#include <stdio.h>
#include <stdint.h>
#include <mach-o/dyld.h>
#include <mach/mach.h>

const uint32_t magic64 = 0xfeedfacf;
const uint32_t magic32 = 0xfeedface;

struct ProgramVars {
  void*	mh; // mach_header or mach_header64
  int*		NXArgcPtr;
  const char***	NXArgvPtr;
  const char***	environPtr;
  const char**	__prognamePtr;
};

extern "C" uint32_t dyld_get_sdk_version(const mach_header* mh);

void decode_uleb128(char*& addr, uint32_t* ret) {
  uint32_t result = 0;
  int shift = 0;

  while (1) {
    unsigned char byte = *(unsigned char*)(addr);
    addr++;

    result |= (byte & 0x7f) << shift;
    shift += 7;

    if (!(byte & 0x80)) break;
  }

  *ret = result;
}

void* find_header(void* _func) {
  // Approach 1: (not stable)
  // we assume that text section is small enough to fit on 1 page
  // so the header should stay at the top of the page due to allocation logic
  // the slice/slide is random but always align 0x1000 so we test a few values
  // to see if the magic value is found
  //
  // Guaranteed to stop, but search range is small

  // const uint64_t page_size = 0x4000;
  // uint64_t func = (uint64_t)_func;
  // uint64_t potential_head = func + (0x4000 - (func % page_size));
  // void* head = 0;
  // for (uint64_t i = 0x1000; i < 0xf000; i+=0x1000) {
  //   uint32_t* x = (uint32_t*)(potential_head - i);
  //   if (*x == magic64 || *x == magic32) {
  //     head = (void*)x;
  //     break;
  //   }
  // }
  // return head;

  // Approach 2: (more stable)
  // We know that the header is 0x1000 aligned,
  // just loop until the magic value is found
  // Using while loop so ¯\_(ツ)_/¯
  const uint64_t page_size = 0x1000;
  uint64_t func = (uint64_t)_func;
  uint64_t potential_head = func + (0x1000 - (func % page_size));

  void* head = 0;
  uint32_t* x = (uint32_t*)(potential_head);
  while (*x != magic64 && *x != magic32) {
    x -= 0x1000/4;
  }
  return (void*)x;
}

void print_macho_summary(const void* header) {
  const uint32_t magic = *(uint32_t*)header;
  char* ptr = (char*)header;
  if (magic == magic64) {
    ptr += 0x20;
  } else {
    ptr += 0x20 - 0x4;
  }

  const uint32_t ncmds = *((uint32_t*)header + 4);
  printf("parsing macho at %p\n", header);
  printf("ncmds %x\n", ncmds);
  for (int i = 0; i < ncmds; i++) {
    const uint32_t cmd = *((uint32_t*)ptr + 0);
    const uint32_t cmdsize = *((uint32_t*)ptr + 1);
    printf(" cmd %x %x\n", cmd, cmdsize);
    if (cmd == LC_DYLD_EXPORTS_TRIE) {
      const uint32_t offset = *((uint32_t*)ptr + 2);
      const uint32_t size = *((uint32_t*)ptr + 3);
      printf("  export trie: offset=0x%x size=0x%x\n", offset, size);
    }
    if (cmd == LC_SEGMENT_64) {
      char* name = (char*)((uint64_t*)ptr + 1);
      uint64_t vmaddr = *((uint64_t*)ptr + 3);
      uint64_t vmsize = *((uint64_t*)ptr + 4);
      uint64_t fileoffset = *((uint64_t*)ptr + 5);
      uint64_t filesize = *((uint64_t*)ptr + 6);
      if (strcmp(name, "__TEXT") == 0) {
        uint64_t slide = (uint64_t)header - vmaddr;
        printf(" --- slide=0x%llx ---\n", slide);
      }
      printf("  Segment %s\n", name);
      printf("    vmaddr=0x%llx fileoffset=0x%llx\n", vmaddr, fileoffset);
      printf("    vmsize=0x%llx filesize=0x%llx\n", vmsize, filesize);
    }
    ptr += cmdsize;
  }
}

void* get_export_trie(const void* header, uint32_t& size) {
  const uint32_t magic = *(uint32_t*)header;
  char* ptr = (char*)header;
  if (magic == magic64) {
    ptr += 0x20;
  } else {
    ptr += 0x20 - 0x4;
  }

