//
//  MPSumFunction.m
//  MathPad
//
//  Created by Kim Wittenburg on 22.04.14.
//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
//

#import "MPSumFunction.h"
#import "MPExpression.h"

#import "MPExpressionEvaluator.h"
#import "MPEvaluationContext.h"

// TODO: Use this macro elsewhere
#define ReturnIfNil(test) if(test == nil) return nil

@implementation MPSumFunction

MPFunctionAccessorImplementation(StartExpression, _startExpression)
MPFunctionAccessorImplementation(TargetExpression, _targetExpression)
MPFunctionAccessorImplementation(SumExpression, _sumExpression)

- (NSArray *)childrenAccessors
{
    return @[@"startExpression", @"targetExpression", @"sumExpression"];
}

#pragma mark Evaluating Functions
- (MPTerm *)parseWithError:(MPParseError *__autoreleasing *)error
{
    MPExpressionEvaluator *startEvaluator = [[MPExpressionEvaluator alloc] initWithExpression:self.startExpression];
    MPTerm *start = [startEvaluator parseExpectingVariable:YES
                                                     error:error];
    ReturnIfNil(start);

    MPExpressionEvaluator *targetEvaluator = [[MPExpressionEvaluator alloc] initWithExpression:self.targetExpression];
    MPTerm *target = [targetEvaluator parseExpectingVariable:NO
                                                       error:error];
    ReturnIfNil(target);
    
    NSString *variable = startEvaluator.definedVariable.copy;
    
    [[MPEvaluationContext sharedContext] push];
    [[MPEvaluationContext sharedContext] defineVariable:variable withValue:[NSNull null]];
    MPExpressionEvaluator *sumEvaluator = [[MPExpressionEvaluator alloc] initWithExpression:self.sumExpression];
    MPTerm *sum = [sumEvaluator parseExpectingVariable:NO
                                                 error:error];
    ReturnIfNil(sum);
    [[MPEvaluationContext sharedContext] pop];
    
    return [[MPTerm alloc] initWithBlock:^NSDecimalNumber *{
        [[MPEvaluationContext sharedContext] push];
        NSDecimalNumber *value = [NSDecimalNumber zero];
        NSDecimalNumber *startValue = [start evaluate];
        NSDecimalNumber *targetValue = [target evaluate];
        for (NSDecimalNumber *iterator = startValue;
             [iterator compare:targetValue] <= 0 ;
             iterator = [iterator decimalNumberByAdding:[[NSDecimalNumber alloc] initWithInteger:1]]) {
            [[MPEvaluationContext sharedContext] defineVariable:variable withValue:iterator];
            value = [value decimalNumberByAdding:[sum evaluate]];
        }
        [[MPEvaluationContext sharedContext] pop];
        return value;
    }];
}

#pragma mark Working With Functions
/*
- (BOOL)isEqualToFunction:(MPFunction *)aFunction
{
    if (![aFunction isKindOfClass:[MPSumFunction class]]) {
        return NO;
    }
    MPSumFunction *sumFunction = (MPSumFunction *)aFunction;
    if (![self.startExpression isEqualToExpression:sumFunction.startExpression]) {
        return NO;
    }
    if (![self.targetExpression isEqualToExpression:sumFunction.targetExpression]) {
        return NO;
    }
    return [self.sumExpression isEqualToExpression:sumFunction.sumExpression];
}*/

- (NSString *)description
{
    return [NSString stringWithFormat:@"Sum(From: %@; To: %@; Using: %@)", self.startExpression, self.targetExpression, self.sumExpression];
}

@end