Add missing files

ios/Classes/BarcodeScannerViewController.h

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+//
+// Created by Matthew Smith on 11/7/17.
+//
+
+#import <Foundation/Foundation.h>
+#import <MTBBarcodeScanner/MTBBarcodeScanner.h>
+
+#import "BarcodeScannerViewControllerDelegate.h"
+
+
+@interface BarcodeScannerViewController : UIViewController
+@property(nonatomic, retain) UIView *previewView;
+@property(nonatomic, retain) MTBBarcodeScanner *scanner;
+@property(nonatomic, weak) id<BarcodeScannerViewControllerDelegate> delegate;
+
+@end

ios/Classes/BarcodeScannerViewController.m

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+//
+// Created by Matthew Smith on 11/7/17.
+//
+
+#import "BarcodeScannerViewController.h"
+#import <MTBBarcodeScanner/MTBBarcodeScanner.h>
+
+
+@implementation BarcodeScannerViewController {
+}
+
+
+- (void)viewDidLoad {
+    [super viewDidLoad];
+    self.previewView = [[UIView alloc] initWithFrame:self.view.bounds];
+    self.previewView.translatesAutoresizingMaskIntoConstraints = NO;
+    [self.view addSubview:_previewView];
+    [self.view addConstraints:[NSLayoutConstraint
+            constraintsWithVisualFormat:@"V:[previewView]"
+                                options:NSLayoutFormatAlignAllBottom
+                                metrics:nil
+                                  views:@{@"previewView": _previewView}]];
+    [self.view addConstraints:[NSLayoutConstraint
+            constraintsWithVisualFormat:@"H:[previewView]"
+                                options:NSLayoutFormatAlignAllBottom
+                                metrics:nil
+                                  views:@{@"previewView": _previewView}]];
+    self.scanner = [[MTBBarcodeScanner alloc] initWithPreviewView:_previewView];
+    self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemCancel target:self action:@selector(cancel)];
+}
+
+- (void)viewDidAppear:(BOOL)animated {
+    [super viewDidAppear:animated];
+    if (self.scanner.isScanning) {
+        [self.scanner stopScanning];
+    }
+    [MTBBarcodeScanner requestCameraPermissionWithSuccess:^(BOOL success) {
+        if (success) {
+            [self startScan];
+        } else {
+            [self showNoCameraAccessAlert];
+        }
+    }];
+}
+
+- (void)viewWillDisappear:(BOOL)animated {
+    [super viewWillDisappear:animated];
+    if ([self isFlashOn]) {
+        [self toggleFlash:NO];
+    }
+}
+
+- (void)startScan {
+    NSError *error;
+    [self.scanner startScanningWithResultBlock:^(NSArray<AVMetadataMachineReadableCodeObject *> *codes) {
+        [self.scanner stopScanning];
+         AVMetadataMachineReadableCodeObject *code = codes.firstObject;
+        if (code) {
+            [self.delegate barcodeScannerViewController:self didScanBarcodeWithResult:code.stringValue];
+            [self dismissViewControllerAnimated:NO completion:nil];
+        }
+    } error:&error];
+}
+
+- (void)cancel {
+    [self dismissViewControllerAnimated:true completion:nil];
+}
+
+- (void)updateFlashButton {
+    if (!self.hasTorch) {
+        return;
+    }
+    if (self.isFlashOn) {
+        self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"Flash Off"
+                                                                                  style:UIBarButtonItemStylePlain
+                                                                                 target:self action:@selector(toggle)];
+    } else {
+        self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"Flash On"
+                                                                                  style:UIBarButtonItemStylePlain
+                                                                                 target:self action:@selector(toggle)];
+    }
+}
+
+- (void)showNoCameraAccessAlert {
+    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Camera access denied"
+                                                                             message:@"Camera access has been disabled for this application. To turn camera access back on, please go to the iOS settings application."
+                                                                      preferredStyle:UIAlertControllerStyleAlert];
+    [alertController addAction:[UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
+        [self dismissViewControllerAnimated:YES completion:nil];
+    }]];
+    [self presentViewController:alertController animated:YES completion:nil];
+}
+
+- (void)toggle {
+    [self toggleFlash:!self.isFlashOn];
+    [self updateFlashButton];
+}
+
+- (BOOL)isFlashOn {
+    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
+    if (device) {
+        return device.torchMode == AVCaptureFlashModeOn || AVCaptureTorchModeOn;
+    }
+    return NO;
+}
+
+- (BOOL)hasTorch {
+    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
+    if (device) {
+        return device.hasTorch;
+    }
+    return false;
+}
+
+- (void)toggleFlash:(BOOL)on {
+    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
+    if (!device) return;
+
+    NSError *err;
+    if (device.hasFlash && device.hasTorch) {
+        [device lockForConfiguration:&err];
+        if (err != nil) return;
+        if (on) {
+            device.flashMode = AVCaptureFlashModeOn;
+            device.torchMode = AVCaptureTorchModeOn;
+        } else {
+            device.flashMode = AVCaptureFlashModeOff;
+            device.torchMode = AVCaptureTorchModeOff;
+        }
+        [device unlockForConfiguration];
+    }
+}
+
+
+@end

ios/Classes/BarcodeScannerViewControllerDelegate.h

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+//
+// Created by Matthew Smith on 11/7/17.
+//
+
+#import <Foundation/Foundation.h>
+
+@class BarcodeScannerViewController;
+
+@protocol BarcodeScannerViewControllerDelegate <NSObject>
+
+- (void)barcodeScannerViewController:(BarcodeScannerViewController *)controller didScanBarcodeWithResult:(NSString *)result;
+
+@end