///////////////////////////////////////////////////////////////////////////////
//
/// \file       lz_decoder.c
/// \brief      LZ out window
///
//  Authors:    Igor Pavlov
//              Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

// liblzma supports multiple LZ77-based filters. The LZ part is shared
// between these filters. The LZ code takes care of dictionary handling
// and passing the data between filters in the chain. The filter-specific
// part decodes from the input buffer to the dictionary.


#include "lz_decoder.h"


typedef struct {
    /// Dictionary (history buffer)
    lzma_dict dict;

    /// The actual LZ-based decoder e.g. LZMA
    lzma_lz_decoder lz;

    /// Next filter in the chain, if any. Note that LZMA and LZMA2 are
    /// only allowed as the last filter, but the long-range filter in
    /// future can be in the middle of the chain.
    lzma_next_coder next;

    /// True if the next filter in the chain has returned LZMA_STREAM_END.
    bool next_finished;

    /// True if the LZ decoder (e.g. LZMA) has detected end of payload
    /// marker. This may become true before next_finished becomes true.
    bool this_finished;

    /// Temporary buffer needed when the LZ-based filter is not the last
    /// filter in the chain. The output of the next filter is first
    /// decoded into buffer[], which is then used as input for the actual
    /// LZ-based decoder.
    struct {
        size_t pos;
        size_t size;
        uint8_t buffer[LZMA_BUFFER_SIZE];
    } temp;
} lzma_coder;


static void
lz_decoder_reset(lzma_coder *coder)
{
    coder->dict.pos = 0;
    coder->dict.full = 0;
    coder->dict.buf[coder->dict.size - 1] = '\0';
    coder->dict.need_reset = false;
    return;
}


static lzma_ret
decode_buffer(lzma_coder *coder,
        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)
{
    while (true) {
        // Wrap the dictionary if needed.
        if (coder->dict.pos == coder->dict.size)
            coder->dict.pos = 0;

        // Store the current dictionary position. It is needed to know
        // where to start copying to the out[] buffer.
        const size_t dict_start = coder->dict.pos;

        // Calculate how much we allow coder->lz.code() to decode.
        // It must not decode past the end of the dictionary
        // buffer, and we don't want it to decode more than is
        // actually needed to fill the out[] buffer.
        coder->dict.limit = coder->dict.pos
                + my_min(out_size - *out_pos,
                    coder->dict.size - coder->dict.pos);

        // Call the coder->lz.code() to do the actual decoding.
        const lzma_ret ret = coder->lz.code(
                coder->lz.coder, &coder->dict,
                in, in_pos, in_size);

        // Copy the decoded data from the dictionary to the out[]
        // buffer.
        const size_t copy_size = coder->dict.pos - dict_start;
        assert(copy_size <= out_size - *out_pos);
        memcpy(out + *out_pos, coder->dict.buf + dict_start,
                copy_size);
        *out_pos += copy_size;

        // Reset the dictionary if so requested by coder->lz.code().
        if (coder->dict.need_reset) {
            lz_decoder_reset(coder);

            // Since we reset dictionary, we don't check if
            // dictionary became full.
            if (ret != LZMA_OK || *out_pos == out_size)
                return ret;
        } else {
            // Return if everything got decoded or an error
            // occurred, or if there's no more data to decode.
            //
            // Note that detecting if there's something to decode
            // is done by looking if dictionary become full
            // instead of looking if *in_pos == in_size. This
            // is because it is possible that all the input was
            // consumed already but some data is pending to be
            // written to the dictionary.
            if (ret != LZMA_OK || *out_pos == out_size
                    || coder->dict.pos < coder->dict.size)
                return ret;
        }
    }
}


static lzma_ret
lz_decode(void *coder_ptr,
        const lzma_allocator *allocator lzma_attribute((__unused__)),
        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_coder *coder = coder_ptr;

    if (coder->next.code == NULL)
        return decode_buffer(coder, in, in_pos, in_size,
                out, out_pos, out_size);

    // We aren't the last coder in the chain, we need to decode
    // our input to a temporary buffer.
    while (*out_pos < out_size) {
        // Fill the temporary buffer if it is empty.
        if (!coder->next_finished
                && coder->temp.pos == coder->temp.size) {
            coder->temp.pos = 0;
            coder->temp.size = 0;

            const lzma_ret ret = coder->next.code(
                    coder->next.coder,
                    allocator, in, in_pos, in_size,
                    coder->temp.buffer, &coder->temp.size,
                    LZMA_BUFFER_SIZE, action);

            if (ret == LZMA_STREAM_END)
                coder->next_finished = true;
            else if (ret != LZMA_OK || coder->temp.size == 0)
                return ret;
        }

