/*
 * tinflate - tiny inflate
 *
 * Copyright (c) 2003-2019 Joergen Ibsen
 *
 * This software is provided 'as-is', without any express or implied
 * warranty. In no event will the authors be held liable for any damages
 * arising from the use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 *   1. The origin of this software must not be misrepresented; you must
 *      not claim that you wrote the original software. If you use this
 *      software in a product, an acknowledgment in the product
 *      documentation would be appreciated but is not required.
 *
 *   2. Altered source versions must be plainly marked as such, and must
 *      not be misrepresented as being the original software.
 *
 *   3. This notice may not be removed or altered from any source
 *      distribution.
 */

#include "tinf.h"

/* -- Internal data structures -- */

struct tinf_tree {
    unsigned short counts[16]; /* Number of codes with a given length */
    unsigned short symbols[288]; /* Symbols sorted by code */
    int max_sym;
};

struct tinf_data {
    const unsigned char *source;
    const unsigned char *source_end;
    unsigned int tag;
    int bitcount;
    int overflow;

    unsigned char *dest_start;
    unsigned char *dest;

    struct tinf_tree ltree; /* Literal/length tree */
    struct tinf_tree dtree; /* Distance tree */
};

/* -- Utility functions -- */

static unsigned int read_le16(const unsigned char *p) {
    return ((unsigned int) p[0])
         | ((unsigned int) p[1] << 8);
}

/* Build fixed Huffman trees */
static void tinf_build_fixed_trees(struct tinf_tree *lt, struct tinf_tree *dt) {
    int i;

    /* Build fixed literal/length tree */
    for (i = 0; i < 16; ++i) {
        lt->counts[i] = 0;
    }

    lt->counts[7] = 24;
    lt->counts[8] = 152;
    lt->counts[9] = 112;

    for (i = 0; i < 24; ++i) {
        lt->symbols[i] = 256 + i;
    }
    for (i = 0; i < 144; ++i) {
        lt->symbols[24 + i] = i;
    }
    for (i = 0; i < 8; ++i) {
        lt->symbols[24 + 144 + i] = 280 + i;
    }
    for (i = 0; i < 112; ++i) {
        lt->symbols[24 + 144 + 8 + i] = 144 + i;
    }

    lt->max_sym = 285;

    /* Build fixed distance tree */
    for (i = 0; i < 16; ++i) {
        dt->counts[i] = 0;
    }

    dt->counts[5] = 32;

    for (i = 0; i < 32; ++i) {
        dt->symbols[i] = i;
    }

    dt->max_sym = 29;
}

/* Given an array of code lengths, build a tree */
static int tinf_build_tree(struct tinf_tree *t, const unsigned char *lengths,
                           unsigned int num) {
    unsigned short offs[16];
    unsigned int i, num_codes, available;

    for (i = 0; i < 16; ++i) {
        t->counts[i] = 0;
    }

    t->max_sym = -1;

    /* Count number of codes for each non-zero length */
    for (i = 0; i < num; ++i) {

        if (lengths[i]) {
            t->max_sym = i;
            t->counts[lengths[i]]++;
        }
    }

    /* Compute offset table for distribution sort */
    for (available = 1, num_codes = 0, i = 0; i < 16; ++i) {
        unsigned int used = t->counts[i];

        /* Check length contains no more codes than available */
        if (used > available) {
            return TINF_DATA_ERROR;
        }
        available = 2 * (available - used);

        offs[i] = num_codes;
        num_codes += used;
    }

    /*
     * Check all codes were used, or for the special case of only one
     * code that it has length 1
     */
    if ((num_codes > 1 && available > 0)
     || (num_codes == 1 && t->counts[1] != 1)) {
        return TINF_DATA_ERROR;
    }

    /* Fill in symbols sorted by code */
    for (i = 0; i < num; ++i) {
        if (lengths[i]) {
            t->symbols[offs[lengths[i]]++] = i;
        }
    }

