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/*

 * Audible AA demuxer

 * Copyright (c) 2015 Vesselin Bontchev

 *

 * Header parsing is borrowed from https://github.com/jteeuwen/audible project.

 * Copyright (c) 2001-2014, Jim Teeuwen

 *

 * Redistribution and use in source and binary forms, with or without modification,

 * are permitted provided that the following conditions are met:

 *

 * 1. Redistributions of source code must retain the above copyright notice, this

 *    list of conditions and the following disclaimer.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR

 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES

 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;

 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON

 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS

 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

#include "avformat.h"

#include "internal.h"

#include "libavutil/intreadwrite.h"

#include "libavutil/tea.h"

#include "libavutil/opt.h"

#define AA_MAGIC 1469084982 /* this identifies an audible .aa file */

#define MAX_CODEC_SECOND_SIZE 3982

#define MAX_TOC_ENTRIES 16

#define MAX_DICTIONARY_ENTRIES 128

#define TEA_BLOCK_SIZE 8

typedef struct AADemuxContext {

    AVClass *class;

    uint8_t *aa_fixed_key;

    int aa_fixed_key_len;

    int codec_second_size;

    int current_codec_second_size;

    int chapter_idx;

    struct AVTEA *tea_ctx;

    uint8_t file_key[16];

    int64_t current_chapter_size;

} AADemuxContext;

static int get_second_size(char *codec_name)

{

    int result = -1;

    if (!strcmp(codec_name, "mp332")) {

        result = 3982;

    } else if (!strcmp(codec_name, "acelp16")) {

        result = 2000;

    } else if (!strcmp(codec_name, "acelp85")) {

        result = 1045;

    }

    return result;

}

static int aa_read_header(AVFormatContext *s)

{

    int i, j, idx, largest_idx = -1;

    uint32_t nkey, nval, toc_size, npairs, header_seed, start;

    char key[128], val[128], codec_name[64] = {0};

    uint8_t output[24], dst[8], src[8];

    int64_t largest_size = -1, current_size = -1;

    struct toc_entry {

        uint32_t offset;

        uint32_t size;

    } TOC[MAX_TOC_ENTRIES];

    uint32_t header_key_part[4];

    uint8_t header_key[16];

    AADemuxContext *c = s->priv_data;

    AVIOContext *pb = s->pb;

    AVStream *st;

    /* parse .aa header */

    avio_skip(pb, 4); // file size

    avio_skip(pb, 4); // magic string

    toc_size = avio_rb32(pb); // TOC size

    avio_skip(pb, 4); // unidentified integer

    if (toc_size > MAX_TOC_ENTRIES)

        return AVERROR_INVALIDDATA;

    for (i = 0; i < toc_size; i++) { // read TOC

        avio_skip(pb, 4); // TOC entry index

        TOC[i].offset = avio_rb32(pb); // block offset

        TOC[i].size = avio_rb32(pb); // block size

    }

    avio_skip(pb, 24); // header termination block (ignored)

    npairs = avio_rb32(pb); // read dictionary entries

    if (npairs > MAX_DICTIONARY_ENTRIES)

        return AVERROR_INVALIDDATA;

    for (i = 0; i < npairs; i++) {

        memset(val, 0, sizeof(val));

        memset(key, 0, sizeof(key));

        avio_skip(pb, 1); // unidentified integer

        nkey = avio_rb32(pb); // key string length

        nval = avio_rb32(pb); // value string length

        if (nkey > sizeof(key)) {

            avio_skip(pb, nkey);

        } else {

            avio_read(pb, key, nkey); // key string

        }

        if (nval > sizeof(val)) {

            avio_skip(pb, nval);

        } else {

            avio_read(pb, val, nval); // value string

        }

        if (!strcmp(key, "codec")) {

            av_log(s, AV_LOG_DEBUG, "Codec is <%s>\n", val);

            strncpy(codec_name, val, sizeof(codec_name) - 1);

        }

        if (!strcmp(key, "HeaderSeed")) {

            av_log(s, AV_LOG_DEBUG, "HeaderSeed is <%s>\n", val);

            header_seed = atoi(val);

        }

        if (!strcmp(key, "HeaderKey")) { // this looks like "1234567890 1234567890 1234567890 1234567890"

            av_log(s, AV_LOG_DEBUG, "HeaderKey is <%s>\n", val);

            sscanf(val, "%u%u%u%u", &header_key_part[0], &header_key_part[1], &header_key_part[2], &header_key_part[3]);

            for (idx = 0; idx < 4; idx++) {

                AV_WB32(&header_key[idx * 4], header_key_part[idx]); // convert each part to BE!

