//
//  MPExpression.m
//  MathPad
//
//  Created by Kim Wittenburg on 10.08.14.
//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
//

#import "MPExpression.h"
#import "MPFunction.h"
#import "MPRangePath.h"

#import "NSIndexPath+MPAdditions.h"
#import "MPException.h"

#import "MPExpressionTokenizer.h"
#import "MPExpressionEvaluator.h"
#import "MPToken.h"



@interface MPExpression () {
    NSMutableArray * _elements;
}

- (NSArray *)tokens;

- (void)validateElements:(NSArray *)elements;
- (void)fixElements;

- (void)_replaceSymbolsInRange:(NSRange)range
                  withElements:(NSArray *)elements;
- (BOOL)_splitElementsAtLocation:(NSUInteger)location
                  insertionIndex:(out NSUInteger *)insertionIndex;

@end



@implementation MPExpression {
    NSArray *_tokenCache;
    
    NSRange _editedRange;
    BOOL _didSplitStartOnEditing;
    BOOL _didSplitEndOnEditing;
    NSUInteger _replacementLength;
}


#pragma mark Creation Methods


- (instancetype)init
{
    return [self initWithElements:@[]];
}

- (instancetype)initWithElement:(id<MPExpressionElement>)element
{
    return [self initWithElements:@[element]];
}

- (instancetype)initWithElements:(NSArray *)elements
{
    self = [super init];
    if (self) {
        [self validateElements:elements];
        _elements = [[NSMutableArray alloc] initWithArray:elements
                                                copyItems:YES];
        [self fixElements];
    }
    return self;
}


#pragma mark Private Methods


- (NSArray *)tokens
{
    if (!_tokenCache) {
        _tokenCache = [MPExpressionTokenizer tokenizeExpression:self];
    }
    return _tokenCache;
}


- (void)validateElements:(NSArray *)elements
{
    for (id element in elements) {
        if (![element conformsToProtocol:@protocol(MPExpressionElement)]) {
            @throw [NSException exceptionWithName:MPIllegalElementException
                                           reason:@"Elements must conform to the MPExpressionElement protocol."
                                         userInfo:@{MPIllegalElementExceptionElementKey: element}];
        }
    }
}


- (void)fixElements
{
    for (NSUInteger index = 0; index < _elements.count; index++) {
        id<MPExpressionElement> next = index+1 < _elements.count ? _elements[index+1] : nil;
        id<MPExpressionElement> current = _elements[index];
        if ([current isString]) {
            if (current.length == 0) {
                [_elements removeObjectAtIndex:index];
                if (index >= _editedRange.location && index < NSMaxRange(_editedRange)) {
                    --_replacementLength;
                }
                --index;
            } else if ([next isString]) {
                NSString *new = [NSString stringWithFormat:@"%@%@", current, next];
                [_elements replaceObjectsInRange:NSMakeRange(index, 2)
                                withObjectsFromArray:@[new]];
                NSUInteger maxReplacementIndex = _editedRange.location + _replacementLength;
                if (index == _editedRange.location-1 && !_didSplitStartOnEditing) {
                    --_editedRange.location;
                    ++_editedRange.length;
                    if (index == maxReplacementIndex-1 && !_didSplitEndOnEditing) {
                        ++_editedRange.length;
                        ++_replacementLength;
                    }
                } else if (index >= _editedRange.location && index < maxReplacementIndex - 1) {
                    --_replacementLength;
                } else if (index == maxReplacementIndex-1 && !_didSplitEndOnEditing) {
                    ++_editedRange.length;
                }
                --index;
            }
        } else {
            [(MPFunction *)current setParent:self];
        }
    }
}

#pragma mark Querying Expressions


- (MPExpression *)rootExpression
{
    if (self.parent == nil) {
        return self;
    }
    return [self.parent rootExpression];
}

- (NSIndexPath *)indexPath
{
    if (self.parent) {
        NSUInteger selfIndex = [self.parent indexOfChild:self];
        return [[self.parent indexPath] indexPathByAddingIndex:selfIndex];
    } else {
        return [[NSIndexPath alloc] init];
    }
}