    /*
     * For the special case of only one code (which will be 0) add a
     * code 1 which results in a symbol that is too large
     */
    if (num_codes == 1) {
        t->counts[1] = 2;
        t->symbols[1] = t->max_sym + 1;
    }

    return TINF_OK;
}

/* -- Decode functions -- */

static void tinf_refill(struct tinf_data *d, int num) {

    /* Read bytes until at least num bits available */
    while (d->bitcount < num) {
        if (d->source != d->source_end) {
            d->tag |= (unsigned int) *d->source++ << d->bitcount;
        }
        else {
            d->overflow = 1;
        }
        d->bitcount += 8;
    }

}

static unsigned int tinf_getbits_no_refill(struct tinf_data *d, int num) {
    unsigned int bits;


    /* Get bits from tag */
    bits = d->tag & ((1UL << num) - 1);

    /* Remove bits from tag */
    d->tag >>= num;
    d->bitcount -= num;

    return bits;
}

/* Get num bits from source stream */
static unsigned int tinf_getbits(struct tinf_data *d, int num) {
    tinf_refill(d, num);
    return tinf_getbits_no_refill(d, num);
}

/* Read a num bit value from stream and add base */
static unsigned int tinf_getbits_base(struct tinf_data *d, int num, int base) {
    return base + (num ? tinf_getbits(d, num) : 0);
}

/* Given a data stream and a tree, decode a symbol */
static int tinf_decode_symbol(struct tinf_data *d, const struct tinf_tree *t) {
    int base = 0, offs = 0;
    int len;

    /*
     * Get more bits while code index is above number of codes
     *
     * Rather than the actual code, we are computing the position of the
     * code in the sorted order of codes, which is the index of the
     * corresponding symbol.
     *
     * Conceptually, for each code length (level in the tree), there are
     * counts[len] leaves on the left and internal nodes on the right.
     * The index we have decoded so far is base + offs, and if that
     * falls within the leaves we are done. Otherwise we adjust the range
     * of offs and add one more bit to it.
     */
    for (len = 1; ; ++len) {
        offs = 2 * offs + tinf_getbits(d, 1);

        if (offs < t->counts[len]) {
            break;
        }

        base += t->counts[len];
        offs -= t->counts[len];
    }


    return t->symbols[base + offs];
}

/* Given a data stream, decode dynamic trees from it */
static int tinf_decode_trees(struct tinf_data *d, struct tinf_tree *lt,
                             struct tinf_tree *dt) {
    unsigned char lengths[288 + 32];

    /* Special ordering of code length codes */
    static const unsigned char clcidx[19] = {
        16, 17, 18, 0,  8, 7,  9, 6, 10, 5,
        11,  4, 12, 3, 13, 2, 14, 1, 15
    };

    unsigned int hlit, hdist, hclen;
    unsigned int i, num, length;
    int res;

    /* Get 5 bits HLIT (257-286) */
    hlit = tinf_getbits_base(d, 5, 257);

    /* Get 5 bits HDIST (1-32) */
    hdist = tinf_getbits_base(d, 5, 1);

    /* Get 4 bits HCLEN (4-19) */
    hclen = tinf_getbits_base(d, 4, 4);

    /*
     * The RFC limits the range of HLIT to 286, but lists HDIST as range
     * 1-32, even though distance codes 30 and 31 have no meaning. While
     * we could allow the full range of HLIT and HDIST to make it possible
     * to decode the fixed trees with this function, we consider it an
     * error here.
     *
     * See also: https://github.com/madler/zlib/issues/82
     */
    if (hlit > 286 || hdist > 30) {
        return TINF_DATA_ERROR;
    }

    for (i = 0; i < 19; ++i) {
        lengths[i] = 0;
    }

    /* Read code lengths for code length alphabet */
    for (i = 0; i < hclen; ++i) {
        /* Get 3 bits code length (0-7) */
        unsigned int clen = tinf_getbits(d, 3);

        lengths[clcidx[i]] = clen;
    }

    /* Build code length tree (in literal/length tree to save space) */
    res = tinf_build_tree(lt, lengths, 19);

    if (res != TINF_OK) {
        return res;
    }

    /* Check code length tree is not empty */
    if (lt->max_sym == -1) {
        return TINF_DATA_ERROR;
    }

