package pins25.phase;

import java.io.*;

import pins25.common.*;

/**
 * Leksikalni analizator.
 */
public class LexAn implements AutoCloseable {

    /**
     * Izvorna datoteka.
     */
    private final Reader srcFile;

    /**
     * Ustvari nov leksikalni analizator.
     *
     * @param srcFileName Ime izvorne datoteke.
     */
    public LexAn(final String srcFileName) {
        try {
            srcFile = new BufferedReader(new InputStreamReader(new FileInputStream(new File(srcFileName))));
            nextChar(); // Pripravi prvi znak izvorne datoteke (glej {@link nextChar}).
        } catch (FileNotFoundException __) {
            throw new Report.Error("Source file '" + srcFileName + "' not found.");
        }
    }

    @Override
    public void close() {
        try {
            srcFile.close();
        } catch (IOException __) {
            throw new Report.Error("Cannot close source file.");
        }
    }

    /**
     * Trenutni znak izvorne datoteke (glej {@link nextChar}).
     */
    private int buffChar = -2;

    /**
     * Vrstica trenutnega znaka izvorne datoteke (glej {@link nextChar}).
     */
    private int buffCharLine = 0;

    /**
     * Stolpec trenutnega znaka izvorne datoteke (glej {@link nextChar}).
     */
    private int buffCharColumn = 0;

    /**
     * Prebere naslednji znak izvorne datoteke.
     * <p>
     * Izvorno datoteko beremo znak po znak. Trenutni znak izvorne datoteke je
     * shranjen v spremenljivki {@link buffChar}, vrstica in stolpec trenutnega
     * znaka izvorne datoteke sta shranjena v spremenljivkah {@link buffCharLine} in
     * {@link buffCharColumn}.
     * <p>
     * Zacetne vrednosti {@link buffChar}, {@link buffCharLine} in
     * {@link buffCharColumn} so {@code '\n'}, {@code 0} in {@code 0}: branje prvega
     * znaka izvorne datoteke bo na osnovi vrednosti {@code '\n'} spremenljivke
     * {@link buffChar} prvemu znaku izvorne datoteke priredilo vrstico 1 in stolpec
     * 1.
     * <p>
     * Pri branju izvorne datoteke se predpostavlja, da je v spremenljivki
     * {@link buffChar} ves "cas veljaven znak. Zunaj metode {@link nextChar} so vse
     * spremenljivke {@link buffChar}, {@link buffCharLine} in
     * {@link buffCharColumn} namenjene le branju.
     * <p>
     * Vrednost {@code -1} v spremenljivki {@link buffChar} pomeni konec datoteke
     * (vrednosti spremenljivk {@link buffCharLine} in {@link buffCharColumn} pa
     * nista ve"c veljavni).
     */
    private void nextChar() {
        try {
            switch (buffChar) {
                case -2: // Noben znak "se ni bil prebran.
                    buffChar = srcFile.read();
                    buffCharLine = buffChar == -1 ? 0 : 1;
                    buffCharColumn = buffChar == -1 ? 0 : 1;
                    return;
                case -1: // Konec datoteke je bil ze viden.
                    return;
                case '\n': // Prejsnji znak je koncal vrstico, zacne se nova vrstica.
                    buffChar = srcFile.read();
                    buffCharLine = buffChar == -1 ? buffCharLine : buffCharLine + 1;
                    buffCharColumn = buffChar == -1 ? buffCharColumn : 1;
                    return;
                case '\t': // Prejsnji znak je tabulator, ta znak je morda potisnjen v desno.
                    buffChar = srcFile.read();
                    while (buffCharColumn % 4 != 0)
                        buffCharColumn += 1;
                    buffCharColumn += 1;
                    return;
                default: // Prejsnji znak je brez posebnosti.
                    buffChar = srcFile.read();
                    buffCharColumn += 1;
            }
        } catch (IOException __) {
            throw new Report.Error("Cannot read source file.");
        }
    }

    private Report.Location currentLocation() {
        return new Report.Location(buffCharLine, buffCharColumn);
    }

