/* main.c
 * Created: 2023-09-02
 * Author: Aryadev Chavali
 * Description: Entrypoint of compiler
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MEMORY_DEFAULT 30000

typedef struct
{
  size_t dp;
  uint8_t memory[MEMORY_DEFAULT];
} machine_t;

bool usable_character(char c)
{
  return c == '>' || c == '<' || c == '+' || c == '-' || c == '-' || c == '.' ||
         c == ',' || c == '[' || c == ']';
}

typedef struct AST
{
  size_t col, row;
  enum
  {
    NEXT = 0,
    PREV,
    INC,
    DEC,
    OUT,
    READ,
    LIN,
    LOUT
  } type;
  int loop_ref;
} node_t;

typedef struct Buffer
{
  const char *name;
  size_t size;
  char data[];
} buffer_t;

buffer_t *buffer_init_str(const char *name, const char *str, size_t str_size)
{
  buffer_t *buf = malloc(sizeof(*buf) + str_size + 1);
  buf->name     = name;
  buf->size     = str_size;
  memcpy(buf->data, str, str_size);
  buf->data[str_size] = '\0';
  return buf;
}

void print_error(const char *handle, size_t row, size_t column,
                 const char *reason)
{
  fprintf(stderr, "%s:%lu:%lu:%s\n", handle, row, column, reason);
}

struct PResult
{
  node_t *nodes;
  size_t size;
} parse_input(buffer_t *buffer)
{
  node_t *nodes = NULL;
  size_t usable = 0, loops = 0;
  for (size_t i = 0; i < buffer->size; ++i)
    if (usable_character(buffer->data[i]))
    {
      ++usable;
      if (buffer->data[i] == '[')
        ++loops;
    }
  nodes = calloc(usable, sizeof(*nodes));

  // First pass: Get my info
  for (size_t i = 0, col = 0, row = 1, nptr = 0; i < buffer->size; ++i)
  {
    ++col;
    if (buffer->data[i] == '\n')
    {
      ++row;
      col = 0;
    }
    else if (usable_character(buffer->data[i]))
    {
      nodes[nptr].col = col;
      nodes[nptr].row = row;
      switch (buffer->data[i])
      {
      case '>':
        nodes[nptr].type = NEXT;
        break;
      case '<':
        nodes[nptr].type = PREV;
        break;
      case '+':
        nodes[nptr].type = INC;
        break;
      case '-':
        nodes[nptr].type = DEC;
        break;
      case '.':
        nodes[nptr].type = OUT;
        break;
      case ',':
        nodes[nptr].type = READ;
        break;
      case '[':
        nodes[nptr].type     = LIN;
        nodes[nptr].loop_ref = -1;
        break;
      case ']':
        nodes[nptr].type     = LOUT;
        nodes[nptr].loop_ref = -1;
        break;
      }
      ++nptr;
    }
  }

  // Second pass: setup any loop references
  node_t *stack[loops];
  memset(stack, 0, loops);
  size_t stackptr = 0;
  for (size_t i = 0; i < usable; ++i)
  {
    node_t *node = nodes + i;
    if (node->type == LIN)
      stack[stackptr++] = node;
    else if (node->type == LOUT)
    {
      if (stackptr == 0)
      {
        print_error(buffer->name, node->row, node->col,
                    "ERROR: Unbalanced square brackets!");
        goto error;
      }
      // Access last IN loop
      --stackptr;
      node->loop_ref            = stack[stackptr] - nodes;
      stack[stackptr]->loop_ref = i;
    }
  }

  if (stackptr > 0)
  {
    node_t *node = nodes + usable - 1;
    print_error(buffer->name, node->row, node->col,
                "ERROR: Unbalanced square brackets!");
    goto error;
  }

  return (struct PResult){nodes, usable};
error:
  if (nodes)
    free(nodes);
  return (struct PResult){0};
}

char *ast_to_str(node_t *ast, size_t size)
{
  char *out = calloc(size + 1, 1);
  for (size_t i = 0; i < size; ++i)
  {
    switch (ast[i].type)
    {
    case NEXT:
      out[i] = '>';
      break;
    case PREV:
      out[i] = '<';
      break;
    case INC:
      out[i] = '+';
      break;
    case DEC:
      out[i] = '-';
      break;
    case OUT:
      out[i] = '.';
      break;
    case READ:
      out[i] = ',';
      break;
    case LIN:
      out[i] = '[';
      break;
    case LOUT:
      out[i] = ']';
      break;
    }
  }
  out[size] = '\0';
  return out;
}

int main(void)
{
  const char input[] = "[->+<]]";
  buffer_t *buffer =
      buffer_init_str("*internal*", input, sizeof(input) / sizeof(input[0]));
  struct PResult res = parse_input(buffer);
  if (res.nodes == NULL)
  {
    fputs("Exiting early...\n", stderr);
    free(buffer);
    return 1;
  }
  char *str = ast_to_str(res.nodes, res.size);

  free(str);
  free(res.nodes);
  free(buffer);
  return 0;
}