    /* Decode code lengths for the dynamic trees */
    for (num = 0; num < hlit + hdist; ) {
        int sym = tinf_decode_symbol(d, lt);

        if (sym > lt->max_sym) {
            return TINF_DATA_ERROR;
        }

        switch (sym) {
        case 16:
            /* Copy previous code length 3-6 times (read 2 bits) */
            if (num == 0) {
                return TINF_DATA_ERROR;
            }
            sym = lengths[num - 1];
            length = tinf_getbits_base(d, 2, 3);
            break;
        case 17:
            /* Repeat code length 0 for 3-10 times (read 3 bits) */
            sym = 0;
            length = tinf_getbits_base(d, 3, 3);
            break;
        case 18:
            /* Repeat code length 0 for 11-138 times (read 7 bits) */
            sym = 0;
            length = tinf_getbits_base(d, 7, 11);
            break;
        default:
            /* Values 0-15 represent the actual code lengths */
            length = 1;
            break;
        }

        if (length > hlit + hdist - num) {
            return TINF_DATA_ERROR;
        }

        while (length--) {
            lengths[num++] = sym;
        }
    }

    /* Check EOB symbol is present */
    if (lengths[256] == 0) {
        return TINF_DATA_ERROR;
    }

    /* Build dynamic trees */
    res = tinf_build_tree(lt, lengths, hlit);

    if (res != TINF_OK) {
        return res;
    }

    res = tinf_build_tree(dt, lengths + hlit, hdist);

    if (res != TINF_OK) {
        return res;
    }

    return TINF_OK;
}

/* -- Block inflate functions -- */

/* Given a stream and two trees, inflate a block of data */
static int tinf_inflate_block_data(struct tinf_data *d, struct tinf_tree *lt,
                                   struct tinf_tree *dt) {
    /* Extra bits and base tables for length codes */
    static const unsigned char length_bits[30] = {
        0, 0, 0, 0, 0, 0, 0, 0, 1, 1,
        1, 1, 2, 2, 2, 2, 3, 3, 3, 3,
        4, 4, 4, 4, 5, 5, 5, 5, 0, 127
    };

    static const unsigned short length_base[30] = {
         3,  4,  5,   6,   7,   8,   9,  10,  11,  13,
        15, 17, 19,  23,  27,  31,  35,  43,  51,  59,
        67, 83, 99, 115, 131, 163, 195, 227, 258,   0
    };

    /* Extra bits and base tables for distance codes */
    static const unsigned char dist_bits[30] = {
        0, 0,  0,  0,  1,  1,  2,  2,  3,  3,
        4, 4,  5,  5,  6,  6,  7,  7,  8,  8,
        9, 9, 10, 10, 11, 11, 12, 12, 13, 13
    };

    static const unsigned short dist_base[30] = {
           1,    2,    3,    4,    5,    7,    9,    13,    17,    25,
          33,   49,   65,   97,  129,  193,  257,   385,   513,   769,
        1025, 1537, 2049, 3073, 4097, 6145, 8193, 12289, 16385, 24577
    };

    for (;;) {
        int sym = tinf_decode_symbol(d, lt);

        /* Check for overflow in bit reader */
        if (d->overflow) {
            return TINF_DATA_ERROR;
        }

        if (sym < 256) {
            *d->dest++ = sym;
        }
        else {
            int length, dist, offs;
            int i;

            /* Check for end of block */
            if (sym == 256) {
                return TINF_OK;
            }

