/*
 * 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/io.h>
#include <nw/log.h>
#include <nw/routines.h>
#include <string.h>

static enum nw_state entry_loop(struct nw_mod *);
static enum nw_state find_import(struct nw_mod *);

static enum nw_state get_function_type(struct nw_mod *const m)
{
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_imp *const imp = &m->sm.import;
    struct nw_sm_leb128 *const l = &imp->leb128;
    struct nw_import_index *const ii = &m->cfg.imp_indexes[imp->imp_i];
    nw_varuint32 type;
    const enum nw_state n = nwp_varuint32(cfg, l, &type, cfg->user);

    if (n)
        return n;
    else if (imp->entry_i >= m->cfg.n_imports)
    {
#ifdef NW_LOG
        nwp_log("too many import entries\n");
#endif
        return NW_FATAL;
    }

    ii->index = imp->entry_i++;
    m->next = entry_loop;
    return NW_AGAIN;
}

static enum nw_state skip_import(struct nw_mod *const m)
{
    struct nw_sm_imp *const imp = &m->sm.import;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    const enum nw_state n = cfg->seek(imp->mod_off, cfg->user);

    if (n)
        return n;

    imp->len_i = 0;
    imp->imp_i++;
    m->next = find_import;
    return NW_AGAIN;
}

static enum nw_state get_kind(struct nw_mod *const m)
{
    unsigned char kind;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_imp *const imp = &m->sm.import;
    const struct nw_import *const i = &m->cfg.imports[imp->imp_i];
    struct nw_sm_io io = {0};
    enum nw_state n;

    io.buf = &kind;
    io.n = sizeof kind;

    if ((n = nwp_io_read(cfg, &io, cfg->user)))
        return n;
    else if (kind != i->kind)
        m->next = skip_import;
    /* TODO: process every import type. */
    else if (kind != NW_KIND_FUNCTION)
        m->next = nwp_section_exit;
    else
        m->next = get_function_type;

    return NW_AGAIN;
}

static enum nw_state compare_field(struct nw_mod *const m)
{
    unsigned char byte;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_imp *const imp = &m->sm.import;
    const struct nw_import *const i = &m->cfg.imports[imp->imp_i];
    struct nw_sm_io io = {0};
    enum nw_state n;

    io.buf = &byte;
    io.n = sizeof byte;

    if ((n = nwp_io_read(cfg, &io, cfg->user)))
        return n;
    else if (byte != i->field[imp->len_i])
        m->next = skip_import;
    else if (++imp->len_i >= imp->field_len)
    {
        m->next = get_kind;
        imp->len_i = 0;
    }

    return NW_AGAIN;
}

static enum nw_state get_field_offset(struct nw_mod *const m)
{
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_imp *const imp = &m->sm.import;
    const enum nw_state n = cfg->tell(&imp->field_off, cfg->user);
    const struct nw_import *const i = &m->cfg.imports[imp->imp_i];

    if (n)
        return n;

    m->next = imp->field_len != strlen(i->field) ? skip_import : compare_field;
    return NW_AGAIN;
}

static enum nw_state get_field_len(struct nw_mod *const m)
{
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_imp *const imp = &m->sm.import;
    struct nw_sm_leb128 *const l = &imp->leb128;
    const enum nw_state n = nwp_varuint32(cfg, l, &imp->field_len, cfg->user);

    if (n)
        return n;

    m->next = get_field_offset;
    return NW_AGAIN;
}

static enum nw_state compare_name(struct nw_mod *const m)
{
    unsigned char byte;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_imp *const imp = &m->sm.import;
    const struct nw_import *const i = &m->cfg.imports[imp->imp_i];
    struct nw_sm_io io = {0};
    enum nw_state n;

    io.buf = &byte;
    io.n = sizeof byte;

    if ((n = nwp_io_read(cfg, &io, cfg->user)))
        return n;
    else if (byte != i->module[imp->len_i])
        m->next = skip_import;
    else if (++imp->len_i >= imp->mod_len)
    {
        m->next = get_field_len;
        imp->len_i = 0;
    }

    return NW_AGAIN;
}

static enum nw_state dump_import_field_name(struct nw_mod *const m)
{
    unsigned char byte;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_io io = {0};
    struct nw_sm_imp *const imp = &m->sm.import;
    enum nw_state n;

    io.buf = &byte;
    io.n = sizeof byte;

    if ((n = nwp_io_read(cfg, &io, cfg->user)))
        return n;

