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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.
 */

#include "cx/buffer.h"

#include <stdio.h>
#include <string.h>
#include <errno.h>

static int buffer_copy_on_write(CxBuffer* buffer) {
    if (0 == (buffer->flags & CX_BUFFER_COPY_ON_WRITE)) return 0;
    void *newspace = cxMalloc(buffer->allocator, buffer->capacity);
    if (NULL == newspace) return -1;
    memcpy(newspace, buffer->space, buffer->size);
    buffer->space = newspace;
    buffer->flags &= ~CX_BUFFER_COPY_ON_WRITE;
    buffer->flags |= CX_BUFFER_FREE_CONTENTS;
    return 0;
}

int cxBufferInit(
        CxBuffer *buffer,
        void *space,
        size_t capacity,
        const CxAllocator *allocator,
        int flags
) {
    if (allocator == NULL) {
        allocator = cxDefaultAllocator;
    }
    if (flags & CX_BUFFER_COPY_ON_EXTEND) {
        flags |= CX_BUFFER_AUTO_EXTEND;
    }
    buffer->allocator = allocator;
    buffer->flags = flags;
    if (!space) {
        buffer->bytes = cxMalloc(allocator, capacity);
        if (buffer->bytes == NULL) {
            return -1;
        }
        buffer->flags |= CX_BUFFER_FREE_CONTENTS;
    } else {
        buffer->bytes = space;
    }
    buffer->capacity = capacity;
    buffer->size = 0;
    buffer->pos = 0;

    buffer->flush_func = NULL;
    buffer->flush_target = NULL;
    buffer->flush_blkmax = 0;
    buffer->flush_blksize = 4096;
    buffer->flush_threshold = SIZE_MAX;

    return 0;
}

void cxBufferDestroy(CxBuffer *buffer) {
    if (buffer->flags & CX_BUFFER_FREE_CONTENTS) {
        cxFree(buffer->allocator, buffer->bytes);
    }
    memset(buffer, 0, sizeof(CxBuffer));
}

CxBuffer *cxBufferCreate(
        void *space,
        size_t capacity,
        const CxAllocator *allocator,
        int flags
) {
    if (allocator == NULL) {
        allocator = cxDefaultAllocator;
    }
    CxBuffer *buf = cxMalloc(allocator, sizeof(CxBuffer));
    if (buf == NULL) return NULL;
    if (0 == cxBufferInit(buf, space, capacity, allocator, flags)) {
        return buf;
    } else {
        cxFree(allocator, buf);
        return NULL;
    }
}

void cxBufferFree(CxBuffer *buffer) {
    if (buffer == NULL) return;
    const CxAllocator *allocator = buffer->allocator;
    cxBufferDestroy(buffer);
    cxFree(allocator, buffer);
}

int cxBufferSeek(
        CxBuffer *buffer,
        off_t offset,
        int whence
) {
    size_t npos;
    switch (whence) {
        case SEEK_CUR:
            npos = buffer->pos;
            break;
        case SEEK_END:
            npos = buffer->size;
            break;
        case SEEK_SET:
            npos = 0;
            break;
        default:
            return -1;
    }

    size_t opos = npos;
    npos += offset;

    if ((offset > 0 && npos < opos) || (offset < 0 && npos > opos)) {
        errno = EOVERFLOW;
        return -1;
    }

    if (npos > buffer->size) {
        return -1;
    } else {
        buffer->pos = npos;
        return 0;
    }

}

void cxBufferClear(CxBuffer *buffer) {
    if (0 == (buffer->flags & CX_BUFFER_COPY_ON_WRITE)) {
        memset(buffer->bytes, 0, buffer->size);
    }
    buffer->size = 0;
    buffer->pos = 0;
}

void cxBufferReset(CxBuffer *buffer) {
    buffer->size = 0;
    buffer->pos = 0;
}

bool cxBufferEof(const CxBuffer *buffer) {
    return buffer->pos >= buffer->size;
}

int cxBufferMinimumCapacity(
        CxBuffer *buffer,
        size_t newcap
) {
    if (newcap <= buffer->capacity) {
        return 0;
    }

    const int force_copy_flags = CX_BUFFER_COPY_ON_WRITE | CX_BUFFER_COPY_ON_EXTEND;
    if (buffer->flags & force_copy_flags) {
        void *newspace = cxMalloc(buffer->allocator, newcap);
        if (NULL == newspace) return -1;
        memcpy(newspace, buffer->space, buffer->size);
        buffer->space = newspace;
        buffer->capacity = newcap;
        buffer->flags &= ~force_copy_flags;
        buffer->flags |= CX_BUFFER_FREE_CONTENTS;
        return 0;
    } else if (cxReallocate(buffer->allocator,
                     (void **) &buffer->bytes, newcap) == 0) {
        buffer->capacity = newcap;
        return 0;
    } else {
        return -1;
    }
}

