/*
 * Copyright (C) 2024 olang maintainers
 *
 * 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 <assert.h>
#include <stdint.h>
#include <stdio.h>

#include "codegen_aarch64.h"
#include "list.h"

#define SYS_exit (93)

/**
 *  ───────────────────────────────────────────────────────────────────
 *  Arch/ABI    Instruction           System  Ret  Ret  Error    Notes
 *                                    call #  val  val2
 *  ───────────────────────────────────────────────────────────────────
 *  arm64       svc #0                w8      x0   x1   -
 *  ──────────────────────────────────────────────────────────────
 *  Arch/ABI      arg1  arg2  arg3  arg4  arg5  arg6  arg7  Notes
 *  ──────────────────────────────────────────────────────────────
 *  arm64         x0    x1    x2    x3    x4    x5    -
 */

static void
codegen_aarch64_emit_start_entrypoint(FILE *out);

static void
codegen_aarch64_emit_function(FILE *out, ast_fn_definition_t *fn);

void
codegen_aarch64_emit_translation_unit(FILE *out, ast_node_t *node)
{
    codegen_aarch64_emit_start_entrypoint(out);

    assert(node->kind == AST_NODE_TRANSLATION_UNIT);
    ast_translation_unit_t translation_unit = node->as_translation_unit;

    list_item_t *item = list_head(translation_unit.decls);

    bool main_found = false;

    while (item != NULL) {
        ast_node_t *decl = (ast_node_t *)item->value;

        if (decl->kind == AST_NODE_FN_DEF) {
            ast_fn_definition_t fn = decl->as_fn_def;
            codegen_aarch64_emit_function(out, &fn);

            main_found = main_found || string_view_eq_to_cstr(fn.id, "main");
        } else {
            assert(0 && "translation unit only supports function declarations");
        }

        item = list_next(item);
    }

    assert(main_found && "main function is required.");
}

static void
codegen_aarch64_emit_start_entrypoint(FILE *out)
{
    fprintf(out, ".text\n");
    fprintf(out, ".globl _start\n\n");

    fprintf(out, "_start:\n");
    fprintf(out, "    bl main\n");
    fprintf(out, "    mov w8, #%d\n", SYS_exit);
    fprintf(out, "    svc #0\n");
}

static void
codegen_aarch64_emit_function(FILE *out, ast_fn_definition_t *fn)
{
    ast_node_t *block_node = fn->block;
    assert(block_node->kind == AST_NODE_BLOCK);
    ast_block_t block = block_node->as_block;

    assert(list_size(block.nodes) == 1);

    list_item_t *nodes_item = list_get(block.nodes, 0);
    ast_node_t *return_node = nodes_item->value;
    assert(return_node->kind == AST_NODE_RETURN_STMT);
    ast_return_stmt_t return_stmt = return_node->as_return_stmt;

    ast_node_t *literal_node = return_stmt.value;
    assert(literal_node->kind == AST_NODE_LITERAL);
    ast_literal_t literal_u32 = literal_node->as_literal;

    assert(literal_u32.kind == AST_LITERAL_U32);
    uint32_t exit_code = literal_u32.as_u32;

    fprintf(out, "" SV_FMT ":\n", SV_ARG(fn->id));
    fprintf(out, "    mov x0, #%d\n", exit_code);
    fprintf(out, "    ret\n");
}