#include "utils.h"

#include <ctype.h>
#include <math.h>
#include <openssl/bn.h>
#include <openssl/sha.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static char to_hex_digit(unsigned int v) {
    if (v < 10U) {
        return (char)('0' + v);
    }
    return (char)('a' + (v - 10U));
}

void sb_init(StrBuf *sb) {
    sb->data = NULL;
    sb->len = 0;
    sb->cap = 0;
}

void sb_free(StrBuf *sb) {
    free(sb->data);
    sb->data = NULL;
    sb->len = 0;
    sb->cap = 0;
}

int sb_reserve(StrBuf *sb, size_t extra) {
    size_t need;
    size_t new_cap;
    char *p;

    need = sb->len + extra + 1;
    if (need <= sb->cap) {
        return 1;
    }

    new_cap = (sb->cap == 0) ? 128 : sb->cap;
    while (new_cap < need) {
        new_cap *= 2;
    }

    p = (char *)realloc(sb->data, new_cap);
    if (p == NULL) {
        return 0;
    }

    sb->data = p;
    sb->cap = new_cap;

    if (sb->len == 0) {
        sb->data[0] = '\0';
    }

    return 1;
}

int sb_append(StrBuf *sb, const char *s) {
    size_t n = strlen(s);

    if (sb_reserve(sb, n) == 0) {
        return 0;
    }

    memcpy(sb->data + sb->len, s, n + 1);
    sb->len += n;
    return 1;
}

int sb_append_n(StrBuf *sb, const char *s, size_t n) {
    if (sb_reserve(sb, n) == 0) {
        return 0;
    }

    memcpy(sb->data + sb->len, s, n);
    sb->len += n;
    sb->data[sb->len] = '\0';
    return 1;
}

int sb_append_byte_hex(StrBuf *sb, uint8_t b) {
    char tmp[3];

    tmp[0] = to_hex_digit((unsigned int)(b >> 4));
    tmp[1] = to_hex_digit((unsigned int)(b & 0x0F));
    tmp[2] = '\0';
    return sb_append(sb, tmp);
}

char *sb_take(StrBuf *sb) {
    char *out = sb->data;
    sb->data = NULL;
    sb->len = 0;
    sb->cap = 0;
    return out;
}

int hex_char_to_val(char c) {
    if (c >= '0' && c <= '9') {
        return c - '0';
    }
    if (c >= 'a' && c <= 'f') {
        return 10 + (c - 'a');
    }
    if (c >= 'A' && c <= 'F') {
        return 10 + (c - 'A');
    }
    return -1;
}

int hex_to_bytes(const char *hex, uint8_t **out, size_t *out_len) {
    size_t n;
    size_t i;
    uint8_t *buf;

    if (hex == NULL || out == NULL || out_len == NULL) {
        return 0;
    }

    n = strlen(hex);
    if ((n % 2) != 0) {
        return 0;
    }

    buf = (uint8_t *)malloc(n / 2);
    if (buf == NULL) {
        return 0;
    }

    for (i = 0; i < n; i += 2) {
        int hi = hex_char_to_val(hex[i]);
        int lo = hex_char_to_val(hex[i + 1]);
        if (hi < 0 || lo < 0) {
            free(buf);
            return 0;
        }
        buf[i / 2] = (uint8_t)((hi << 4) | lo);
    }

    *out = buf;
    *out_len = n / 2;
    return 1;
}

int hex_to_fixed_bytes(const char *hex, uint8_t *out, size_t out_len) {
    size_t n;
    size_t i;

    if (hex == NULL || out == NULL) {
        return 0;
    }

    n = strlen(hex);
    if (n != out_len * 2) {
        return 0;
    }

    for (i = 0; i < n; i += 2) {
        int hi = hex_char_to_val(hex[i]);
        int lo = hex_char_to_val(hex[i + 1]);
        if (hi < 0 || lo < 0) {
            return 0;
        }
        out[i / 2] = (uint8_t)((hi << 4) | lo);
    }

