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

#define TODO_PROGRAM "todo"
#define TODO_VERSION "0.1.0"

#define MAX_ITEMS 4096
#define MAX_TEXT  256
#define MAX_COMMAND 64

#define LEFT_MARGIN    2
#define SECTION_INDENT 2
#define SUBTASK_INDENT 4

enum State
{
    STATE_TODO,
    STATE_DOING,
    STATE_DONE
};

struct Item
{
    enum State state;
    char text[MAX_TEXT];
};

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

enum Mode
{
    MODE_NORMAL,
    MODE_INSERT,
    MODE_REPLACE,
    MODE_COMMAND,
    MODE_SEARCH,
    MODE_CONFIRM
};

enum Pending
{
    PENDING_NONE,
    PENDING_RESET,
    PENDING_CLEAR
};

enum Key
{
    KEY_UP = 256,
    KEY_DOWN,
    KEY_LEFT,
    KEY_RIGHT
};

static const char* mode_name(enum Mode mode)
{
    switch (mode)
    {
        case MODE_NORMAL: return "NORMAL";
        case MODE_INSERT: return "INSERT";
        case MODE_REPLACE: return "REPLACE";
        case MODE_COMMAND: return "COMMAND";
        case MODE_SEARCH: return "SEARCH";
        case MODE_CONFIRM: return "CONFIRM";
    }

    return "?";
}

static int is_editing(enum Mode mode)
{
    return mode == MODE_INSERT || mode == MODE_REPLACE;
}

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

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

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

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

static void strip_newline(char* string)
{
    size_t length = strlen(string);

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

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);

        enum State state = STATE_TODO;
        char* text = line;

        if (line[0] == '[' && line[1] != '\0' && line[2] == ']')
        {
            if (line[1] == 'x' || line[1] == 'X')
                state = STATE_DONE;
            else if (line[1] == '-')
                state = STATE_DOING;

            text = line + 3;

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

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

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

    (void) fclose(file);
}

static int is_section(const struct Item* item)
{
    return item->text[0] == '=';
}

static int is_subtask(const struct Item* item)
{
    return item->text[0] == '-';
}

static int is_optional(const struct Item* item)
{
    return item->text[0] == '*';
}

static int task_group(const struct Item* item)
{
    if (item->state == STATE_DONE)
        return 2;

    if (is_optional(item))
        return 1;

    return 0;
}

static int section_level(const struct Item* item)
{
    int level = 0;

    while (item->text[level] == '=')
        level++;

    return level;
}

static void normalize_tasks(struct List* list)
{
    for (int i = 0; i < list->count; i++)
    {
        if (is_section(&list->items[i]) || is_subtask(&list->items[i]))
            continue;

        int total = 0;
        int done = 0;
        int active = 0;

        for (int j = i + 1; j < list->count && is_subtask(&list->items[j]); j++)
        {
            total++;

            if (list->items[j].state == STATE_DONE)
                done++;
            else if (list->items[j].state == STATE_DOING)
                active++;
        }

        if (total == 0)
            continue;

        if (done == total)
            list->items[i].state = STATE_DONE;
        else if (done > 0 || active > 0)
            list->items[i].state = STATE_DOING;
        else
            list->items[i].state = STATE_TODO;
    }
}

static void sort_list(struct List* list)
{
    struct Item* sorted = malloc((size_t) list->count * sizeof *sorted);

    if (sorted == NULL)
        return;

    int out = 0;
    int i = 0;

    while (i < list->count)
    {
        if (is_section(&list->items[i]))
        {
            sorted[out++] = list->items[i];
            i++;
            continue;
        }

        int segment = i;

        while (segment < list->count && !is_section(&list->items[segment]))
            segment++;

        for (int group = 0; group < 3; group++)
        {
            int k = i;

            while (k < segment)
            {
                int block = k + 1;

                while (block < segment && is_subtask(&list->items[block]))
                    block++;

                if (task_group(&list->items[k]) == group)
                {
                    sorted[out++] = list->items[k];