        if (coder->this_finished) {
            if (coder->temp.size != 0)
                return LZMA_DATA_ERROR;

            if (coder->next_finished)
                return LZMA_STREAM_END;

            return LZMA_OK;
        }

        const lzma_ret ret = decode_buffer(coder, coder->temp.buffer,
                &coder->temp.pos, coder->temp.size,
                out, out_pos, out_size);

        if (ret == LZMA_STREAM_END)
            coder->this_finished = true;
        else if (ret != LZMA_OK)
            return ret;
        else if (coder->next_finished && *out_pos < out_size)
            return LZMA_DATA_ERROR;
    }

    return LZMA_OK;
}


static void
lz_decoder_end(void *coder_ptr, const lzma_allocator *allocator)
{
    lzma_coder *coder = coder_ptr;

    lzma_next_end(&coder->next, allocator);
    lzma_free(coder->dict.buf, allocator);

    if (coder->lz.end != NULL)
        coder->lz.end(coder->lz.coder, allocator);
    else
        lzma_free(coder->lz.coder, allocator);

    lzma_free(coder, allocator);
    return;
}


extern lzma_ret
lzma_lz_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
        const lzma_filter_info *filters,
        lzma_ret (*lz_init)(lzma_lz_decoder *lz,
            const lzma_allocator *allocator, const void *options,
            lzma_lz_options *lz_options))
{
    // Allocate the base structure if it isn't already allocated.
    lzma_coder *coder = next->coder;
    if (coder == NULL) {
        coder = lzma_alloc(sizeof(lzma_coder), allocator);
        if (coder == NULL)
            return LZMA_MEM_ERROR;

        next->coder = coder;
        next->code = &lz_decode;
        next->end = &lz_decoder_end;

        coder->dict.buf = NULL;
        coder->dict.size = 0;
        coder->lz = LZMA_LZ_DECODER_INIT;
        coder->next = LZMA_NEXT_CODER_INIT;
    }

    // Allocate and initialize the LZ-based decoder. It will also give
    // us the dictionary size.
    lzma_lz_options lz_options;
    return_if_error(lz_init(&coder->lz, allocator,
            filters[0].options, &lz_options));

    // If the dictionary size is very small, increase it to 4096 bytes.
    // This is to prevent constant wrapping of the dictionary, which
    // would slow things down. The downside is that since we don't check
    // separately for the real dictionary size, we may happily accept
    // corrupt files.
    if (lz_options.dict_size < 4096)
        lz_options.dict_size = 4096;

    // Make dictionary size a multipe of 16. Some LZ-based decoders like
    // LZMA use the lowest bits lzma_dict.pos to know the alignment of the
    // data. Aligned buffer is also good when memcpying from the
    // dictionary to the output buffer, since applications are
    // recommended to give aligned buffers to liblzma.
    //
    // Avoid integer overflow.
    if (lz_options.dict_size > SIZE_MAX - 15)
        return LZMA_MEM_ERROR;

    lz_options.dict_size = (lz_options.dict_size + 15) & ~((size_t)(15));

    // Allocate and initialize the dictionary.
    if (coder->dict.size != lz_options.dict_size) {
        lzma_free(coder->dict.buf, allocator);
        coder->dict.buf
                = lzma_alloc(lz_options.dict_size, allocator);
        if (coder->dict.buf == NULL)
            return LZMA_MEM_ERROR;

        coder->dict.size = lz_options.dict_size;
    }

    lz_decoder_reset(next->coder);

    // Use the preset dictionary if it was given to us.
    if (lz_options.preset_dict != NULL
            && lz_options.preset_dict_size > 0) {
        // If the preset dictionary is bigger than the actual
        // dictionary, copy only the tail.
        const size_t copy_size = my_min(lz_options.preset_dict_size,
                lz_options.dict_size);
        const size_t offset = lz_options.preset_dict_size - copy_size;
        memcpy(coder->dict.buf, lz_options.preset_dict + offset,
                copy_size);
        coder->dict.pos = copy_size;
        coder->dict.full = copy_size;
    }

    // Miscellaneous initializations
    coder->next_finished = false;
    coder->this_finished = false;
    coder->temp.pos = 0;
    coder->temp.size = 0;

    // Initialize the next filter in the chain, if any.
    return lzma_next_filter_init(&coder->next, allocator, filters + 1);
}


extern uint64_t
lzma_lz_decoder_memusage(size_t dictionary_size)
{
    return sizeof(lzma_coder) + (uint64_t)(dictionary_size);
}


extern void
lzma_lz_decoder_uncompressed(void *coder_ptr, lzma_vli uncompressed_size)
{
    lzma_coder *coder = coder_ptr;
    coder->lz.set_uncompressed(coder->lz.coder, uncompressed_size);
}