- (NSUInteger)countItemsInReferenceFrame:(MPReferenceFrame)referenceFrame
{
    switch (referenceFrame) {
        case MPElementReferenceFrame:
            return _elements.count;
            
        case MPSymbolReferenceFrame:
        {
            NSUInteger count = 0;
            for (id<MPExpressionElement> element in _elements) {
                count += element.length;
            }
            return count;
        }
            
        case MPTokenReferenceFrame:
            return self.tokens.count;
    }
}

- (id)itemAtIndex:(NSUInteger)anIndex
   referenceFrame:(MPReferenceFrame)referenceFrame
{
    switch (referenceFrame) {
        case MPElementReferenceFrame:
            return _elements[anIndex];
            
        case MPSymbolReferenceFrame:
        {
            NSUInteger location = 0;
            NSUInteger elementIndex = 0;
            id <MPExpressionElement> element = nil;
            while (location < anIndex) {
                element = _elements[elementIndex++];
                location += element.length;
            }
            if (location == anIndex && element.isFunction) {
                return element;
            }
            NSUInteger indexInString = location - element.length + anIndex;
            return [((NSString *)element) substringWithRange:NSMakeRange(indexInString, 1)];
        }
            
        case MPTokenReferenceFrame:
            return self.tokens[anIndex];
    }
}

- (id<MPExpressionElement>)elementAtIndex:(NSUInteger)anIndex
                           referenceFrame:(MPReferenceFrame)referenceFrame
{
    NSUInteger elementIndex = [self convertIndex:anIndex
                              fromReferenceFrame:referenceFrame
                                toReferenceFrame:MPElementReferenceFrame];
    return _elements[elementIndex];
}

#warning If multiple equal expressions exist errors may occur...
- (NSUInteger)indexOfElement:(id<MPExpressionElement>)element
{
    return [_elements indexOfObject:element];
}

- (NSArray *)itemsInRange:(NSRange)range
           referenceFrame:(MPReferenceFrame)referenceFrame
{
    MPExpression *subexpression = [self subexpressionWithRange:range
                                                referenceFrame:referenceFrame];
    return [subexpression allItemsInReferenceFrame:referenceFrame];
}

- (NSArray *)allItemsInReferenceFrame:(MPReferenceFrame)referenceFrame
{
    switch (referenceFrame) {
        case MPElementReferenceFrame:
            return _elements;
            
        case MPSymbolReferenceFrame:
        {
            NSMutableArray *symbols = [[NSMutableArray alloc] init];
            for (id<MPExpressionElement> element in _elements) {
                if ([element isString]) {
                    for (NSUInteger i = 0; i < [element length]; i++) {
                        NSString *ichar  = [NSString stringWithFormat:@"%c", [((NSString *)element) characterAtIndex:i]];
                        [symbols addObject:ichar];
                    }
                } else {
                    [symbols addObject:element];
                }
            }
        }
            
        case MPTokenReferenceFrame:
            return self.tokens;
    }
}

- (id)elementAtIndexPath:(NSIndexPath *)indexPath
{
    if (indexPath.length == 0) {
        return self;
    }
    id<MPExpressionElement> element = _elements[[indexPath indexAtPosition:0]];
    if (indexPath.length == 1) {
        return element;
    }
    if ([element isFunction]) {
        return [(MPFunction *)element elementAtIndexPath:[indexPath indexPathByRemovingFirstIndex]];
    }
    // TODO: Raise appropriate exeption.
    return nil;
}

- (NSUInteger)convertIndex:(NSUInteger)index
        fromReferenceFrame:(MPReferenceFrame)fromReferenceFrame
          toReferenceFrame:(MPReferenceFrame)toReferenceFrame
{
    return [self convertIndex:index
           fromReferenceFrame:fromReferenceFrame
             toReferenceFrame:toReferenceFrame
                       offset:NULL];
}

- (NSUInteger)convertIndex:(NSUInteger)index
        fromReferenceFrame:(MPReferenceFrame)fromReferenceFrame
          toReferenceFrame:(MPReferenceFrame)toReferenceFrame
                    offset:(NSUInteger *)offset
{
    if (fromReferenceFrame == toReferenceFrame || index == 0) {
        if (offset) {
            *offset = 0;
        }
        return index;
    }
    