                    for (int sub_pass = 0; sub_pass < 2; sub_pass++)
                        for (int s = k + 1; s < block; s++)
                            if ((list->items[s].state == STATE_DONE) == sub_pass)
                                sorted[out++] = list->items[s];
                }

                k = block;
            }
        }

        i = segment;
    }

    for (int x = 0; x < list->count; x++)
        list->items[x] = sorted[x];

    free(sorted);
}

static int block_end(const struct List* list, int start)
{
    int i = start + 1;

    while (i < list->count && !is_section(&list->items[i]))
        i++;

    return i;
}

static void reverse_items(struct List* list, int low, int high)
{
    while (low < high - 1)
    {
        struct Item moved = list->items[low];
        list->items[low] = list->items[high - 1];
        list->items[high - 1] = moved;
        low++;
        high--;
    }
}

static void save(struct List* list, const char* path)
{
    normalize_tasks(list);

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

    if (file == NULL)
        return;

    for (int i = 0; i < list->count; i++)
    {
        if (is_section(&list->items[i]))
        {
            (void) fprintf(file, "%s\n", list->items[i].text);
            continue;
        }

        char marker = list->items[i].state == STATE_DONE ? 'x'
                    : list->items[i].state == STATE_DOING ? '-'
                                                          : ' ';

        (void) fprintf(file, "[%c] %s\n", marker, list->items[i].text);
    }

    (void) fclose(file);
}

static void commit(struct List* list)
{
    normalize_tasks(list);
    sort_list(list);
}

#define MAX_HISTORY 64

struct Snapshot
{
    struct Item* items;
    int count;
};

static struct Snapshot undo_stack[MAX_HISTORY];
static struct Snapshot redo_stack[MAX_HISTORY];
static int undo_count;
static int redo_count;

static struct Snapshot snapshot_take(const struct List* list)
{
    struct Snapshot snap;
    snap.count = list->count;
    snap.items = malloc((size_t) list->count * sizeof *snap.items);

    if (snap.items != NULL)
        memcpy(snap.items, list->items, (size_t) list->count * sizeof *snap.items);

    return snap;
}

static void snapshot_apply(struct List* list, const struct Snapshot* snap)
{
    list->count = snap->count;
    memcpy(list->items, snap->items, (size_t) snap->count * sizeof *snap->items);
}

static void stack_push(struct Snapshot* stack, int* count, struct Snapshot snap)
{
    if (*count == MAX_HISTORY)
    {
        free(stack[0].items);
        memmove(&stack[0], &stack[1], (size_t) (MAX_HISTORY - 1) * sizeof *stack);
        (*count)--;
    }

    stack[(*count)++] = snap;
}

static void stack_clear(struct Snapshot* stack, int* count)
{
    while (*count > 0)
        free(stack[--(*count)].items);
}

static void history_record(struct List* list)
{
    struct Snapshot snap = snapshot_take(list);

    if (snap.items == NULL)
        return;

    stack_push(undo_stack, &undo_count, snap);
    stack_clear(redo_stack, &redo_count);
}

static void history_undo(struct List* list)
{
    if (undo_count == 0)
        return;

    stack_push(redo_stack, &redo_count, snapshot_take(list));

    struct Snapshot snap = undo_stack[--undo_count];
    snapshot_apply(list, &snap);
    free(snap.items);
}

static void history_redo(struct List* list)
{
    if (redo_count == 0)
        return;

    stack_push(undo_stack, &undo_count, snapshot_take(list));

    struct Snapshot snap = redo_stack[--redo_count];
    snapshot_apply(list, &snap);
    free(snap.items);
}

static void insert_item(struct List* list, int index);

static struct Item yank_register;
static int yank_full;

static enum Pending pending_action;

static char replace_original[MAX_TEXT];
static int replace_start;

static void paste_item(struct List* list, int index, int* cursor)
{
    if (list->count >= MAX_ITEMS || !yank_full)
        return;

    history_record(list);
    insert_item(list, index);

    if (index >= 0 && index < list->count)
    {
        list->items[index] = yank_register;
        *cursor = index;
    }
}