/**
 * Helps flushing data to the flush target of a buffer.
 *
 * @param buffer the buffer containing the config
 * @param space the data to flush
 * @param size the element size
 * @param nitems the number of items
 * @return the number of items flushed
 */
static size_t cx_buffer_write_flush_helper(
        CxBuffer *buffer,
        const unsigned char *space,
        size_t size,
        size_t nitems
) {
    size_t pos = 0;
    size_t remaining = nitems;
    size_t max_items = buffer->flush_blksize / size;
    while (remaining > 0) {
        size_t items = remaining > max_items ? max_items : remaining;
        size_t flushed = buffer->flush_func(
                space + pos,
                size, items,
                buffer->flush_target);
        if (flushed > 0) {
            pos += (flushed * size);
            remaining -= flushed;
        } else {
            // if no bytes can be flushed out anymore, we give up
            break;
        }
    }
    return nitems - remaining;
}

size_t cxBufferWrite(
        const void *ptr,
        size_t size,
        size_t nitems,
        CxBuffer *buffer
) {
    // optimize for easy case
    if (size == 1 && (buffer->capacity - buffer->pos) >= nitems) {
        if (buffer_copy_on_write(buffer)) return 0;
        memcpy(buffer->bytes + buffer->pos, ptr, nitems);
        buffer->pos += nitems;
        if (buffer->pos > buffer->size) {
            buffer->size = buffer->pos;
        }
        return nitems;
    }

    size_t len;
    size_t nitems_out = nitems;
    if (cx_szmul(size, nitems, &len)) {
        errno = EOVERFLOW;
        return 0;
    }
    size_t required = buffer->pos + len;
    if (buffer->pos > required) {
        return 0;
    }

    bool perform_flush = false;
    if (required > buffer->capacity) {
        if (buffer->flags & CX_BUFFER_AUTO_EXTEND) {
            if (buffer->flush_blkmax > 0 && required > buffer->flush_threshold) {
                perform_flush = true;
            } else {
                if (cxBufferMinimumCapacity(buffer, required)) {
                    return 0;
                }
            }
        } else {
            if (buffer->flush_blkmax > 0) {
                perform_flush = true;
            } else {
                // truncate data to be written, if we can neither extend nor flush
                len = buffer->capacity - buffer->pos;
                if (size > 1) {
                    len -= len % size;
                }
                nitems_out = len / size;
            }
        }
    }

    if (len == 0) {
        return len;
    }

    if (perform_flush) {
        size_t flush_max;
        if (cx_szmul(buffer->flush_blkmax, buffer->flush_blksize, &flush_max)) {
            errno = EOVERFLOW;
            return 0;
        }
        size_t flush_pos = buffer->flush_func == NULL || buffer->flush_target == NULL
                           ? buffer->pos
                           : cx_buffer_write_flush_helper(buffer, buffer->bytes, 1, buffer->pos);
        if (flush_pos == buffer->pos) {
            // entire buffer has been flushed, we can reset
            buffer->size = buffer->pos = 0;

            size_t items_flush; // how many items can also be directly flushed
            size_t items_keep; // how many items have to be written to the buffer

            items_flush = flush_max >= required ? nitems : (flush_max - flush_pos) / size;
            if (items_flush > 0) {
                items_flush = cx_buffer_write_flush_helper(buffer, ptr, size, items_flush / size);
                // in case we could not flush everything, keep the rest
            }
            items_keep = nitems - items_flush;
            if (items_keep > 0) {
                // try again with the remaining stuff
                const unsigned char *new_ptr = ptr;
                new_ptr += items_flush * size;
                // report the directly flushed items as written plus the remaining stuff
                return items_flush + cxBufferWrite(new_ptr, size, items_keep, buffer);
            } else {
                // all items have been flushed - report them as written
                return nitems;
            }
        } else if (flush_pos == 0) {
            // nothing could be flushed at all, we immediately give up without writing any data
            return 0;
        } else {
            // we were partially successful, we shift left and try again
            cxBufferShiftLeft(buffer, flush_pos);
            return cxBufferWrite(ptr, size, nitems, buffer);
        }
    } else {
        if (buffer_copy_on_write(buffer)) return 0;
        memcpy(buffer->bytes + buffer->pos, ptr, len);
        buffer->pos += len;
        if (buffer->pos > buffer->size) {
            buffer->size = buffer->pos;
        }
        return nitems_out;
    }