    NSUInteger symbolIndex __block = 0;
    switch (fromReferenceFrame) {
        case MPElementReferenceFrame:
            [_elements enumerateObjectsUsingBlock:^(id<MPExpressionElement> obj, NSUInteger idx, BOOL *stop) {
                symbolIndex += obj.length;
                *stop = idx >= index - 1;
            }];
            break;
            
        case MPSymbolReferenceFrame:
            symbolIndex = index;
            break;
            
        case MPTokenReferenceFrame:
            [_elements enumerateObjectsUsingBlock:^(id<MPToken> obj, NSUInteger idx, BOOL *stop) {
                symbolIndex = NSMaxRange(obj.range);
                *stop = idx >= index - 1;
            }];
            break;
    }
    
    switch (toReferenceFrame) {
        case MPElementReferenceFrame:
        {
            NSUInteger totalLength = 0;
            NSUInteger elementIndex = 0;
            id<MPExpressionElement> element;
            while (totalLength < symbolIndex) {
                element = _elements[elementIndex++];
                totalLength += element.length;
            }
            --elementIndex;
            NSUInteger offsetInElement = element.length - totalLength + symbolIndex;
            if (offsetInElement == element.length) {
                offsetInElement = 0;
                elementIndex++;
            }
            if (offset) {
                *offset = offsetInElement;
            }
            return elementIndex;
        }
            
        case MPSymbolReferenceFrame:
            if (offset) {
                *offset = 0;
            }
            return symbolIndex;
            
        case MPTokenReferenceFrame:
        {
            NSUInteger totalLength = 0;
            NSUInteger tokenIndex = 0;
            id<MPToken> token;
            while (totalLength < symbolIndex) {
                token = self.tokens[tokenIndex++];
                totalLength = NSMaxRange(token.range);
            }
            NSUInteger offsetInToken = token.range.length - totalLength + symbolIndex;
            if (offsetInToken == token.range.length) {
                offsetInToken = 0;
                tokenIndex++;
            }
            if (offset) {
                *offset = offsetInToken;
            }
            return tokenIndex;
        }
    }
}

- (NSRange)convertRange:(NSRange)aRange
     fromReferenceFrame:(MPReferenceFrame)fromReferenceFrame
       toReferenceFrame:(MPReferenceFrame)toReferenceFrame
{
    return [self convertRange:aRange
           fromReferenceFrame:fromReferenceFrame
             toReferenceFrame:toReferenceFrame
                leadingOffset:NULL
               trailingOffset:NULL];
}

- (NSRange)convertRange:(NSRange)aRange
     fromReferenceFrame:(MPReferenceFrame)fromReferenceFrame
       toReferenceFrame:(MPReferenceFrame)toReferenceFrame
          leadingOffset:(NSUInteger *)leadingOffset
         trailingOffset:(NSUInteger *)trailingOffset
{
    NSUInteger start = [self convertIndex:aRange.location
                       fromReferenceFrame:fromReferenceFrame
                         toReferenceFrame:toReferenceFrame
                                   offset:leadingOffset];
    NSUInteger end = [self convertIndex:NSMaxRange(aRange)
                     fromReferenceFrame:fromReferenceFrame
                       toReferenceFrame:toReferenceFrame
                                 offset:trailingOffset];
    return NSMakeRange(start, end - start);
}


#pragma mark Mutating Expressions


- (void)replaceItemsInRange:(NSRange)range
             referenceFrame:(MPReferenceFrame)referenceFrame
               withElements:(NSArray *)elements
{
    NSUInteger start = [self convertIndex:range.location
                       fromReferenceFrame:referenceFrame
                         toReferenceFrame:MPSymbolReferenceFrame];
    NSUInteger end = [self convertIndex:NSMaxRange(range)
                     fromReferenceFrame:referenceFrame
                       toReferenceFrame:MPSymbolReferenceFrame];
    [self _replaceSymbolsInRange:NSMakeRange(start, end - start)
                    withElements:elements];
}

- (void)_replaceSymbolsInRange:(NSRange)range
                  withElements:(NSArray *)elements
{
    if (NSMaxRange(range) > [self countItemsInReferenceFrame:MPSymbolReferenceFrame]) {
        @throw [NSException exceptionWithName:NSRangeException
                                       reason:@"Range out of bounds of expression"
                                     userInfo:nil];
    }
    [self validateElements:elements];
    
    // Locate the position, split the elements
    NSUInteger startIndex; // startIndex is inclusive
    BOOL didSplitStart = NO;
    if (_elements.count == 0) {
        startIndex = 0;
    } else {
        didSplitStart = [self _splitElementsAtLocation:range.location
                                        insertionIndex:&startIndex];
    }
    NSUInteger endIndex; // endIndex is exclusive
    BOOL didSplitEnd = [self _splitElementsAtLocation:NSMaxRange(range)
                                       insertionIndex:&endIndex];
    