  uint64_t slice = 0;
  uint64_t linkedit_vmaddr = 0;
  uint64_t linkedit_fileoffset = 0;
  const uint32_t ncmds = *((uint32_t*)header + 4);
  for (int i = 0; i < ncmds; i++) {
    const uint32_t cmd = *((uint32_t*)ptr + 0);
    const uint32_t cmdsize = *((uint32_t*)ptr + 1);
    if (cmd == LC_DYLD_EXPORTS_TRIE) {
      const uint32_t offset = *((uint32_t*)ptr + 2);
      size = *((uint32_t*)ptr + 3);
      uint64_t offset_in_linkedit = (uint64_t)offset - linkedit_fileoffset;
      return (void*)(linkedit_vmaddr + slice + offset_in_linkedit);
    }
    if (cmd == LC_SEGMENT_64) {
      char* name = (char*)((uint64_t*)ptr + 1);
      uint64_t vmaddr = *((uint64_t*)ptr + 3);
      uint64_t fileoffset = *((uint64_t*)ptr + 5);
      if (strcmp(name, "__TEXT") == 0) {
        slice = (uint64_t)header - vmaddr;
      } else if (strcmp(name, "__LINKEDIT") == 0) {
        linkedit_vmaddr = vmaddr;
        linkedit_fileoffset = fileoffset;
      }
    }
    ptr += cmdsize;
  }
  return 0;
}

uint32_t should_follow_symbol(char*& buffer, char*& _find) {
  // printf("follow check %s has prefix: %s\n", _find, buffer);
  char* find = _find;
  char is_prefix = true;
  while (1) {
    int find_end = *find == 0;
    int buffer_end = *buffer == 0;
    int check = *buffer == *find;
    // printf("check is %x == %x\n", *buffer, *find);

    if (buffer_end) {
      // we must always run to the end of buffer, marked 0x00
      buffer++;
      break;
    }
    if (find_end) {
      // symbol to find is shorter than current buffer string
      // but we still need to run to the end of buffer
      // so just set not prefix
      is_prefix = false;
    }
    if (!check) {
      is_prefix = false;
    }
    buffer++;
    find++;
  }
  // only move forward if is_prefix
  if (is_prefix) {
    _find = find;
    // printf("prefix is found\n");
  }
  return is_prefix;
}

void* find_in_export_trie(const void* header, void* trie, char* symbol) {
  uint32_t func = 0;

  char* ptr = (char*)trie;
  char* find = symbol;
  while (1) {
    // terminal node will have data
    uint32_t data_count = 0;
    decode_uleb128(ptr, &data_count);
    if (data_count != 0) {
      // printf("reached terminal node\n");
      break;
    }
    char num_child = ptr[0];
    ptr++;

    // printf("num child %d\n", num_child);
    int still_following = 0;
    for (char i = 0; i < num_child; i++) {
      still_following = should_follow_symbol(ptr, find);
      uint32_t follow_offset;
      decode_uleb128(ptr, &follow_offset);
      if (still_following) {
        ptr = (char*)trie + follow_offset;
        break;
      }
    }

    if (!still_following) {
      // symbol not found
      return 0;
    }
  }

  char count = *(ptr - 1);
  ptr++; // flags
  // uleb128 offset
  decode_uleb128(ptr, &func);
  return (void*)((char*)header + func);
}

int hook_printf (const char * format, ... ) {
  va_list args;
  va_start(args, format);

  printf("HOOKED BEGIN LOL\n");
  int status = printf(format, args);
  printf("HOOKED  END  LOL\n");

  va_end(args);
  return status;
}

__attribute__((constructor))
static void bruh(int argc, const char* const argv[], const char* const envp[], const char* const apple[], const struct ProgramVars* vars) {
  // ProgramVars contains pointer to main executable (mapped) file
  const void* main = (int*)(vars->mh);
  // Find our lib (mapped) file
  const void* thislib = find_header((void*)bruh);
  // Find dyld lib (mapped) file using a no-sus function
  const void* libdyld = find_header((void*)dyld_get_sdk_version);

  const void* libc = find_header((void*)printf);

  // From libdyld header, we can list exports table
  // to find all function we want to use
  //
  // This way there is no leakage of functions we use to do our trick
  // mostly to hide
  //  - _dyld_image_count
  //  - _dyld_get_image_name
  //  - _dyld_get_image_header
  //  - _dyld_get_image_vmaddr_slide

