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

#import "MPExpressionTree.h"

@implementation MPExpressionTree {
    NSRange _variableDefinitionRange;
    NSMutableArray *_summands;
    NSRange _range;
}

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

- (instancetype)initWithTokenStream:(MPTokenStream *)tokenStream
{
    self = [self init];
    if (self) {
        MPTokenStreamRecordCurrentLocation(tokenStream);
        
        [tokenStream beginIgnoringWhitespaceTokens];
        
        _variableDefinitionRange = NSMakeRange(NSNotFound, 0);
        self.definedVariable = nil;
        if (tokenStream.currentToken.tokenType == MPVariableToken) {
            if (tokenStream.peekNextToken.tokenType == MPEqualsToken) {
                self.definedVariable = tokenStream.currentToken.stringValue;
                NSRange variableRange = tokenStream.currentToken.range;
                [tokenStream currentTokenConsumed];
                NSRange equalsRange = tokenStream.currentToken.range;
                [tokenStream currentTokenConsumed];
                _variableDefinitionRange = NSUnionRange(variableRange, equalsRange);
            }
        }
        while ([tokenStream hasMoreTokens]) {
            [_summands addObject:[[MPSummand alloc] initWithTokenStream:tokenStream]];
        }
        
        [tokenStream endIgnoringOrAcceptingWhitespaceTokens];
        _range = MPTokenStreamRecordedRange(tokenStream);
    }
    return self;
}

- (NSRange)range
{
    return _range;
}

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

- (BOOL)validateExpectingVariableDefinition:(BOOL)flag
                                      error:(MPParseError *__autoreleasing *)error
{
    if (flag) {
        if (!self.definedVariable) {
            if (error) {
                *error = MPParseError(NSMakeRange(self.range.location, 0), @"Expected Variable Definition.");
            }
            return NO;
        }
    } else {
        if (self.definedVariable) {
            if (error) {
                *error = MPParseError(_variableDefinitionRange, @"Unexpected Variable Definition");
            }
            return NO;
        }
    }
    if (_summands.count == 0) {
        if (error) {
            *error = MPParseError(self.range, @"Empty Expression.");
        }
        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;
}


- (NSArray *)expressionElements
{
    NSMutableArray *elements = [[NSMutableArray alloc] init];
    if (self.definedVariable) {
        [elements addObject:[NSString stringWithFormat:@"%@=", self.definedVariable]];
    }
    for (MPSummand *summand in _summands) {
        [elements addObjectsFromArray:summand.expressionElements];
    }
    return elements;
}

- (NSArray *)summands
{
    return _summands;
}

- (void)appendSummand:(MPSummand *)summand
{
    [_summands addObject:summand];
}

- (void)insertSummand:(MPSummand *)summand
              atIndex:(NSUInteger)index
{
    [_summands insertObject:summand
                    atIndex:index];
}

- (void)removeSummand:(MPSummand *)summand
{
    [_summands removeObject:summand];
}

- (void)removeSummandAtIndex:(NSUInteger)index
{
    [_summands removeObjectAtIndex:index];
}

- (MPSummand *)summandAtIndex:(NSUInteger)index
{
    return [_summands objectAtIndex:index];
}

@end