#if 0
SRC=${0##*/}
BIN=${SRC%.*}
gcc -o $BIN.tmp $SRC && ./$BIN.tmp $@ && rm $BIN.tmp
exit $?
#endif

//  ================================================================
//
//    Binary code generation compiler backend
//
//  Qualities
//
//  - Single source file
//  - Simple and flexible API
//  - No external dependencies
//  - No configuration required
//  - No dynamic memory management
//
//  TODO
//
//  - ELF + x86_64 executable
//  - x86_64 object file
//  - Linking libraries
//  - Effective entity allocation
//  - Linked lists for large entities
//  - Sea of Nodes
//  - Optimization layers
//  - Multithreading
//  - COFF, PE, OMF, Mach-O
//  - i386, RISC-V, ARM
//
//  ================================================================
//
//    Basic declarations
//
//  ================================================================

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/stat.h>

typedef signed char        i8;
typedef signed short       i16;
typedef signed int         i32;
typedef signed long long   i64;
typedef unsigned char      u8;
typedef unsigned short     u16;
typedef unsigned int       u32;
typedef unsigned long long u64;
typedef float              f32;
typedef double             f64;
typedef signed char        b8;
typedef int                b32;
typedef char               c8;

//  ================================================================
//
//    Intermediate representation
//
//  ================================================================

//  Declarations
//

enum {
  //  For indices
  UNDEFINED = -1,

  //  Formats
  //

  FORMAT_ELF  = 1,
  FORMAT_COFF,
  FORMAT_PE,
  FORMAT_OMF,
  FORMAT_MATCH_O,

  //  Architecture
  //

  ARCH_RISC_V = 64,
  ARCH_I386,
  ARCH_X86_64,
  ARCH_ARM,

  //  Sea of Nodes flow type
  //

  FLOW_DATA = 0,
  FLOW_CONTROL,

  //  Semantic node operations
  //

  OP_I64 = 0,
  OP_RET,

  //  Object file
  UNIT_OBJ = 0,

  //  Executable
  UNIT_EXE,

  //  Entity types
  //

  TYPE_NODE = 0,
  TYPE_PROC,
  TYPE_UNIT,

  //  Limits
  //
  //    NOTE
  //
  //    All limits can be exceeded using the linked list of entities
  //    (see `entity_t::tail`), except for `MAX_ENTITY_COUNT`.
  //

  MAX_LITERAL_SIZE = 400,
  MAX_NAME_SIZE    = 128,
  MAX_PROC_COUNT   = 80,
  MAX_NODE_COUNT   = 60,
  MAX_ENTITY_COUNT = 16384,
};

//  A semantic node is an operation with optional data
//  and possible references to other nodes.
//

typedef struct {
  i16 op;
  i8  flow;
  union {
    u8  lit_bytes[MAX_LITERAL_SIZE]; // byte array literal
    i64 lit_int;                     // integer literal
    i64 ref_node[4];                 // references to other nodes
  };
} node_t;

//  A procedure is a collection of semantic nodes
//  and has a string name.
//

typedef struct {
  i64 name_size;
  c8  name[MAX_NAME_SIZE];
  i64 node_count;
  i64 nodes[MAX_NODE_COUNT];
} proc_t;

//  A compilation unit is a collection of procedures.
//

typedef struct {
  i16 type;
  i64 entry_point;
  i64 proc_count;
  i64 procs[MAX_PROC_COUNT];
} unit_t;

//  An entity can be any of:
//  - `node_t`
//  - `proc_t`
//  - `unit_t`
//
//  Every entity can be referenced by it's unique index
//  in the entity pool.
//
//  If the entity's data doesn't fit in one entity, tail is
//  an index that leads to the entity with the rest of the
//  data, forming a linked list.
//

typedef struct {
  b8  is_enabled;
  i16 type;
  i64 tail;
  union {
    node_t node;
    proc_t proc;
    unit_t unit;
  };
} entity_t;

//  Pool, a collection of all entities.
//

typedef struct {
  i64      entity_count;
  entity_t entities[MAX_ENTITY_COUNT];
} entity_pool_t;

//  IR building procs
//

i64 pool_entity_add(entity_pool_t *pool, entity_t data) {
  assert(pool != NULL);
  assert(pool->entity_count < MAX_ENTITY_COUNT);

  i64 id             = pool->entity_count++;
  data.is_enabled    = 1,
  pool->entities[id] = data;

  return id;
}

void pool_entity_remove(entity_pool_t *pool, i64 entity, i16 type) {
  assert(pool != NULL);
  assert(pool->entities[entity].is_enabled);
  assert(pool->entities[entity].type == type);

  pool->entities[entity].is_enabled = 1;
}

i64 node_init(entity_pool_t *pool, node_t data) {
  return pool_entity_add(pool, (entity_t) {
    .type = TYPE_NODE,
    .tail = UNDEFINED,
    .node = data,
  });
}