static char lower(char c)
{
    return c >= 'A' && c <= 'Z' ? (char) (c + 32) : c;
}

static int contains_fold(const char* haystack, const char* needle)
{
    if (needle[0] == '\0')
        return 0;

    for (; *haystack != '\0'; haystack++)
    {
        const char* h = haystack;
        const char* n = needle;

        while (*h != '\0' && *n != '\0' && lower(*h) == lower(*n))
        {
            h++;
            n++;
        }

        if (*n == '\0')
            return 1;
    }

    return 0;
}

static int find_match(const struct List* list, int from, int direction, const char* query)
{
    if (list->count == 0 || query[0] == '\0')
        return -1;

    for (int step = 1; step <= list->count; step++)
    {
        int index = ((from + direction * step) % list->count + list->count) % list->count;

        if (contains_fold(list->items[index].text, query))
            return index;
    }

    return -1;
}

static void insert_item(struct List* list, int index)
{
    if (list->count >= MAX_ITEMS)
        return;

    if (index < 0)
        index = 0;

    if (index > list->count)
        index = list->count;

    for (int i = list->count; i > index; i--)
        list->items[i] = list->items[i - 1];

    list->items[index].state = STATE_TODO;
    list->items[index].text[0] = '\0';
    list->count++;
}

static void delete_item(struct List* list, int index)
{
    if (index < 0 || index >= list->count)
        return;

    for (int i = index; i < list->count - 1; i++)
        list->items[i] = list->items[i + 1];

    list->count--;
}


static struct termios saved_termios;

static void restore_terminal(void)
{
    static const char reset[] = "\x1b[?25h\x1b[0 q\x1b[?1049l";

    (void) tcsetattr(STDIN_FILENO, TCSAFLUSH, &saved_termios);
    (void) write(STDOUT_FILENO, reset, sizeof reset - 1);
}

static void on_signal(int signal_number)
{
    (void) signal_number;
    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 window;

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

    return 24;
}

static int content_rows(void)
{
    int rows = screen_rows() - 4;

    return rows < 1 ? 1 : rows;
}

static void to_roman(int number, char* buffer, size_t size)
{
    static const int values[] = { 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 };
    static const char* const symbols[] = { "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I" };

    size_t length = 0;
    buffer[0] = '\0';

    for (int i = 0; i < 13; i++)
        while (number >= values[i] && length + 2 < size)
        {
            length += (size_t) snprintf(buffer + length, size - length, "%s", symbols[i]);
            number -= values[i];
        }
}

static void render(const struct List* list, int cursor, int scroll, enum Mode mode, int edit_pos, const char* command)
{
    int rows = screen_rows();
    int visible = content_rows();

    int total_items = 0;
    int done = 0;

    for (int i = 0; i < list->count; i++)
        if (!is_section(&list->items[i]) && !is_subtask(&list->items[i]))
        {
            total_items++;
            done += list->items[i].state == STATE_DONE;
        }

    int max_run = 0;
    int run = 0;

    for (int i = 0; i < list->count; i++)
    {
        if (is_section(&list->items[i]))
            run = 0;
        else if (!is_subtask(&list->items[i]) && ++run > max_run)
            max_run = run;
    }

    int number_width = 1;

    for (int count = max_run; count >= 10; count /= 10)
        number_width++;

    char date[64];
    char clock[32];
    time_t now = time(NULL);
    struct tm* local = localtime(&now);

    if (local == NULL || strftime(date, sizeof date, "%a %d %b %Y", local) == 0)
        date[0] = '\0';

    if (local == NULL || strftime(clock, sizeof clock, "%H:%M", local) == 0)
        clock[0] = '\0';

    char buffer[64 * 1024];
    int length = 0;

    length += snprintf(buffer + length, sizeof buffer - (size_t) length,
                       "\x1b[H%*s\x1b[2m%s\x1b[0m\x1b[K\r\n%*s\x1b[2m%s\x1b[0m\x1b[K\r\n\x1b[K\r\n",
                       LEFT_MARGIN, "", date, LEFT_MARGIN, "", clock);

