/*
* Copyright (C) 2023 Johnny Richard
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/
#include "gas_assembly_generator.h"

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>

static void gas_assembly_generator_visit_function(ast_visitor_t *visitor, ast_function_declaration_t *func);
static void gas_assembly_generator_visit_return_stmt(ast_visitor_t *visitor, ast_return_stmt_t *return_stmt);
static void gas_assembly_generator_visit_literal(ast_visitor_t *visitor, ast_literal_t *return_stmt);

void
gas_assembly_generator_init(gas_assembly_generator_t *gen, FILE *out)
{
  assert(gen && out);
  gen->super = (ast_visitor_t) {
    .visit_function = &gas_assembly_generator_visit_function,
    .visit_literal = &gas_assembly_generator_visit_literal,
    .visit_return_stmt = &gas_assembly_generator_visit_return_stmt
  };
  gen->out = out;
}

static void
gas_assembly_generator_visit_function(ast_visitor_t *visitor, ast_function_declaration_t *func)
{
  assert(visitor && func);

  if (!string_view_eq(func->name, string_view_from_str("main"))) {
    fprintf(stderr, "[ERROR]: no main function has been defined!\n");
    exit(EXIT_FAILURE);
  }

  gas_assembly_generator_t *gen = (gas_assembly_generator_t *) visitor;

  fprintf(gen->out,".global _start\n");
  fprintf(gen->out,".text\n");
  fprintf(gen->out,"_start:\n");

  ast_visitor_visit(visitor, func->body);
}

static void
gas_assembly_generator_visit_return_stmt(ast_visitor_t *visitor, ast_return_stmt_t *return_stmt)
{
  assert(visitor && return_stmt);
  gas_assembly_generator_t *gen = (gas_assembly_generator_t *) visitor;

  ast_visitor_visit(visitor, return_stmt->argument);

  fprintf(gen->out, "  mov %%eax, %%ebx\n");
  fprintf(gen->out, "  mov $1, %%al\n");
  fprintf(gen->out, "  mov $1, %%al\n");
  fprintf(gen->out, "  int $0x80\n");
}

static void
gas_assembly_generator_visit_literal(ast_visitor_t *visitor, ast_literal_t *literal)
{
  gas_assembly_generator_t *gen = (gas_assembly_generator_t *) visitor;
  switch (literal->kind) {
    case AST_LITERAL_INTEGER:
      fprintf(gen->out, "  mov $%d, %%eax\n", literal->value.integer);
      return;
    default:
      assert(false && "No code generation strategy.");
  }
}