    return 1;
}

char *bytes_to_hex(const uint8_t *data, size_t len) {
    static const char tab[] = "0123456789abcdef";
    char *out;
    size_t i;

    out = (char *)malloc(len * 2 + 1);
    if (out == NULL) {
        return NULL;
    }

    for (i = 0; i < len; ++i) {
        out[2 * i] = tab[data[i] >> 4];
        out[2 * i + 1] = tab[data[i] & 0x0F];
    }
    out[len * 2] = '\0';

    return out;
}

void reverse_bytes(uint8_t *data, size_t n) {
    size_t i;

    for (i = 0; i < n / 2; ++i) {
        uint8_t t = data[i];
        data[i] = data[n - 1 - i];
        data[n - 1 - i] = t;
    }
}

void double_sha256(const uint8_t *data, size_t len, uint8_t out[32]) {
    uint8_t tmp[SHA256_DIGEST_LENGTH];

    SHA256(data, len, tmp);
    SHA256(tmp, SHA256_DIGEST_LENGTH, out);
}

int encode_varint_hex(uint64_t value, StrBuf *sb) {
    uint8_t bytes[9];
    size_t n = 0;
    size_t i;

    if (value < 0xFD) {
        bytes[n++] = (uint8_t)value;
    } else if (value <= 0xFFFFULL) {
        bytes[n++] = 0xFD;
        bytes[n++] = (uint8_t)(value & 0xFF);
        bytes[n++] = (uint8_t)((value >> 8) & 0xFF);
    } else if (value <= 0xFFFFFFFFULL) {
        bytes[n++] = 0xFE;
        bytes[n++] = (uint8_t)(value & 0xFF);
        bytes[n++] = (uint8_t)((value >> 8) & 0xFF);
        bytes[n++] = (uint8_t)((value >> 16) & 0xFF);
        bytes[n++] = (uint8_t)((value >> 24) & 0xFF);
    } else {
        bytes[n++] = 0xFF;
        bytes[n++] = (uint8_t)(value & 0xFF);
        bytes[n++] = (uint8_t)((value >> 8) & 0xFF);
        bytes[n++] = (uint8_t)((value >> 16) & 0xFF);
        bytes[n++] = (uint8_t)((value >> 24) & 0xFF);
        bytes[n++] = (uint8_t)((value >> 32) & 0xFF);
        bytes[n++] = (uint8_t)((value >> 40) & 0xFF);
        bytes[n++] = (uint8_t)((value >> 48) & 0xFF);
        bytes[n++] = (uint8_t)((value >> 56) & 0xFF);
    }

    for (i = 0; i < n; ++i) {
        if (sb_append_byte_hex(sb, bytes[i]) == 0) {
            return 0;
        }
    }

    return 1;
}

static char *bn_to_fixed_hex64(const BIGNUM *bn) {
    char *tmp;
    char *out;
    size_t n;
    size_t i;

    tmp = BN_bn2hex(bn);
    if (tmp == NULL) {
        return NULL;
    }

    n = strlen(tmp);
    if (n > 64) {
        OPENSSL_free(tmp);
        return NULL;
    }

    out = (char *)malloc(65);
    if (out == NULL) {
        OPENSSL_free(tmp);
        return NULL;
    }

    for (i = 0; i < 64; ++i) {
        out[i] = '0';
    }
    out[64] = '\0';

    for (i = 0; i < n; ++i) {
        char c = tmp[i];
        if (isupper((unsigned char)c)) {
            c = (char)tolower((unsigned char)c);
        }
        out[64 - n + i] = c;
    }

    OPENSSL_free(tmp);
    return out;
}

char *decode_nbits_hex(uint32_t nbits) {
    BN_CTX *ctx;
    BIGNUM *bn;
    BIGNUM *sig;
    char *out;
    uint32_t exponent;
    uint32_t significand;

    exponent = (nbits >> 24) & 0xFF;
    significand = nbits & 0x007FFFFF;

    ctx = BN_CTX_new();
    bn = BN_new();
    sig = BN_new();

    if (ctx == NULL || bn == NULL || sig == NULL) {
        BN_CTX_free(ctx);
        BN_free(bn);
        BN_free(sig);
        return NULL;
    }