            }

            av_log(s, AV_LOG_DEBUG, "Processed HeaderKey is ");

            for (i = 0; i < 16; i++)

                av_log(s, AV_LOG_DEBUG, "%02x", header_key[i]);

            av_log(s, AV_LOG_DEBUG, "\n");

        }

    }

    /* verify fixed key */

    if (c->aa_fixed_key_len != 16) {

        av_log(s, AV_LOG_ERROR, "aa_fixed_key value needs to be 16 bytes!\n");

        return AVERROR(EINVAL);

    }

    /* verify codec */

    if ((c->codec_second_size = get_second_size(codec_name)) == -1) {

        av_log(s, AV_LOG_ERROR, "unknown codec <%s>!\n", codec_name);

        return AVERROR(EINVAL);

    }

    /* decryption key derivation */

    c->tea_ctx = av_tea_alloc();

    if (!c->tea_ctx)

        return AVERROR(ENOMEM);

    av_tea_init(c->tea_ctx, c->aa_fixed_key, 16);

    output[0] = output[1] = 0; // purely for padding purposes

    memcpy(output + 2, header_key, 16);

    idx = 0;

    for (i = 0; i < 3; i++) { // TEA CBC with weird mixed endianness

        AV_WB32(src, header_seed);

        AV_WB32(src + 4, header_seed + 1);

        header_seed += 2;

        av_tea_crypt(c->tea_ctx, dst, src, 1, NULL, 0); // TEA ECB encrypt

        for (j = 0; j < TEA_BLOCK_SIZE && idx < 18; j+=1, idx+=1) {

            output[idx] = output[idx] ^ dst[j];

        }

    }

    memcpy(c->file_key, output + 2, 16); // skip first 2 bytes of output

    av_log(s, AV_LOG_DEBUG, "File key is ");

    for (i = 0; i < 16; i++)

        av_log(s, AV_LOG_DEBUG, "%02x", c->file_key[i]);

    av_log(s, AV_LOG_DEBUG, "\n");

    /* decoder setup */

    st = avformat_new_stream(s, NULL);

    if (!st) {

        av_freep(&c->tea_ctx);

        return AVERROR(ENOMEM);

    }

    st->codec->codec_type = AVMEDIA_TYPE_AUDIO;

    if (!strcmp(codec_name, "mp332")) {

        st->codec->codec_id = AV_CODEC_ID_MP3;

        st->codec->sample_rate = 22050;

        st->need_parsing = AVSTREAM_PARSE_FULL_RAW;

        st->start_time = 0;

    } else if (!strcmp(codec_name, "acelp85")) {

        st->codec->codec_id = AV_CODEC_ID_SIPR;

        st->codec->block_align = 19;

        st->codec->channels = 1;

        st->codec->sample_rate = 8500;

    } else if (!strcmp(codec_name, "acelp16")) {

        st->codec->codec_id = AV_CODEC_ID_SIPR;

        st->codec->block_align = 20;

        st->codec->channels = 1;

        st->codec->sample_rate = 16000;

    }

    /* determine, and jump to audio start offset */

    for (i = 1; i < toc_size; i++) { // skip the first entry!

        current_size = TOC[i].size;

        if (current_size > largest_size) {

            largest_idx = i;

            largest_size = current_size;

        }

    }

    start = TOC[largest_idx].offset;

    avio_seek(pb, start, SEEK_SET);

    c->current_chapter_size = 0;

    return 0;

