#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include <inttypes.h>
#include <ctype.h>
#include <string.h>
#include <time.h>
#include <openssl/sha.h>

//Copied from Bitcoin source
const uint64_t COIN = 100000000;
const uint64_t CENT = 1000000;

uint32_t OP_CHECKSIG = 172; // This is expressed as 0xAC
bool generateBlock = false;
uint32_t startNonce = 0;
uint32_t unixtime = 0;

typedef struct {
    /* Hash of Tx */
    uint8_t merkleHash[32];

    /* Tx serialization before hashing */
    uint8_t *serializedData;

    /* Tx version */
    uint32_t version;

    /* Input */
    uint8_t numInputs; // Program assumes one input
    uint8_t prevOutput[32];
    uint32_t prevoutIndex;
    uint8_t *scriptSig;// nBitsLen + nBits + 0x01 + 0x04 + ScriptSig_len + timestamp
    uint32_t sequence;

    /* Output */
    uint8_t numOutputs; // Program assumes one output
    uint64_t outValue;
    uint8_t *pubkeyScript;//0x41 + pubkey + OP_CHECKSIG

    /* Final */
    uint32_t locktime;
} Transaction;

// Got this off the internet. Am not sure if it can fail in some circumstances
void byteswap(uint8_t *buf, int length)
{
    int i;
    uint8_t temp;

    for (i = 0; i < length / 2; i++)
    {
        temp = buf[i];
        buf[i] = buf[length - i - 1];
        buf[length - i - 1] = temp;
    }
}

// Following two functions are borrowed from cgminer.
char *bin2hex(const unsigned char *p, size_t len)
{
    char *s = (char*)malloc((len * 2) + 1);
    unsigned int i;

    if (!s)
        return NULL;

    for (i = 0; i < len; i++)
        sprintf_s(s + (i * 2), 3, "%02x", (unsigned int)p[i]);


    return s;
}

size_t hex2bin(unsigned char *p, const char *hexstr, size_t len)
{
    int ret = 0;
    size_t retlen = len;

    while (*hexstr && len) {
        char hex_byte[4];
        unsigned int v;

        if (!hexstr[1]) {
            return ret;
        }

        memset(hex_byte, 0, 4);
        hex_byte[0] = hexstr[0];
        hex_byte[1] = hexstr[1];

        if (sscanf_s(hex_byte, "%x", &v) != 1) {
            return ret;
        }

        *p = (unsigned char)v;

        p++;
        hexstr += 2;
        len--;
    }

    if (len == 0 && *hexstr == 0)
        ret = retlen;

    return ret;
}

Transaction *InitTransaction()
{
    Transaction *transaction;

    transaction = (Transaction *)calloc(1, sizeof(*transaction));
    if (!transaction)
    {
        return NULL;
    }

    // Set some initial data that will remain constant throughout the program
    transaction->version = 1;
    transaction->numInputs = 1;
    transaction->numOutputs = 1;
    transaction->locktime = 0;
    transaction->prevoutIndex = 0xFFFFFFFF;
    transaction->sequence = 0xFFFFFFFF;
    transaction->outValue = 50 * COIN;

    // We initialize the previous output to 0 as there is none
    memset(transaction->prevOutput, 0, 32);

    return transaction;
}

//运行命令：./genesisgen [PubKey] [TimeStamp] [nBits]
int main(int argc, char *argv[])
{
    Transaction *transaction;
    unsigned char hash1[32], hash2[32];
    char timestamp[255], pubkey[132];
    uint32_t timestamp_len = 0, scriptSig_len = 0, pubkey_len = 0, pubkeyScript_len = 0;
    uint32_t nBits = 0;

    if ((argc - 1) < 3)
    {
        fprintf(stderr, "Usage: genesisgen [options] <pubkey> \"<timestamp>\" <nBits>\n");
        return 0;
    }

    pubkey_len = strlen(argv[1]) / 2; // One byte is represented as two hex characters, thus we divide by two to get real length.
    timestamp_len = strlen(argv[2]);

    if (pubkey_len != 65)
    {
        fprintf(stderr, "Invalid public key length! %s\n", argv[1]);
        return 0;
    }

    if (timestamp_len > 254 || timestamp_len <= 0)
    {
        fprintf(stderr, "Size of timestamp is 0 or exceeds maximum length of 254 characters!\n");
        return 0;
    }

    transaction = InitTransaction();
    if (!transaction)
    {
        fprintf(stderr, "Could not allocate memory! Exiting...\n");
        return 0;
    }

    strncpy_s(pubkey, argv[1], sizeof(pubkey));
    strncpy_s(timestamp, argv[2], sizeof(timestamp));
    sscanf_s(argv[3], "%lu", (long unsigned int *)&nBits);

    pubkey_len = strlen(pubkey) >> 1;
    scriptSig_len = timestamp_len;