            /* Check sym is within range and distance tree is not empty */
            if (sym > lt->max_sym || sym - 257 > 28 || dt->max_sym == -1) {
                return TINF_DATA_ERROR;
            }

            sym -= 257;

            /* Possibly get more bits from length code */
            length = tinf_getbits_base(d, length_bits[sym],
                                       length_base[sym]);

            dist = tinf_decode_symbol(d, dt);

            /* Check dist is within range */
            if (dist > dt->max_sym || dist > 29) {
                return TINF_DATA_ERROR;
            }

            /* Possibly get more bits from distance code */
            offs = tinf_getbits_base(d, dist_bits[dist],
                                     dist_base[dist]);

            if (offs > d->dest - d->dest_start) {
                return TINF_DATA_ERROR;
            }

            /* Copy match */
            for (i = 0; i < length; ++i) {
                d->dest[i] = d->dest[i - offs];
            }

            d->dest += length;
        }
    }
}

/* Inflate an uncompressed block of data */
static int tinf_inflate_uncompressed_block(struct tinf_data *d) {
    unsigned int length, invlength;

    if (d->source_end - d->source < 4) {
        return TINF_DATA_ERROR;
    }

    /* Get length */
    length = read_le16(d->source);

    /* Get one's complement of length */
    invlength = read_le16(d->source + 2);

    /* Check length */
    if (length != (~invlength & 0x0000FFFF)) {
        return TINF_DATA_ERROR;
    }

    d->source += 4;

    /* Copy block */
    while (length--) {
        *d->dest++ = *d->source++;
    }

    /* Make sure we start next block on a byte boundary */
    d->tag = 0;
    d->bitcount = 0;

    return TINF_OK;
}

/* Inflate a block of data compressed with fixed Huffman trees */
static int tinf_inflate_fixed_block(struct tinf_data *d) {
    /* Build fixed Huffman trees */
    tinf_build_fixed_trees(&d->ltree, &d->dtree);

    /* Decode block using fixed trees */
    return tinf_inflate_block_data(d, &d->ltree, &d->dtree);
}

/* Inflate a block of data compressed with dynamic Huffman trees */
static int tinf_inflate_dynamic_block(struct tinf_data *d) {
    /* Decode trees from stream */
    int res = tinf_decode_trees(d, &d->ltree, &d->dtree);

    if (res != TINF_OK) {
        return res;
    }

    /* Decode block using decoded trees */
    return tinf_inflate_block_data(d, &d->ltree, &d->dtree);
}

/* -- Public functions -- */

/* Inflate stream from source to dest */
int tinf_uncompress(void *dest,
                    const void *source, unsigned int sourceLen) {
    struct tinf_data d;
    int bfinal;

    /* Initialise data */
    d.source = (const unsigned char *) source;
    d.source_end = d.source + sourceLen;
    d.tag = 0;
    d.bitcount = 0;
    d.overflow = 0;

    d.dest = (unsigned char *) dest;
    d.dest_start = d.dest;

    do {
        unsigned int btype;
        int res;

        /* Read final block flag */
        bfinal = tinf_getbits(&d, 1);

        /* Read block type (2 bits) */
        btype = tinf_getbits(&d, 2);

        /* Decompress block */
        switch (btype) {
        case 0:
            /* Decompress uncompressed block */
            res = tinf_inflate_uncompressed_block(&d);
            break;
        case 1:
            /* Decompress block with fixed Huffman trees */
            res = tinf_inflate_fixed_block(&d);
            break;
        case 2:
            /* Decompress block with dynamic Huffman trees */
            res = tinf_inflate_dynamic_block(&d);
            break;
        default:
            res = TINF_DATA_ERROR;
            break;
        }

        if (res != TINF_OK) {
            return res;
        }
    } while (!bfinal);

    /* Check for overflow in bit reader */
    if (d.overflow) {
        return TINF_DATA_ERROR;
    }

    return TINF_OK;
}