/*
 * nanowasm, a tiny WebAssembly/Wasm interpreter
 * Copyright (C) 2023-2024  Xavier Del Campo Romero
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

#include <nw/log.h>
#include <nw/ops.h>
#include <nanowasm/nw.h>
#include <nw/interp.h>
#include <nw/types.h>
#include <errno.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>

static int branch(struct nw_interp *const i, const varuint32 relative_depth)
{
    const struct nw_block *b = i->fp->last_block;
    static const char exc[] = "relative depth and block count mismatch";

    for (varuint32 d = 0; b && d < relative_depth; d++)
        b = b->prev;

    if (!b)
    {
        LOG("%s: %s\n", __func__, exc);
        i->exception = exc;
        return -1;
    }

    if (fseek(i->f, b->pc, SEEK_SET))
    {
        LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
        i->exception = "I/O error";
        return -1;
    }

    return 0;
}

static bool cond(struct nw_interp *const i)
{
    int32_t value;

    if (interp_stack_pop(i, &value, sizeof value))
    {
        LOG("%s: interp_stack_pop failed\n", __func__);
        return -1;
    }

    return value;
}

static int br_if(struct nw_interp *const i, const varuint32 relative_depth)
{
    if (cond(i) && branch(i, relative_depth))
    {
        LOG("%s: branch failed\n", __func__);
        return -1;
    }

    return 0;
}

static int op(struct nw_interp *const i, FILE *const f)
{
    varuint32 relative_depth;

    if (varuint32_read(f, &relative_depth))
    {
        LOG("%s: varuint32_read failed\n", __func__);
        return 1;
    }
    else if (i && br_if(i, relative_depth))
    {
        LOG("%s: br_if failed\n", __func__);
        return -1;
    }

    return 0;
}

int op_br_if(struct nw_interp *const i)
{
    return op(i, i->f);
}

int check_br_if(FILE *const f)
{
    return op(NULL, f);
}