    // Encode pubkey to binary and prepend pubkey size, then append the OP_CHECKSIG byte
    transaction->pubkeyScript = (uint8_t*)malloc((pubkey_len + 2) * sizeof(uint8_t));
    pubkeyScript_len = hex2bin(transaction->pubkeyScript + 1, pubkey, pubkey_len); // No error checking, yeah.
    transaction->pubkeyScript[0] = 0x41; // A public key is 32 bytes X coordinate, 32 bytes Y coordinate and one byte 0x04, so 65 bytes i.e 0x41 in Hex.
    pubkeyScript_len += 1;
    transaction->pubkeyScript[pubkeyScript_len++] = OP_CHECKSIG;

    // Encode timestamp to binary
    transaction->scriptSig = (uint8_t*)malloc(scriptSig_len * sizeof(uint8_t));
    uint32_t scriptSig_pos = 0;


    // This is basically how I believe the size of the nBits is calculated
    if (nBits <= 255)
    {
        transaction->scriptSig[scriptSig_pos++] = 0x01;
        transaction->scriptSig[scriptSig_pos++] = (uint8_t)nBits;
    }
    else if (nBits <= 65535)
    {
        transaction->scriptSig[scriptSig_pos++] = 0x02;
        memcpy(transaction->scriptSig + scriptSig_pos, &nBits, 2);
        scriptSig_pos += 2;
    }
    else if (nBits <= 16777215)
    {
        transaction->scriptSig[scriptSig_pos++] = 0x03;
        memcpy(transaction->scriptSig + scriptSig_pos, &nBits, 3);
        scriptSig_pos += 3;
    }
    else //else if(nBits <= 4294967296LL)
    {
        transaction->scriptSig[scriptSig_pos++] = 0x04;
        memcpy(transaction->scriptSig + scriptSig_pos, &nBits, 4);
        scriptSig_pos += 4;
    }

    // Important! In the Bitcoin code there is a statement 'CBigNum(4)' 
    // i've been wondering for a while what it is but
    // seeing as alt-coins keep it the same, we'll do it here as well
    // It should essentially mean PUSH 1 byte on the stack which in this case is 0x04 or just 4
    transaction->scriptSig[scriptSig_pos++] = 0x01;
    transaction->scriptSig[scriptSig_pos++] = 0x04;

    transaction->scriptSig[scriptSig_pos++] = (uint8_t)scriptSig_len;

    scriptSig_len += scriptSig_pos;
    transaction->scriptSig = (uint8_t*)realloc(transaction->scriptSig, scriptSig_len * sizeof(uint8_t));
    memcpy(transaction->scriptSig + scriptSig_pos, (const unsigned char *)timestamp, timestamp_len);

    // Here we are asuming some values will have the same size
    uint32_t serializedLen =
        4    // tx version
        + 1   // number of inputs
        + 32  // hash of previous output
        + 4   // previous output's index
        + 1   // 1 byte for the size of scriptSig
        + scriptSig_len
        + 4   // size of sequence
        + 1   // number of outputs
        + 8   // 8 bytes for coin value
        + 1   // 1 byte to represent size of the pubkey Script
        + pubkeyScript_len
        + 4;   // 4 bytes for lock time

