//
//  MPExpressionEvaluator.m
//  MathPad
//
//  Created by Kim Wittenburg on 31.08.14.
//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
//

#import "MPExpressionEvaluator.h"
#import "MPExpression.h"
#import "MPFunction.h"

@interface MPExpressionEvaluator ()
@property (readwrite, nonatomic, strong) NSString *definedVariable;

@end

@implementation MPExpressionEvaluator {
    NSMutableDictionary *_variableBindings;
    MPElementParser *parser;
}
- (id)initWithExpression:(MPExpression *)expression
{
    self = [super init];
    if (self) {
        _expression = expression;
        _variableBindings = [[NSMutableDictionary alloc] init];
        parser = [[MPElementParser alloc] init];
    }
    return self;
}

#pragma mark Evaluating Expressions
- (NSDictionary *)variableBindings
{
    return [_variableBindings copy];
}

- (void)bindValue:(NSDecimalNumber *)value toVariableName:(NSString *)name
{
    [_variableBindings setObject:value
                          forKey:name];
}

- (void)unbindVariableName:(NSString *)name
{
    [_variableBindings removeObjectForKey:name];
}

- (NSDecimalNumber *)evaluateWithError:(MPParseError *__autoreleasing *)error
{
    return [self evaluateVariableDefinition:NO error:error];
}

- (NSDecimalNumber *)evaluateVariableDefinition:(BOOL)flag error:(MPParseError *__autoreleasing *)error
{
    // Empty Expression
    if (self.expression.numberOfElements == 0) {
        *error = MPParseError(NSMakeRange(0, 0), @"Expected Expression");
        return nil;
    }

    NSMutableArray *products = [[NSMutableArray alloc] init];
    MPParsedProduct *currentProduct = nil;
    
    for (NSUInteger elementIndex = 0; elementIndex < self.expression.numberOfElements; elementIndex++) {
        
        id<MPExpressionElement> element = [self.expression elementAtIndex:elementIndex];
        
        if ([element isString]) {
            MPParsedFactor *nextFactor = nil;
            if (elementIndex < self.expression.numberOfElements - 1) {
                MPFunction *nextFunction = (MPFunction *)[self.expression elementAtIndex:elementIndex+1];
                NSDecimalNumber *functionValue = [nextFunction evaluate:error];
                if (!functionValue) {
                    return nil;
                }
                nextFactor = [MPParsedFactor factorWithDecimalNumber:functionValue];
            }
            
            NSArray *newProducts;
            if (elementIndex == 0 && flag) {
                NSString *definedVariable;
                newProducts = [parser parseElement:(NSString *)element
                                   previousProduct:currentProduct
                                        nextFactor:nextFactor
                                   definesVariable:YES
                                   definedVariable:&definedVariable
                                             error:error];
                self.definedVariable = definedVariable;
            } else {
                newProducts = [parser parseElement:(NSString *)element
                                   previousProduct:currentProduct
                                        nextFactor:nextFactor
                                             error:error];
            }
            if (!newProducts) {
                return nil;
            }
            
            for (NSUInteger productIndex = 0; productIndex < newProducts.count-1; productIndex++) {
                [products addObject:newProducts[productIndex]];
            }
            currentProduct = newProducts.lastObject;
            
            elementIndex++;
        } else {
            NSDecimalNumber *functionValue = [(MPFunction *)element evaluate:error];
            if (!functionValue) {
                return nil;
            }
            if (!currentProduct) {
                currentProduct = [[MPParsedProduct alloc] init];
            }
            [currentProduct addFactor:[MPParsedFactor factorWithDecimalNumber:functionValue]];
        }
    }
    
    [products addObject:currentProduct];
    
    NSDecimalNumber *value = [NSDecimalNumber zero];
    for (MPParsedProduct *product in products) {
        value = [value decimalNumberByAdding:product.value];
    }
    return value;
}

@end