  // The above functions are crucial to find all libraries loaded
  // From which we will traverse the exports table to replace
  // _got and _la_symbol_pointer data

  // Our lib can hide more details too
  // We can resolve all functions we use
  // before resolving the main executable imports
  //
  // This will make our lib use only dyld_get_sdk_version
  // For the main executable, imports are empty due to manual resolve

  printf("executable header at %p\n", main);
  printf("lib header at %p\n", thislib);
  printf("libdyld header at %p\n", libdyld);

  for (int i = 0; i < _dyld_image_count(); i++) {
    void* header = (void*)_dyld_get_image_header(i);
    char* name = (char*)_dyld_get_image_name(i);
    int offset = _dyld_get_image_vmaddr_slide(i);
    printf("%p 0x%x name=%s\n", header, offset, name);
  }

  uint32_t trie_size;
  void* thislib_export_trie = get_export_trie(thislib, trie_size);
  void* libdyld_export_trie = get_export_trie(libdyld, trie_size);
  void* libc_export_trie = get_export_trie(libc, trie_size);

  // printf("export this lib address %p\n", thislib_export_trie);
  // for (int i = 0; i < 136; i++) {
  //   if (i % 0x10 == 0) printf("\n");
  //   printf("%02x ", *((unsigned char*)thislib_export_trie + i));
  // }
  // printf("\n");


  // printf("export dyld lib address %llx\n", (uint64_t)libdyld_export_trie);
  // for (int i = 0; i < 0x11e0; i++) {
  //   if (i % 0x10 == 0) printf("\n");
  //   printf("%02x ", *((unsigned char*)libdyld_export_trie + i));
  // }
  // printf("\n");

  // printf("export system lib address %llx\n", (uint64_t)system_export_trie);
  // for (int i = 0; i < 0x10f30; i++) {
  //   if (i % 0x10 == 0) printf("\n");
  //   printf("%02x ", *((unsigned char*)system_export_trie + i));
  // }

  // printf("\n");
  // FILE *write_ptr = fopen("../tmp/libc_export_trie.bin","wb");
  // fwrite(system_export_trie, trie_size, 1, write_ptr);

  struct test_find_export {
    const char* name;
    const void* lib;
    void* trie;
    void* original;
  };

  struct test_find_export find_export_testcases[] = {
    {"__Z11find_headerPv", thislib, thislib_export_trie, (void*)find_header},
    {"__dyld_get_image_name", libdyld, libdyld_export_trie, (void*)_dyld_get_image_name},
    {"__dyld_image_count", libdyld, libdyld_export_trie, (void*)_dyld_image_count},
    {"_printf",libc, libc_export_trie, (void*)printf},
  };

  for (int i = 0; i < 4; i++) {
    struct test_find_export test = find_export_testcases[i];
    void* found = find_in_export_trie(test.lib, test.trie, (char*)test.name);
    printf("%s: Found=%p | Expect=%p\n", test.name, found, test.original);
  }

  // legacy symbol resolve
  //    fix got and la_symbol_ptr
  // modern symbol resolve
  //    fix got

  uint64_t* got = (uint64_t*)((char*)main + 0x4000);


  printf("BEFORE symbol bind code is %llx\n", *got);
  vm_protect(mach_task_self(), (uint64_t)got, 0x4000, 0, VM_PROT_READ | VM_PROT_WRITE);

  // fix got table
  // *got = (uint64_t)find_in_export_trie(libc, libc_export_trie, "_printf");
  *got = (uint64_t)hook_printf;

  // unsigned char* opcodes = (unsigned char*)got + 0x20;
  // unsigned char original[] = {
  //   0x73, 0x00, 0x13, 0x40, 0x5f, 0x70, 0x72, 0x69,
  //   0x6e, 0x74, 0x66, 0x00, 0x90, 0x00, 0x00, 0x00
  // };
  // for (int i = 0; i < 0x10; i++) {
  //   printf("CHANGE AT %p %x => %x\n", opcodes+i, opcodes[i], original[i]);
  //   // opcodes[i] = original[i];
  // }

  vm_protect(mach_task_self(), (uint64_t)got, 0x4000, 0, VM_PROT_READ);
  printf("AFTER symbol bind code is %llx\n", *got);

  printf("symbol should bind to %p\n", printf);
}