/*
 * 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/sections.h>
#include <nw/fstring.h>
#include <nw/log.h>
#include <nw/types.h>
#include <errno.h>
#include <inttypes.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>

static int dump_import_name(FILE *const f, const varuint32 len)
{
    for (varuint32 i = 0; i < len; i++)
    {
        uint8_t byte;

        if (!fread(&byte, sizeof byte, 1, f))
        {
            LOG("%s: fread(3) failed, feof=%d, ferror=%d\n",
                __func__, feof(f), ferror(f));
            return -1;
        }

        LOG("%c", (char)byte);
    }

    return 0;
}

static int check_module_string(const struct nw_mod_cfg *const cfg,
    FILE *const f)
{
    varuint32 len;

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

    for (size_t i = 0; i < cfg->n_imports; i++)
    {
        const struct nw_import *const im = &cfg->imports[i];
        const char *const mod = im->module;

        if (strlen(mod) == len)
        {
            const long offset = ftell(f);

            if (offset < 0)
            {
                LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
                return -1;
            }
            else if (!fstrcmp(mod, f, true))
                return 0;
            else if (fseek(f, offset, SEEK_SET))
            {
                LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
                return -1;
            }
        }
    }

    LOG("%s: required imported module ", __func__);
    dump_import_name(f, len);
    LOG(" not found\n");
    return -1;
}

static int check_field_string(const struct nw_mod_cfg *const cfg,
    FILE *const f)
{
    varuint32 len;

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

    for (size_t i = 0; i < cfg->n_imports; i++)
    {
        const struct nw_import *const im = &cfg->imports[i];
        const char *const field = im->field;

        if (strlen(field) == len)
        {
            const long offset = ftell(f);

            if (offset < 0)
            {
                LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
                return -1;
            }
            else if (!fstrcmp(field, f, true))
                return 0;
            else if (fseek(f, offset, SEEK_SET))
            {
                LOG("%s: fseek(3): %s\n", __func__, strerror(errno));
                return -1;
            }
        }
    }

    LOG("%s: required imported field ", __func__);
    dump_import_name(f, len);
    LOG(" not found\n");
    return -1;
}

static int check_function_kind(FILE *const f)
{
    varuint32 type;

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

    return 0;
}

static int check_table_kind(FILE *const f)
{
    varint7 type;

    if (varint7_read(f, &type))
    {
        LOG("%s: varint7_read failed\n", __func__);
        return -1;
    }

    return 0;
}

static int check_memory_kind(FILE *const f)
{
    /* TODO. */
    return -1;
}

static int check_global_kind(FILE *const f)
{
    /* TODO. */
    return -1;
}

static int check_import_entry(const struct nw_mod_cfg *const cfg,
    FILE *const f)
{
    if (check_module_string(cfg, f))
    {
        LOG("%s: check_module_string failed\n", __func__);
        return -1;
    }
    else if (check_field_string(cfg, f))
    {
        LOG("%s: check_field_string failed\n", __func__);
        return -1;
    }

    uint8_t kind;

    if (!fread(&kind, sizeof kind, 1, f))
    {
        LOG("%s: fread(3) failed, feof=%d, ferror=%d\n",
            __func__, feof(f), ferror(f));
        return -1;
    }

    static int (*const fn[])(FILE *) =
    {
        [NW_KIND_FUNCTION] = check_function_kind,
        [NW_KIND_TABLE] = check_table_kind,
        [NW_KIND_MEMORY] = check_memory_kind,
        [NW_KIND_GLOBAL] = check_global_kind
    };

    if (kind >= sizeof fn / sizeof *fn)
    {
        LOG("%s: unexpected kind %#" PRIx8 "\n", __func__, kind);
        return -1;
    }

    return fn[kind](f);
}

static int check(const struct nw_mod_cfg *const cfg, FILE *const f,
    const unsigned long len)
{
    const long start = ftell(f);

    if (start < 0)
    {
        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
        return -1;
    }

    varuint32 count;

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

    for (varuint32 i = 0; i < count; i++)
        if (check_import_entry(cfg, f))
        {
            LOG("%s: check_import_entry failed\n", __func__);
            return -1;
        }

    const long end = ftell(f);

    if (end < 0)
    {
        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
        return -1;
    }

    const unsigned long size = end - start;

    if (size != len)
    {
        LOG("%s: size exceeded (%lu expected, got %lu)\n",
                __func__, len, size);
        return -1;
    }

    return 0;
}

int section_import_check(const struct section *const s, struct nw_mod *m,
    const unsigned long len)
{
    const struct nw_mod_cfg *const cfg = s->cfg;
    FILE *const f = s->f;

    if (m->sections.import)
    {
        LOG("%s: ignoring duplicate section\n", __func__);
        return fseek(f, len, SEEK_CUR);
    }

    const long offset = ftell(f);

    if (offset < 0)
    {
        LOG("%s: ftell(3): %s\n", __func__, strerror(errno));
        return -1;
    }
    else if (check(cfg, f, len))
    {
        LOG("%s: check failed\n", __func__);
        return -1;
    }

    m->sections.import = offset;
    return 0;
}