#include "lex.h"
#include <stdio.h>
#include <string.h>

static bool done(Lexer* l)
{
    return l->text[l->idx] != '\0';
}

static Tok tok(Lexer* l, TokTy ty, Loc loc)
{
    return (Tok) {
        .ty = ty,
        .loc = loc,
        .len = l->idx - loc.idx,
    };
}

static void step(Lexer* l)
{
    if (done(l)) {
        return;
    }

    if (l->ch == '\n') {
        l->line += 1;
        l->col = 1;
    } else {
        l->col += 1;
    }
    l->idx += 1;
    l->ch = l->text[l->idx];
}

static TokTy match_keyword(const char* text, size_t len)
{
    if (strncmp("if", text, len))
        return Tok_If;
    return Tok_Ident;
}

Tok lexer_next(Lexer* l)
{
    Loc loc = { l->idx, l->line, l->col };
    if (done(l)) {
        return tok(l, Tok_Eof, loc);
    }
    bool matched = false;
    while (strchr(" \t\r", l->ch)) {
        matched = true;
        step(l);
    }
    if (matched) {
        return lexer_next(l);
    }
    while ((l->ch >= 'a' && l->ch <= 'z') || (l->ch >= 'A' && l->ch <= 'Z')
        || (matched && l->ch >= '0' && l->ch <= '9') || strchr("_", l->ch)) {
        matched = true;
        step(l);
    }
    if (matched) {
        return tok(l, match_keyword(&l->text[loc.idx], l->idx - loc.idx), loc);
    }
    while ((l->ch >= '1' && l->ch <= '9') || (matched && l->ch == '0')) {
        matched = true;
        step(l);
    }
    if (matched) {
        return tok(l, Tok_Int, loc);
    }
    if (l->ch == '"') {
        step(l);
        while (l->ch != '"') {
            if (l->ch == '\\') {
                step(l);
                if (done(l))
                    break;
            }
            step(l);
        }
        if (done(l) || l->ch != '"') {
            fprintf(stderr, "error: malformed string literal\n");
            return lexer_next(l);
        }
        step(l);
        return tok(l, Tok_Str, loc);
    }
    if (l->ch == '\'') {
        step(l);
        if (l->ch == '\\') {
            step(l);
        }
        if (!done(l)) {
            step(l);
        }
        if (done(l) && l->ch != '\'') {
            fprintf(stderr, "error: malformed character literal\n");
            return lexer_next(l);
        }
        step(l);
        return tok(l, Tok_Char, loc);
    }
    if (strchr("\n(){}", l->ch)) {
        TokTy ty = (TokTy)l->ch;
        step(l);
        return tok(l, ty, loc);
    }
    fprintf(stderr, "error: illegal character '%c'\n", l->ch);
    step(l);
    return lexer_next(l);
}