    /**
     * Trenutni leksikalni simbol.
     * <p>
     * "Ce vrednost spremenljivke {@code buffToken} ni {@code null}, je simbol "ze
     * prebran iz vhodne datoteke, ni pa "se predan naprej sintaksnemu analizatorju.
     * Ta simbol je dostopen z metodama {@link peekToken} in {@link takeToken}.
     */
    private Token buffToken = null;

    /**
     * Prebere naslednji leksikalni simbol, ki je nato dostopen preko metod
     * {@link peekToken} in {@link takeToken}.
     */
    private void nextToken() {
        while (buffChar == ' ' || buffChar == '\n' || buffChar == '\t' || buffChar == '\r') {
            nextChar();
        }

        Report.Location start = currentLocation();
        switch (buffChar) {
            case -1: // EOF
                buffToken = new Token(start, Token.Symbol.EOF, "EOF");
                return;

            case '\'':
                charConst();
                return;

            case '"':
                stringConst();
                return;

            case '=':
                nextChar();
                if (buffChar == '=') {
                    buffToken = new Token(
                            new Report.Location(start, currentLocation()),
                            Token.Symbol.EQU,
                            "=="
                    );
                    nextChar();
                    return;
                }

                buffToken = new Token(start, Token.Symbol.ASSIGN, "=");
                return;

            case ',':
                buffToken = new Token(currentLocation(), Token.Symbol.COMMA, ",");
                nextChar();
                return;

            case '&':
                nextChar();
                if (buffChar != '&') {
                    throw new Report.Error(currentLocation(), "Invalid character '" + (char) buffChar + "'");
                }
                buffToken = new Token(new Report.Location(start, currentLocation()), Token.Symbol.AND, "&&");
                nextChar();
                return;

            case '|':
                nextChar();
                if (buffChar != '|') {
                    throw new Report.Error(currentLocation(), "Invalid character '" + (char) buffChar + "'");
                }
                buffToken = new Token(new Report.Location(start, currentLocation()), Token.Symbol.OR, "||");
                nextChar();
                return;

            case '!':
                nextChar();
                if (buffChar == '=') {
                    buffToken = new Token(
                            new Report.Location(start, currentLocation()),
                            Token.Symbol.NEQ,
                            "!="
                    );
                    nextChar();
                    return;
                }

                buffToken = new Token(start, Token.Symbol.NOT, "!");
                return;

            case '>':
                nextChar();
                if (buffChar == '=') {
                    buffToken = new Token(
                            new Report.Location(start, currentLocation()),
                            Token.Symbol.GEQ,
                            ">="
                    );
                    nextChar();
                    return;
                }

                buffToken = new Token(start, Token.Symbol.GTH, ">");
                return;

            case '<':
                nextChar();
                if (buffChar == '=') {
                    buffToken = new Token(
                            new Report.Location(start, currentLocation()),
                            Token.Symbol.LEQ,
                            "<="
                    );
                    nextChar();
                    return;
                }

                buffToken = new Token(start, Token.Symbol.LTH, "<");
                return;

            case '+':
                buffToken = new Token(currentLocation(), Token.Symbol.ADD, "+");
                nextChar();
                return;

            case '-':
                buffToken = new Token(currentLocation(), Token.Symbol.SUB, "-");
                nextChar();
                return;

            case '*':
                buffToken = new Token(currentLocation(), Token.Symbol.MUL, "*");
                nextChar();
                return;

            case '/':
                start = currentLocation();
                nextChar();
                if (buffChar != '/') {
                    buffToken = new Token(start, Token.Symbol.DIV, "/");
                    return;
                }

                while (buffChar != '\n' && buffChar != -1) {
                    nextChar();
                }

                nextToken();
                return;

            case '%':
                buffToken = new Token(currentLocation(), Token.Symbol.MOD, "%");
                nextChar();
                return;

            case '^':
                buffToken = new Token(currentLocation(), Token.Symbol.PTR, "^");
                nextChar();
                return;

