Category on NSApplication that makes it easy to use a Markdown-formatted Credits file, or to use your README as the Credits file.

NSApplication+MarkdownCredits.h

//
//  NSApplication+MarkdownCredits.h
//  ALUtilities
//
//	Copyright (c) 2013 Andy Lee
//
//	Permission is hereby granted, free of charge, to any person obtaining a copy of this software
//	and associated documentation files (the "Software"), to deal in the Software without restriction,
//	including without limitation the rights to use, copy, modify, merge, publish, distribute,
//	sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
//	furnished to do so. Attribution is not required for either source or binary forms of the Software.
//
//	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
//	BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
//	NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
//	DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

#import <Cocoa/Cocoa.h>

/*!
 * This category adds a showAboutPanelWithDerivedCredits: method, plus methods
 * that support it.  This allows you to easily use a Markdown-formatted file as
 * your Credits file in the standard info panel.  The easiest way to do this is:
 *
 * - Replace Credits.rtf with Credits.markdown, or Credits.mdown or Credits.md
 *   if you prefer.
 * - Change the action of the "About" menu item to showAboutPanelWithDerivedCredits:.
 * - Add the MMMarkdown project to your project. <https://github.com/mdiep/MMMarkdown>
 *
 * If you prefer a Markdown library other than MMMarkdown, you'll have to
 * implement application:creditsStringFromData: in your app delegate to use that
 * library.  You can also implement it if you don't want to use Markdown at all,
 * and have another way you'd like to generate the attributed string used for
 * Credits.
 *
 * If there is no Credits.(markdown|mdown|md) file, showAboutPanelWithDerivedCredits:
 * searches for a README file with one of those extensions.  If you want your
 * README to be your Credits file, remember to add it to your application's
 * build target.
 *
 * You can specify a different file name altogether by implementing
 * creditsFileNameForApplication:.  This will be used regardless of whether
 * Credits or README files are present.
 */
@interface NSApplication (MarkdownCredits)

/*!
 * Used internally to provide the Credits string used by
 * showAboutPanelWithDerivedCredits:.  You might want to use this to implement
 * your own info panel if you don't like the standard one.
 */
- (NSAttributedString *)derivedCreditsString;

#pragma mark - Action methods

/*!
 * Opens the standard info panel, using different logic to derive the
 * attributed string used for Credits.
 */
- (IBAction)showAboutPanelWithDerivedCredits:(id)sender;

@end


#pragma mark - Informal protocol that supports showAboutPanelWithDerivedCredits:

@interface NSObject (MarkdownCredits)

/*!
 * File name to look for in the application bundle.  showAboutPanelWithDerivedCredits:
 * passes the contents of this file to application:creditsStringFromData:.  If this
 * method is not implemented or if it returns nil, a search is done for README.(markdown|mdown|md).
 * If no credits file is found in the application bundle, we call orderFrontStandardAboutPanel:.
 */
- (NSString *)creditsFileNameForApplication:(NSApplication *)application;

/*!
 * If the app delegate doesn't implement this, showAboutPanelWithDerivedCredits:
 * checks whether the MMMarkdown library is present.  If so, uses it to convert
 * the data, on the assumption that it's in Markdown format.
 */
- (NSAttributedString *)application:(NSApplication *)application
			  creditsStringFromData:(NSData *)creditsData;

@end

NSApplication+MarkdownCredits.m

//
//  NSApplication+MarkdownCredits.m
//  ALUtilities
//
//	Copyright (c) 2013 Andy Lee
//
//	Permission is hereby granted, free of charge, to any person obtaining a copy of this software
//	and associated documentation files (the "Software"), to deal in the Software without restriction,
//	including without limitation the rights to use, copy, modify, merge, publish, distribute,
//	sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
//	furnished to do so. Attribution is not required for either source or binary forms of the Software.
//
//	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
//	BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
//	NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
//	DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

#import "NSApplication+MarkdownCredits.h"

@implementation NSApplication (MarkdownCredits)

- (NSAttributedString *)derivedCreditsString
{
	// Load data from the credits file.
	NSString *creditsFilePath = [self _creditsFilePath];
	if (creditsFilePath == nil)
	{
		return nil;
	}

