#include <stdexcept>

#include "hex.h"

static void hex_encode(char c, char out[2]);
static inline char hex_decode(char nibble1, char nibble2);


std::string hex_encode(const char* in, size_t in_size) {
    std::string out;

    out.reserve(in_size * 2);
    for (size_t i = 0; i < in_size; i++) {
        char encoded[2];
        hex_encode(in[i], encoded);
        out.append(encoded, 2);
    }

    return out;
}

std::string percent_encode(std::string_view in) {
    std::string out;
    char encoded[2];
    size_t pos = 0;
    size_t last_pos = 0;

    out.reserve(in.size());
    while ((pos = in.find_first_not_of("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789", pos)) != std::string::npos) {
        out.append(in, last_pos, pos - last_pos);
        hex_encode(in[pos], encoded);
        out += '%';
        out.append(encoded, 2);
        pos++;
        last_pos = pos;
    }

    if (in.size() > last_pos) {
        out.append(in, last_pos);
    }

    return out;
}

std::vector<char> hex_decode(std::string_view in) {
    if (in.size() % 2 != 0) {
        throw std::invalid_argument("hex_decode(): hex string with an odd size passed");
    }
    std::vector<char> out;

    out.reserve(in.size() / 2);
    for (size_t i = 0; i < in.size(); i += 2) {
        out.push_back(hex_decode(in[i], in[i + 1]));
    }

    return out;
}


static void hex_encode(char c, char out[2]) {
    char nibble1 = (c >> 4) & 0xF;
    char nibble2 = c & 0xF;

    auto hex_encode = [](char nibble) {
        return static_cast<char>(nibble < 10
            ? '0' + nibble
            : 'A' + nibble - 10);
    };
    out[0] = hex_encode(nibble1);
    out[1] = hex_encode(nibble2);
}

static inline char hex_decode(char nibble1, char nibble2) {
    auto hex_decode = [](char nibble) {
        if (nibble >= '0' && nibble <= '9') return nibble - '0';
        if (nibble >= 'a' && nibble <= 'f') return nibble - 'a' + 10;
        if (nibble >= 'A' && nibble <= 'F') return nibble - 'A' + 10;
        throw std::invalid_argument("hex_decode(): invalid nibble");
    };

    return static_cast<char>((hex_decode(nibble1) << 4) | hex_decode(nibble2));
}