#ifdef NW_LOG
    nwp_log("%c", (char)byte);
#endif

    if (++imp->len_i >= imp->field_len)
    {
#ifdef NW_LOG
        nwp_log("\n");
#endif
        return NW_FATAL;
    }

    return NW_AGAIN;
}

static enum nw_state rewind_to_field_name(struct nw_mod *const m)
{
    struct nw_sm_imp *const imp = &m->sm.import;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    const enum nw_state n = cfg->seek(imp->field_off, cfg->user);

    if (n)
        return n;

    m->next = dump_import_field_name;
    return NW_AGAIN;
}

static enum nw_state dump_import_mod_name(struct nw_mod *const m)
{
    unsigned char byte;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_imp *const imp = &m->sm.import;
    struct nw_sm_io io = {0};
    enum nw_state n;

    io.buf = &byte;
    io.n = sizeof byte;

    if ((n = nwp_io_read(cfg, &io, cfg->user)))
        return n;

#ifdef NW_LOG
    nwp_log("%c", (char)byte);
#endif

    if (++imp->len_i >= imp->mod_len)
    {
        imp->len_i = 0;

        if (imp->field_off)
        {
#ifdef NW_LOG
            nwp_log("::");
#endif
            m->next = rewind_to_field_name;
        }
        else
        {
#ifdef NW_LOG
            nwp_log("\n");
#endif
            return NW_FATAL;
        }
    }

    return NW_AGAIN;
}

static enum nw_state rewind_to_mod_name(struct nw_mod *const m)
{
    struct nw_sm_imp *const imp = &m->sm.import;
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    const enum nw_state n = cfg->seek(imp->mod_off, cfg->user);

    if (n)
        return n;

    m->next = dump_import_mod_name;
    return NW_AGAIN;
}

static enum nw_state find_import(struct nw_mod *const m)
{
    struct nw_sm_imp *const imp = &m->sm.import;
    const struct nw_import *i;

    if (imp->imp_i >= m->cfg.n_imports)
    {
#ifdef NW_LOG
        nwp_log("required import: ");
#endif
        m->next = rewind_to_mod_name;
        return NW_AGAIN;
    }

    i = &m->cfg.imports[imp->imp_i];

    if (imp->mod_len == strlen(i->module))
        m->next = compare_name;
    else
        imp->imp_i++;

    return NW_AGAIN;
}

static enum nw_state get_module_offset(struct nw_mod *const m)
{
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_imp *const imp = &m->sm.import;
    const enum nw_state n = cfg->tell(&imp->mod_off, cfg->user);

    if (n)
        return n;

    m->next = find_import;
    return NW_AGAIN;
}

static enum nw_state get_module_len(struct nw_mod *const m)
{
    const struct nw_io_cfg *const cfg = &m->cfg.io;
    struct nw_sm_imp *const imp = &m->sm.import;
    struct nw_sm_leb128 *const l = &imp->leb128;
    const enum nw_state n = nwp_varuint32(cfg, l, &imp->mod_len, cfg->user);

    if (n)
        return n;

    m->next = get_module_offset;
    return NW_AGAIN;
}

static enum nw_state entry_loop(struct nw_mod *const m)
{
    struct nw_sm_imp *const imp = &m->sm.import;

    imp->len_i = 0;
    imp->imp_i = 0;
    m->next = imp->entry_i < m->import_count ?
        get_module_len : 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_imp *const imp = &m->sm.import;
    struct nw_sm_leb128 *const l = &imp->leb128;
    const enum nw_state n = nwp_varuint32(cfg, l, &m->import_count, cfg->user);

    if (n)
        return n;

    m->next = entry_loop;
    return NW_AGAIN;
}

void nwp_section_import(struct nw_mod *const m)
{
    const struct nw_sm_imp imp = {0};

    m->next = get_count;
    m->sm.import = imp;
}