/*

     File: MYVolumeUnitMeterView.m

 Abstract: Volume unit meter view

  Version: 1.0.1

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 */

#import "MYVolumeUnitMeterView.h"

#import <QuartzCore/QuartzCore.h>

// This is an arbitrary calibration to define 0 db in the VU meter.

#define MYVolumeUnitMeterView_CALIBRATION 12.0f

#define DEGREE_TO_RADIAN M_PI / 180.0f

static CGFloat convertValueToNeedleAngle(CGFloat value);

@interface MYVolumeUnitMeterView ()

@property (readonly, strong, nonatomic) CALayer *needleLayer;

@end

@implementation MYVolumeUnitMeterView

- (id)initWithFrame:(CGRect)frame

{

    self = [super initWithFrame:frame];

    if (self)

    {

        [self setupLayerTree];

    }

    return self;

}

- (id)initWithCoder:(NSCoder *)aDecoder

{

    self = [super initWithCoder:aDecoder];

    if (self)

    {

        [self setupLayerTree];

    }

    return self;

}

#pragma mark -

- (void)setupLayerTree

{

    CGRect viewLayerBounds = self.layer.bounds;

    // Set layer background image.

    self.layer.contents = (id)[[UIImage imageNamed:@"VUMeterBackground"] CGImage];

    // Add shadow layer for needle.

    CALayer *shadowLayer = [CALayer layer];

    shadowLayer.shadowColor = [[UIColor blackColor] CGColor];

    shadowLayer.shadowOffset = CGSizeMake(0.0f, 6.0f);

    shadowLayer.shadowOpacity = 0.5f;

    shadowLayer.shadowRadius = 2.0f;

    [self.layer addSublayer:shadowLayer];

    // Add needle layer.

    UIImage *needleImage = [UIImage imageNamed:@"VUMeterNeedle"];

    CGSize needleImageSize = [needleImage size];

    _needleLayer = [CALayer layer];

    _needleLayer.affineTransform = CGAffineTransformMakeRotation(convertValueToNeedleAngle(-INFINITY));

    _needleLayer.anchorPoint = CGPointMake(0.5f, 1.0f);

    _needleLayer.bounds = CGRectMake(0.0f, 0.0f, needleImageSize.width, needleImageSize.height);

    _needleLayer.contents = (id)[needleImage CGImage];

    _needleLayer.position = CGPointMake(0.5f * CGRectGetWidth(viewLayerBounds), needleImageSize.height);

    [shadowLayer addSublayer:_needleLayer];

    // Add foreground layer.

    CALayer *foregroundLayer = [CALayer layer];

    foregroundLayer.anchorPoint = CGPointZero;

    foregroundLayer.bounds = viewLayerBounds;

    foregroundLayer.contents = (id)[[UIImage imageNamed:@"VUMeterForeground"] CGImage];

    foregroundLayer.position = CGPointZero;

    [self.layer addSublayer:foregroundLayer];

}

#pragma mark -

- (void)setValue:(float)value

{

    if (_value != value)

    {

        _value = value;

        // Convert RMS amplitude into dB (using some arbitrary calibration values).

        float valueDB = (20.0f * log10(value) + MYVolumeUnitMeterView_CALIBRATION);

        // Update needle layer.

        _needleLayer.affineTransform = CGAffineTransformMakeRotation(convertValueToNeedleAngle(valueDB));

    }

}

@end

#pragma mark Functions

// Note: This calculation is just an approximation to map the artwork.

static CGFloat convertValueToNeedleAngle(CGFloat value)

{

    float degree = (value * 5.0f + 20.0f);

    // The mapping from dB amplitude to angle is not linear on our VU meter.

    if (value < -7.0f && value >= -10.0f)

        degree = (-15.0f + (10.0f / 3.0f) * (value + 7.0f));

    else if (value < -10.0f)

        degree = (-25.0f + (13.0f / 10.0f) * (value + 10.0f));

    // Limit to visible angle.

    degree = MAX(-38.0f, MIN(degree, 43.0f));

    return (DEGREE_TO_RADIAN * degree);

}