#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>

static uint64_t polymod_step(uint64_t pre) {
    uint8_t b = pre >> 55;
    return ((pre & 0x7fffffffffffffULL) << 5) ^
           (-((b >> 0) & 1) & 0x7d52fba40bd886ULL) ^
           (-((b >> 1) & 1) & 0x5e8dbf1a03950cULL) ^
           (-((b >> 2) & 1) & 0x1c3a3c74072a18ULL) ^
           (-((b >> 3) & 1) & 0x385d72fa0e5139ULL) ^
           (-((b >> 4) & 1) & 0x7093e5a608865bULL);
}

static const char *charset = "qpzry9x8gf2tvdw0s3jn54khce6mua7l";

static const int8_t charset_rev[128] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    15, -1, 10, 17, 21, 20, 26, 30,  7,  5, -1, -1, -1, -1, -1, -1,
    -1, 29, -1, 24, 13, 25,  9,  8, 23, -1, 18, 22, 31, 27, 19, -1,
    1,  0,  3, 16, 11, 28, 12, 14,  6,  4,  2, -1, -1, -1, -1, -1,
    -1, 29, -1, 24, 13, 25,  9,  8, 23, -1, 18, 22, 31, 27, 19, -1,
    1,  0,  3, 16, 11, 28, 12, 14,  6,  4,  2, -1, -1, -1, -1, -1
};

#define MAXLEN ((size_t) 1000)

static void clear_2(void *p, size_t len, void *p2, size_t len2) {
    memset(p, 0, len);
    memset(p2, 0, len2);
}

int encode(char *output, const char *hrp, const uint8_t *data, size_t data_len, size_t max_input_len) {
    uint64_t chk = 1;
    size_t i = 0;
    while (hrp[i] != 0) {
        int ch = hrp[i];
        if (ch < 33 || ch > 126) {
            return 0;
        }

        if (ch >= 'A' && ch <= 'Z') return 0;
        chk = polymod_step(chk) ^ (ch >> 5);
        ++i;
    }
    if (i + 13 + data_len > max_input_len) return 0;
    chk = polymod_step(chk);
    while (*hrp != 0) {
        chk = polymod_step(chk) ^ (*hrp & 0x1f);
        *(output++) = *(hrp++);
    }
    *(output++) = '1';
    for (i = 0; i < data_len; ++i) {
        if (*data >> 5) return 0;
        chk = polymod_step(chk) ^ (*data);
        *(output++) = charset[*(data++)];
    }
    for (i = 0; i < 12; ++i) {
        chk = polymod_step(chk);
    }
    chk ^= 1;
    for (i = 0; i < 12; ++i) {
        *(output++) = charset[(chk >> ((11 - i) * 5)) & 0x1f];
    }
    *output = 0;
    return 1;
}

int decode(char *hrp, uint8_t *data, size_t *data_len, const char *input, size_t max_input_len) {
    uint64_t chk = 1;
    size_t i;
    size_t input_len = strlen(input);
    size_t hrp_len;
    int have_lower = 0, have_upper = 0;
    if (input_len < 8 || input_len > max_input_len) {
        return 0;
    }
    *data_len = 0;
    while (*data_len < input_len && input[(input_len - 1) - *data_len] != '1') {
        ++(*data_len);
    }
    if (1 + *data_len >= input_len || *data_len < 12) {
        return 0;
    }
    hrp_len = input_len - (1 + *data_len);
    *(data_len) -= 12;
    for (i = 0; i < hrp_len; ++i) {
        int ch = input[i];
        if (ch < 33 || ch > 126) {
            return 0;
        }
        if (ch >= 'a' && ch <= 'z') {
            have_lower = 1;
        } else if (ch >= 'A' && ch <= 'Z') {
            have_upper = 1;
            ch = (ch - 'A') + 'a';
        }
        hrp[i] = ch;
        chk = polymod_step(chk) ^ (ch >> 5);
    }
    hrp[i] = 0;
    chk = polymod_step(chk);
    for (i = 0; i < hrp_len; ++i) {
        chk = polymod_step(chk) ^ (input[i] & 0x1f);
    }
    ++i;
    while (i < input_len) {
        int v = (input[i] & 0x80) ? -1 : charset_rev[(int)input[i]];
        if (input[i] >= 'a' && input[i] <= 'z') have_lower = 1;
        if (input[i] >= 'A' && input[i] <= 'Z') have_upper = 1;
        if (v == -1) {
            return 0;
        }
        chk = polymod_step(chk) ^ v;
        if (i + 12 < input_len) {
            data[i - (1 + hrp_len)] = v;
        }
        ++i;
    }
    if (have_lower && have_upper) {
        return 0;
    }
    return chk == 1;
}

int convert_bits(uint8_t *out, size_t *outlen, int outbits, const uint8_t *in, size_t inlen, int inbits, int pad) {
    uint32_t val = 0;
    int bits = 0;
    uint32_t maxv = (((uint32_t)1) << outbits) - 1;
    while (inlen--) {
        val = (val << inbits) | *(in++);
        bits += inbits;
        while (bits >= outbits) {
            bits -= outbits;
            out[(*outlen)++] = (val >> bits) & maxv;
        }
    }
    if (pad) {
        if (bits) {
            out[(*outlen)++] = (val << (outbits - bits)) & maxv;
        }
    } else if (((val << (outbits - bits)) & maxv) || bits >= inbits) {
        return 0;
    }
    return 1;
}

int addr_encode(char *output, size_t *output_len, const char *hrp, int witver, const uint8_t *witprog, size_t witprog_len) {
    uint8_t data[MAXLEN];
    size_t datalen = 0;
    if (witver > 16) goto fail;
    if (witver == 0 && witprog_len != 53 && witprog_len != 65) goto fail;
    if (witprog_len < 2 || witprog_len > 65) goto fail;
    data[0] = witver;
    convert_bits(data + 1, &datalen, 5, witprog, witprog_len, 8, 1);
    ++datalen;
    int ret = encode(output, hrp, data, datalen, MAXLEN);
    size_t len = strlen(output);
    memcpy(output_len, &len, 4);
    clear_2(data, sizeof(data), NULL, 0);
    return ret;
fail:
    clear_2(data, sizeof(data), NULL, 0);
    return 0;
}

int addr_decode(int *witver, uint8_t *witdata, size_t *witdata_len, const char *hrp, const char *addr) {
    uint8_t data[MAXLEN];
    char hrp_actual[MAXLEN];
    size_t data_len;
    if (!decode(hrp_actual, data, &data_len, addr, MAXLEN)) goto fail;
    if (data_len == 0 || data_len > (MAXLEN - 4)) goto fail;
    if (strncmp(hrp, hrp_actual, MAXLEN - 5) != 0) goto fail;
    if (data[0] > 16) goto fail;
    *witdata_len = 0;
    if (!convert_bits(witdata, witdata_len, 8, data + 1, data_len - 1, 5, 0)) goto fail;
    if (*witdata_len < 2 || *witdata_len > 65) goto fail;
    if (data[0] == 0 && *witdata_len != 53 && *witdata_len != 65) goto fail;
    *witver = data[0];
    clear_2(data, sizeof(data), hrp_actual, sizeof(hrp_actual));
    return 1;
fail:
    clear_2(data, sizeof(data), hrp_actual, sizeof(hrp_actual));
    return 0;
}