               // Now let's serialize the data
    uint32_t serializedData_pos = 0;
    transaction->serializedData = (uint8_t*)malloc(serializedLen * sizeof(uint8_t));
    memcpy(transaction->serializedData + serializedData_pos, &transaction->version, 4);
    serializedData_pos += 4;
    memcpy(transaction->serializedData + serializedData_pos, &transaction->numInputs, 1);
    serializedData_pos += 1;
    memcpy(transaction->serializedData + serializedData_pos, transaction->prevOutput, 32);
    serializedData_pos += 32;
    memcpy(transaction->serializedData + serializedData_pos, &transaction->prevoutIndex, 4);
    serializedData_pos += 4;
    memcpy(transaction->serializedData + serializedData_pos, &scriptSig_len, 1);
    serializedData_pos += 1;
    memcpy(transaction->serializedData + serializedData_pos, transaction->scriptSig, scriptSig_len);
    serializedData_pos += scriptSig_len;
    memcpy(transaction->serializedData + serializedData_pos, &transaction->sequence, 4);
    serializedData_pos += 4;
    memcpy(transaction->serializedData + serializedData_pos, &transaction->numOutputs, 1);
    serializedData_pos += 1;
    memcpy(transaction->serializedData + serializedData_pos, &transaction->outValue, 8);
    serializedData_pos += 8;
    memcpy(transaction->serializedData + serializedData_pos, &pubkeyScript_len, 1);
    serializedData_pos += 1;
    memcpy(transaction->serializedData + serializedData_pos, transaction->pubkeyScript, pubkeyScript_len);
    serializedData_pos += pubkeyScript_len;
    memcpy(transaction->serializedData + serializedData_pos, &transaction->locktime, 4);
    serializedData_pos += 4;

    // Now that the data is serialized
    // we hash it with SHA256 and then hash that result to get merkle hash
    SHA256(transaction->serializedData, serializedLen, hash1);
    SHA256(hash1, 32, hash2);

    // This copy isn't necessary imo, but here for clarity
    memcpy(transaction->merkleHash, hash2, 32);

    char *merkleHash = bin2hex(transaction->merkleHash, 32);
    byteswap(transaction->merkleHash, 32);
    char *merkleHashSwapped = bin2hex(transaction->merkleHash, 32);
    char *txScriptSig = bin2hex(transaction->scriptSig, scriptSig_len);
    char *pubScriptSig = bin2hex(transaction->pubkeyScript, pubkeyScript_len);
    printf("\nCoinbase: %s\n\nPubkeyScript: %s\n\nMerkle Hash: %s\nByteswapped: %s\n", txScriptSig, pubScriptSig, merkleHash, merkleHashSwapped);

    //if(generateBlock)
    {
        printf("Generating block...\n");
        if (!unixtime)
        {
            unixtime = time(NULL);
        }

        unsigned char block_header[80], block_hash1[32], block_hash2[32];
        uint32_t blockversion = 1;
        memcpy(block_header, &blockversion, 4);
        memset(block_header + 4, 0, 32);
        byteswap(transaction->merkleHash, 32); // We swapped it before, so do it again now.
        memcpy(block_header + 36, transaction->merkleHash, 32);
        memcpy(block_header + 68, &unixtime, 4);
        memcpy(block_header + 72, &nBits, 4);
        memcpy(block_header + 76, &startNonce, 4);

        uint32_t *pNonce = (uint32_t *)(block_header + 76);
        uint32_t *pUnixtime = (uint32_t *)(block_header + 68);
        unsigned int counter = 0, start = time(NULL);
        while (1)
        {
            SHA256(block_header, 80, block_hash1);
            SHA256(block_hash1, 32, block_hash2);

            unsigned int check = *((uint32_t *)(block_hash2 + 28)); // The hash is in little-endian, so we check the last 4 bytes.
            if (check == 0) // \x00\x00\x00\x00
            {
                byteswap(block_hash2, 32);
                char *blockHash = bin2hex(block_hash2, 32);
                printf("\nBlock found!\nHash: %s\nNonce: %u\nUnix time: %u", blockHash, startNonce, unixtime);
                free(blockHash);
                break;
            }

            startNonce++;
            counter += 1;
            if (time(NULL) - start >= 1)
            {
                printf("\r%d Hashes/s, Nonce %u\r", counter, startNonce);
                counter = 0;
                start = time(NULL);
            }
            *pNonce = startNonce;
            if (startNonce > 4294967294LL)
            {
                //printf("\nBlock found!\nHash: %s\nNonce: %u\nUnix time: %u", blockHash, startNonce, unixtime);
                unixtime++;
                *pUnixtime = unixtime;
                startNonce = 0;
            }
        }
    }

    // Lots of cleanup
    free(merkleHash);
    free(merkleHashSwapped);
    free(txScriptSig);
    free(pubScriptSig);
    free(transaction->serializedData);
    free(transaction->scriptSig);
    free(transaction->pubkeyScript);
    free(transaction);

    getchar();
    return 0;
}

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