            case '(':
                buffToken = new Token(currentLocation(), Token.Symbol.LPAREN, "(");
                nextChar();
                return;

            case ')':
                buffToken = new Token(currentLocation(), Token.Symbol.RPAREN, ")");
                nextChar();
                return;
        }

        if (isNumeric()) {
            intConst();
            return;
        }
        if (isAlpha()) {
            identifier();
            return;
        }

        throw new Report.Error(currentLocation(), "Unrecognized character '" + (char) buffChar + "'.");
    }

    private boolean isNumeric() {
        return buffChar >= '0' && buffChar <= '9';
    }

    private boolean isChar() {
        return buffChar >= ' ' && buffChar <= '~';
    }

    private boolean isHex() {
        return buffChar >= '0' && buffChar <= '9' || buffChar >= 'a' && buffChar <= 'f';
    }

    private boolean isAlpha() {
        return buffChar >= 'a' && buffChar <= 'z' || buffChar >= 'A' && buffChar <= 'Z' || buffChar == '_';
    }

    private boolean isAlphaNumeric() {
        return buffChar >= 'a' && buffChar <= 'z' || buffChar >= 'A' && buffChar <= 'Z' || buffChar >= '0' && buffChar <= '9' || buffChar == '_';
    }

    private Token.Symbol getReservedWordSymbol(String word) {
        return switch (word) {
            case "fun" -> Token.Symbol.FUN;
            case "var" -> Token.Symbol.VAR;
            case "if" -> Token.Symbol.IF;
            case "then" -> Token.Symbol.THEN;
            case "else" -> Token.Symbol.ELSE;
            case "while" -> Token.Symbol.WHILE;
            case "do" -> Token.Symbol.DO;
            case "let" -> Token.Symbol.LET;
            case "in" -> Token.Symbol.IN;
            case "end" -> Token.Symbol.END;
            case "__LINE__" -> Token.Symbol.LINE;
            default -> null;
        };
    }

    private void intConst() {
        Report.Location startLocation = currentLocation();
        Report.Location endLocation = currentLocation();
        StringBuilder lexeme = new StringBuilder();

        if (buffChar == '0') {
            lexeme.append((char) buffChar);
            nextChar();
            if (isNumeric()) {
                throw new Report.Error(startLocation, "Leading zero is not allowed.");
            }
        } else {
            while (isNumeric()) {
                lexeme.append((char) buffChar);
                endLocation = currentLocation();
                nextChar();
            }
        }

        buffToken = new Token(
                new Report.Location(startLocation, endLocation),
                Token.Symbol.INTCONST,
                lexeme.toString()
        );
    }

    private void charConst() {
        Report.Location startLocation = currentLocation();
        StringBuilder lexeme = new StringBuilder();

        lexeme.append((char) buffChar);
        nextChar();

        if (!isChar()) {
            throw new Report.Error(startLocation, "Invalid character '" + (char) buffChar + "'.");
        }

        lexeme.append((char) buffChar);
        if (buffChar == '\\') {
            nextChar();
            lexeme.append((char) buffChar);
            if (buffChar == 'n' || buffChar == '\\' || buffChar == '\'') {

            } else if (isHex()) {
                nextChar();
                lexeme.append((char) buffChar);
                if (!isHex()) {
                    throw new Report.Error(currentLocation(), "Invalid ascii code '" + (char) buffChar + "'.");
                }
            } else {
                throw new Report.Error(currentLocation(), "Invalid escaped character '" + (char) buffChar + "'.");
            }
        }

        nextChar();
        if (buffChar != '\'') {
            throw new Report.Error(new Report.Location(startLocation, currentLocation()), "Invalid character '" + (char) buffChar + "'.");
        }
        lexeme.append((char) buffChar);

        buffToken = new Token(
                new Report.Location(startLocation, currentLocation()),
                Token.Symbol.CHARCONST,
                lexeme.toString()
        );

