#include <sections.h>
#include <wasm_types.h>
#include <errno.h>
#include <inttypes.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>

static int check_string(FILE *const f)
{
    varuint32 len;

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

    for (varuint32 i = 0; i < len; i++)
    {
        uint8_t byte;

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

    return 0;
}

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

    if (varuint32_read(f, &type))
    {
        fprintf(stderr, "%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))
    {
        fprintf(stderr, "%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(FILE *const f)
{
    if (check_string(f))
    {
        fprintf(stderr, "%s: check_string module failed\n", __func__);
        return -1;
    }
    else if (check_string(f))
    {
        fprintf(stderr, "%s: check_string field failed\n", __func__);
        return -1;
    }

    uint8_t kind;

    enum
    {
        FUNCTION,
        TABLE,
        MEMORY,
        GLOBAL
    };

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

    static int (*const fn[])(FILE *) =
    {
        [FUNCTION] = check_function_kind,
        [TABLE] = check_table_kind,
        [MEMORY] = check_memory_kind,
        [GLOBAL] = check_global_kind
    };

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

    return fn[kind](f);
}

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

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

    varuint32 count;

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

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

    const long end = ftell(f);

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

    const unsigned long size = end - start;

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

    return 0;
}

int section_import(struct wasmfs *const w, FILE *const f,
    const unsigned long len)
{
    if (w->sections.import)
    {
        fprintf(stderr, "%s: ignoring duplicate section\n", __func__);
        return 0;
    }

    const long offset = ftell(f);

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

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