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

#import "Interpreter.h"

#import "Lexer.h"

@implementation Interpreter {
    NSMutableArray *a;
    NSInteger level;
    NSString *input;
    NSInteger inPos;
}

@synthesize printer;

+ (Interpreter *)interpreter
{
    return [[self alloc] init];
}

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

- (void)execute:(NSString *)script withInput:(NSString *)i error:(NSError *__autoreleasing *)error
{
    input = i;
    inPos = 0;
    Lexer *lexer = [Lexer lexer];
    NSArray *cmds = [lexer performLexingOnString:script error:error];
    level = 0;
    a = [NSMutableArray new];
    [a addObject:[NSNumber numberWithInt:0]];
    [self executeCommands:cmds];
}

- (void)executeCommands:(NSArray *)cmds
{
    for (id cmd in cmds) {
        if ([cmd isKindOfClass:[NSArray class]]) {
            [self loop:cmd];
        } else {
            [self executeCommand:cmd];
        }
    }
}

- (void)executeCommand:(NSString *)cmd
{
    int c = [cmd characterAtIndex:0];
    if (c == '+') {
        [self increment];
    } else if (c == '-') {
        [self decrement];
    } else if (c == '<') {
        [self previousCell];
    } else if (c == '>') {
        [self nextCell];
    } else if (c == '.') {
        [self printCellValue];
    } else if (c == ',') {
        [self readNextInput];
    }
}

- (void)increment
{
    NSNumber *number = a[level];
    number = [NSNumber numberWithInt:number.intValue+1];
     a[level] = number;
}

- (void)decrement
{
    NSNumber *number = a[level];
    number = [NSNumber numberWithInt:number.intValue-1];
    a[level] = number;
}

- (void)nextCell
{
    if (++level == a.count) {
        [a addObject:[NSNumber numberWithInt:0]];
    }
}

- (void)previousCell
{
    if (--level == -1) {
        [a insertObject:[NSNumber numberWithInt:0] atIndex:0];
        level++;
    }
}

- (void)printCellValue
{
    NSNumber *ascii = a[level];
    NSString *text = [NSString stringWithFormat:@"%c", ascii.intValue];
    [self.printer print:text];
}

- (void)readNextInput
{
    int ascii;
    if (inPos == input.length) {
        ascii = 0;
    } else {
        ascii = [input characterAtIndex:inPos++];
    }
    a[level] = [NSNumber numberWithInt:ascii];
}

- (void)loop:(NSArray *)cmds
{
    while (((NSNumber *)a[level]).intValue != 0) {
        [self executeCommands:cmds];
    }
}

@end