//
//  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 "MPEvaluationContext.h"

#import "MPExpressionTree.h"

@implementation MPSumFunction

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

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

#pragma mark Evaluating Functions

- (BOOL)validate:(NSError *__autoreleasing *)error
{
    MPExpressionTree *startTree = [self.startExpression parse];
    if (![startTree validateExpectingVariableDefinition:YES error:error]) {
        return NO;
    }
    
    MPExpressionTree *targetTree = [self.targetExpression parse];
    if (![targetTree validate:error]) {
        return NO;
    }
    
    [[MPEvaluationContext sharedContext] push];
    [[MPEvaluationContext sharedContext] defineVariable:startTree.definedVariable withValue:[NSDecimalNumber notANumber]];
    MPExpressionTree *sumTree = [self.sumExpression parse];
    if (![sumTree validate:error]) {
        return NO;
    }
    [[MPEvaluationContext sharedContext] pop];
    return YES;
}

- (NSDecimalNumber *)evaluate
{
    MPExpressionTree *startTree = [self.startExpression parse];
    NSDecimalNumber *start = [startTree evaluate];
    NSDecimalNumber *target = [[self.targetExpression parse] evaluate];
    MPExpressionTree *sumTree = [self.sumExpression parse];
    
    NSDecimalNumber *value = [NSDecimalNumber zero];
    
    [[MPEvaluationContext sharedContext] push];
    for (NSDecimalNumber *current = start;
         [current compare:target] <= 0;
         current = [current decimalNumberByAdding:[[NSDecimalNumber alloc] initWithInteger:1]]) {
        [[MPEvaluationContext sharedContext] defineVariable:startTree.definedVariable withValue:current];
        value = [value decimalNumberByAdding:[sumTree evaluate]];
    }
    [[MPEvaluationContext sharedContext] pop];
    return value;
}

#pragma mark Working With Functions

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

@end