/*  =========================================================================
    zdigest - provides hashing functions (SHA-1 at present)

    Copyright (c) the Contributors as noted in the AUTHORS file.
    This file is part of CZMQ, the high-level C binding for 0MQ:
    http://czmq.zeromq.org.

    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 http://mozilla.org/MPL/2.0/.
    =========================================================================
*/

/*
@header
    The zdigest class generates a hash from zchunks of data. The current
    algorithm is SHA-1, chosen for speed. We are aiming to generate a
    unique digest for a file, and there are no security issues in this
    use case.
@discuss
    The current code depends on OpenSSL, which might be replaced by hard
    coded SHA-1 implementation to reduce build dependencies.
@end
*/

#include "czmq_classes.h"
#ifdef HAVE_LIBNSS
#include <secoid.h>
#include <sechash.h>
#define SHA_DIGEST_LENGTH 20
#else
#include "foreign/sha1/sha1.inc_c"
#endif


//  Structure of our class

struct _zdigest_t {
#ifdef HAVE_LIBNSS
    HASHContext *context;       //  Digest context
    bool begun;                 //  Calculating has already started
#else
    SHA_CTX context;            //  Digest context
#endif
    //  Binary hash
    byte hash [SHA_DIGEST_LENGTH];
    //  ASCII representation (hex)
    char string [SHA_DIGEST_LENGTH * 2 + 1];
    bool final;                 //  Finished calculating
};


//  --------------------------------------------------------------------------
//  Constructor - creates new digest object, which you use to build up a
//  digest by repeatedly calling zdigest_update() on chunks of data.

zdigest_t *
zdigest_new (void)
{
    zdigest_t *self = (zdigest_t *) zmalloc (sizeof (zdigest_t));
    assert (self);
#ifdef HAVE_LIBNSS
    HASH_HashType type = HASH_GetHashTypeByOidTag (SEC_OID_SHA1);
    self->context = HASH_Create (type);
    assert (self->context);
#else
    SHA1_Init (&self->context);
#endif
    return self;
}


//  --------------------------------------------------------------------------
//  Destroy a digest object

void
zdigest_destroy (zdigest_t **self_p)
{
    assert (self_p);
    if (*self_p) {
        zdigest_t *self = *self_p;
#ifdef HAVE_LIBNSS
        HASH_Destroy (self->context);
#endif
        freen (self);
        *self_p = NULL;
    }
}


//  --------------------------------------------------------------------------
//  Add buffer into digest calculation

void
zdigest_update (zdigest_t *self, const byte *buffer, size_t length)
{
    //  Calling this after zdigest_data() is illegal use of the API
    assert (self);
    assert (!self->final);
#ifdef HAVE_LIBNSS
    if (!self->begun) {
        HASH_Begin (self->context);
        self->begun = true;
    }
    HASH_Update (self->context, (unsigned char *) buffer, (unsigned int) length);
#else
    SHA1_Update (&self->context, buffer, length);
#endif
}


//  --------------------------------------------------------------------------
//  Return final digest hash data. If built without crypto support, returns
//  NULL.

const byte *
zdigest_data (zdigest_t *self)
{
    assert (self);
    if (!self->final) {
#ifdef HAVE_LIBNSS
        unsigned int len;
        HASH_End (self->context, self->hash, &len, SHA_DIGEST_LENGTH);
#else
        SHA1_Final (self->hash, &self->context);
#endif
        self->final = true;
    }
    return self->hash;
}


//  --------------------------------------------------------------------------
//  Return final digest hash size

size_t
zdigest_size (zdigest_t *self)
{
    assert (self);
    return SHA_DIGEST_LENGTH;
}


//  --------------------------------------------------------------------------
//  Return digest as printable hex string; caller should not modify nor
//  free this string. After calling this, you may not use zdigest_update()
//  on the same digest. If built without crypto support, returns NULL.

char *
zdigest_string (zdigest_t *self)
{
    assert (self);
    const byte *data = zdigest_data (self);
    char hex_char [] = "0123456789ABCDEF";
    int byte_nbr;
    for (byte_nbr = 0; byte_nbr < SHA_DIGEST_LENGTH; byte_nbr++) {
        self->string [byte_nbr * 2 + 0] = hex_char [data [byte_nbr] >> 4];
        self->string [byte_nbr * 2 + 1] = hex_char [data [byte_nbr] & 15];
    }
    self->string [SHA_DIGEST_LENGTH * 2] = 0;
    return self->string;
}


//  --------------------------------------------------------------------------
//  Self test of this class

void
zdigest_test (bool verbose)
{
    printf (" * zdigest: ");

    //  @selftest
    byte *buffer = (byte *) zmalloc (1024);
    memset (buffer, 0xAA, 1024);

    zdigest_t *digest = zdigest_new ();
    assert (digest);
    zdigest_update (digest, buffer, 1024);
    const byte *data = zdigest_data (digest);
    assert (data [0] == 0xDE);
    assert (data [1] == 0xB2);
    assert (data [2] == 0x38);
    assert (data [3] == 0x07);
    assert (streq (zdigest_string (digest),
                   "DEB23807D4FE025E900FE9A9C7D8410C3DDE9671"));
    zdigest_destroy (&digest);
    freen (buffer);

#if defined (__WINDOWS__)
    zsys_shutdown();
#endif
    //  @end

    printf ("OK\n");
}