        nextChar();
    }

    private void stringConst() {
        Report.Location startLocation = currentLocation();
        StringBuilder lexeme = new StringBuilder();

        lexeme.append((char) buffChar);
        nextChar();

        while (buffChar != '"') {
            if (buffChar == '\n' || buffChar == -1) {
                throw new Report.Error(currentLocation(), "Unterminated string.");
            }

            if (buffChar == '\\') {
                lexeme.append((char) buffChar);
                nextChar();
                if (buffChar == 'n' || buffChar == '\\' || buffChar == '"') {
                } else if (isHex()) {
                    lexeme.append((char) buffChar);
                    nextChar();
                    if (!isHex()) {
                        throw new Report.Error(currentLocation(), "Invalid ascii code '" + (char) buffChar + "'.");
                    }
                } else {
                    throw new Report.Error(currentLocation(), "Invalid escaped character '" + (char) buffChar + "'.");
                }
            } else if (!isChar()) {
                throw new Report.Error(currentLocation(), "Invalid character '" + (char) buffChar + "'.");
            }

            lexeme.append((char) buffChar);
            nextChar();
        }

        lexeme.append((char) buffChar);
        buffToken = new Token(
                new Report.Location(startLocation, currentLocation()),
                Token.Symbol.STRINGCONST,
                lexeme.toString()
        );

        nextChar();
    }

    private void identifier() {
        Report.Location startLocation = currentLocation();
        Report.Location endLocation = currentLocation();
        StringBuilder lexeme = new StringBuilder();

        while (isAlphaNumeric()) {
            lexeme.append((char) buffChar);
            endLocation = currentLocation();
            nextChar();
        }

        Token.Symbol symbol = getReservedWordSymbol(lexeme.toString());
        if (symbol == null) {
            symbol = Token.Symbol.IDENTIFIER;
        }

        if (symbol == Token.Symbol.LINE) {
            buffToken = new Token(
                    new Report.Location(startLocation, endLocation),
                    Token.Symbol.INTCONST,
                    Integer.toString(startLocation.begLine())
            );
            return;
        }

        buffToken = new Token(
                new Report.Location(startLocation, endLocation),
                symbol,
                lexeme.toString()
        );
    }

    /**
     * Vrne trenutni leksikalni simbol, ki ostane v lastnistvu leksikalnega
     * analizatorja.
     *
     * @return Leksikalni simbol.
     */
    public Token peekToken() {
        if (buffToken == null)
            nextToken();
        return buffToken;
    }

    /**
     * Vrne trenutni leksikalni simbol, ki preide v lastnistvo klicoce kode.
     *
     * @return Leksikalni simbol.
     */
    public Token takeToken() {
        if (buffToken == null)
            nextToken();
        final Token thisToken = buffToken;
        buffToken = null;
        return thisToken;
    }

// --- ZAGON ---

    /**
     * Zagon leksikalnega analizatorja kot samostojnega programa.
     *
     * @param cmdLineArgs Argumenti v ukazni vrstici.
     */
    public static void main(final String[] cmdLineArgs) {
        System.out.println("This is PINS'25 compiler (lexical analysis):");

        try {
            if (cmdLineArgs.length == 0)
                throw new Report.Error("No source file specified in the command line.");
            if (cmdLineArgs.length > 1)
                Report.warning("Unused arguments in the command line.");

            try (LexAn lexAn = new LexAn(cmdLineArgs[0])) {
                while (lexAn.peekToken().symbol() != Token.Symbol.EOF)
                    System.out.println(lexAn.takeToken());
                System.out.println(lexAn.takeToken());
            }

            // Upajmo, da kdaj pridemo to te tocke.
            // A zavedajmo se sledecega:
            // 1. Prevod je zaradi napak v programu lahko napacen :-o
            // 2. Izvorni program se zdalec ni tisto, kar je programer hotel, da bi bil ;-)
            Report.info("Done.");
        } catch (Report.Error error) {
            // Izpis opisa napake.
            System.err.println(error.getMessage());
            System.exit(1);
        }
    }

}