}

static int aa_read_packet(AVFormatContext *s, AVPacket *pkt)

{

    uint8_t dst[TEA_BLOCK_SIZE];

    uint8_t src[TEA_BLOCK_SIZE];

    int i;

    int trailing_bytes;

    int blocks;

    uint8_t buf[MAX_CODEC_SECOND_SIZE * 2];

    int written = 0;

    int ret;

    AADemuxContext *c = s->priv_data;

    // are we at the start of a chapter?

    if (c->current_chapter_size == 0) {

        c->current_chapter_size = avio_rb32(s->pb);

        if (c->current_chapter_size == 0) {

            return AVERROR_EOF;

        }

        av_log(s, AV_LOG_DEBUG, "Chapter %d (%" PRId64 " bytes)\n", c->chapter_idx, c->current_chapter_size);

        c->chapter_idx = c->chapter_idx + 1;

        avio_skip(s->pb, 4); // data start offset

        c->current_codec_second_size = c->codec_second_size;

    }

    // is this the last block in this chapter?

    if (c->current_chapter_size / c->current_codec_second_size == 0) {

        c->current_codec_second_size = c->current_chapter_size % c->current_codec_second_size;

    }

    // decrypt c->current_codec_second_size bytes

    blocks = c->current_codec_second_size / TEA_BLOCK_SIZE;

    for (i = 0; i < blocks; i++) {

        avio_read(s->pb, src, TEA_BLOCK_SIZE);

        av_tea_init(c->tea_ctx, c->file_key, 16);

        av_tea_crypt(c->tea_ctx, dst, src, 1, NULL, 1);

        memcpy(buf + written, dst, TEA_BLOCK_SIZE);

        written = written + TEA_BLOCK_SIZE;

    }

    trailing_bytes = c->current_codec_second_size % TEA_BLOCK_SIZE;

    if (trailing_bytes != 0) { // trailing bytes are left unencrypted!

        avio_read(s->pb, src, trailing_bytes);

        memcpy(buf + written, src, trailing_bytes);

        written = written + trailing_bytes;

    }

    // update state

    c->current_chapter_size = c->current_chapter_size - c->current_codec_second_size;

    if (c->current_chapter_size <= 0)

        c->current_chapter_size = 0;

    ret = av_new_packet(pkt, written);

    if (ret < 0)

        return ret;

    memcpy(pkt->data, buf, written);

    return 0;

}

static int aa_probe(AVProbeData *p)

{

    uint8_t *buf = p->buf;

    // first 4 bytes are file size, next 4 bytes are the magic

    if (AV_RB32(buf+4) != AA_MAGIC)

        return 0;

    return AVPROBE_SCORE_MAX / 2;

}

static int aa_read_close(AVFormatContext *s)

{

    AADemuxContext *c = s->priv_data;

    av_freep(&c->tea_ctx);

    return 0;

}

#define OFFSET(x) offsetof(AADemuxContext, x)

static const AVOption aa_options[] = {

    { "aa_fixed_key", // extracted from libAAX_SDK.so and AAXSDKWin.dll files!

        "Fixed key used for handling Audible AA files", OFFSET(aa_fixed_key),

        AV_OPT_TYPE_BINARY, {.str="77214d4b196a87cd520045fd2a51d673"},

        .flags = AV_OPT_FLAG_DECODING_PARAM },

    { NULL },

};

static const AVClass aa_class = {

    .class_name = "aa",

    .item_name  = av_default_item_name,

    .option     = aa_options,

    .version    = LIBAVUTIL_VERSION_INT,

};

AVInputFormat ff_aa_demuxer = {

    .name           = "aa",

    .long_name      = NULL_IF_CONFIG_SMALL("Audible AA format files"),

    .priv_class     = &aa_class,

    .priv_data_size = sizeof(AADemuxContext),

    .extensions     = "aa",

    .read_probe     = aa_probe,

    .read_header    = aa_read_header,

    .read_packet    = aa_read_packet,

    .read_close     = aa_read_close,

    .flags          = AVFMT_GENERIC_INDEX,

};