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

#include "index.h"
#include "check.h"


typedef struct {
    enum {
        SEQ_INDICATOR,
        SEQ_COUNT,
        SEQ_MEMUSAGE,
        SEQ_UNPADDED,
        SEQ_UNCOMPRESSED,
        SEQ_PADDING_INIT,
        SEQ_PADDING,
        SEQ_CRC32,
    } sequence;

    /// Memory usage limit
    uint64_t memlimit;

    /// Target Index
    lzma_index *index;

    /// Pointer give by the application, which is set after
    /// successful decoding.
    lzma_index **index_ptr;

    /// Number of Records left to decode.
    lzma_vli count;

    /// The most recent Unpadded Size field
    lzma_vli unpadded_size;

    /// The most recent Uncompressed Size field
    lzma_vli uncompressed_size;

    /// Position in integers
    size_t pos;

    /// CRC32 of the List of Records field
    uint32_t crc32;
} lzma_index_coder;


static lzma_ret
index_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 lzma_attribute((__unused__)),
        size_t *restrict out_pos lzma_attribute((__unused__)),
        size_t out_size lzma_attribute((__unused__)),
        lzma_action action lzma_attribute((__unused__)))
{
    lzma_index_coder *coder = coder_ptr;

    // Similar optimization as in index_encoder.c
    const size_t in_start = *in_pos;
    lzma_ret ret = LZMA_OK;

    while (*in_pos < in_size)
    switch (coder->sequence) {
    case SEQ_INDICATOR:
        // Return LZMA_DATA_ERROR instead of e.g. LZMA_PROG_ERROR or
        // LZMA_FORMAT_ERROR, because a typical usage case for Index
        // decoder is when parsing the Stream backwards. If seeking
        // backward from the Stream Footer gives us something that
        // doesn't begin with Index Indicator, the file is considered
        // corrupt, not "programming error" or "unrecognized file
        // format". One could argue that the application should
        // verify the Index Indicator before trying to decode the
        // Index, but well, I suppose it is simpler this way.
        if (in[(*in_pos)++] != 0x00)
            return LZMA_DATA_ERROR;

        coder->sequence = SEQ_COUNT;
        break;

    case SEQ_COUNT:
        ret = lzma_vli_decode(&coder->count, &coder->pos,
                in, in_pos, in_size);
        if (ret != LZMA_STREAM_END)
            goto out;

        coder->pos = 0;
        coder->sequence = SEQ_MEMUSAGE;

    // Fall through

    case SEQ_MEMUSAGE:
        if (lzma_index_memusage(1, coder->count) > coder->memlimit) {
            ret = LZMA_MEMLIMIT_ERROR;
            goto out;
        }

        // Tell the Index handling code how many Records this
        // Index has to allow it to allocate memory more efficiently.
        lzma_index_prealloc(coder->index, coder->count);

        ret = LZMA_OK;
        coder->sequence = coder->count == 0
                ? SEQ_PADDING_INIT : SEQ_UNPADDED;
        break;

    case SEQ_UNPADDED:
    case SEQ_UNCOMPRESSED: {
        lzma_vli *size = coder->sequence == SEQ_UNPADDED
                ? &coder->unpadded_size
                : &coder->uncompressed_size;

        ret = lzma_vli_decode(size, &coder->pos,
                in, in_pos, in_size);
        if (ret != LZMA_STREAM_END)
            goto out;

        ret = LZMA_OK;
        coder->pos = 0;

        if (coder->sequence == SEQ_UNPADDED) {
            // Validate that encoded Unpadded Size isn't too small
            // or too big.
            if (coder->unpadded_size < UNPADDED_SIZE_MIN
                    || coder->unpadded_size
                        > UNPADDED_SIZE_MAX)
                return LZMA_DATA_ERROR;

            coder->sequence = SEQ_UNCOMPRESSED;
        } else {
            // Add the decoded Record to the Index.
            return_if_error(lzma_index_append(
                    coder->index, allocator,
                    coder->unpadded_size,
                    coder->uncompressed_size));

            // Check if this was the last Record.
            coder->sequence = --coder->count == 0
                    ? SEQ_PADDING_INIT
                    : SEQ_UNPADDED;
        }

        break;
    }

    case SEQ_PADDING_INIT:
        coder->pos = lzma_index_padding_size(coder->index);
        coder->sequence = SEQ_PADDING;

    // Fall through

    case SEQ_PADDING:
        if (coder->pos > 0) {
            --coder->pos;
            if (in[(*in_pos)++] != 0x00)
                return LZMA_DATA_ERROR;

            break;
        }

        // Finish the CRC32 calculation.
        coder->crc32 = lzma_crc32(in + in_start,
                *in_pos - in_start, coder->crc32);

        coder->sequence = SEQ_CRC32;

