/*
 * todo - a little modal todo list.
 *
 * Author:  hachem <im@hachem.wtf>
 * Version: 0.1.0
 */

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <termios.h>
#include <unistd.h>

#define todo_program "todo"
#define todo_version "0.1.0"

#define max_items 4096
#define max_text  256

struct Item
{
    int done;
    char text[max_text];
};

struct List
{
    struct Item items[max_items];
    int count;
};

enum Mode
{
    mode_normal
};

static const char* mode_name(enum Mode mode)
{
    switch (mode)
    {
        case mode_normal: return "NORMAL";
    }

    return "?";
}

static void todo_path(char* buf, size_t size)
{
    const char* env = getenv("TODO_FILE");

    if (env != NULL && env[0] != '\0')
    {
        (void) snprintf(buf, size, "%s", env);
        return;
    }

    const char* home = getenv("HOME");

    (void) snprintf(buf, size, "%s/.todo.txt", home != NULL ? home : ".");
}

static void strip_newline(char* s)
{
    size_t len = strlen(s);

    while (len > 0 && (s[len - 1] == '\n' || s[len - 1] == '\r'))
        s[--len] = '\0';
}

/* read the list file. each line is "[ ] text" or "[x] text"; anything else is
 * treated as an undone item so hand-edited files still load. */
static void load(struct List* list, const char* path)
{
    list->count = 0;

    FILE* file = fopen(path, "r");

    if (file == NULL)
        return;

    char line[max_text + 8];

    while (list->count < max_items && fgets(line, sizeof line, file) != NULL)
    {
        strip_newline(line);

        int done = 0;
        char* text = line;

        if (line[0] == '[' && line[1] != '\0' && line[2] == ']')
        {
            done = line[1] == 'x' || line[1] == 'X';
            text = line + 3;

            while (*text == ' ')
                text++;
        }

        if (*text == '\0')
            continue;

        struct Item* item = &list->items[list->count++];
        item->done = done;
        (void) snprintf(item->text, sizeof item->text, "%s", text);
    }

    (void) fclose(file);
}

static void save(const struct List* list, const char* path)
{
    FILE* file = fopen(path, "w");

    if (file == NULL)
        return;

    for (int i = 0; i < list->count; i++)
        (void) fprintf(file, "[%c] %s\n", list->items[i].done ? 'x' : ' ', list->items[i].text);

    (void) fclose(file);
}

static struct termios saved_termios;

static void restore_terminal(void)
{
    (void) tcsetattr(STDIN_FILENO, TCSAFLUSH, &saved_termios);
    (void) write(STDOUT_FILENO, "\x1b[?25h\x1b[?1049l", 14);
}

static void on_signal(int signum)
{
    (void) signum;
    exit(EXIT_SUCCESS);
}

static int enter_raw_mode(void)
{
    if (!isatty(STDIN_FILENO))
    {
        (void) fprintf(stderr, "%s: not a terminal\n", todo_program);
        return -1;
    }

    if (tcgetattr(STDIN_FILENO, &saved_termios) != 0)
        return -1;

    struct termios raw = saved_termios;
    raw.c_lflag &= ~((tcflag_t) (ICANON | ECHO | ISIG));
    raw.c_cc[VMIN] = 1;
    raw.c_cc[VTIME] = 0;

    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &raw) != 0)
        return -1;

    (void) atexit(restore_terminal);
    (void) signal(SIGINT, on_signal);
    (void) signal(SIGTERM, on_signal);

    (void) write(STDOUT_FILENO, "\x1b[?1049h\x1b[?25l", 14);

    return 0;
}

static int screen_rows(void)
{
    struct winsize ws;

    if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) == 0 && ws.ws_row > 0)
        return ws.ws_row;

    return 24;
}

static void render(const struct List* list, int cursor, int scroll, enum Mode mode)
{
    int rows = screen_rows();
    int visible = rows - 1;

    if (visible < 1)
        visible = 1;

    char buf[64 * 1024];
    int n = 0;

    n += snprintf(buf + n, sizeof buf - (size_t) n, "\x1b[H");

    for (int row = 0; row < visible; row++)
    {
        int i = scroll + row;

        if (i >= list->count)
        {
            n += snprintf(buf + n, sizeof buf - (size_t) n, "\x1b[K\r\n");
            continue;
        }

        const struct Item* item = &list->items[i];
        const char* highlight = i == cursor ? "\x1b[7m" : "";
        const char* box = item->done ? "\x1b[32m[x]\x1b[0m" : "[ ]";
        const char* dim = item->done ? "\x1b[2m" : "";

        n += snprintf(buf + n, sizeof buf - (size_t) n,
                      "%s %s %s%s\x1b[0m\x1b[K\r\n", highlight, box, dim, item->text);
    }

    int done = 0;

    for (int i = 0; i < list->count; i++)
        done += list->items[i].done;

    n += snprintf(buf + n, sizeof buf - (size_t) n,
                  "\x1b[2m-- %s --  %d/%d done\x1b[0m\x1b[K\x1b[J", mode_name(mode), done, list->count);

    (void) write(STDOUT_FILENO, buf, (size_t) n);
}

static int normal_key(struct List* list, const char* path, int* cursor, char c)
{
    switch (c)
    {
        case 'q':
            return 0;

        case 'j':
            (*cursor)++;
            break;

        case 'k':
            (*cursor)--;
            break;

        case ' ':
        case 'x':
            if (*cursor >= 0 && *cursor < list->count)
            {
                list->items[*cursor].done = !list->items[*cursor].done;
                save(list, path);
            }

            break;

        default:
            break;
    }

    return 1;
}

static void run(struct List* list, const char* path)
{
    if (enter_raw_mode() != 0)
        exit(EXIT_FAILURE);

    enum Mode mode = mode_normal;
    int cursor = 0;
    int scroll = 0;

    for (;;)
    {
        int visible = screen_rows() - 1;

        if (visible < 1)
            visible = 1;

        if (cursor >= list->count)
            cursor = list->count - 1;

        if (cursor < 0)
            cursor = 0;

        if (cursor < scroll)
            scroll = cursor;

        if (cursor >= scroll + visible)
            scroll = cursor - visible + 1;

        render(list, cursor, scroll, mode);

        char c;

        if (read(STDIN_FILENO, &c, 1) != 1)
            break;

        int keep = 1;

        switch (mode)
        {
            case mode_normal:
                keep = normal_key(list, path, &cursor, c);
                break;
        }

        if (!keep)
            break;
    }
}

int main(void)
{
    char path[4096];
    todo_path(path, sizeof path);

    struct List* list = malloc(sizeof *list);

    if (list == NULL)
    {
        (void) fprintf(stderr, "%s: out of memory\n", todo_program);
        return EXIT_FAILURE;
    }

    load(list, path);
    run(list, path);
    free(list);

    return EXIT_SUCCESS;
}