/*  Starshatter OpenSource Distribution
    Copyright (c) 1997-2004, Destroyer Studios LLC.
    All Rights Reserved.

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      this list of conditions and the following disclaimer.
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      this list of conditions and the following disclaimer in the documentation
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    * Neither the name "Destroyer Studios" nor the names of its contributors
      may be used to endorse or promote products derived from this software
      without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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    POSSIBILITY OF SUCH DAMAGE.

    SUBSYSTEM:    Stars.exe
    FILE:         SeekerAI.cpp
    AUTHOR:       John DiCamillo


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

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

#include "Game.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 -= Game::FrameTime();
    }
    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;
}