/*

 File: PongAI.m

 Version: 1.0

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 */ 

/*************************************************************

/* The PongAI class decides the AI's next move by returning

/* a Direction from -nextMove. Behind the scenes, it manages

/* a JavaScript execution context, and calls a "nextMove"

/* function defined in JavaScript in order to decide how to 

/* move.

/************************************************************/

#import "PongAI.h"

#import "JSShape.h"

#import "Shape.h"

/* Convenience function for getting a property that is an object. */

static JSObjectRef getObjectProperty(JSContextRef ctx, JSObjectRef object, CFStringRef name)

{

    JSStringRef nameJS = JSStringCreateWithCFString(name);

    JSValueRef function = JSObjectGetProperty(ctx, object, nameJS, NULL);

    JSStringRelease(nameJS);

    if (!function || !JSValueIsObject(ctx, function))

        return NULL;

    return (JSObjectRef)function;

}

/* Convenience function for setting a property that is a numeric constant. */

static void setConstantNumberProperty(JSContextRef ctx, JSObjectRef object, CFStringRef name, double value)

{

    JSStringRef nameJS = JSStringCreateWithCFString(name);

    JSValueRef exception = NULL;

    JSObjectSetProperty(ctx, object, nameJS, JSValueMakeNumber(ctx, value), kJSPropertyAttributeDontDelete | kJSPropertyAttributeReadOnly, &exception);

    assert(exception == NULL);

    JSStringRelease(nameJS);

}

@implementation PongAI

- (PongAI *)initWithPaddle:(Shape *)paddle ball:(Shape *)ball script:(NSString *)script

{

    self = [super init];

    if (!self)

        return nil;

    // Create execution context.

    JSGlobalContextRef ctx = JSGlobalContextCreate(NULL);

    [self setJSGlobalContext:ctx];

    JSGlobalContextRelease(ctx);

    // Retrieve global object.

    JSObjectRef jsGlobalObject = JSContextGetGlobalObject(ctx);

    // Set kUpDirection, kDownDirection, and kStationaryDirection global constants.

    setConstantNumberProperty(ctx, jsGlobalObject, CFSTR("kUpDirection"), kUpDirection);

    setConstantNumberProperty(ctx, jsGlobalObject, CFSTR("kDownDirection"), kDownDirection);

    setConstantNumberProperty(ctx, jsGlobalObject, CFSTR("kStationaryDirection"), kStationaryDirection);

    // Evaluate AI script.

    JSStringRef scriptJS = JSStringCreateWithCFString((CFStringRef)script);

    JSEvaluateScript(ctx, scriptJS, NULL, NULL, 0, NULL);

    JSStringRelease(scriptJS);

    // Extract and store 'nextMove' function.

    [self setJSNextMoveFunction:getObjectProperty(ctx, jsGlobalObject, CFSTR("nextMove"))];

    // Cache 'paddle' and 'ball' wrapper objects to pass to 'nextMove' function.

    [self setJSPaddle:JSObjectMake(ctx, JSShape_class(ctx), paddle)];

    [self setJSBall:JSObjectMake(ctx, JSShape_class(ctx), ball)];

    return self;

}

- (Direction)nextMove

{

    JSContextRef ctx = [self jsGlobalContext];

    JSObjectRef function = [self jsNextMoveFunction];

    if (!function) // In case the AI script was malformed.

        return kStationaryDirection;

    // Call 'nextMove' function, passing in 'paddle' and 'ball' arguments.

    JSValueRef arguments[] = { [self jsPaddle], [self jsBall] };

    JSValueRef result = JSObjectCallAsFunction(ctx, function, NULL, 2, arguments, NULL);

    if (!result) // In case the nextMove function threw an exception.

        return kStationaryDirection;

    // Return result as a number.

    return JSValueToNumber(ctx, result, NULL);

}

- (JSObjectRef)jsBall

{

    return _jsBall;

}

- (void)setJSBall:(JSObjectRef)jsBall

{

    JSContextRef ctx = [self jsGlobalContext];

    // Protect the JavaScript object because we are storing it on the heap.

    if (_jsBall)

        JSValueUnprotect(ctx, _jsBall);

    if (jsBall)

        JSValueProtect(ctx, jsBall);

    _jsBall = jsBall;

}

- (JSObjectRef)jsPaddle

{

    return _jsPaddle;

}

- (void)setJSPaddle:(JSObjectRef)jsPaddle

{

    JSContextRef ctx = [self jsGlobalContext];

    // Protect the JavaScript object because we are storing it on the heap.

    if (_jsPaddle)

        JSValueUnprotect(ctx, _jsPaddle);

    if (jsPaddle)

        JSValueProtect(ctx, jsPaddle);

    _jsPaddle = jsPaddle;

}

- (JSObjectRef)jsNextMoveFunction

{

    return _jsNextMoveFunction;

}

- (void)setJSNextMoveFunction:(JSObjectRef)jsNextMoveFunction

{

    JSContextRef ctx = [self jsGlobalContext];

    // Protect the JavaScript object because we are storing it on the heap.

    if (_jsNextMoveFunction)

        JSValueUnprotect(ctx, _jsNextMoveFunction);

    if (jsNextMoveFunction)

        JSValueProtect(ctx, jsNextMoveFunction);

    _jsNextMoveFunction = jsNextMoveFunction;

}

- (JSGlobalContextRef)jsGlobalContext

{

    return _ctx;

}

- (void)setJSGlobalContext:(JSGlobalContextRef)ctx

{

    if (ctx == _ctx)

        return;

    if (_ctx)

        JSGlobalContextRelease(_ctx);

    if (ctx)

        JSGlobalContextRetain(ctx);

    _ctx = ctx;

}

- (void)dealloc

{

    // Release JavaScript resources.

    [self setJSBall:NULL];

    [self setJSPaddle:NULL];

    [self setJSNextMoveFunction:NULL];

    [self setJSGlobalContext:NULL];

    [super dealloc];

}

@end