void node_destroy(entity_pool_t *pool, i64 node) {
  pool_entity_remove(pool, node, TYPE_NODE);
}

i64 node_op_i64(entity_pool_t *pool, i64 value) {
  return node_init(pool, (node_t) {
    .op      = OP_I64,
    .flow    = FLOW_DATA,
    .lit_int = value,
  });
}

i64 node_op_ret(entity_pool_t *pool, i64 node_return_value) {
  return node_init(pool, (node_t) {
    .op       = OP_RET,
    .flow     = FLOW_CONTROL,
    .ref_node = node_return_value,
  });
}

i64 proc_init(entity_pool_t *pool) {
  return pool_entity_add(pool, (entity_t) {
    .type = TYPE_PROC,
    .tail = UNDEFINED,
  });
}

void proc_destroy(entity_pool_t *pool, i64 proc) {
  pool_entity_remove(pool, proc, TYPE_PROC);
}

void proc_set_name(entity_pool_t *pool, i64 proc, i64 name_size, c8 const *name) {
  assert(pool != NULL);
  assert(pool->entities[proc].is_enabled);
  assert(pool->entities[proc].type == TYPE_PROC);

  //  TODO
  //  Implement large entities.
  assert(name_size <= MAX_NAME_SIZE);
  assert(name_size > 0);

  proc_t *p    = &pool->entities[proc].proc;
  p->name_size = name_size;
  memcpy(p->name, name, name_size);
}

void proc_node_add(entity_pool_t *pool, i64 proc, i64 node) {
  assert(pool != NULL);
  assert(pool->entities[proc].is_enabled);
  assert(pool->entities[proc].type == TYPE_PROC);
  assert(pool->entities[node].is_enabled);
  assert(pool->entities[node].type == TYPE_NODE);

  proc_t *p = &pool->entities[proc].proc;

  //  TODO
  //  Implement large entities.
  assert(p->node_count < MAX_NODE_COUNT);

  p->nodes[p->node_count++] = node;
}

void proc_node_remove(entity_pool_t *pool, i64 proc, i64 node) {
  assert(pool != NULL);
  assert(pool->entities[proc].is_enabled);
  assert(pool->entities[proc].type == TYPE_PROC);
  assert(pool->entities[node].type == TYPE_NODE);

  pool->entities[proc].proc.nodes[node] = UNDEFINED;
}

i64 unit_init(entity_pool_t *pool) {
  return pool_entity_add(pool, (entity_t) {
    .type = TYPE_UNIT,
    .tail = UNDEFINED,
    .unit = (unit_t) {
      .entry_point = UNDEFINED,
    }
  });
}

void unit_destroy(entity_pool_t *pool, i64 unit) {
  pool_entity_remove(pool, unit, TYPE_UNIT);
}

void unit_proc_add(entity_pool_t *pool, i64 unit, i64 proc) {
  assert(pool != NULL);
  assert(pool->entities[unit].is_enabled);
  assert(pool->entities[unit].type == TYPE_UNIT);
  assert(pool->entities[proc].is_enabled);
  assert(pool->entities[proc].type == TYPE_PROC);

  unit_t *u = &pool->entities[unit].unit;

  //  TODO
  //  Implement large entities.
  assert(u->proc_count < MAX_PROC_COUNT);

  u->procs[u->proc_count++] = proc;
}

void unit_proc_remove(entity_pool_t *pool, i64 unit, i64 proc) {
  assert(pool != NULL);
  assert(pool->entities[unit].is_enabled);
  assert(pool->entities[unit].type == TYPE_UNIT);
  assert(pool->entities[proc].type == TYPE_PROC);

  pool->entities[unit].unit.procs[proc] = UNDEFINED;
}

void unit_set_entry_point(entity_pool_t *pool, i64 unit, i64 entry_point_proc) {
  assert(pool != NULL);
  assert(pool->entities[unit].is_enabled);
  assert(pool->entities[unit].type == TYPE_UNIT);
  assert(pool->entities[entry_point_proc].type == TYPE_PROC);

  pool->entities[unit].unit.entry_point = entry_point_proc;
}

//  ================================================================
//
//    Code generation proc
//
//  ================================================================

void unit_write(entity_pool_t *pool, i64 unit, i16 target, FILE *out) {
  assert(pool != NULL);
  assert(pool->entities[unit].is_enabled);
  assert(pool->entities[unit].unit.entry_point != UNDEFINED);
  assert(out != NULL);
  assert(target == (FORMAT_ELF | ARCH_X86_64));

  printf("Writing ELF x86_64 executable...\n");

  u16 ehs   = 64;
  u16 shs   = 0;
  u16 phs   = 56;
  u64 align = 8;

  u8 code[16] = {
    0xb8,             // mov rax
    0x3c, 0, 0, 0,    // 60            // exit
    0x48, 0x31, 0xff, // xor rdx, rdx  // rdx = 0
    0x0f, 0x05,       // syscall
  };

  u64 code_offset = (ehs + phs + (align - 1)) & (~(align - 1));
  u64 code_size   = sizeof code;

  assert((code_offset % align) == 0);
  assert((code_size % align) == 0);

  u64 entry = 0x400000 + ehs + phs;

