package serene.simple;

import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PushbackReader;
import java.util.ArrayList;
import java.util.List;


public class Reader {
    public static Node readNode(PushbackReader inputStream) throws IOException {
        char c = (char) inputStream.read();
        inputStream.unread(c);

        if (c == '(') {
            return readList(inputStream);
        }
        else if (Character.isDigit(c)) {
            return readNumber(inputStream);
        }
        else if (c == ')') {
            throw new IllegalArgumentException("Unmatch paranthesis.");
        }
        else {
            return readSymbol(inputStream);
        }
    }

    public static ListNode<Node> read(InputStream inputStream) throws IOException {
        return read(new PushbackReader(new InputStreamReader(inputStream)));
    }

    public static ListNode<Node> read(PushbackReader inputStream) throws IOException {
        List<Node> nodes = new ArrayList<Node>();

        skipWhiteSpaces(inputStream);

        char c = (char) inputStream.read();
        while ((byte) c != -1) {
            inputStream.unread(c);
            nodes.add(readNode(inputStream));
            skipWhiteSpaces(inputStream);
            c = (char) inputStream.read();
        }

        return ListNode.list(nodes);
    }

    private static Node readList(PushbackReader inputStream) throws IOException {
        char opening = (char) inputStream.read();
        assert opening == '(' : "Lists must start with a '('";

        List<Node> nodes = new ArrayList<Node>();

        do {
            skipWhiteSpaces(inputStream);
            char c = (char) inputStream.read();

            if (c == ')') {
                break;
            } else if ((byte) c == -1) {
                throw new EOFException("EOF reached before closing of list");
            } else {
                inputStream.unread(c);
                nodes.add(readNode(inputStream));
            }
        } while(true);

        return SpecialForm.check(ListNode.list(nodes));
    }

    private static Node readSymbol(PushbackReader inputStream) throws IOException {

      String str = "";

      while (true) {
          int ch = inputStream.read();
          if(isWhiteSpace(ch)) {
              inputStream.unread(ch);
              break;
          };
          str = str + (char) ch;
      }

      return new SymbolNode(str);
    }

    private static Node readNumber(PushbackReader inputStream) throws IOException {

      String number = "";

      while (true) {
          int ch = inputStream.read();
          if(isWhiteSpace(ch)) {
              inputStream.unread(ch);
              break;
          };
          number = number + (char) ch;
      }

      return new NumberNode(Long.parseLong(number, 10));
    }

    private static void skipWhiteSpaces(PushbackReader inputStream) throws IOException {
      int ch = inputStream.read();
      while (isWhiteSpace(ch)) {
        ch = inputStream.read();
      }
      inputStream.unread(ch);
    }

    private static boolean isWhiteSpace(int ch) {
        return (ch == ' ' || ch == '\t' || ch == '\f' || ch == '\r' || ch == '\n');
    }
}