}

size_t cxBufferAppend(
        const void *ptr,
        size_t size,
        size_t nitems,
        CxBuffer *buffer
) {
    size_t pos = buffer->pos;
    buffer->pos = buffer->size;
    size_t written = cxBufferWrite(ptr, size, nitems, buffer);
    buffer->pos = pos;
    return written;
}

int cxBufferPut(
        CxBuffer *buffer,
        int c
) {
    c &= 0xFF;
    unsigned char const ch = c;
    if (cxBufferWrite(&ch, 1, 1, buffer) == 1) {
        return c;
    } else {
        return EOF;
    }
}

int cxBufferTerminate(CxBuffer *buffer) {
    bool success = 0 == cxBufferPut(buffer, 0);
    if (success) {
        buffer->pos--;
        buffer->size--;
        return 0;
    } else {
        return -1;
    }
}

size_t cxBufferPutString(
        CxBuffer *buffer,
        const char *str
) {
    return cxBufferWrite(str, 1, strlen(str), buffer);
}

size_t cxBufferRead(
        void *ptr,
        size_t size,
        size_t nitems,
        CxBuffer *buffer
) {
    size_t len;
    if (cx_szmul(size, nitems, &len)) {
        errno = EOVERFLOW;
        return 0;
    }
    if (buffer->pos + len > buffer->size) {
        len = buffer->size - buffer->pos;
        if (size > 1) len -= len % size;
    }

    if (len <= 0) {
        return len;
    }

    memcpy(ptr, buffer->bytes + buffer->pos, len);
    buffer->pos += len;

    return len / size;
}

int cxBufferGet(CxBuffer *buffer) {
    if (cxBufferEof(buffer)) {
        return EOF;
    } else {
        int c = buffer->bytes[buffer->pos];
        buffer->pos++;
        return c;
    }
}

int cxBufferShiftLeft(
        CxBuffer *buffer,
        size_t shift
) {
    if (shift >= buffer->size) {
        buffer->pos = buffer->size = 0;
    } else {
        if (buffer_copy_on_write(buffer)) return -1;
        memmove(buffer->bytes, buffer->bytes + shift, buffer->size - shift);
        buffer->size -= shift;

        if (buffer->pos >= shift) {
            buffer->pos -= shift;
        } else {
            buffer->pos = 0;
        }
    }
    return 0;
}

int cxBufferShiftRight(
        CxBuffer *buffer,
        size_t shift
) {
    if (buffer->size > SIZE_MAX - shift) {
        errno = EOVERFLOW;
        return -1;
    }
    size_t req_capacity = buffer->size + shift;
    size_t movebytes;

    // auto extend buffer, if required and enabled
    if (buffer->capacity < req_capacity) {
        if (buffer->flags & CX_BUFFER_AUTO_EXTEND) {
            if (cxBufferMinimumCapacity(buffer, req_capacity)) {
                return -1;
            }
            movebytes = buffer->size;
        } else {
            movebytes = buffer->capacity - shift;
        }
    } else {
        movebytes = buffer->size;
    }

    if (movebytes > 0) {
        if (buffer_copy_on_write(buffer)) return -1;
        memmove(buffer->bytes + shift, buffer->bytes, movebytes);
        buffer->size = shift + movebytes;
    }

    buffer->pos += shift;
    if (buffer->pos > buffer->size) {
        buffer->pos = buffer->size;
    }

    return 0;
}

int cxBufferShift(
        CxBuffer *buffer,
        off_t shift
) {
    if (shift < 0) {
        return cxBufferShiftLeft(buffer, (size_t) (-shift));
    } else if (shift > 0) {
        return cxBufferShiftRight(buffer, (size_t) shift);
    } else {
        return 0;
    }
}