#include <stdlib.h>
#include <dlfcn.h>
#include <string.h>

#import <Cocoa/Cocoa.h>

static int
check_mono_version (const char *version, const char *req_version)
{
	char *req_end, *end;
	long req_val, val;

	while (*req_version && *version) {
		req_val = strtol (req_version, &req_end, 10);
		if (req_version == req_end || (*req_end && *req_end != '.')) {
			NSLog (@"Bad version requirement string '%s'", req_end);
			return FALSE;
		}

		val = strtol (version, &end, 10);
		if (version == end || val < req_val)
			return FALSE;

		if (val > req_val) {
			return TRUE;
		}

		if (*req_end == '.' && *end != '.')
			return FALSE;

		req_version = req_end;
		if (*req_version)
			req_version++;

		version = end + 1;
	}

	return TRUE;
}

static NSString *
xcode_get_dev_path ()
{
	NSString *xcode_link = [[NSFileManager defaultManager]
		destinationOfSymbolicLinkAtPath:@"/var/db/xcode_select_link"
		error:nil
	];

	return xcode_link ?: @"/Applications/Xcode.app/Contents/Developer";
}

static NSArray<NSString *> *
generate_fallback_paths (NSString *binDir)
{
	NSString *lib_path = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"lib"];

	return @[
		/* Inject our Resources/lib and bin dirs dir */
		binDir,
		lib_path,
		/* Add Xcode's CommandLineTools dev lib dir before Xcode's Developer dir */
		@"/Library/Developer/CommandLineTools/usr/lib",
		/* Add Xcode's dev lib dir into the DYLD_FALLBACK_LIBRARY_PATH */
		[xcode_get_dev_path() stringByAppendingString:@"/usr/lib"],
		/* Add Mono's lib dir */
		@"/Library/Frameworks/Mono.framework/Libraries",
		@"/usr/lib",
		@"/usr/local/lib",
	];
}

static bool
push_env (const char *variable, const char *value, BOOL push_to_end)
{
	const char *current;
	size_t len;
	char *buf;
	BOOL updated = YES;

	if ((current = getenv (variable)) && *current) {
		char *token, *copy, *tofree;
		size_t current_length;

		tofree = copy = strdup (current);
		current_length = strlen (current);
		len = strlen (value);
		while ((token = strsep(&copy, ":"))) {
			if (!strncmp (token, value, len)) {
				while ((strsep(&copy, ":")))
					continue;

				updated = NO;
				goto done;
			}
		}

		if (!(buf = (char *)malloc (len + current_length + 2)))
			return NO;

		if (push_to_end) {
			memcpy (buf, current, current_length);
			buf[current_length] = ':';
			strcpy (buf + current_length + 1, value);
		} else {
			memcpy (buf, value, len);
			buf[len] = ':';
			strcpy (buf + len + 1, current);
		}
		setenv (variable, buf, 1);
		free (buf);
done:
		free (tofree);
	} else {
		setenv (variable, value, 1);
	}

	return updated;
}

static bool
push_env_to_start (const char *variable, const char *value)
{
	return push_env (variable, value, NO);
}

static bool
push_env_to_end (const char *variable, const char *value)
{
	return push_env (variable, value, YES);
}

static bool
replace_env (const char *variable, const char *value)
{
	const char *old = getenv (variable);

	if (old && !strcmp (old, value))
		return false;

	setenv (variable, value, true);
	return true;
}

static bool
update_environment (NSString *binDir)
{
	NSArray<NSString *> *array;
	bool updated = NO;
	NSString *value;

	if ((array = generate_fallback_paths (binDir))) {
			for (value in array) {
				if (push_env_to_end ("DYLD_FALLBACK_LIBRARY_PATH", [value UTF8String]))
					updated = YES;
			}
	}

	if (push_env_to_start ("PKG_CONFIG_PATH", "/Library/Frameworks/Mono.framework/External/pkgconfig"))
		updated = YES;

	NSBundle *bundle = [NSBundle mainBundle];

	NSString *resourcePath = [bundle resourcePath];
	/* Enable the use of stuff bundled into the app bundle and the Mono "External" directory */
	value = [resourcePath stringByAppendingPathComponent:@"lib/pkgconfig"];
	if (push_env_to_start ("PKG_CONFIG_PATH", [value UTF8String])) {
		updated = YES;
	}

	value = [[bundle executablePath] stringByDeletingLastPathComponent];
	if (push_env_to_start ("PATH", [value UTF8String]))
		updated = YES;

	if (push_env_to_start ("MONO_GAC_PREFIX", [resourcePath UTF8String]))
			updated = YES;

	// Note: older versions of Xamarin Studio incorrectly set the PATH to the Resources dir instead of the MacOS dir
	// and older versions of mtouch relied on this broken behavior.
	if (push_env_to_start ("PATH", [resourcePath UTF8String]))
		updated = YES;

	if (push_env_to_start ("PATH", "/Library/Frameworks/Mono.framework/Commands"))
		updated = YES;

	if (push_env_to_end ("PATH", "/usr/local/bin"))
		updated = YES;

	if (push_env_to_end ("PATH", "~/.dotnet/tools"))
		updated = YES;

	if (replace_env ("LC_NUMERIC", "C"))
		updated = YES;

	return updated;
}