    // Perform the replacement
    NSMutableArray *newElements = [[NSMutableArray alloc] initWithArray:elements
                                                              copyItems:YES];
    [_elements replaceObjectsInRange:NSMakeRange(startIndex, endIndex-startIndex)
                    withObjectsFromArray:newElements];
    
    _tokenCache = nil;
    
    NSUInteger editLocation = startIndex - (didSplitStart ? 1 : 0);
    NSUInteger editLength = endIndex - startIndex;
    if (range.length == 0 && didSplitStart) {
        editLength = 1;
    }

    _editedRange = NSMakeRange(editLocation, editLength);
    _didSplitStartOnEditing = didSplitStart;
    _didSplitEndOnEditing = didSplitEnd;
    _replacementLength = elements.count;
    if (didSplitStart) {
        _replacementLength++;
        if (range.length == 0) {
            _replacementLength++;
        }
    }
    if (didSplitEnd) {
        _replacementLength++;
    }

    [self fixElements];
    [self didChangeElementsInRangePath:[[MPRangePath alloc] initWithRange:_editedRange]
                     replacementLength:_replacementLength];
}

- (BOOL)_splitElementsAtLocation:(NSUInteger)location
                  insertionIndex:(out NSUInteger *)insertionIndex
{
    if (location == 0) {
        *insertionIndex = 0;
        return NO;
    }
    
    NSUInteger splitOffset;
    NSUInteger splitElementIndex = [self convertIndex:location
                                   fromReferenceFrame:MPSymbolReferenceFrame
                                     toReferenceFrame:MPElementReferenceFrame
                                               offset:&splitOffset];
    if (splitOffset != 0) {
        NSString *splitElement = (NSString *)_elements[splitElementIndex];
        NSString *leftPart = [splitElement substringToIndex:splitOffset];
        NSString *rightPart = [splitElement substringFromIndex:splitOffset];
        [_elements replaceObjectsInRange:NSMakeRange(splitElementIndex, 1)
                    withObjectsFromArray:@[leftPart, rightPart]];
        ++splitElementIndex;
    }
    *insertionIndex = splitElementIndex;
    return splitOffset != 0;
}

- (MPExpression *)subexpressionFromIndex:(NSUInteger)from
                          referenceFrame:(MPReferenceFrame)referenceFrame
{
    return [self subexpressionWithRange:NSMakeRange(from, [self countItemsInReferenceFrame:referenceFrame] - from)
                         referenceFrame:referenceFrame];
}

- (MPExpression *)subexpressionToIndex:(NSUInteger)to
                        referenceFrame:(MPReferenceFrame)referenceFrame
{
    return [self subexpressionWithRange:NSMakeRange(0, to)
                         referenceFrame:referenceFrame];
}

- (MPExpression *)subexpressionWithRange:(NSRange)range
                          referenceFrame:(MPReferenceFrame)referenceFrame
{
    MPExpression *subexpression = [self copy];
    NSRange preceedingRange = NSMakeRange(0, range.location);
    NSUInteger firstOut = NSMaxRange(range);
    NSRange exceedingRange = NSMakeRange(firstOut, [self countItemsInReferenceFrame:referenceFrame] - firstOut);
    [subexpression deleteElementsInRange:exceedingRange
                          referenceFrame:referenceFrame];
    [subexpression deleteElementsInRange:preceedingRange
                          referenceFrame:referenceFrame];
    return subexpression;
}

#pragma mark Evaluating Expressions


- (NSDecimalNumber *)evaluateWithError:(MPParseError *__autoreleasing *)error
{
    MPExpressionEvaluator *evaluator = [[MPExpressionEvaluator alloc] initWithExpression:self];
    MPTerm *term = [evaluator parseExpectingVariable:NO
                                               error:error];
    return [term evaluate];
}

#pragma mark Notifications


- (void)didChangeElementsInRangePath:(MPRangePath *)rangePath
                   replacementLength:(NSUInteger)replacementLength
{
    NSUInteger selfIndex = [self.parent indexOfChild:self];
    MPRangePath *newPath = MPMakeRangePath([rangePath.location indexPathByPreceedingIndex:selfIndex], rangePath.length);
    [self.parent didChangeElementsInRangePath:newPath
                            replacementLength:replacementLength];
}


