// Adapted from: https://github.com/kstenerud/KSCrash
//
//  SentryCrashMemory.c
//
//  Created by Karl Stenerud on 2012-01-29.
//
//  Copyright (c) 2012 Karl Stenerud. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall remain in place
// in this source code.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//

#include "SentryCrashMemory.h"

// #define SentryCrashLogger_LocalLevel TRACE
#include "SentryCrashLogger.h"

#include <_types/_uint8_t.h>
#include <mach/mach.h>

static inline int
copySafely(const void *restrict const src, void *restrict const dst, const int byteCount)
{
    vm_size_t bytesCopied = 0;
    kern_return_t result = vm_read_overwrite(
        mach_task_self(), (vm_address_t)src, (vm_size_t)byteCount, (vm_address_t)dst, &bytesCopied);
    if (result != KERN_SUCCESS) {
        return 0;
    }
    return (int)bytesCopied;
}

static inline int
copyMaxPossible(const void *restrict const src, void *restrict const dst, const int byteCount)
{
    const uint8_t *pSrc = src;
    const uint8_t *pSrcMax = (uint8_t *)src + byteCount;
    const uint8_t *pSrcEnd = (uint8_t *)src + byteCount;
    uint8_t *pDst = dst;

    int bytesCopied = 0;

    // Short-circuit if no memory is readable
    if (copySafely(src, dst, 1) != 1) {
        return 0;
    } else if (byteCount <= 1) {
        return byteCount;
    }

    for (;;) {
        int copyLength = (int)(pSrcEnd - pSrc);
        if (copyLength <= 0) {
            break;
        }

        if (copySafely(pSrc, pDst, copyLength) == copyLength) {
            bytesCopied += copyLength;
            pSrc += copyLength;
            pDst += copyLength;
            pSrcEnd = pSrc + (pSrcMax - pSrc) / 2;
        } else {
            if (copyLength <= 1) {
                break;
            }
            pSrcMax = pSrcEnd;
            pSrcEnd = pSrc + copyLength / 2;
        }
    }
    return bytesCopied;
}

static char g_memoryTestBuffer[10240];
static inline bool
isMemoryReadable(const void *const memory, const int byteCount)
{
    const int testBufferSize = sizeof(g_memoryTestBuffer);
    int bytesRemaining = byteCount;

    while (bytesRemaining > 0) {
        int bytesToCopy = bytesRemaining > testBufferSize ? testBufferSize : bytesRemaining;
        if (copySafely(memory, g_memoryTestBuffer, bytesToCopy) != bytesToCopy) {
            break;
        }
        bytesRemaining -= bytesToCopy;
    }
    return bytesRemaining == 0;
}

int
sentrycrashmem_maxReadableBytes(const void *const memory, const int tryByteCount)
{
    const int testBufferSize = sizeof(g_memoryTestBuffer);
    const uint8_t *currentPosition = memory;
    int bytesRemaining = tryByteCount;

    while (bytesRemaining > testBufferSize) {
        if (!isMemoryReadable(currentPosition, testBufferSize)) {
            break;
        }
        currentPosition += testBufferSize;
        bytesRemaining -= testBufferSize;
    }
    bytesRemaining -= copyMaxPossible(currentPosition, g_memoryTestBuffer, testBufferSize);
    return tryByteCount - bytesRemaining;
}

bool
sentrycrashmem_isMemoryReadable(const void *const memory, const int byteCount)
{
    return isMemoryReadable(memory, byteCount);
}

int
sentrycrashmem_copyMaxPossible(
    const void *restrict const src, void *restrict const dst, const int byteCount)
{
    return copyMaxPossible(src, dst, byteCount);
}

bool
sentrycrashmem_copySafely(
    const void *restrict const src, void *restrict const dst, const int byteCount)
{
    return copySafely(src, dst, byteCount);
}