    // Fall through

    case SEQ_CRC32:
        do {
            if (*in_pos == in_size)
                return LZMA_OK;

            if (((coder->crc32 >> (coder->pos * 8)) & 0xFF)
                    != in[(*in_pos)++])
                return LZMA_DATA_ERROR;

        } while (++coder->pos < 4);

        // Decoding was successful, now we can let the application
        // see the decoded Index.
        *coder->index_ptr = coder->index;

        // Make index NULL so we don't free it unintentionally.
        coder->index = NULL;

        return LZMA_STREAM_END;

    default:
        assert(0);
        return LZMA_PROG_ERROR;
    }

out:
    // Update the CRC32,
    coder->crc32 = lzma_crc32(in + in_start,
            *in_pos - in_start, coder->crc32);

    return ret;
}


static void
index_decoder_end(void *coder_ptr, const lzma_allocator *allocator)
{
    lzma_index_coder *coder = coder_ptr;
    lzma_index_end(coder->index, allocator);
    lzma_free(coder, allocator);
    return;
}


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

    *memusage = lzma_index_memusage(1, coder->count);
    *old_memlimit = coder->memlimit;

    if (new_memlimit != 0) {
        if (new_memlimit < *memusage)
            return LZMA_MEMLIMIT_ERROR;

        coder->memlimit = new_memlimit;
    }

    return LZMA_OK;
}


static lzma_ret
index_decoder_reset(lzma_index_coder *coder, const lzma_allocator *allocator,
        lzma_index **i, uint64_t memlimit)
{
    // Remember the pointer given by the application. We will set it
    // to point to the decoded Index only if decoding is successful.
    // Before that, keep it NULL so that applications can always safely
    // pass it to lzma_index_end() no matter did decoding succeed or not.
    coder->index_ptr = i;
    *i = NULL;

    // We always allocate a new lzma_index.
    coder->index = lzma_index_init(allocator);
    if (coder->index == NULL)
        return LZMA_MEM_ERROR;

    // Initialize the rest.
    coder->sequence = SEQ_INDICATOR;
    coder->memlimit = memlimit;
    coder->count = 0; // Needs to be initialized due to _memconfig().
    coder->pos = 0;
    coder->crc32 = 0;

    return LZMA_OK;
}


static lzma_ret
index_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
        lzma_index **i, uint64_t memlimit)
{
    lzma_next_coder_init(&index_decoder_init, next, allocator);

    if (i == NULL || memlimit == 0)
        return LZMA_PROG_ERROR;

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

        next->coder = coder;
        next->code = &index_decode;
        next->end = &index_decoder_end;
        next->memconfig = &index_decoder_memconfig;
        coder->index = NULL;
    } else {
        lzma_index_end(coder->index, allocator);
    }

    return index_decoder_reset(coder, allocator, i, memlimit);
}


extern LZMA_API(lzma_ret)
lzma_index_decoder(lzma_stream *strm, lzma_index **i, uint64_t memlimit)
{
    lzma_next_strm_init(index_decoder_init, strm, i, memlimit);

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

    return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_index_buffer_decode(lzma_index **i, uint64_t *memlimit,
        const lzma_allocator *allocator,
        const uint8_t *in, size_t *in_pos, size_t in_size)
{
    // Sanity checks
    if (i == NULL || memlimit == NULL
            || in == NULL || in_pos == NULL || *in_pos > in_size)
        return LZMA_PROG_ERROR;

    // Initialize the decoder.
    lzma_index_coder coder;
    return_if_error(index_decoder_reset(&coder, allocator, i, *memlimit));

    // Store the input start position so that we can restore it in case
    // of an error.
    const size_t in_start = *in_pos;

    // Do the actual decoding.
    lzma_ret ret = index_decode(&coder, allocator, in, in_pos, in_size,
            NULL, NULL, 0, LZMA_RUN);

    if (ret == LZMA_STREAM_END) {
        ret = LZMA_OK;
    } else {
        // Something went wrong, free the Index structure and restore
        // the input position.
        lzma_index_end(coder.index, allocator);
        *in_pos = in_start;

        if (ret == LZMA_OK) {
            // The input is truncated or otherwise corrupt.
            // Use LZMA_DATA_ERROR instead of LZMA_BUF_ERROR
            // like lzma_vli_decode() does in single-call mode.
            ret = LZMA_DATA_ERROR;

        } else if (ret == LZMA_MEMLIMIT_ERROR) {
            // Tell the caller how much memory would have
            // been needed.
            *memlimit = lzma_index_memusage(1, coder.count);
        }
    }

    return ret;
}