    BN_set_word(sig, significand);
    BN_copy(bn, sig);

    if (exponent >= 3) {
        BN_lshift(bn, bn, 8 * ((int)exponent - 3));
    } else {
        BN_rshift(bn, bn, 8 * (3 - (int)exponent));
    }

    out = bn_to_fixed_hex64(bn);

    BN_CTX_free(ctx);
    BN_free(bn);
    BN_free(sig);
    return out;
}

char *calculate_target_hex(const char *bits_hex, double difficulty_factor, const char *network) {
    static const char *MAX_TARGET_HEX = "00000000ffff0000000000000000000000000000000000000000000000000000";
    BIGNUM *max_bn;
    BIGNUM *limit_bn;
    BIGNUM *num_bn;
    BIGNUM *den_bn;
    BIGNUM *result_bn;
    BN_CTX *ctx;
    char *original;
    char *out;
    uint64_t scaled_factor;
    const uint64_t SCALE = 1000000000ULL;
    uint32_t nbits;

    if (bits_hex == NULL || network == NULL) {
        return NULL;
    }

    nbits = (uint32_t)strtoul(bits_hex, NULL, 16);
    original = decode_nbits_hex(nbits);
    if (original == NULL) {
        return NULL;
    }

    if (strcmp(network, "regtest") == 0) {
        if (difficulty_factor < 0.0) {
            difficulty_factor = 0.1;
        }
    } else {
        difficulty_factor = 1.0;
    }

    if (difficulty_factor == 0.0) {
        return original;
    }

    scaled_factor = (uint64_t)llround(difficulty_factor * (double)SCALE);
    if (scaled_factor == 0ULL) {
        scaled_factor = 1ULL;
    }

    ctx = BN_CTX_new();
    max_bn = BN_new();
    limit_bn = BN_new();
    num_bn = BN_new();
    den_bn = BN_new();
    result_bn = BN_new();

    if (ctx == NULL || max_bn == NULL || limit_bn == NULL || num_bn == NULL || den_bn == NULL || result_bn == NULL) {
        BN_CTX_free(ctx);
        BN_free(max_bn);
        BN_free(limit_bn);
        BN_free(num_bn);
        BN_free(den_bn);
        BN_free(result_bn);
        free(original);
        return NULL;
    }

    BN_hex2bn(&max_bn, MAX_TARGET_HEX);
    BN_hex2bn(&limit_bn, "ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff");

    BN_copy(num_bn, max_bn);
    BN_mul_word(num_bn, (BN_ULONG)SCALE);
    BN_set_word(den_bn, (BN_ULONG)scaled_factor);
    BN_div(result_bn, NULL, num_bn, den_bn, ctx);

    if (BN_cmp(result_bn, limit_bn) > 0) {
        BN_copy(result_bn, limit_bn);
    }

    out = bn_to_fixed_hex64(result_bn);

    BN_CTX_free(ctx);
    BN_free(max_bn);
    BN_free(limit_bn);
    BN_free(num_bn);
    BN_free(den_bn);
    BN_free(result_bn);
    free(original);

    return out;
}

char *hex_add_width(const char *base_hex, int add_value) {
    static const char *hex_digits = "0123456789abcdef";
    char *out;
    size_t n;
    int carry;
    size_t pos;

    if (base_hex == NULL || add_value < 0) {
        return NULL;
    }

    n = strlen(base_hex);
    if (n == 0) {
        return NULL;
    }

    out = strdup(base_hex);
    if (out == NULL) {
        return NULL;
    }

    carry = add_value;
    pos = n;
    while (pos > 0 && carry > 0) {
        int digit = hex_char_to_val(out[pos - 1]);
        int sum;

        if (digit < 0) {
            free(out);
            return NULL;
        }

        sum = digit + carry;
        out[pos - 1] = hex_digits[sum & 0x0F];
        carry = sum >> 4;
        --pos;
    }

    return out;
}