//
//  Lexer.m
//  Brainfuck
//
//  Created by Kim Wittenburg on 20.05.13.
//  Copyright (c) 2013 brainfuck. All rights reserved.
//

#import "Lexer.h"

@implementation Lexer {
    NSString *script;
    NSInteger pos;
    NSInteger loopNestingLevel;
    NSMutableArray *tokens;
}

+ (Lexer *)lexer
{
    return [[self alloc] init];
}

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

- (NSArray *)performLexingOnString:(NSString *)s error:(NSError *__autoreleasing *)error
{
    pos = 0;
    loopNestingLevel = -1;
    script = s;
    tokens = [[NSMutableArray alloc] init];
    [self matchNextTokensInto:tokens error:error];
    if (error) {
        return nil;
    }
    return tokens;
}

- (void)matchNextTokensInto:(NSMutableArray *)target error:(NSError *__autoreleasing *)error;
{
    while (pos < script.length) {
        int c = [script characterAtIndex:pos++];
        NSString *character = [NSString stringWithFormat:@"%c", c];
        if (c == '-' || c == '+' || c == '<' || c == '>' || c == '.' || c == ',') {
            [target addObject:character];
        } else if (c == '[') {
            loopNestingLevel++;
            NSMutableArray *subTokens = [NSMutableArray new];
            [self matchNextTokensInto:subTokens error:error];
            [target addObject:subTokens];
        } else if (c == ']') {
            if (loopNestingLevel-- == -1) {
                NSError *err = [NSError errorWithDomain:@"Lexer" code:101 userInfo:@{NSLocalizedDescriptionKey: @"] without mathcing ["}];
                *error = err;
                return;
            }
            return;
        }
    }
    if (loopNestingLevel >= 0) {
        *error = [NSError errorWithDomain:@"Lexer" code:102 userInfo:@{NSLocalizedDescriptionKey: @"unclosed loop"}];
    }
}

@end