using System;
using System.IO;
using System.Text;

/// <summary>
/// The Scanner for the Z# Compiler.
/// </summary>
public class Scanner
{
    const char EOF = '\u0080';  // return this for end of file
    const char CR = '\r';
    const char LF = '\n';

    // Alphbetically sorted list of the keywords.
    static readonly string[] keywords = {
            "class", "const", "else", "if", "new",
            "read", "return", "void", "while", "write"
    };
    // Token codes in the same order as the keywords.
    static readonly int[] kwCodes = {
            Token.CLASS, Token.CONST, Token.ELSE, Token.IF, Token.NEW,
            Token.READ, Token.RETURN, Token.VOID, Token.WHILE, Token.WRITE
    };

    static TextReader input;

    static char ch;            // lookahead character (= next (unprocessed) character in input stream)
    static int line, col;      // line and column number of ch in input stream

    // Initializes the scanner.
    public static void Init (TextReader r)
    {
        input = r;
        line = 1;
        col = 0;
        // read 1st char into ch, increment col to 1
        NextCh();
    }

    // Reads next character from input stream into ch.
    // Keeps pos, line and col in sync with reading position.
    static void NextCh ()
    {
        // TODO
    }

    // Returns next token.
    // To be used by parser.
    public static Token Next ()
    {
        // TODO

        return null;
    }  // end Next()

    // Error handling for the scanner.
    // Prints error message to System.Console.
    static void Error (string msg)
    {
        Errors.Error(msg, line, col);
    }

    // Reads a name into the Token t.
    static void ReadName (Token t)
    {
        StringBuilder sb = new StringBuilder();
        do {
            sb.Append(ch);
            NextCh();
        } while (IsLetter(ch) || IsDigit(ch) || ch == '_');
        t.str = sb.ToString();
        t.kind = KeywordKind(t.str);
    }

    // Reads a number into the Token t.
    static void ReadNumber (Token t)
    {
        StringBuilder sb = new StringBuilder();
        do {
            sb.Append(ch);
            NextCh();
        } while (IsDigit(ch));
        t.str = sb.ToString();
        t.kind = Token.NUMBER;
        try {
            t.val = Convert.ToInt32(t.str);
        } catch (OverflowException) {
            Error("Number to big: " + t.str);
        }
    }

    // Skips nested multi-line comments.
    static void SkipComment ()
    {
        // TODO
    }

    // if str is a keyword, returns specific keyword token code,
    // otherwise returns ident token code.
    static int KeywordKind (string str)
    {
        int idx = Array.BinarySearch(keywords, str);
        return (idx < 0) ? Token.IDENT : kwCodes[idx];
    }

    static bool IsPrintableChar (char c)
    {
        return ' ' <= c && c <= '~';
    }

    static bool IsLetter (char c)
    {
        return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z');
    }

    static bool IsDigit (char c)
    {
        return '0' <= c && c <= '9';
    }
}