#include <cmath>
#include <cctype>

#include "cs_std.hh"

namespace cscript {

static inline char const *p_skip_white(char const *beg, char const *end) {
    while ((beg != end) && isspace(*beg)) {
        ++beg;
    }
    return beg;
}

static inline void p_set_end(
    char const *nbeg, char const *nend, std::string_view *end
) {
    if (!end) {
        return;
    }
    *end = std::string_view{nbeg, nend};
}
/* this function assumes the input is definitely a hex digit */
static inline cs_int p_hexd_to_int(char c) {
    if (c >= 97) { /* a-f */
        return (c - 'a') + 10;
    } else if (c >= 65) { /* A-F */
        return (c - 'A') + 10;
    }
    /* 0-9 */
    return c - '0';
}

static inline bool p_check_neg(char const *&input) {
    bool neg = (*input == '-');
    if (neg || (*input == '+')) {
        ++input;
    }
    return neg;
}

cs_int parse_int(std::string_view input, std::string_view *endstr) {
    char const *beg = input.begin();
    char const *end = input.end();
    char const *orig = beg;
    beg = p_skip_white(beg, end);
    if (beg == end) {
        p_set_end(orig, end, endstr);
        return cs_int(0);
    }
    bool neg = p_check_neg(beg);
    cs_int ret = 0;
    char const *past = beg;
    if ((end - beg) >= 2) {
        std::string_view pfx = std::string_view{beg, 2};
        if ((pfx == "0x") || (pfx == "0X")) {
            beg += 2;
            past = beg;
            while ((past != end) && std::isxdigit(*past)) {
                ret = ret * 16 + p_hexd_to_int(*past++);
            }
            goto done;
        } else if ((pfx == "0b") || (pfx == "0B")) {
            beg += 2;
            past = beg;
            while ((past != end) && ((*past == '0') || (*past == '1'))) {
                ret = ret * 2 + (*past++ - '0');
            }
            goto done;
        }
    }
    while ((past != end) && std::isdigit(*past)) {
        ret = ret * 10 + (*past++ - '0');
    }
done:
    p_set_end((past == beg) ? orig : past, end, endstr);
    if (neg) {
        return -ret;
    }
    return ret;
}

template<bool Hex, char e1 = Hex ? 'p' : 'e', char e2 = Hex ? 'P' : 'E'>
static inline bool p_read_exp(char const *&beg, char const *end, cs_int &fn) {
    if (beg == end) {
        return true;
    }
    if ((*beg != e1) && (*beg != e2)) {
        return true;
    }
    if (++beg == end) {
        return false;
    }
    bool neg = p_check_neg(beg);
    if ((beg == end) || !std::isdigit(*beg)) {
        return false;
    }
    cs_int exp = 0;
    while ((beg != end) && std::isdigit(*beg)) {
        exp = exp * 10 + (*beg++ - '0');
    }
    if (neg) {
        exp = -exp;
    }
    fn += exp;
    return true;
}

template<bool Hex>
static inline bool parse_gen_float(
    char const *&beg, char const *end, std::string_view *endstr, cs_float &ret
) {
    auto read_digits = [&beg, end](double r, cs_int &n) {
        while (
            (beg != end) &&
            (Hex ? std::isxdigit(*beg) : std::isdigit(*beg))
        ) {
            if (Hex) {
                r = r * 16.0 + double(p_hexd_to_int(*beg));
            } else {
                r = r * 10.0 + double(*beg - '0');
            }
            ++n;
            ++beg;
        }
        return r;
    };
    cs_int wn = 0, fn = 0;
    double r = read_digits(0.0, wn);
    if ((beg != end) && (*beg == '.')) {
        ++beg;
        r = read_digits(r, fn);
    }
    if (!wn && !fn) {
        return false;
    }
    fn = -fn;
    p_set_end(beg, end, endstr); /* we have a valid number until here */
    if (p_read_exp<Hex>(beg, end, fn)) {
        p_set_end(beg, end, endstr);
    }
    if (Hex) {
        ret = cs_float(ldexp(r, fn * 4));
    } else {
        ret = cs_float(r * pow(10, fn));
    }
    return true;
}

cs_float parse_float(std::string_view input, std::string_view *endstr) {
    char const *beg = input.begin();
    char const *end = input.end();
    char const *orig = beg;
    beg = p_skip_white(beg, end);
    if (beg == end) {
        p_set_end(orig, end, endstr);
        return cs_float(0);
    }
    bool neg = p_check_neg(beg);
    cs_float ret = cs_float(0);
    if ((end - beg) >= 2) {
        std::string_view pfx = std::string_view{beg, 2};
        if ((pfx == "0x") || (pfx == "0X")) {
            beg += 2;
            if (!parse_gen_float<true>(beg, end, endstr, ret)) {
                p_set_end(orig, end, endstr);
                return ret;
            }
            goto done;
        }
    }
    if (!parse_gen_float<false>(beg, end, endstr, ret)) {
        p_set_end(orig, end, endstr);
        return ret;
    }
done:
    if (neg) {
        return -ret;
    }
    return ret;
}

} /* namespace cscript */