/*

     File: AVSECropCommand.m

 Abstract: A subclass of AVSECommand which uses AVMutableVideoComposition to achieve a crop effect. This tool crops the bottom right quadrant of a composition. This is achieved by reducing the video composition's render size to half of original and then applying a CGAffineTransformMakeTranslation transform to move the appropriate quadrant into view.

  Version: 1.1

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 */

#import "AVSECropCommand.h"

@implementation AVSECropCommand

- (void)performWithAsset:(AVAsset*)asset

{

    AVMutableVideoCompositionInstruction *instruction = nil;

    AVMutableVideoCompositionLayerInstruction *layerInstruction = nil;

    CGAffineTransform t1;

    AVAssetTrack *assetVideoTrack = nil;

    AVAssetTrack *assetAudioTrack = nil;

    // Check if the asset contains video and audio tracks

    if ([[asset tracksWithMediaType:AVMediaTypeVideo] count] != 0) {

        assetVideoTrack = [asset tracksWithMediaType:AVMediaTypeVideo][0];

    }

    if ([[asset tracksWithMediaType:AVMediaTypeAudio] count] != 0) {

        assetAudioTrack = [asset tracksWithMediaType:AVMediaTypeAudio][0];

    }

    CMTime insertionPoint = kCMTimeZero;

    NSError *error = nil;

    // Step 1

    // Create a composition with the given asset and insert audio and video tracks into it from the asset

    if (!self.mutableComposition) {

        // Check whether a composition has already been created, i.e, some other tool has already been applied.

        // Create a new composition

        self.mutableComposition = [AVMutableComposition composition];

        // Insert the video and audio tracks from AVAsset

        if (assetVideoTrack != nil) {

            AVMutableCompositionTrack *compositionVideoTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

            [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:assetVideoTrack atTime:insertionPoint error:&error];

        }

        if (assetAudioTrack != nil) {

            AVMutableCompositionTrack *compositionAudioTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

            [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:assetAudioTrack atTime:insertionPoint error:&error];

        }

    }

    // Step 2

    // Set the appropriate render sizes and transforms to achieve cropping 

    if (!self.mutableVideoComposition) {

        // Create a new video composition

        self.mutableVideoComposition = [AVMutableVideoComposition videoComposition];

        // Render size reduced to half to achieve the crop effect

        self.mutableVideoComposition.renderSize = CGSizeMake(assetVideoTrack.naturalSize.width/2, assetVideoTrack.naturalSize.height/2);

        self.mutableVideoComposition.frameDuration = CMTimeMake(1, 30);

        // The crop transform is set on a layer instruction

        instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];

        instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [self.mutableComposition duration]);

        layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:(self.mutableComposition.tracks)[0]];

        // Crop transformation (translation to move the bottom right half into the view)

        t1 = CGAffineTransformMakeTranslation(-1*assetVideoTrack.naturalSize.width/2, -1*assetVideoTrack.naturalSize.height/2);

        [layerInstruction setTransform:t1 atTime:kCMTimeZero];

    } else {

        self.mutableVideoComposition.renderSize = CGSizeMake(self.mutableVideoComposition.renderSize.width/2, self.mutableVideoComposition.renderSize.height/2);

        // Extract the existing layer instruction on the mutableVideoComposition

        instruction = (self.mutableVideoComposition.instructions)[0];

        layerInstruction = (instruction.layerInstructions)[0];

        // Check if a transform already exists on this layer instruction, this is done to add the current transform on top of previous edits

        CGAffineTransform existingTransform;

        if (![layerInstruction getTransformRampForTime:[self.mutableComposition duration] startTransform:&existingTransform endTransform:NULL timeRange:NULL]) {

            t1 = CGAffineTransformMakeTranslation(-1*assetVideoTrack.naturalSize.width/2, -1*assetVideoTrack.naturalSize.height/2);

            [layerInstruction setTransform:t1 atTime:kCMTimeZero];

        } else {

            t1 = CGAffineTransformMakeTranslation(-1*assetVideoTrack.naturalSize.height/2, -1*assetVideoTrack.naturalSize.width/2);

            CGAffineTransform newTransform = CGAffineTransformConcat(existingTransform, t1);

            [layerInstruction setTransform:newTransform atTime:kCMTimeZero];

        }

    }

    // Step 3

    // Add the instructions to the video composition

    instruction.layerInstructions = @[layerInstruction];

    self.mutableVideoComposition.instructions = @[instruction];

    // Step 4

    // Notify AVSEViewController class about crop operation completion

    [[NSNotificationCenter defaultCenter] postNotificationName:AVSEEditCommandCompletionNotification object:self];

}

@end