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/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2021 Mike Becker, Olaf Wintermann All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * \file buffer.h
 *
 * \brief Advanced buffer implementation.
 *
 * Instances of CxBuffer can be used to read from or to write to like one
 * would do with a stream.
 *
 * Some features for convenient use of the buffer
 * can be enabled. See the documentation of the macro constants for more
 * information.
 *
 * \author Mike Becker
 * \author Olaf Wintermann
 * \version 3.0
 * \copyright 2-Clause BSD License
 */

#ifndef UCX_BUFFER_H
#define UCX_BUFFER_H

#include "common.h"
#include "allocator.h"

#ifdef    __cplusplus
extern "C" {
#endif

/**
 * No buffer features enabled (all flags cleared).
 */
#define CX_BUFFER_DEFAULT 0x00

/**
 * If this flag is enabled, the buffer will automatically free its contents when destroyed.
 */
#define CX_BUFFER_FREE_CONTENTS 0x01

/**
 * If this flag is enabled, the buffer will automatically extends its capacity.
 */
#define CX_BUFFER_AUTO_EXTEND 0x02

/** Structure for the UCX buffer data. */
typedef struct {
    /** A pointer to the buffer contents. */
    union {
        /**
         * Data is interpreted as text.
         */
        char *space;
        /**
         * Data is interpreted as binary.
         */
        unsigned char *bytes;
    };
    /** The allocator to use for automatic memory management. */
    CxAllocator const *allocator;
    /** Current position of the buffer. */
    size_t pos;
    /** Current capacity (i.e. maximum size) of the buffer. */
    size_t capacity;
    /** Current size of the buffer content. */
    size_t size;
    /**
     * The buffer may not extend beyond this threshold before starting to flush.
     * Default is \c SIZE_MAX (flushing disabled when auto extension is enabled).
     */
    size_t flush_threshold;
    /**
     * The block size for the elements to flush.
     * Default is 4096 bytes.
     */
    size_t flush_blksize;
    /**
     * The maximum number of blocks to flush in one cycle.
     * Zero disables flushing entirely (this is the default).
     * Set this to \c SIZE_MAX to flush the entire buffer.
     *
     * @attention if the maximum number of blocks multiplied with the block size
     * is smaller than the expected contents written to this buffer within one write
     * operation, multiple flush cycles are performed after that write.
     * That means the total number of blocks flushed after one write to this buffer may
     * be larger than \c flush_blkmax.
     */
    size_t flush_blkmax;

    /**
     * The write function used for flushing.
     * If NULL, the flushed content gets discarded.
     */
    cx_write_func flush_func;

    /**
     * The target for \c flush_func.
     */
    void *flush_target;

    /**
     * Flag register for buffer features.
     * @see #CX_BUFFER_DEFAULT
     * @see #CX_BUFFER_FREE_CONTENTS
     * @see #CX_BUFFER_AUTO_EXTEND
     */
    int flags;
} cx_buffer_s;

/**
 * UCX buffer.
 */
typedef cx_buffer_s CxBuffer;

/**
 * Initializes a fresh buffer.
 *
 * \note You may provide \c NULL as argument for \p space.
 * Then this function will allocate the space and enforce
 * the #CX_BUFFER_FREE_CONTENTS flag.
 *
 * @param buffer the buffer to initialize
 * @param space pointer to the memory area, or \c NULL to allocate
 * new memory
 * @param capacity the capacity of the buffer
 * @param allocator the allocator this buffer shall use for automatic memory management
 * @param flags buffer features (see cx_buffer_s.flags)
 * @return zero on success, non-zero if a required allocation failed
 */
__attribute__((__nonnull__(1, 4)))
int cxBufferInit(
        CxBuffer *buffer,
        void *space,
        size_t capacity,
        CxAllocator const *allocator,
        int flags
);

/**
 * Destroys the buffer contents.
 *
 * Has no effect if the #CX_BUFFER_FREE_CONTENTS feature is not enabled.
 *
 * @param buffer the buffer which contents shall be destroyed
 */
__attribute__((__nonnull__))
void cxBufferDestroy(CxBuffer *buffer);

/**
 * Shifts the contents of the buffer by the given offset.
 *
 * If the offset is positive, the contents are shifted to the right.
 * If auto extension is enabled, the buffer grows, if necessary.
 * In case the auto extension fails, this function returns a non-zero value and
 * no contents are changed.
 * If auto extension is disabled, the contents that do not fit into the buffer
 * are discarded.
 *
 * If the offset is negative, the contents are shifted to the left where the
 * first \p shift bytes are discarded.
 * The new size of the buffer is the old size minus the absolute shift value.
 * If this value is larger than the buffer size, the buffer is emptied (but
 * not cleared, see the security note below).
 *
 * The buffer position gets shifted alongside with the content but is kept
 * within the boundaries of the buffer.
 *
 * \note For situations where \c off_t is not large enough, there are specialized cxBufferShiftLeft() and
 * cxBufferShiftRight() functions using a \c size_t as parameter type.
 *
 * \attention
 * Security Note: The shifting operation does \em not erase the previously occupied memory cells.
 * But you can easily do that manually, e.g. by calling
 * <code>memset(buffer->bytes, 0, shift)</code> for a right shift or
 * <code>memset(buffer->bytes + buffer->size, 0, buffer->capacity - buffer->size)</code>
 * for a left shift.
 *
 * @param buffer the buffer
 * @param shift the shift offset (negative means left shift)
 * @return 0 on success, non-zero if a required auto-extension fails
 */
__attribute__((__nonnull__))
int cxBufferShift(
        CxBuffer *buffer,
        off_t shift
);

