/*
 * 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 <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>
#include <inttypes.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 void (*const checks[])(struct nw_mod *) =
{
    [OP_UNREACHABLE] = nwp_op_check_no_immediate,
    [OP_NOP] = nwp_op_check_no_immediate,
    [OP_END] = nwp_op_check_end,
    [OP_BLOCK] = nwp_op_check_block,
    [OP_BR_IF] = nwp_op_check_br_if,
    [OP_RETURN] = nwp_op_check_no_immediate,
    [OP_CALL] = nwp_op_check_call,
    [OP_GET_LOCAL] = nwp_op_check_local_index,
    [OP_SET_LOCAL] = nwp_op_check_local_index,
    [OP_TEE_LOCAL] = nwp_op_check_local_index,
    [OP_GET_GLOBAL] = nwp_op_check_global_index,
    [OP_SET_GLOBAL] = nwp_op_check_global_index,
    [OP_I32_LOAD] = nwp_op_check_memory_immediate,
    [OP_I32_STORE] = nwp_op_check_memory_immediate,
    [OP_I64_STORE] = nwp_op_check_memory_immediate,
    [OP_F32_STORE] = nwp_op_check_memory_immediate,
    [OP_F64_STORE] = nwp_op_check_memory_immediate,
    [OP_I32_CONST] = nwp_op_check_i32_const,
    [OP_I64_CONST] = nwp_op_check_i64_const,
    [OP_I32_SUB] = nwp_op_check_no_immediate
};

static enum nw_state get_post_offset(struct nw_mod *const m)
{
    long offset;
    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;

    const unsigned long consumed = offset - c->op_off;

    if (consumed && consumed >= c->rem)
    {
        LOG("%s: parameters exceed expected body length\n", __func__);
        return NW_FATAL;
    }

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

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);
    void (*const fn)(struct nw_mod *) = checks[c->op];

    if (n)
        return n;
    else if (!fn)
    {
        LOG("%s: invalid opcode %#" PRIx8 "\n", __func__, c->op);
        return NW_FATAL;
    }

    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)
    {
        LOG("%s: mismatched number of blocks in function %lu\n", __func__,
            (unsigned long)c->entry_i);
        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;

    if (!c->rem)
        return check_exit(m);

    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_io io = {.buf = &c->op, .n = sizeof c->op};
    const enum nw_state n = nwp_io_read(cfg, &io);

    if (n)
        return n;
    else if (c->rem == 1 && c->op != OP_END)
    {
        LOG("%s: unexpected opcode %#" PRIx8 " at body end\n",
            __func__, c->op);
        return NW_FATAL;
    }
    else if (c->op >= sizeof checks / sizeof *checks)
    {
        LOG("%s: invalid opcode %#" PRIx8 "\n", __func__, c->op);
        return NW_FATAL;
    }

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

static enum nw_state get_rem(struct nw_mod *const m)
{
    long offset;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    const enum nw_state n = cfg->tell(&offset, cfg->user);

    if (n)
        return n;

    struct nw_sm_c *const c = &m->sm.code;
    const unsigned long consumed = offset - c->start;

    if (consumed >= c->body_size)
    {
        LOG("%s: exceeded function body size\n", __func__);
        return NW_FATAL;
    }

    c->rem = c->body_size - consumed;
    m->next = get_opcode;
    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);

    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);

    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);

    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);

    if (n)
        return n;

    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;

    c->fn = (const struct nw_sm_c_fn){.blocks = 1};
    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);

    if (n)
        return n;

    m->next = entry_loop;
    return NW_AGAIN;
}

void nwp_section_code(struct nw_mod *const m)
{
    struct nw_sm_c *const c = &m->sm.code;

    m->next = get_count;
    *c = (const struct nw_sm_c){0};
}