package no.eliashaugsbakk.kompilator.tokenization;

import static java.lang.Character.isLetterOrDigit;
import static no.eliashaugsbakk.kompilator.tokenization.LexerState.IN_STRING;
import static no.eliashaugsbakk.kompilator.tokenization.LexerState.IN_TYPE;
import static no.eliashaugsbakk.kompilator.tokenization.LexerState.IN_WORD;
import static no.eliashaugsbakk.kompilator.tokenization.LexerState.NORMAL;
import static no.eliashaugsbakk.kompilator.tokenization.TokenType.ASSIGN;
import static no.eliashaugsbakk.kompilator.tokenization.TokenType.EOF;
import static no.eliashaugsbakk.kompilator.tokenization.TokenType.IDENTIFIER;
import static no.eliashaugsbakk.kompilator.tokenization.TokenType.KEYWORD;
import static no.eliashaugsbakk.kompilator.tokenization.TokenType.LPAREN;
import static no.eliashaugsbakk.kompilator.tokenization.TokenType.RPAREN;
import static no.eliashaugsbakk.kompilator.tokenization.TokenType.SEMICOLON;
import static no.eliashaugsbakk.kompilator.tokenization.TokenType.STRING;
import static no.eliashaugsbakk.kompilator.tokenization.TokenType.TYPE;
import static no.eliashaugsbakk.kompilator.tokenization.TokenType.TYPE_DECLARATION;

import java.util.ArrayList;
import java.util.List;

public class Lexer {
  private char current;
  private int line = 1;
  private int column = 0;

  private final String input;
  private int position = 0;
  private final List<Token> tokens = new ArrayList<>();
  private final StringBuilder wordBuffer = new StringBuilder();
  LexerState state = NORMAL;


  public Lexer(String input) {
    this.input = input;
    this.current = input.charAt(position);
  }

  public List<Token> tokenize() {

    while (position < input.length()) {
      if (current == '\n') {
        line++;
        column = 0;
      } else {
        column++;
      }

      current = input.charAt(position);
      if (!Character.isWhitespace(current)) {

        if (state == IN_WORD) {
          inWord();
        } else if (state == IN_STRING) {
          inString();
        } else if (state == IN_TYPE) {
          inType();
        }

        if (state == NORMAL) {
          normal();
        }
      }
      position++;
    }
    tokens.add(new Token(EOF, "End of File", line, column));
    // tokens.forEach(token -> IO.println(token.type().toString() + ": " + token.value()));
    return tokens;
  }

  private void normal() {
    if (current == '"') {
      state = IN_STRING;
    } else if (isLetterOrDigit(current)) {
      state = IN_WORD;
      wordBuffer.append(current);

    } else if (current == ':') {
      tokens.add(new Token(TYPE_DECLARATION, ":", line, column));
      state = IN_TYPE;

    } else if (current == '=') {
      tokens.add(new Token(ASSIGN, "=", line, column));
    } else if (current == '(') {
      tokens.add(new Token(LPAREN, Character.toString(current), line, column));
    } else if (current == ')') {
      tokens.add(new Token(RPAREN, Character.toString(current), line, column));
    } else if (current == ';') {
      tokens.add(new Token(SEMICOLON, Character.toString(current), line, column));
    }
  }

  private void inType() {
    if (current == '=' || current == ';') {
      state = NORMAL;
      tokens.add(new Token(TYPE, wordBuffer.toString(), line, column - wordBuffer.length()));
      clearWordBuffer();
    } else {
      wordBuffer.append(current);
    }
  }

  private void inString() {
    if (current == '"') {
      position++; // skip closing "
      current = input.charAt(position);
      state = NORMAL;
      tokens.add(new Token(STRING, wordBuffer.toString(), line, column));
      wordBuffer.delete(0, wordBuffer.length());
    } else {
      wordBuffer.append(current);
    }
  }

  private void inWord() {
    if (!isLetterOrDigit(current) && current != '_') {
      state = NORMAL;
      characterizeWord();
    } else {
      wordBuffer.append(current);
    }

  }

  private void characterizeWord() {
    if (Keywords.KEYWORDS.contains(wordBuffer.toString())) {
      tokens.add(new Token(KEYWORD, wordBuffer.toString(), line, column - wordBuffer.length()));
    } else {
      tokens.add(new Token(IDENTIFIER, wordBuffer.toString(), line, column - wordBuffer.length()));
    }
    clearWordBuffer();
  }

  private void clearWordBuffer() {
    wordBuffer.delete(0, wordBuffer.length());
  }
}