#include <stdbool.h>
#include <stdio.h>

#include "lexer.h"

struct Token token;

//------------------------------------------------------------------------------

// position of current character ch
static struct TokenPos curr = {
    1,
    0,
};

static int ch;

static int
nextCh(void)
{
    ++curr.col;
    ch = getchar();
    if (ch == '\n') {
        ++curr.line;
        curr.col = 0;
    }
    return ch;
}

static bool
isWhiteSpace(int ch)
{
    return ch == ' ' || ch == '\t';
}

static bool
isDecDigit(int ch)
{
    return ch >= '0' && ch <= '9';
}

static bool
isOctDigit(int ch)
{
    return ch >= '0' && ch <= '7';
}

static bool
isHexDigit(int ch)
{
    return isDecDigit(ch) || (ch >= 'a' && ch <= 'f') ||
           (ch >= 'A' && ch <= 'F');
}

static bool
isLetter(int ch)
{
    return ((ch >= 'a') && (ch <= 'z')) || ((ch >= 'A' && ch <= 'Z')) ||
           ch == '_';
}

enum TokenKind
getToken(void)
{
    unsigned long long val = 0;

    // init ch, skip white spaces and newlines
    while (ch == 0 || isWhiteSpace(ch) || ch == '\n') {
        nextCh();
    }

    token.pos.line = curr.line;
    token.pos.col = curr.col;

    clearStr(&token.val);

    if (ch == EOF) {
        return token.kind = EOI;
    } else if (isDecDigit(ch)) {
        // parse literal
        if (ch == '0') {
            appendCharToStr(&token.val, ch);
            nextCh();
            if (ch == 'x') {
                appendCharToStr(&token.val, ch);
                nextCh();
                if (isHexDigit(ch)) {
                    while (isHexDigit(ch)) {
                        appendCharToStr(&token.val, ch);
                        nextCh();
                    }
                    return token.kind = HEX_LITERAL;
                }
                return token.kind = BAD_TOKEN;
            }
            while (isOctDigit(ch)) {
                appendCharToStr(&token.val, ch);
                nextCh();
            }
            return token.kind = OCT_LITERAL;
        } else if (isDecDigit(ch)) {
            while (isDecDigit(ch)) {
                appendCharToStr(&token.val, ch);
                nextCh();
            }
            return token.kind = DEC_LITERAL;
        }
    } else if (ch == '+') {
        appendCharToStr(&token.val, ch);
        nextCh();
        return token.kind = PLUS;
    } else if (ch == '-') {
        appendCharToStr(&token.val, ch);
        nextCh();
        return token.kind = MINUS;
    } else if (ch == '*') {
        appendCharToStr(&token.val, ch);
        nextCh();
        return token.kind = ASTERISK;
    } else if (ch == '/') {
        appendCharToStr(&token.val, ch);
        nextCh();
        return token.kind = SLASH;
    } else if (ch == '%') {
        appendCharToStr(&token.val, ch);
        nextCh();
        return token.kind = PERCENT;
    } else if (ch == '=') {
        appendCharToStr(&token.val, ch);
        nextCh();
        return token.kind = EQUAL;
    } else if (ch == '(') {
        appendCharToStr(&token.val, ch);
        nextCh();
        return token.kind = LPAREN;
    } else if (ch == ')') {
        appendCharToStr(&token.val, ch);
        nextCh();
        return token.kind = RPAREN;
    } else if (ch == ';') {
        appendCharToStr(&token.val, ch);
        nextCh();
        return token.kind = SEMICOLON;
    } else if (ch == '^') {
        appendCharToStr(&token.val, ch);
        nextCh();
        return token.kind = CARET;
    } else if (isLetter(ch)) {
        do {
            appendCharToStr(&token.val, ch);
            nextCh();
        } while (isLetter(ch) || isDecDigit(ch));
        return token.kind = IDENTIFIER;
    }

    nextCh();
    return token.kind = BAD_TOKEN;
}