#include "fgc/Hash.h"

#include <cstdio>
#include <fstream>
#include <sstream>
#include <stdexcept>

namespace fgc {

namespace {
constexpr uint64_t kOffsetBasis = 0xcbf29ce484222325ULL;
constexpr uint64_t kPrime       = 0x00000100000001b3ULL;
}  // namespace

uint64_t fnv1a64(const std::string& data) {
    uint64_t h = kOffsetBasis;
    for (unsigned char c : data) {
        h ^= c;
        h *= kPrime;
    }
    return h;
}

std::string hashLabel(uint64_t digest) {
    char buf[32];
    std::snprintf(buf, sizeof(buf), "fnv1a64:%016llx", static_cast<unsigned long long>(digest));
    return buf;
}

uint64_t fnv1a64File(const std::string& path) {
    // Binary: the digest must not depend on how the platform treats line endings,
    // or a file copied between machines would look changed when it is not.
    std::ifstream in(path, std::ios::binary);
    if (!in) throw std::runtime_error("cannot read file for hashing: " + path);
    std::ostringstream ss;
    ss << in.rdbuf();
    return fnv1a64(ss.str());
}

}  // namespace fgc