/*

    File: GraphView.m

Abstract: A custom view for plotting history of x, y, and z magnetic values.

 Version: 1.3

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*/

#import "GraphView.h"

@interface GraphView ()

@property (assign) NSUInteger nextIndex;

@end

#pragma mark -

@implementation GraphView

- (void)updateHistoryWithX:(CLHeadingComponentValue)x y:(CLHeadingComponentValue)y z:(CLHeadingComponentValue)z {

    // Add to history.

    history[self.nextIndex][0] = x;

    history[self.nextIndex][1] = y;

    history[self.nextIndex][2] = z;

    // Advance the index counter.

    _nextIndex = (self.nextIndex + 1) % 150;

    // Mark itself as needing to be redrawn.

    [self setNeedsDisplay];

}

- (void)drawGraphInContext:(CGContextRef)context withBounds:(CGRect)bounds {

    CGFloat value, temp;

    // Save any previous graphics state settings before setting the color and line width for the current draw.

    CGContextSaveGState(context);

    CGContextSetLineWidth(context, 1.0);

    // Draw the intermediate lines

    CGContextSetGrayStrokeColor(context, 0.6, 1.0);

    CGContextBeginPath(context);

    for (value = -5 + 1.0; value <= 5 - 1.0; value += 1.0) {

        if (value == 0.0) {

            continue;

        }

        temp = 0.5 + roundf(bounds.origin.y + bounds.size.height / 2 + value / (2 * 5) * bounds.size.height);

        CGContextMoveToPoint(context, bounds.origin.x, temp);

        CGContextAddLineToPoint(context, bounds.origin.x + bounds.size.width, temp);

    }

    CGContextStrokePath(context);

    // Draw the center line

    CGContextSetGrayStrokeColor(context, 0.25, 1.0);

    CGContextBeginPath(context);

    temp = 0.5 + roundf(bounds.origin.y + bounds.size.height / 2);

    CGContextMoveToPoint(context, bounds.origin.x, temp);

    CGContextAddLineToPoint(context, bounds.origin.x + bounds.size.width, temp);

    CGContextStrokePath(context);

    // Restore previous graphics state.

    CGContextRestoreGState(context);

}

- (void)drawHistory:(NSUInteger)axis fromIndex:(NSUInteger)index inContext:(CGContextRef)context bounds:(CGRect)bounds {

    CGFloat value;

    CGContextBeginPath(context);

    for (NSUInteger counter = 0; counter < 150; ++counter) {

        // UIView referential has the Y axis going down, so we need to draw upside-down.

        value = history[(index + counter) % 150][axis] / -128; 

        if (counter > 0) {

            CGContextAddLineToPoint(context, bounds.origin.x + (float)counter / (float)(150 - 1) * bounds.size.width, bounds.origin.y + bounds.size.height / 2 + value * bounds.size.height / 2);

        } else {

            CGContextMoveToPoint(context, bounds.origin.x + (float)counter / (float)(150 - 1) * bounds.size.width, bounds.origin.y + bounds.size.height / 2 + value * bounds.size.height / 2);

        }

    }

    // Save any previous graphics state settings before setting the color and line width for the current draw.

    CGContextSaveGState(context);

    CGContextSetRGBStrokeColor(context, (axis == 0 ? 1.0 : 0.0), (axis == 1 ? 1.0 : 0.0), (axis == 2 ? 1.0 : 0.0), 1.0);

    CGContextSetLineWidth(context, 2.0);

    CGContextStrokePath(context);

    // Restore previous graphics state.

    CGContextRestoreGState(context);

}

- (void)drawRect:(CGRect)clip {

    NSUInteger index = self.nextIndex;

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGRect bounds = CGRectMake(0, 0, [self bounds].size.width, [self bounds].size.height);

    // create the graph

    [self drawGraphInContext:context withBounds:bounds];

    // plot x,y,z with anti-aliasing turned off

    CGContextSetAllowsAntialiasing(context, false);

    for (NSUInteger i = 0; i < 3; ++i) {

        [self drawHistory:i fromIndex:index inContext:context bounds:bounds];

    }

    CGContextSetAllowsAntialiasing(context, true);

}

@end