///////////////////////////////////////////////////////////////////////////////
//
/// \file       stream_decoder.c
/// \brief      Decodes .xz Streams
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "stream_decoder.h"
#include "block_decoder.h"


typedef struct {
    enum {
        SEQ_STREAM_HEADER,
        SEQ_BLOCK_HEADER,
        SEQ_BLOCK,
        SEQ_INDEX,
        SEQ_STREAM_FOOTER,
        SEQ_STREAM_PADDING,
    } sequence;

    /// Block or Metadata decoder. This takes little memory and the same
    /// data structure can be used to decode every Block Header, so it's
    /// a good idea to have a separate lzma_next_coder structure for it.
    lzma_next_coder block_decoder;

    /// Block options decoded by the Block Header decoder and used by
    /// the Block decoder.
    lzma_block block_options;

    /// Stream Flags from Stream Header
    lzma_stream_flags stream_flags;

    /// Index is hashed so that it can be compared to the sizes of Blocks
    /// with O(1) memory usage.
    lzma_index_hash *index_hash;

    /// Memory usage limit
    uint64_t memlimit;

    /// Amount of memory actually needed (only an estimate)
    uint64_t memusage;

    /// If true, LZMA_NO_CHECK is returned if the Stream has
    /// no integrity check.
    bool tell_no_check;

    /// If true, LZMA_UNSUPPORTED_CHECK is returned if the Stream has
    /// an integrity check that isn't supported by this liblzma build.
    bool tell_unsupported_check;

    /// If true, LZMA_GET_CHECK is returned after decoding Stream Header.
    bool tell_any_check;

    /// If true, we will tell the Block decoder to skip calculating
    /// and verifying the integrity check.
    bool ignore_check;

    /// If true, we will decode concatenated Streams that possibly have
    /// Stream Padding between or after them. LZMA_STREAM_END is returned
    /// once the application isn't giving us any new input, and we aren't
    /// in the middle of a Stream, and possible Stream Padding is a
    /// multiple of four bytes.
    bool concatenated;

    /// When decoding concatenated Streams, this is true as long as we
    /// are decoding the first Stream. This is needed to avoid misleading
    /// LZMA_FORMAT_ERROR in case the later Streams don't have valid magic
    /// bytes.
    bool first_stream;

    /// Write position in buffer[] and position in Stream Padding
    size_t pos;

    /// Buffer to hold Stream Header, Block Header, and Stream Footer.
    /// Block Header has biggest maximum size.
    uint8_t buffer[LZMA_BLOCK_HEADER_SIZE_MAX];
} lzma_stream_coder;


static lzma_ret
stream_decoder_reset(lzma_stream_coder *coder, const lzma_allocator *allocator)
{
    // Initialize the Index hash used to verify the Index.
    coder->index_hash = lzma_index_hash_init(coder->index_hash, allocator);
    if (coder->index_hash == NULL)
        return LZMA_MEM_ERROR;

    // Reset the rest of the variables.
    coder->sequence = SEQ_STREAM_HEADER;
    coder->pos = 0;

    return LZMA_OK;
}


static lzma_ret
stream_decode(void *coder_ptr, const lzma_allocator *allocator,
        const uint8_t *restrict in, size_t *restrict in_pos,
        size_t in_size, uint8_t *restrict out,
        size_t *restrict out_pos, size_t out_size, lzma_action action)
{
    lzma_stream_coder *coder = coder_ptr;

    // When decoding the actual Block, it may be able to produce more
    // output even if we don't give it any new input.
    while (true)
    switch (coder->sequence) {
    case SEQ_STREAM_HEADER: {
        // Copy the Stream Header to the internal buffer.
        lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
                LZMA_STREAM_HEADER_SIZE);

        // Return if we didn't get the whole Stream Header yet.
        if (coder->pos < LZMA_STREAM_HEADER_SIZE)
            return LZMA_OK;

        coder->pos = 0;

        // Decode the Stream Header.
        const lzma_ret ret = lzma_stream_header_decode(
                &coder->stream_flags, coder->buffer);
        if (ret != LZMA_OK)
            return ret == LZMA_FORMAT_ERROR && !coder->first_stream
                    ? LZMA_DATA_ERROR : ret;

        // If we are decoding concatenated Streams, and the later
        // Streams have invalid Header Magic Bytes, we give
        // LZMA_DATA_ERROR instead of LZMA_FORMAT_ERROR.
        coder->first_stream = false;

        // Copy the type of the Check so that Block Header and Block
        // decoders see it.
        coder->block_options.check = coder->stream_flags.check;

        // Even if we return LZMA_*_CHECK below, we want
        // to continue from Block Header decoding.
        coder->sequence = SEQ_BLOCK_HEADER;

