- thrust for pop-up phase
local maxSpeedForClimb = 40 -- max target speed (m/s) where the missile will do a pop-up attack

local beginAttackPhase = 400 -- distance (m) to begin the down part of the top down attack
local attackThrust = 30000 -- thrust for attack phase


function Update(I)
    -- will sea skim before rising up for a more top down attack

    -- if no target already set or target can no longer be found set a target for the missile

    local targetInfo = FindTarget(I)
    if (targetInfo ~= nil) then
        for t = 0, I:GetLuaTransceiverCount() do
            for m = 0, I:GetLuaControlledMissileCount(t) - 1 do

                local targetPosition = targetInfo.AimPointPosition
                local targetVelocity = targetInfo.Velocity


                local missilePosition = I:GetLuaControlledMissileInfo(t, m).Position
                local missileSpeed = Vector3.Magnitude(I:GetLuaControlledMissileInfo(t, m).Velocity)

                local targetDistance = Vector3.Distance(targetPosition, missilePosition)
                local targetVector = Vector3.Normalize(targetPosition - missilePosition)

                local relativeSpeed = missileSpeed - Vector3.Dot(targetVector, targetVelocity)
                local prediction = targetVelocity*targetDistance/relativeSpeed
                local intercept = targetPosition + prediction
                local interceptVector = Vector3.Normalize(intercept - missilePosition)

                local point = missilePosition + interceptVector*missileSpeed
                local interceptDistance = InterceptDistance2D(missilePosition,intercept)
                local parts = I:GetMissileInfo(t, m).Parts
                if (interceptDistance > beginClimbPhase) then
                    for i=1, #parts do
                        if parts[i].Name:find("thruster") then
                            parts[i]:SendRegister(2, cruiseThrust)
                            break
                        end
                    end
                    I:LogToHud("sea skimming")
                    point.y = skimAlt
                elseif (interceptDistance <= beginClimbPhase and interceptDistance > beginAttackPhase) then
                    for i=1, #parts do
                        if parts[i].Name:find("thruster") then
                            parts[i]:SendRegister(2, climbThrust)
                            break
                        end
                    end

                    if (Vector3.Magnitude(targetVelocity) <= maxSpeedForClimb) then
                        I:LogToHud("performing pop-up attack")
                        point.y = climbAimHeight
                    else
                        I:LogToHud("target too fast for pop-up, going for direct attack")
                    end
                elseif (interceptDistance <= beginAttackPhase) then
                    for i=1, #parts do
                        if parts[i].Name:find("thruster") then
                            parts[i]:SendRegister(2, attackThrust)
                            break
                        end
                    end
                end
                I:SetLuaControlledMissileAimPoint(t, m, point.x, point.y, point.z)
            end
        end
    end
end

function InterceptDistance2D(missile,intercept)
    -- returns distance to target ignoring difference in altitude (m)
    return math.sqrt((missile.x - intercept.x)^2 + (missile.z - intercept.z)^2)
end

function FindTarget(I)
    -- Finds and sets a target
    hasTarget = false

    for i = 0, I:GetNumberOfMainframes() do
        for e = 0, I:GetNumberOfTargets(i) do
            TargetInfo = I:GetTargetInfo(i, e)
            local targetPosition = TargetInfo.AimPointPosition
            if (targetPosition.y < 20 and targetPosition.y > -10) then
                targetIDs = {i, TargetInfo.Id}  -- Update global targetIDs
                hasTarget = true
                break
            end
        end
        if hasTarget then break end  -- Exit loop if target is found
    end
    if (hasTarget) then
        return TargetInfo
    else
        return nil
    end
end