#include "../include/tokenizer.h"
#include <string.h>
#include <stdio.h>

void tsl_tokenizer_init(TslTokenizer *self, const char *code, size_t code_size) {
    self->code = code;
    self->code_size = code_size;
    self->code_index = 0;

    self->identifier.data = NULL;
    self->identifier.size = 0;
    self->bool_value = 0;
    self->number_value = 0;
}

static char tsl_tokenizer_get_char(TslTokenizer *self) {
    if(self->code_index < self->code_size)
        return self->code[self->code_index];
    return '\0';
}

static void tsl_tokenizer_skip_whitespace(TslTokenizer *self) {
    for(;;) {
        char c = tsl_tokenizer_get_char(self);
        switch(c) {
            case ' ':
            case '\n':
            case '\t':
            case '\r':
                ++self->code_index;
                break;
            default:
                return;
        }
    }
}

static int is_alpha(char c) {
    return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
}

static int is_num(char c) {
    return c >= '0' && c <= '9';
}

static int is_identifier_start(char c) {
    return is_alpha(c) || c == '_';
}

static int is_identifier_continue(char c) {
    return is_alpha(c) || is_num(c) || c == '_';
}

const int64_t num_multipliers[] = {
    1,
    10,
    100,
    1000,
    10000,
    100000,
    1000000,
    10000000,
    100000000,
    1000000000,
    10000000000,
    100000000000,
    1000000000000,
    10000000000000,
    100000000000000,
    1000000000000000,
    10000000000000000,
    100000000000000000,
    1000000000000000000
};

/* TODO: Check if the number if too large to fit into the result */
static int64_t string_to_int(TslStringView *str) {
    int64_t num = 0;
    for(size_t i = 0; i < str->size; ++i) {
        char digit = str->data[str->size - 1 - i] - '0';
        num += digit * num_multipliers[i];
    }
    return num;
}

TslToken tsl_tokenizer_next(TslTokenizer *self) {
    char c;
    tsl_tokenizer_skip_whitespace(self);

    c = tsl_tokenizer_get_char(self);
    if(is_identifier_start(c)) {
        size_t identifier_start = self->code_index;
        ++self->code_index;
        for(;;) {
            c = tsl_tokenizer_get_char(self);
            if(!is_identifier_continue(c))
                break;
            ++self->code_index;
        }
        self->identifier.data = self->code + identifier_start;
        self->identifier.size = self->code_index - identifier_start;

        switch(self->identifier.size) {
            case 3: {
                if(memcmp(self->identifier.data, "null", 3) == 0) {
                    return TSL_TOKEN_NULL;
                }
                break;
            }
            case 4: {
                if(memcmp(self->identifier.data, "true", 4) == 0) {
                    self->bool_value = 1;
                    return TSL_TOKEN_BOOL;
                }
                break;
            }
            case 5: {
                if(memcmp(self->identifier.data, "false", 5) == 0) {
                    self->bool_value = 0;
                    return TSL_TOKEN_BOOL;
                }
                break;
            }
        }
        return TSL_TOKEN_IDENTIFIER;
    } else if(is_num(c)) {
        size_t num_start = self->code_index;
        ++self->code_index;
        for(;;) {
            c = tsl_tokenizer_get_char(self);
            if(!is_num(c))
                break;
            ++self->code_index;
        }
        self->identifier.data = self->code + num_start;
        self->identifier.size = self->code_index - num_start;
        self->number_value = string_to_int(&self->identifier);
        return TSL_TOKEN_NUM;
    } else if(c == '=') {
        ++self->code_index;
        return TSL_TOKEN_EQUAL;
    } else if(c == '\0') {
        return TSL_TOKEN_END_OF_FILE;
    } else {
        fprintf(stderr, "Unexpected symbol '%c'\n", c);
        return TSL_TOKEN_UNEXPECTED_SYMBOL;
    }
}