/*
 * nanowasm, a tiny WebAssembly/Wasm interpreter
 * Copyright (C) 2023-2025  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 <nanowasm/nw.h>
#include <nw/interp.h>
#include <nw/io.h>
#include <nw/log.h>
#include <nw/opcodes.h>
#include <nw/ops.h>
#include <nw/routines.h>

static enum nw_state local_loop(struct nw_mod *);
static enum nw_state get_opcode(struct nw_mod *);
static enum nw_state entry_loop(struct nw_mod *);

static enum nw_state get_post_offset(struct nw_mod *const m)
{
    long offset;
    unsigned long consumed;
    struct nw_sm_c *const c = &m->sm.code;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    const enum nw_state n = cfg->tell(&offset, cfg->user);

    if (n)
        return n;
    else if ((consumed = offset - c->op_off) && consumed >= c->rem)
    {
#ifdef NW_LOG
        nwp_log("parameters exceed expected body length\n");
#endif
        return NW_FATAL;
    }

    c->rem -= consumed;
    m->next = get_opcode;
    return NW_AGAIN;
}

typedef void (*op_fn)(struct nw_mod *);

static op_fn find(unsigned char op)
{
    size_t i;

    for (i = 0; i < nwp_check_ops.n; i++)
    {
        const struct nwp_check_op *const o = &nwp_check_ops.ops[i];

        if (op >= o->start && op <= o->end)
            return o->f;
    }

    return NULL;
}

static enum nw_state get_op_offset(struct nw_mod *const m)
{
    struct nw_sm_c *const c = &m->sm.code;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    const enum nw_state n = cfg->tell(&c->op_off, cfg->user);
    op_fn fn;

    if (n)
        return n;
    else if (!(fn = find(c->op)))
    {
#ifdef NW_LOG
        nwp_log("invalid opcode %#hhx\n", (unsigned char)c->op);
#endif
        return NW_FATAL;
    }

#ifdef NW_LOG
    nwp_log("opcode: %#hhx\n", (unsigned char)c->op);
#endif
    c->next = get_post_offset;
    fn(m);
    return NW_AGAIN;
}

static enum nw_state check_exit(struct nw_mod *const m)
{
    struct nw_sm_c *const c = &m->sm.code;
    struct nw_sm_c_fn *const fn = &c->fn;

    if (fn->blocks)
    {
#ifdef NW_LOG
        nwp_log("mismatched number of blocks in function %lu\n",
            (unsigned long)c->entry_i);
#endif
        return NW_FATAL;
    }

    c->entry_i++;
    m->next = entry_loop;
    return NW_AGAIN;
}

static enum nw_state get_opcode(struct nw_mod *const m)
{
    struct nw_sm_c *const c = &m->sm.code;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_io io = {0};
    enum nw_state n;

    io.buf = &c->op;
    io.n = sizeof c->op;

    if (!c->rem)
        return check_exit(m);
    else if ((n = nwp_io_read(cfg, &io, cfg->user)))
        return n;
    else if (c->rem == 1 && c->op != OP_END)
    {
#ifdef NW_LOG
        nwp_log("%s: unexpected opcode %#x at body end\n", (unsigned)c->op);
#endif
        return NW_FATAL;
    }

    c->rem--;
    m->next = get_op_offset;
    return NW_AGAIN;
}

#ifndef NW_CHECK_CODE
static enum nw_state skip(struct nw_mod *const m)
{
    struct nw_sm_c *const c = &m->sm.code;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    const enum nw_state n = cfg->seek(c->body_start + c->rem, cfg->user);

    if (n)
        return n;

    c->entry_i++;
    m->next = entry_loop;
    return NW_AGAIN;
}
#endif

static enum nw_state get_rem(struct nw_mod *const m)
{
    unsigned long consumed;
    struct nw_sm_c *const c = &m->sm.code;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    const enum nw_state n = cfg->tell(&c->body_start, cfg->user);

    if (n)
        return n;
    else if ((consumed = c->body_start - c->start) >= c->body_size)
    {
#ifdef NW_LOG
        nwp_log("exceeded function body size\n");
#endif
        return NW_FATAL;
    }

    c->rem = c->body_size - consumed;
#ifdef NW_CHECK_CODE
    m->next = get_opcode;
#else
    m->next = skip;
#endif

    return NW_AGAIN;
}

static enum nw_state get_type(struct nw_mod *const m)
{
    nw_varint7 type;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_c *const c = &m->sm.code;
    struct nw_sm_leb128 *const l = &c->leb128;
    const enum nw_state n = nwp_varint7(cfg, l, &type, cfg->user);

    if (n)
        return n;

    c->fn.local_i++;
    m->next = local_loop;
    return NW_AGAIN;
}

static enum nw_state get_group_count(struct nw_mod *const m)
{
    nw_varuint32 group_count;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_c *const c = &m->sm.code;
    struct nw_sm_leb128 *const l = &c->leb128;
    const enum nw_state n = nwp_varuint32(cfg, l, &group_count, cfg->user);

    if (n)
        return n;

    c->fn.local_total += group_count;
    m->next = get_type;
    return NW_AGAIN;
}

static enum nw_state local_loop(struct nw_mod *const m)
{
    const struct nw_sm_c_fn *const fn = &m->sm.code.fn;

    m->next = fn->local_i < fn->local_count ? get_group_count : get_rem;
    return NW_AGAIN;
}

static enum nw_state get_local_count(struct nw_mod *const m)
{
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_c *const c = &m->sm.code;
    struct nw_sm_c_fn *const fn = &c->fn;
    struct nw_sm_leb128 *const l = &c->leb128;
    const enum nw_state n = nwp_varuint32(cfg, l, &fn->local_count,
        cfg->user);

    if (n)
        return n;

    m->next = fn->local_count ? local_loop : get_rem;
    return NW_AGAIN;
}

static enum nw_state get_start(struct nw_mod *const m)
{
    struct nw_sm_c *const c = &m->sm.code;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    const enum nw_state n = cfg->tell(&c->start, cfg->user);

    if (n)
        return n;

    m->next = get_local_count;
    return NW_AGAIN;
}

static enum nw_state get_body_size(struct nw_mod *const m)
{
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_c *const c = &m->sm.code;
    struct nw_sm_leb128 *const l = &c->leb128;
    const enum nw_state n = nwp_varuint32(cfg, l, &c->body_size, cfg->user);

    if (n)
        return n;
    else if (!c->body_size)
    {
#ifdef NW_LOG
        nwp_log("unexpected zero size for function body %lu\n",
            (unsigned long)c->entry_i);
#endif
        return NW_FATAL;
    }

    m->next = get_start;
    return NW_AGAIN;
}

static enum nw_state entry_loop(struct nw_mod *const m)
{
    struct nw_sm_c *const c = &m->sm.code;
    struct nw_sm_c_fn fn = {0};

    fn.blocks = 1;
    c->fn = fn;
    m->next = c->entry_i < c->count ? get_body_size : nwp_section_exit;
    return NW_AGAIN;
}

static enum nw_state get_count(struct nw_mod *const m)
{
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_c *const c = &m->sm.code;
    struct nw_sm_leb128 *const l = &c->leb128;
    const enum nw_state n = nwp_varuint32(cfg, l, &c->count, cfg->user);

    if (n)
        return n;

    m->next = entry_loop;
    return NW_AGAIN;
}

void nwp_section_code(struct nw_mod *const m)
{
    const struct nw_sm_c c = {0};

    m->sm.code = c;
    m->next = get_count;
}