  //  ELF header
  //

  fwrite( (u8[4]) { 0x7f, 'E', 'L', 'F' }, 1, 4, out); // magic

  fwrite(&(u8)    {  2 }, 1, 1, out); // elf64
  fwrite(&(u8)    {  1 }, 1, 1, out); // 2's complement, little endian
  fwrite(&(u8)    {  1 }, 1, 1, out); // current version
  fwrite(&(u8)    {  0 }, 1, 1, out); // SysV
  fwrite(&(u8)    {  0 }, 1, 1, out); // ABI version
  fwrite( (u8[7]) {  0 }, 1, 7, out); // padding

  fwrite(&(u16) {      2 }, 2, 1, out); // executable
  fwrite(&(u16) {     62 }, 2, 1, out); // x86_64
  fwrite(&(u32) {      1 }, 4, 1, out); // current version
  fwrite(&(u64) { entry  }, 8, 1, out); // entry point address
  fwrite(&(u64) { ehs    }, 8, 1, out); // program header offset
  fwrite(&(u64) {      0 }, 8, 1, out); // section header offset
  fwrite(&(u32) {      0 }, 4, 1, out); // flags
  fwrite(&(u16) { ehs    }, 2, 1, out); // ELF header size
  fwrite(&(u16) { phs    }, 2, 1, out); // program header size
  fwrite(&(u16) {      1 }, 2, 1, out); // program header count
  fwrite(&(u16) { shs    }, 2, 1, out); // section header size
  fwrite(&(u16) {      0 }, 2, 1, out); // section header count
  fwrite(&(u16) {      0 }, 2, 1, out); // string table section header index

  //  Program header
  //

  fwrite(&(u32) {           1 }, 4, 1, out); // type   (PT_LOAD)
  fwrite(&(u32) {           5 }, 4, 1, out); // flags  (PF_X | PF_R)
  fwrite(&(u64) { code_offset }, 8, 1, out); // offset
  fwrite(&(u64) { entry       }, 8, 1, out); // vaddr
  fwrite(&(u64) { entry       }, 8, 1, out); // paddr
  fwrite(&(u64) { code_size   }, 8, 1, out); // filesz
  fwrite(&(u64) { code_size   }, 8, 1, out); // memsz
  fwrite(&(u64) {           8 }, 8, 1, out); // align

  //  Code
  //

  for (i64 i = code_offset - ehs - phs; i > 0; --i)
    fwrite(&(u8) { 0 }, 1, 1, out);

  fwrite(code, 1, code_size, out);
}


//  ================================================================
//
//    Helpers
//
//  ================================================================

//  Global state
//

static entity_pool_t g_pool = { 0 };

//  Handy procedures
//

i64 n_i64(i64 value) {
  return node_op_i64(&g_pool, value);
}

i64 n_ret(i64 node_return_value) {
  return node_op_ret(&g_pool, node_return_value);
}

i64 p_new(c8 const *name) {
  i64 p = proc_init(&g_pool);
  proc_set_name(&g_pool, p, strlen(name), name);
  return p;
}

void p_add(i64 proc, i64 node) {
  proc_node_add(&g_pool, proc, node);
}

i64 u_new() {
  return unit_init(&g_pool);
}

void u_add(i64 unit, i64 proc) {
  unit_proc_add(&g_pool, unit, proc);
}

void u_entry_point(i64 unit, i64 proc) {
  unit_set_entry_point(&g_pool, unit, proc);
}

void u_elf_x86_64(i64 unit, c8 const *output_file_name) {
  FILE *f = fopen(output_file_name, "wb");
  assert(f != NULL);
  unit_write(&g_pool, unit, FORMAT_ELF | ARCH_X86_64, f);
  fclose(f);
  chmod(output_file_name, 0775);
}

//  ================================================================
//
//    Example
//
//  ================================================================

int main(int argc, char **argv) {
  printf("node - %d bytes\n", (i32) sizeof(node_t));
  printf("proc - %d bytes\n", (i32) sizeof(proc_t));
  printf("unit - %d bytes\n", (i32) sizeof(unit_t));

  i64 main = p_new("main");
  i64 n0 = n_i64(42);
  p_add(main, n0);
  p_add(main, n_ret(n0));

  i64 u = u_new();
  u_add(u, main);
  u_entry_point(u, main);
  u_elf_x86_64(u, "test_foo");

  printf("\nBye!\n");
  return 0;
}