	NSData *creditsData = [NSData dataWithContentsOfFile:creditsFilePath];
	if (creditsData == nil)
	{
		NSLog(@"+++ [ERROR] Could not load contents of file [%@].", creditsFilePath);
		return nil;
	}

	// Convert the data to an attributed string.
	NSAttributedString *creditsString;

	if ([self.delegate respondsToSelector:@selector(application:creditsStringFromData:)])
	{
		creditsString = [(id)self.delegate application:self creditsStringFromData:creditsData];
	}
	else
	{
		creditsString = [self _creditsStringFromMarkdownData:creditsData];
	}

	if (creditsString == nil)
	{
		NSLog(@"+++ [ERROR] Could not convert contents of file [%@] to a Credits string.",
			  creditsFilePath);
	}

	return creditsString;
}

#pragma mark - Action methods

- (IBAction)showAboutPanelWithDerivedCredits:(id)sender
{
	NSAttributedString *creditsString = [self derivedCreditsString];

	if (creditsString == nil)
	{
		[self orderFrontStandardAboutPanel:sender];
	}
	else
	{
		[self orderFrontStandardAboutPanelWithOptions:@{ @"Credits" : creditsString }];
	}
}

#pragma mark - Private methods

- (NSString *)_creditsFilePath
{
	if ([self.delegate respondsToSelector:@selector(creditsFileNameForApplication:)])
	{
		NSString *creditsFileName = [(id)self.delegate creditsFileNameForApplication:self];

		if (creditsFileName)
		{
			NSString *resourcePath = [self _pathForResourceWithFileName:creditsFileName];
			if (resourcePath)
			{
				return resourcePath;
			}
		}
	}

	for (NSString *fileName in @[ @"Credits.markdown", @"Credits.mdown", @"Credits.md", @"README.markdown", @"README.mdown", @"README.md" ])
	{
		NSString *resourcePath = [self _pathForResourceWithFileName:fileName];

		if (resourcePath)
		{
			return resourcePath;
		}
	}

	// If we got this far, we failed.
	return nil;
}

// Assume creditsData contains Markdown.  Check for the presence of various
// Markdown libraries.  If one is found, use it to generate the credits string.
- (NSAttributedString *)_creditsStringFromMarkdownData:(NSData *)markdownData
{
	NSAttributedString *creditsString;
    NSString *markdownString = [[NSString alloc] initWithData:markdownData
													 encoding:NSUTF8StringEncoding];
	if (markdownString == nil)
	{
		return nil;
	}

	// See if the MMMarkdown library is present.
	if ((creditsString = [self _mmmarkdownCreditsStringFromMarkdownString:markdownString]))
	{
		return creditsString;
	}

	//
	// ...[agl] Check for other Markdown libraries -- what are some popular ones?...
	//

	// If we got this far, we failed.
	return nil;
}

// This method is never called.  It's just here to provide a method prototype.
- (NSString *)HTMLStringWithMarkdown:(NSString *)markdownString error:(NSError **)errorPtr
{
	return nil;
}

- (NSAttributedString *)_mmmarkdownCreditsStringFromMarkdownString:(NSString *)markdownString
{
	Class mmmarkdownClass = NSClassFromString(@"MMMarkdown");
	if (mmmarkdownClass == nil)
	{
		return nil;
	}

    NSError *error;
    NSString *htmlString = [(id)mmmarkdownClass HTMLStringWithMarkdown:markdownString error:&error];
    if (htmlString == nil)
    {
        return nil;
    }

    return [self _creditsStringFromHTMLString:htmlString];
}

- (NSString *)_pathForResourceWithFileName:(NSString *)fileName
{
	return [[NSBundle mainBundle] pathForResource:[fileName stringByDeletingPathExtension]
										   ofType:[fileName pathExtension]];
}

- (NSAttributedString *)_creditsStringFromHTMLString:(NSString *)htmlString
{
    return [[NSAttributedString alloc] initWithHTML:[htmlString dataUsingEncoding:NSUTF8StringEncoding]
                                 documentAttributes:NULL];
}

@end