/*  Starshatter: The Open Source Project
    Copyright (c) 2021-2024, Starshatter: The Open Source Project Contributors
    Copyright (c) 2011-2012, Starshatter OpenSource Distribution Contributors
    Copyright (c) 1997-2006, Destroyer Studios LLC.

    AUTHOR:       John DiCamillo


    OVERVIEW
    ========
    Seeker Missile (low-level) Artificial Intelligence class
*/

#include "SeekerAI.h"
#include "Ship.h"
#include "Shot.h"
#include "System.h"
#include "WeaponDesign.h"

#include "Clock.h"

// +----------------------------------------------------------------------+

SeekerAI::SeekerAI(SimObject* s)
    : SteerAI(s), shot((Shot*) s), orig_target(0),
      pursuit(1), delay(0), overshot(false)
{
    ai_type = SEEKER;

    seek_gain = 25;
    seek_damp = 0.55;
}


// +--------------------------------------------------------------------+

SeekerAI::~SeekerAI()
{
    if (shot) {
        if (shot->Owner())
        ((Ship*) shot->Owner())->SetMissileEta(shot->Identity(), 0);
    }
}

// +--------------------------------------------------------------------+

void
SeekerAI::ExecFrame(double seconds)
{
    // setup:
    FindObjective();

    // adaptive behavior:
    Navigator();
}

// +--------------------------------------------------------------------+

void
SeekerAI::Navigator()
{
    if (delay > 0) {
        delay -= Clock::GetInstance()->Delta();
    }
    else {
        Steer s = SeekTarget();
        self->ApplyYaw((float) s.yaw);
        self->ApplyPitch((float) s.pitch);
    }
}

void
SeekerAI::SetTarget(SimObject* targ, System* sub)
{
    if (!orig_target && targ && targ->Type() == SimObject::SIM_SHIP) {
        orig_target = (Ship*) targ;
        Observe(orig_target);
    }

    SteerAI::SetTarget(targ, sub);

    if (!target) {
        shot->SetEta(0);

        if (shot->Owner())
        ((Ship*) shot->Owner())->SetMissileEta(shot->Identity(), 0);
    }
}

void
SeekerAI::FindObjective()
{
    if (!shot || !target) return;

    if (target->Life() == 0) {
        if (target != orig_target)
        SetTarget(orig_target,0);
        else
        SetTarget(0,0);

        return;
    }

    Point tloc = target->Location();
    tloc = Transform(tloc);

    // seeker head limit of 45 degrees:
    if (tloc.z < 0 || tloc.z < fabs(tloc.x) || tloc.z < fabs(tloc.y)) {
        overshot = true;
        SetTarget(0,0);
        return;
    }

    // distance from self to target:
    distance = Point(target->Location() - self->Location()).length();

    // are we being spoofed?
    CheckDecoys(distance);

    Point cv = ClosingVelocity();

    // time to reach target:
    double time    = distance / cv.length();
    double predict = time;
    if (predict > 15)
    predict = 15;

    // pure pursuit:
    if (pursuit == 1 || time < 0.1) {
        obj_w = target->Location();
    }

    // lead pursuit:
    else {
        // where the target will be when we reach it:
        Point run_vec = target->Velocity();
        obj_w   = target->Location() + (run_vec * predict);
    }

    // subsystem offset:
    if (subtarget) {
        Point offset = target->Location() - subtarget->MountLocation();
        obj_w -= offset;
    }
    else if (target->Type() == SimObject::SIM_SHIP) {
        Ship* tgt_ship = (Ship*) target;

        if (tgt_ship->IsGroundUnit())
        obj_w += Point(0,150,0);
    }


    distance = Point(obj_w - self->Location()).length();
    time     = distance / cv.length();

    // where we will be when the target gets there:
    if (predict > 0.1 && predict < 15) {
        Point self_dest = self->Location() + cv * predict;
        Point err = obj_w - self_dest;

        obj_w += err;
    }

    // transform into camera coords:
    objective = Transform(obj_w);
    objective.Normalize();

    shot->SetEta((int) time);

    if (shot->Owner())
    ((Ship*) shot->Owner())->SetMissileEta(shot->Identity(), (int) time);
}

// +--------------------------------------------------------------------+

void
SeekerAI::CheckDecoys(double target_distance)
{
    // if the assigned target has the burner lit,
    // ignore the decoys:
    if (orig_target && orig_target->Augmenter()) {
        SetTarget(orig_target);
        return;
    }

    if (target &&
            target == orig_target &&
            orig_target->GetActiveDecoys().size()) {

        ListIter<Shot> decoy = orig_target->GetActiveDecoys();

        while (++decoy) {
            double decoy_distance = Point(decoy->Location() - self->Location()).length();

            if (decoy_distance < target_distance) {
                if (rand() < 1600) {
                    SetTarget(decoy.value(), 0);
                    return;
                }
            }
        }
    }
}

// +--------------------------------------------------------------------+

bool
SeekerAI::Overshot()
{
    return overshot;
}

// +--------------------------------------------------------------------+

Steer
SeekerAI::AvoidCollision()
{
    return Steer();
}

// +--------------------------------------------------------------------+

Steer
SeekerAI::SeekTarget()
{
    if (!self || !target || Overshot())
    return Steer();

    return Seek(objective);
}

// +--------------------------------------------------------------------+

bool
SeekerAI::Update(SimObject* obj)
{
    if (obj == target) {
        if (obj->Type() == SimObject::SIM_SHOT && orig_target != 0)
        target = orig_target;
    }

    if (obj == orig_target)
    orig_target = 0;

    return SteerAI::Update(obj);
}

const char*
SeekerAI::GetObserverName() const
{
    static char name[64];
    sprintf_s(name, "SeekerAI(%s)", self->Name());
    return name;
}