/* AMS_Trail.h
 */

#import <Foundation/Foundation.h>
#import <SpriteKit/SpriteKit.h>

@interface AMS_TrailPoint : NSObject

@property CGVector m_vPosition;
@property double m_fDistanceToNext;

@end

@interface AMS_Trail : NSObject

@property int m_iMaxPoints;

@property NSMutableArray* m_aPoints;

- (void)addVector:(CGVector)vec;
- (void)addPoint:(AMS_TrailPoint*)pt;

- (CGVector)positionFromHead:(double)fDistance;

@end




/* AMS_Trail.m
 * (CGVectorAdditions is this: https://github.com/samgreen/CGVector-Awesome)
 */

#import "AMS_Trail.h"
#import "../CGVectorAdditions.h"

@implementation AMS_TrailPoint

- (instancetype)init
{
    if(self = [super init]) {

    }
    return self;
}

@end

@implementation AMS_Trail

- (instancetype)init
{
    if(self = [super init]) {
        self.m_iMaxPoints = 1000; // should be enough.. 1000 * (4 + 4 + 8) = up to 16 kB ^.^
        self.m_aPoints = [[NSMutableArray alloc] init];
    }
    return self;
}

- (void)addVector:(CGVector)vec
{
    AMS_TrailPoint* tp = [[AMS_TrailPoint alloc] init];
    tp.m_vPosition = vec;
    if(self.m_aPoints.count > 0) {
        AMS_TrailPoint* tpFirst = [self.m_aPoints firstObject];
        tp.m_fDistanceToNext = CGVectorDistance(vec, tpFirst.m_vPosition);
    }
    [self addPoint:tp];
}

- (void)addPoint:(AMS_TrailPoint*)tp
{
    if(self.m_iMaxPoints != 0 && self.m_aPoints.count >= self.m_iMaxPoints) {
        int iFromIndex = self.m_iMaxPoints - 2;
        [self.m_aPoints removeObjectsInRange:NSMakeRange(iFromIndex, self.m_aPoints.count - iFromIndex)];
    }
    [self.m_aPoints insertObject:tp atIndex:0];
}

- (CGVector)positionFromHead:(double)fDistance
{
    for(int i=0; i<self.m_aPoints.count - 1; i++) {
        AMS_TrailPoint* tp = [self.m_aPoints objectAtIndex:i];
        if(fDistance > tp.m_fDistanceToNext) {
            fDistance -= tp.m_fDistanceToNext;
        } else {
            // lerp between last and current points
            AMS_TrailPoint* tpNext = [self.m_aPoints objectAtIndex:i + 1];
            CGVector vOffset = CGVectorDifference(tpNext.m_vPosition, tp.m_vPosition);
            vOffset = CGVectorNormalize(vOffset);
            vOffset = CGVectorMultiplyByScalar(vOffset, fDistance);
            return CGVectorSum(tp.m_vPosition, vOffset);
        }
    }

    // is last point?
    if(!self.m_aPoints.count == 0) {
        AMS_TrailPoint* tpLast = [self.m_aPoints lastObject];
        return tpLast.m_vPosition;
    }

    // list is empty
    return CGVectorMake(0, 0);
}

@end