/**
 * Shifts the buffer to the right.
 * See cxBufferShift() for details.
 *
 * @param buffer the buffer
 * @param shift the shift offset
 * @return 0 on success, non-zero if a required auto-extension fails
 * @see cxBufferShift()
 */
__attribute__((__nonnull__))
int cxBufferShiftRight(
        CxBuffer *buffer,
        size_t shift
);

/**
 * Shifts the buffer to the left.
 * See cxBufferShift() for details.
 *
 * \note Since a left shift cannot fail due to memory allocation problems, this
 * function always returns zero.
 *
 * @param buffer the buffer
 * @param shift the positive shift offset
 * @return always zero
 * @see cxBufferShift()
 */
__attribute__((__nonnull__))
int cxBufferShiftLeft(
        CxBuffer *buffer,
        size_t shift
);


/**
 * Moves the position of the buffer.
 *
 * The new position is relative to the \p whence argument.
 *
 * \li \c SEEK_SET marks the start of the buffer.
 * \li \c SEEK_CUR marks the current position.
 * \li \c SEEK_END marks the end of the buffer.
 *
 * With an offset of zero, this function sets the buffer position to zero
 * (\c SEEK_SET), the buffer size (\c SEEK_END) or leaves the buffer position
 * unchanged (\c SEEK_CUR).
 *
 * @param buffer the buffer
 * @param offset position offset relative to \p whence
 * @param whence one of \c SEEK_SET, \c SEEK_CUR or \c SEEK_END
 * @return 0 on success, non-zero if the position is invalid
 *
 */
__attribute__((__nonnull__))
int cxBufferSeek(
        CxBuffer *buffer,
        off_t offset,
        int whence
);

/**
 * Clears the buffer by resetting the position and deleting the data.
 *
 * The data is deleted by zeroing it with a call to memset().
 *
 * @param buffer the buffer to be cleared
 */
__attribute__((__nonnull__))
void cxBufferClear(CxBuffer *buffer);

/**
 * Tests, if the buffer position has exceeded the buffer capacity.
 *
 * @param buffer the buffer to test
 * @return non-zero, if the current buffer position has exceeded the last
 * available byte of the buffer.
 */
__attribute__((__nonnull__))
int cxBufferEof(CxBuffer const *buffer);


/**
 * Ensures that the buffer has a minimum capacity.
 *
 * If the current capacity is not sufficient, the buffer will be extended.
 *
 * @param buffer the buffer
 * @param capacity the minimum required capacity for this buffer
 * @return 0 on success or a non-zero value on failure
 */
__attribute__((__nonnull__))
int cxBufferMinimumCapacity(
        CxBuffer *buffer,
        size_t capacity
);

/**
 * Writes data to a CxBuffer.
 *
 * If flushing is enabled and the buffer needs to flush, the data is flushed to
 * the target until the target signals that it cannot take more data by
 * returning zero via the respective write function. In that case, the remaining
 * data in this buffer is shifted to the beginning of this buffer so that the
 * newly available space can be used to append as much data as possible. This
 * function only stops writing more elements, when the flush target and this
 * buffer are both incapable of taking more data or all data has been written.
 * The number returned by this function is the total number of elements that
 * could be written during the process. It does not necessarily mean that those
 * elements are still in this buffer, because some of them could have also be
 * flushed already.
 *
 * If automatic flushing is not enabled, the position of the buffer is increased
 * by the number of bytes written.
 *
 * \note The signature is compatible with the fwrite() family of functions.
 *
 * @param ptr a pointer to the memory area containing the bytes to be written
 * @param size the length of one element
 * @param nitems the element count
 * @param buffer the CxBuffer to write to
 * @return the total count of elements written
 */
__attribute__((__nonnull__))
size_t cxBufferWrite(
        void const *ptr,
        size_t size,
        size_t nitems,
        CxBuffer *buffer
);

/**
 * Reads data from a CxBuffer.
 *
 * The position of the buffer is increased by the number of bytes read.
 *
 * \note The signature is compatible with the fread() family of functions.
 *
 * @param ptr a pointer to the memory area where to store the read data
 * @param size the length of one element
 * @param nitems the element count
 * @param buffer the CxBuffer to read from
 * @return the total number of elements read
 */
__attribute__((__nonnull__))
size_t cxBufferRead(
        void *ptr,
        size_t size,
        size_t nitems,
        CxBuffer *buffer
);

/**
 * Writes a character to a buffer.
 *
 * The least significant byte of the argument is written to the buffer. If the
 * end of the buffer is reached and #CX_BUFFER_AUTO_EXTEND feature is enabled,
 * the buffer capacity is extended by cxBufferMinimumCapacity(). If the feature is
 * disabled or buffer extension fails, \c EOF is returned.
 *
 * On successful write, the position of the buffer is increased.
 *
 * @param buffer the buffer to write to
 * @param c the character to write
 * @return the byte that has bean written or \c EOF when the end of the stream is
 * reached and automatic extension is not enabled or not possible
 */
__attribute__((__nonnull__))
int cxBufferPut(
        CxBuffer *buffer,
        int c
);

/**
 * Writes a string to a buffer.
 *
 * @param buffer the buffer
 * @param str the zero-terminated string
 * @return the number of bytes written
 */
__attribute__((__nonnull__))
size_t cxBufferPutString(
        CxBuffer *buffer,
        const char *str
);

/**
 * Gets a character from a buffer.
 *
 * The current position of the buffer is increased after a successful read.
 *
 * @param buffer the buffer to read from
 * @return the character or \c EOF, if the end of the buffer is reached
 */
__attribute__((__nonnull__))
int cxBufferGet(CxBuffer *buffer);

#ifdef __cplusplus
}
#endif

#endif /* UCX_BUFFER_H */