//
//  MPExpressionTree.m
//  MathPad
//
//  Created by Kim Wittenburg on 09.10.14.
//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
//

#import "MPExpressionTree.h"

#import "MPSummand.h"

#import "MPTokenStream.h"
#import "MPToken.h"

#import "MPExpression.h"

@implementation MPExpressionTree {
    NSMutableArray *_summands;
}

- (id)init
{
    self = [super init];
    if (self) {
        _summands = [[NSMutableArray alloc] init];
    }
    return self;
}

- (instancetype)initWithTokenStream:(MPTokenStream *)tokenStream
{
    self = [self init];
    if (self) {
        [tokenStream beginIgnoringWhitespaceTokens];
        
        self.definedVariable = nil;
        if (tokenStream.currentToken.tokenType == MPVariableToken) {
            if (tokenStream.peekNextToken.tokenType == MPEqualsToken) {
                self.definedVariable = tokenStream.currentToken.stringValue;
                [tokenStream currentTokenConsumed];
                [tokenStream currentTokenConsumed];
            }
        }
        while ([tokenStream hasMoreTokens]) {
            [_summands addObject:[[MPSummand alloc] initWithTokenStream:tokenStream]];
        }
        
        [tokenStream endIgnoringOrAcceptingWhitespaceTokens];
    }
    return self;
}

- (NSArray *)summands
{
    return _summands;
}

- (BOOL)validate:(NSError *__autoreleasing *)error
{
    return [self validateExpectingVariableDefinition:NO
                                               error:error];
}

- (BOOL)validateExpectingVariableDefinition:(BOOL)flag
                                      error:(NSError *__autoreleasing *)error
{
    if (flag) {
        if (!self.definedVariable) {
            if (error) {
                *error = MPParseError(1,
                                      NSLocalizedString(@"Expected Variable Definition.", @"Error message. This is displayed when an expected variable definition was not found."),
                                      nil);
            }
            return NO;
        }
    } else {
        if (self.definedVariable) {
            if (error) {
                *error = MPParseError(2,
                                      NSLocalizedString(@"Unexpected Variable Definition.", @"Error message. This is displayed when no variable definition was expected but one was found."),
                                      nil);
            }
            return NO;
        }
    }
    if (_summands.count == 0) {
        if (error) {
            *error = MPParseError(3,
                                  NSLocalizedString(@"Empty Expression.", @"Error message. This is displayed when the user tried to evaluate an empty expression."),
                                  nil);
        }
        return NO;
    }
    for (MPSummand *summand in _summands) {
        if (![summand validate:error]) {
            return NO;
        }
    }
    return YES;
}

- (NSDecimalNumber *)evaluate
{
    NSDecimalNumber *value = [NSDecimalNumber zero];
    for (MPSummand *summand in _summands) {
        NSDecimalNumber *currentValue = [summand evaluate];
        if ([currentValue isEqualToNumber:[NSDecimalNumber notANumber]]) {
            value = currentValue;
            break;
        }
        value = [value decimalNumberByAdding:currentValue];
    }
    return value;
}


@end