        // Detect if there's no integrity check or if it is
        // unsupported if those were requested by the application.
        if (coder->tell_no_check && coder->stream_flags.check
                == LZMA_CHECK_NONE)
            return LZMA_NO_CHECK;

        if (coder->tell_unsupported_check
                && !lzma_check_is_supported(
                    coder->stream_flags.check))
            return LZMA_UNSUPPORTED_CHECK;

        if (coder->tell_any_check)
            return LZMA_GET_CHECK;
    }

    // Fall through

    case SEQ_BLOCK_HEADER: {
        if (*in_pos >= in_size)
            return LZMA_OK;

        if (coder->pos == 0) {
            // Detect if it's Index.
            if (in[*in_pos] == 0x00) {
                coder->sequence = SEQ_INDEX;
                break;
            }

            // Calculate the size of the Block Header. Note that
            // Block Header decoder wants to see this byte too
            // so don't advance *in_pos.
            coder->block_options.header_size
                    = lzma_block_header_size_decode(
                        in[*in_pos]);
        }

        // Copy the Block Header to the internal buffer.
        lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
                coder->block_options.header_size);

        // Return if we didn't get the whole Block Header yet.
        if (coder->pos < coder->block_options.header_size)
            return LZMA_OK;

        coder->pos = 0;

        // Version 1 is needed to support the .ignore_check option.
        coder->block_options.version = 1;

        // Set up a buffer to hold the filter chain. Block Header
        // decoder will initialize all members of this array so
        // we don't need to do it here.
        lzma_filter filters[LZMA_FILTERS_MAX + 1];
        coder->block_options.filters = filters;

        // Decode the Block Header.
        return_if_error(lzma_block_header_decode(&coder->block_options,
                allocator, coder->buffer));

        // If LZMA_IGNORE_CHECK was used, this flag needs to be set.
        // It has to be set after lzma_block_header_decode() because
        // it always resets this to false.
        coder->block_options.ignore_check = coder->ignore_check;

        // Check the memory usage limit.
        const uint64_t memusage = lzma_raw_decoder_memusage(filters);
        lzma_ret ret;

        if (memusage == UINT64_MAX) {
            // One or more unknown Filter IDs.
            ret = LZMA_OPTIONS_ERROR;
        } else {
            // Now we can set coder->memusage since we know that
            // the filter chain is valid. We don't want
            // lzma_memusage() to return UINT64_MAX in case of
            // invalid filter chain.
            coder->memusage = memusage;

            if (memusage > coder->memlimit) {
                // The chain would need too much memory.
                ret = LZMA_MEMLIMIT_ERROR;
            } else {
                // Memory usage is OK.
                // Initialize the Block decoder.
                ret = lzma_block_decoder_init(
                        &coder->block_decoder,
                        allocator,
                        &coder->block_options);
            }
        }

        // Free the allocated filter options since they are needed
        // only to initialize the Block decoder.
        for (size_t i = 0; i < LZMA_FILTERS_MAX; ++i)
            lzma_free(filters[i].options, allocator);

        coder->block_options.filters = NULL;

        // Check if memory usage calculation and Block enocoder
        // initialization succeeded.
        if (ret != LZMA_OK)
            return ret;

        coder->sequence = SEQ_BLOCK;
    }

    // Fall through

    case SEQ_BLOCK: {
        const lzma_ret ret = coder->block_decoder.code(
                coder->block_decoder.coder, allocator,
                in, in_pos, in_size, out, out_pos, out_size,
                action);

        if (ret != LZMA_STREAM_END)
            return ret;

        // Block decoded successfully. Add the new size pair to
        // the Index hash.
        return_if_error(lzma_index_hash_append(coder->index_hash,
                lzma_block_unpadded_size(
                    &coder->block_options),
                coder->block_options.uncompressed_size));

        coder->sequence = SEQ_BLOCK_HEADER;
        break;
    }

    case SEQ_INDEX: {
        // If we don't have any input, don't call
        // lzma_index_hash_decode() since it would return
        // LZMA_BUF_ERROR, which we must not do here.
        if (*in_pos >= in_size)
            return LZMA_OK;

        // Decode the Index and compare it to the hash calculated
        // from the sizes of the Blocks (if any).
        const lzma_ret ret = lzma_index_hash_decode(coder->index_hash,
                in, in_pos, in_size);
        if (ret != LZMA_STREAM_END)
            return ret;

        coder->sequence = SEQ_STREAM_FOOTER;
    }

    // Fall through

    case SEQ_STREAM_FOOTER: {
        // Copy the Stream Footer to the internal buffer.
        lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
                LZMA_STREAM_HEADER_SIZE);

        // Return if we didn't get the whole Stream Footer yet.
        if (coder->pos < LZMA_STREAM_HEADER_SIZE)
            return LZMA_OK;

        coder->pos = 0;

        // Decode the Stream Footer. The decoder gives
        // LZMA_FORMAT_ERROR if the magic bytes don't match,
        // so convert that return code to LZMA_DATA_ERROR.
        lzma_stream_flags footer_flags;
        const lzma_ret ret = lzma_stream_footer_decode(
                &footer_flags, coder->buffer);
        if (ret != LZMA_OK)
            return ret == LZMA_FORMAT_ERROR
                    ? LZMA_DATA_ERROR : ret;