#pragma mark Basic NSObject Methods


/*
- (BOOL)isEqual:(id)object
{
    if (self == object) {
        return YES;
    }
    if (object == nil) {
        return NO;
    }
    if (![object isKindOfClass:[MPExpression class]]) {
        return NO;
    }
    return [self isEqualToExpression:(MPExpression *)object];
}

- (BOOL)isEqualToExpression:(MPExpression *)anExpression
{
    return [self.elements isEqualToArray:anExpression.elements];
}
*/

- (NSString *)description
{
#warning Bad Implementation
    NSMutableString *description = [[NSMutableString alloc] init];
    NSUInteger index = 0;
    for (id element in _elements) {
        if ([element isString]) {
            NSMutableString *correctedSymbol = [[element stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] mutableCopy];
            // Prefix operator
            if (element != _elements[0]) {
                unichar prefix = [correctedSymbol characterAtIndex:0];
                if ([[NSCharacterSet decimalDigitCharacterSet] characterIsMember:prefix]) {
                    [correctedSymbol insertString:@"*"
                                          atIndex:0];
                }
            }
            // Suffix operator
            if (element != [_elements lastObject]) {
                unichar suffix = [correctedSymbol characterAtIndex:correctedSymbol.length-1];
                if ([[NSCharacterSet decimalDigitCharacterSet] characterIsMember:suffix]) {
                    [correctedSymbol appendString:@"*"];
                }
            }
            [description appendString:correctedSymbol];
        } else if (index > 0 && [_elements[index-1] isKindOfClass:[MPFunction class]]) {
            [description appendFormat:@"*%@", [element description]];
        } else {
            [description appendString:[element description]];
        }
        index++;
    }
    return description;
}

- (NSUInteger)hash
{
    return [_elements hash];
}


#pragma mark - NSCopying


- (id)copyWithZone:(NSZone *)zone
{
    MPExpression *copy = [[MPExpression allocWithZone:zone] initWithElements:_elements];
    return copy;
}


#pragma mark - NSCoding


- (id)initWithCoder:(NSCoder *)aDecoder
{
    // TODO: Test Coding
    return [self initWithElements:[aDecoder decodeObject]];
}

- (void)encodeWithCoder:(NSCoder *)aCoder
{
    [aCoder encodeObject:_elements];
}

@end


@implementation MPExpression (MPExpressionConvenience)

#pragma mark Querying Expressions

- (NSUInteger)countElements
{
    return [self countItemsInReferenceFrame:MPElementReferenceFrame];
}

- (NSUInteger)countSymbols
{
    return [self countItemsInReferenceFrame:MPSymbolReferenceFrame];
}

- (NSUInteger)countTokens
{
    return [self countItemsInReferenceFrame:MPTokenReferenceFrame];
}

- (id<MPExpressionElement>)elementAtIndex:(NSUInteger)index
{
    return [self itemAtIndex:index
              referenceFrame:MPElementReferenceFrame];
}

- (id<MPExpressionElement>)symbolAtIndex:(NSUInteger)index
{
    return [self itemAtIndex:index
              referenceFrame:MPSymbolReferenceFrame];
}

- (id<MPToken>)tokenAtIndex:(NSUInteger)index
{
    return [self itemAtIndex:index
              referenceFrame:MPTokenReferenceFrame];
}


#pragma mark Mutating Expressions

- (void)appendElement:(id<MPExpressionElement>)anElement
{
    [self appendElements:@[anElement]];
}

- (void)appendElements:(NSArray *)elements
{
    [self replaceItemsInRange:NSMakeRange([self countItemsInReferenceFrame:MPSymbolReferenceFrame], 0)
               referenceFrame:MPSymbolReferenceFrame
                 withElements:elements];
}

- (void)insertElement:(id<MPExpressionElement>)anElement
              atIndex:(NSUInteger)index
       referenceFrame:(MPReferenceFrame)referenceFrame
{
    [self insertElements:@[anElement]
                 atIndex:index
          referenceFrame:referenceFrame];
}

- (void)insertElements:(NSArray *)elements
               atIndex:(NSUInteger)index
        referenceFrame:(MPReferenceFrame)referenceFrame
{
    [self replaceItemsInRange:NSMakeRange(index, 0)
               referenceFrame:referenceFrame
                 withElements:elements];
}

- (void)deleteElementsInRange:(NSRange)range
               referenceFrame:(MPReferenceFrame)referenceFrame
{
    [self replaceItemsInRange:range
               referenceFrame:referenceFrame
                 withElements:@[]];
}

@end