#include "guf_common.h"
#include "guf_alloc_libc.h"
#include "guf_str.h"

/*
    - Part 1: 1191 (Example: 3)
        - modular arithmetic

    - Part 2: 6858 (Example: 6)
        - modular arithmetic and integer division 
        - note the special case for handling left turns when the dial is at zero.
        - took me two tries to figure out %)
*/

guf_allocator g_allocator; 
guf_libc_alloc_ctx g_allocator_ctx;

int solution(guf_str_view input, bool part_two)
{
    guf_str_view linebreak_delim = GUF_CSTR_LIT_TO_VIEW("\n"); 
    guf_str_tok_state tokenizer = guf_str_tok_state_new(input, &linebreak_delim, 1, GUF_STR_TOK_DELIM_OPT_MATCH_LONGEST); 

    const int DIAL_SIZE = 100; // 0 to 99
    int cur_dial_pos = 50; 
    int num_zeroes_encountered = 0;

    while (guf_str_tok_next(&tokenizer, false)) { // For each line. 
        guf_str_view line = guf_str_view_trim_left_ascii(tokenizer.cur_tok);
        if (line.len < 2) {
            continue;
        }
        const int dir = line.str[0] == 'L' ? -1 : 1;
        line = guf_str_view_substr(line, 1, line.len - 1); 
        const int num_clicks = guf_str_view_read_uint(&line);

        if (!part_two) { // Part 1:
            cur_dial_pos = ( DIAL_SIZE + ((cur_dial_pos + dir * num_clicks) % DIAL_SIZE) ) % DIAL_SIZE;
            if (cur_dial_pos == 0) {
                ++num_zeroes_encountered;
            }
        } else { // Part 2:
             int passed_zeroes = 0;
            if (dir == -1) { // Left (counter-clockwise) turn 
                passed_zeroes = (DIAL_SIZE - cur_dial_pos + num_clicks) / DIAL_SIZE;
                if (cur_dial_pos == 0 && passed_zeroes > 0 && num_clicks > 0) { // Special case for left turns: Don't count twice if the current position is zero. 
                    passed_zeroes -= 1;
                }
            } else { // Right (clockwise) turn
                passed_zeroes = (cur_dial_pos + num_clicks) / DIAL_SIZE;
            }
            num_zeroes_encountered += passed_zeroes;
            cur_dial_pos = ( DIAL_SIZE + ((cur_dial_pos + dir * num_clicks) % DIAL_SIZE) ) % DIAL_SIZE; // Same as in part one
        }
    }

    return num_zeroes_encountered;
}

int main(int argc, const char **argv)
{
    g_allocator_ctx.zero_init = false;
    guf_alloc_tracker_init(&g_allocator_ctx.tracker, 1, "Day-1 heap allocator", NULL, stderr); 
    guf_libc_allocator_init(&g_allocator, &g_allocator_ctx);

    if (argc < 2) {
        printf("No input file given.\n"); 
        return EXIT_FAILURE;
    }

    guf_str input_str = GUF_STR_UNINITIALISED;
    guf_str_init_empty(&input_str, &g_allocator);
    guf_str_append_file(&input_str, argv[1]);

    const int p1_result = solution(guf_str_view_from_str(&input_str), false);
    printf("Part one: %d\n", p1_result);
    const int p2_result = solution(guf_str_view_from_str(&input_str), true);
    printf("Part two: %d\n", p2_result);

    guf_str_free(&input_str, NULL);

    return EXIT_SUCCESS;
}