#include "libexpr/json-to-value.hh"

#include <cstring>

namespace nix {

static void skipWhitespace(const char*& s) {
  while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') {
    s++;
  }
}

static std::string parseJSONString(const char*& s) {
  std::string res;
  if (*s++ != '"') {
    throw JSONParseError("expected JSON string");
  }
  while (*s != '"') {
    if (*s == 0) {
      throw JSONParseError("got end-of-string in JSON string");
    }
    if (*s == '\\') {
      s++;
      if (*s == '"') {
        res += '"';
      } else if (*s == '\\') {
        res += '\\';
      } else if (*s == '/') {
        res += '/';
      } else if (*s == '/') {
        res += '/';
      } else if (*s == 'b') {
        res += '\b';
      } else if (*s == 'f') {
        res += '\f';
      } else if (*s == 'n') {
        res += '\n';
      } else if (*s == 'r') {
        res += '\r';
      } else if (*s == 't') {
        res += '\t';
      } else if (*s == 'u') {
        throw JSONParseError(
            "\\u characters in JSON strings are currently not supported");
      } else {
        throw JSONParseError("invalid escaped character in JSON string");
      }
      s++;
    } else {
      res += *s++;
    }
  }
  s++;
  return res;
}

static void parseJSON(EvalState& state, const char*& s, Value& v) {
  skipWhitespace(s);

  if (*s == 0) {
    throw JSONParseError("expected JSON value");
  }

  if (*s == '[') {
    s++;
    NixList values;
    values.reserve(128);
    skipWhitespace(s);
    while (true) {
      if (values.empty() && *s == ']') {
        break;
      }
      Value* v2 = state.allocValue();
      parseJSON(state, s, *v2);
      values.push_back(v2);
      skipWhitespace(s);
      if (*s == ']') {
        break;
      }
      if (*s != ',') {
        throw JSONParseError("expected ',' or ']' after JSON array element");
      }
      s++;
    }
    s++;
    state.mkList(v, values.size());
    for (size_t n = 0; n < values.size(); ++n) {
      (*v.list)[n] = values[n];
    }
  }

  else if (*s == '{') {
    s++;
    ValueMap attrs;
    while (true) {
      skipWhitespace(s);
      if (attrs.empty() && *s == '}') {
        break;
      }
      std::string name = parseJSONString(s);
      skipWhitespace(s);
      if (*s != ':') {
        throw JSONParseError("expected ':' in JSON object");
      }
      s++;
      Value* v2 = state.allocValue();
      parseJSON(state, s, *v2);
      attrs[state.symbols.Create(name)] = v2;
      skipWhitespace(s);
      if (*s == '}') {
        break;
      }
      if (*s != ',') {
        throw JSONParseError("expected ',' or '}' after JSON member");
      }
      s++;
    }
    state.mkAttrs(v, attrs.size());
    for (auto& i : attrs) {
      v.attrs->push_back(Attr(i.first, i.second));
    }
    s++;
  }

  else if (*s == '"') {
    mkString(v, parseJSONString(s));
  }

  else if ((isdigit(*s) != 0) || *s == '-' || *s == '.') {
    // Buffer into a std::string first, then use built-in C++ conversions
    std::string tmp_number;
    ValueType number_type = tInt;

    while ((isdigit(*s) != 0) || *s == '-' || *s == '.' || *s == 'e' ||
           *s == 'E') {
      if (*s == '.' || *s == 'e' || *s == 'E') {
        number_type = tFloat;
      }
      tmp_number += *s++;
    }

    try {
      if (number_type == tFloat) {
        mkFloat(v, stod(tmp_number));
      } else {
        mkInt(v, stol(tmp_number));
      }
    } catch (std::invalid_argument& e) {
      throw JSONParseError("invalid JSON number");
    } catch (std::out_of_range& e) {
      throw JSONParseError("out-of-range JSON number");
    }
  }

  else if (strncmp(s, "true", 4) == 0) {
    s += 4;
    mkBool(v, true);
  }

  else if (strncmp(s, "false", 5) == 0) {
    s += 5;
    mkBool(v, false);
  }

  else if (strncmp(s, "null", 4) == 0) {
    s += 4;
    mkNull(v);
  }

  else {
    throw JSONParseError("unrecognised JSON value");
  }
}

void parseJSON(EvalState& state, const std::string& s_, Value& v) {
  const char* s = s_.c_str();
  parseJSON(state, s, v);
  skipWhitespace(s);
  if (*s != 0) {
    throw JSONParseError(
        format("expected end-of-string while parsing JSON value: %1%") % s);
  }
}

}  // namespace nix