/*

 File: FileBuffer.h

 Abstract: FileBuffer represents a simple wrapper around NSFileHandle,

 adding some buffering and byte swapping.  It is deliberately not

 thread-safe; instead, the application serializes it by assigning a

 single instance to a single-threaded NSOperationQueue.

 Version: 1.1

 Disclaimer: IMPORTANT:  This Apple software is supplied to you by 

 Apple Inc. ("Apple") in consideration of your agreement to the

 following terms, and your use, installation, modification or

 redistribution of this Apple software constitutes acceptance of these

 terms.  If you do not agree with these terms, please do not use,

 install, modify or redistribute this Apple software.

 In consideration of your agreement to abide by the following terms, and

 subject to these terms, Apple grants you a personal, non-exclusive

 license, under Apple's copyrights in this original Apple software (the

 "Apple Software"), to use, reproduce, modify and redistribute the Apple

 Software, with or without modifications, in source and/or binary forms;

 provided that if you redistribute the Apple Software in its entirety and

 without modifications, you must retain this notice and the following

 text and disclaimers in all such redistributions of the Apple Software. 

 Neither the name, trademarks, service marks or logos of Apple Inc. 

 may be used to endorse or promote products derived from the Apple

 Software without specific prior written permission from Apple.  Except

 as expressly stated in this notice, no other rights or licenses, express

 or implied, are granted by Apple herein, including but not limited to

 any patent rights that may be infringed by your derivative works or by

 other works in which the Apple Software may be incorporated.

 The Apple Software is provided by Apple on an "AS IS" basis.  APPLE

 MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION

 THE IMPLIED WARRANTIES OF NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS

 FOR A PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND

 OPERATION ALONE OR IN COMBINATION WITH YOUR PRODUCTS.

 IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL

 OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF

 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS

 INTERRUPTION) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION,

 MODIFICATION AND/OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED

 AND WHETHER UNDER THEORY OF CONTRACT, TORT (INCLUDING NEGLIGENCE),

 STRICT LIABILITY OR OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE

 POSSIBILITY OF SUCH DAMAGE.

 Copyright (C) 2008-2009 Apple Inc. All Rights Reserved.

 */ 

#import "FileBuffer.h"

#define FILE_BUFFER_QUANTUM 512

@implementation FileBuffer 

- (NSData *)readDataAtOffset:(unsigned long long)offset length:(NSUInteger)length {

    NSData *data = nil;

    @try {

        [fileHandle seekToFileOffset:offset];

        data = [fileHandle readDataOfLength:length];

    } @catch (NSException *exception) {

        data = nil;

    }

    return data;

}

- (BOOL)getBytes:(void *)buffer length:(NSUInteger)length atOffset:(unsigned long long)offset {

    BOOL retval = YES;

    NSUInteger currentLength = [currentData length];

    unsigned long long end = offset + length, currentEnd = currentOffset + currentLength, targetOffset;

    size_t bytesMoved = (size_t)-1;

    while (retval && length > 0 && offset < fileLength) {

        if (offset >= currentOffset && offset < currentEnd && end > currentOffset) {

            bytesMoved = (end > currentEnd) ? currentEnd - offset : length;

            memmove(buffer, [currentData bytes] + offset - currentOffset, bytesMoved);

            buffer += bytesMoved;

            length -= bytesMoved;

            offset += bytesMoved;

        } else if (offset < currentOffset && end > currentOffset && end <= currentEnd) {

            bytesMoved = end - currentOffset;

            memmove(buffer + currentOffset - offset, [currentData bytes], bytesMoved);

            length -= bytesMoved;

            end -= bytesMoved;

        } else {

            if (bytesMoved == 0) retval = NO;

            bytesMoved = 0;

            targetOffset = FILE_BUFFER_QUANTUM * (offset / FILE_BUFFER_QUANTUM);

            currentData = [self readDataAtOffset:targetOffset length:2 * FILE_BUFFER_QUANTUM];

            currentOffset = targetOffset;

            currentLength = [currentData length];

            currentEnd = currentOffset + currentLength;

        }

    }

    return retval;

}

- (id)initWithURL:(NSURL *)url error:(NSError **)error {

    self = [super init];

    if (self) {

        fileHandle = [NSFileHandle fileHandleForReadingAtPath:[url path]];

        if (fileHandle) {

            @try {

                fileLength = [fileHandle seekToEndOfFile];

            } @catch (NSException *exception) {

                [fileHandle closeFile];

                fileHandle = nil;

                fileLength = 0;

            }

            if (fileLength > 0) {

                uint8_t val;

                if (![self getBytes:&val length:1 atOffset:fileLength - 1]) {

                    [fileHandle closeFile];

                    fileHandle = nil;

                }

            }

        }

    }

    if (!fileHandle && error) *error = [NSError errorWithDomain:NSCocoaErrorDomain code:NSFileReadUnknownError userInfo:[NSDictionary dictionaryWithObjectsAndKeys:url, NSURLErrorKey, nil]];

    return fileHandle ? self : nil;

}

- (void)close {

    [fileHandle closeFile];

    fileHandle = nil;

}

- (void)finalize {

    [self close];

    [super finalize];

}

- (unsigned long long)fileLength {

    return fileLength;

}

- (uint8_t)byteAtOffset:(unsigned long long)offset {

    uint8_t val = 0;

    (void)[self getBytes:&val length:sizeof(val) atOffset:offset];

    return val;

}

- (uint16_t)littleUnsignedShortAtOffset:(unsigned long long)offset {

    uint16_t val = 0;

    (void)[self getBytes:&val length:sizeof(val) atOffset:offset];

    return NSSwapLittleShortToHost(val);

}

- (uint32_t)littleUnsignedIntAtOffset:(unsigned long long)offset {

    uint32_t val = 0;

    (void)[self getBytes:&val length:sizeof(val) atOffset:offset];

    return NSSwapLittleIntToHost(val);

}

- (NSData *)dataAtOffset:(unsigned long long)offset length:(NSUInteger)length {

    NSData *data = nil;

    if (length <= FILE_BUFFER_QUANTUM) {

        uint8_t buffer[FILE_BUFFER_QUANTUM] = {0};

        (void)[self getBytes:buffer length:length atOffset:offset];

        data = [NSData dataWithBytes:buffer length:length];

    } else {

        data = [self readDataAtOffset:offset length:length];

    }

    return data;

}

@end