/*
 * 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 *literal);
static void
gas_assembly_generator_binary_operation(ast_visitor_t *visitor, ast_binary_operation_t *binary_operation);

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,
                                .visit_binary_operation = &gas_assembly_generator_binary_operation };
  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");

  for (size_t i = 0; i < func->body->size; i++) {
    ast_visitor_visit(visitor, vector_at(func->body, i));
  }
}

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 %%rax, %%rbx\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, %%rax\n", literal->value.integer);
      return;
    default:
      assert(false && "no code generation strategy.");
  }
}

static void
gas_assembly_generator_binary_operation(ast_visitor_t *visitor, ast_binary_operation_t *binary_operation)
{
  gas_assembly_generator_t *gen = (gas_assembly_generator_t *)visitor;

  ast_visitor_visit(visitor, binary_operation->right);

  fprintf(gen->out, "  push %%rax\n");

  ast_visitor_visit(visitor, binary_operation->left);

  fprintf(gen->out, "  pop %%rcx\n");

  if (string_view_eq(binary_operation->op, string_view_from_str("+"))) {
    fprintf(gen->out, "  add %%rcx, %%rax\n");
    return;
  }

  if (string_view_eq(binary_operation->op, string_view_from_str("-"))) {
    fprintf(gen->out, "  sub %%rcx, %%rax\n");
    return;
  }

  if (string_view_eq(binary_operation->op, string_view_from_str("*"))) {
    fprintf(gen->out, "  mul %%rcx\n");
    return;
  }

  if (string_view_eq(binary_operation->op, string_view_from_str("/"))) {
    fprintf(gen->out, "  xor %%rdx, %%rdx\n");
    fprintf(gen->out, "  div %%rcx\n");
    return;
  }

  fprintf(stderr, "no strategy defined for: " SVFMT "\n", SVARG(&binary_operation->op));
  assert(false);
}