        // Check that Index Size stored in the Stream Footer matches
        // the real size of the Index field.
        if (lzma_index_hash_size(coder->index_hash)
                != footer_flags.backward_size)
            return LZMA_DATA_ERROR;

        // Compare that the Stream Flags fields are identical in
        // both Stream Header and Stream Footer.
        return_if_error(lzma_stream_flags_compare(
                &coder->stream_flags, &footer_flags));

        if (!coder->concatenated)
            return LZMA_STREAM_END;

        coder->sequence = SEQ_STREAM_PADDING;
    }

    // Fall through

    case SEQ_STREAM_PADDING:
        assert(coder->concatenated);

        // Skip over possible Stream Padding.
        while (true) {
            if (*in_pos >= in_size) {
                // Unless LZMA_FINISH was used, we cannot
                // know if there's more input coming later.
                if (action != LZMA_FINISH)
                    return LZMA_OK;

                // Stream Padding must be a multiple of
                // four bytes.
                return coder->pos == 0
                        ? LZMA_STREAM_END
                        : LZMA_DATA_ERROR;
            }

            // If the byte is not zero, it probably indicates
            // beginning of a new Stream (or the file is corrupt).
            if (in[*in_pos] != 0x00)
                break;

            ++*in_pos;
            coder->pos = (coder->pos + 1) & 3;
        }

        // Stream Padding must be a multiple of four bytes (empty
        // Stream Padding is OK).
        if (coder->pos != 0) {
            ++*in_pos;
            return LZMA_DATA_ERROR;
        }

        // Prepare to decode the next Stream.
        return_if_error(stream_decoder_reset(coder, allocator));
        break;

    default:
        assert(0);
        return LZMA_PROG_ERROR;
    }

    // Never reached
}


static void
stream_decoder_end(void *coder_ptr, const lzma_allocator *allocator)
{
    lzma_stream_coder *coder = coder_ptr;
    lzma_next_end(&coder->block_decoder, allocator);
    lzma_index_hash_end(coder->index_hash, allocator);
    lzma_free(coder, allocator);
    return;
}


static lzma_check
stream_decoder_get_check(const void *coder_ptr)
{
    const lzma_stream_coder *coder = coder_ptr;
    return coder->stream_flags.check;
}


static lzma_ret
stream_decoder_memconfig(void *coder_ptr, uint64_t *memusage,
        uint64_t *old_memlimit, uint64_t new_memlimit)
{
    lzma_stream_coder *coder = coder_ptr;

    *memusage = coder->memusage;
    *old_memlimit = coder->memlimit;

    if (new_memlimit != 0) {
        if (new_memlimit < coder->memusage)
            return LZMA_MEMLIMIT_ERROR;

        coder->memlimit = new_memlimit;
    }

    return LZMA_OK;
}


extern lzma_ret
lzma_stream_decoder_init(
        lzma_next_coder *next, const lzma_allocator *allocator,
        uint64_t memlimit, uint32_t flags)
{
    lzma_next_coder_init(&lzma_stream_decoder_init, next, allocator);

    if (memlimit == 0)
        return LZMA_PROG_ERROR;

    if (flags & ~LZMA_SUPPORTED_FLAGS)
        return LZMA_OPTIONS_ERROR;

    lzma_stream_coder *coder = next->coder;
    if (coder == NULL) {
        coder = lzma_alloc(sizeof(lzma_stream_coder), allocator);
        if (coder == NULL)
            return LZMA_MEM_ERROR;

        next->coder = coder;
        next->code = &stream_decode;
        next->end = &stream_decoder_end;
        next->get_check = &stream_decoder_get_check;
        next->memconfig = &stream_decoder_memconfig;

        coder->block_decoder = LZMA_NEXT_CODER_INIT;
        coder->index_hash = NULL;
    }

    coder->memlimit = memlimit;
    coder->memusage = LZMA_MEMUSAGE_BASE;
    coder->tell_no_check = (flags & LZMA_TELL_NO_CHECK) != 0;
    coder->tell_unsupported_check
            = (flags & LZMA_TELL_UNSUPPORTED_CHECK) != 0;
    coder->tell_any_check = (flags & LZMA_TELL_ANY_CHECK) != 0;
    coder->ignore_check = (flags & LZMA_IGNORE_CHECK) != 0;
    coder->concatenated = (flags & LZMA_CONCATENATED) != 0;
    coder->first_stream = true;

    return stream_decoder_reset(coder, allocator);
}


extern LZMA_API(lzma_ret)
lzma_stream_decoder(lzma_stream *strm, uint64_t memlimit, uint32_t flags)
{
    lzma_next_strm_init(lzma_stream_decoder_init, strm, memlimit, flags);

    strm->internal->supported_actions[LZMA_RUN] = true;
    strm->internal->supported_actions[LZMA_FINISH] = true;

    return LZMA_OK;
}