    int emitted = 0;
    int index = scroll;
    int prev_group = -1;
    int cursor_row = -1;

    while (emitted < visible && index < list->count)
    {
        const struct Item* item = &list->items[index];

        const char* background       = index == cursor ? "\x1b[48;5;235m" : "";
        const char* background_reset = index == cursor ? "\x1b[49m" : "";

        if (is_section(item))
        {
            if (emitted > 0)
            {
                length += snprintf(buffer + length, sizeof buffer - (size_t) length, "\x1b[K\r\n");
                emitted++;

                if (emitted >= visible)
                    break;
            }

            prev_group = -1;

            if (index == cursor)
                cursor_row = 4 + emitted;

            int level = section_level(item);
            int section_indent = LEFT_MARGIN + (level - 1) * SECTION_INDENT;

            if (is_editing(mode) && index == cursor)
            {
                length += snprintf(buffer + length, sizeof buffer - (size_t) length,
                                   "%s%*s\x1b[1m%s\x1b[22m\x1b[K%s\r\n",
                                   background, section_indent, "", item->text, background_reset);
            }
            else
            {
                int section_number = 0;

                for (int k = index; k >= 0; k--)
                    if (is_section(&list->items[k]))
                    {
                        int other = section_level(&list->items[k]);

                        if (other == level)
                            section_number++;
                        else if (other < level)
                            break;
                    }

                char roman[16];
                to_roman(section_number, roman, sizeof roman);

                if (level >= 2)
                    for (char* letter = roman; *letter != '\0'; letter++)
                        if (*letter >= 'A' && *letter <= 'Z')
                            *letter = (char) (*letter + 32);

                const char* name = item->text + level;

                while (*name == ' ')
                    name++;

                length += snprintf(buffer + length, sizeof buffer - (size_t) length,
                                   "%s%*s\x1b[1m%s. %s\x1b[22m\x1b[K%s\r\n",
                                   background, section_indent, "", roman, name, background_reset);
            }

            emitted++;
            index++;
            continue;
        }

        int heading_level = 0;

        for (int k = index - 1; k >= 0; k--)
            if (is_section(&list->items[k]))
            {
                heading_level = section_level(&list->items[k]);
                break;
            }

        int base_indent = LEFT_MARGIN + heading_level * SECTION_INDENT;

        const char* box              = item->state == STATE_DONE ? "[x]"
                                     : item->state == STATE_DOING ? "[-]"
                                                                  : "[ ]";
        const char* dim              = item->state == STATE_DONE ? "\x1b[2m" : "";
        const char* dim_reset        = item->state == STATE_DONE ? "\x1b[22m" : "";

        if (is_subtask(item))
        {
            int indent = base_indent + number_width + SUBTASK_INDENT;
            const char* name = item->text;

            if (!(is_editing(mode) && index == cursor))
            {
                name = item->text + 1;

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

            if (index == cursor)
                cursor_row = 4 + emitted;

            length += snprintf(buffer + length, sizeof buffer - (size_t) length,
                               "%s%*s%s %s%s%s\x1b[K%s\r\n",
                               background, indent, "", box, dim, name, dim_reset, background_reset);
        }
        else
        {
            int group = task_group(item);

            if (prev_group >= 0 && group != prev_group)
            {
                length += snprintf(buffer + length, sizeof buffer - (size_t) length, "\x1b[K\r\n");
                emitted++;

                if (emitted >= visible)
                    break;
            }

            prev_group = group;

            int number = 0;

            for (int k = index; k >= 0 && !is_section(&list->items[k]); k--)
                if (!is_subtask(&list->items[k]))
                    number++;

            const char* task_box = is_optional(item)
                ? (item->state == STATE_DONE ? "(x)" : item->state == STATE_DOING ? "(-)" : "( )")
                : box;
            const char* name = item->text;

            if (is_optional(item) && !(is_editing(mode) && index == cursor))
            {
                name = item->text + 1;

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

            if (index == cursor)
                cursor_row = 4 + emitted;

            length += snprintf(buffer + length, sizeof buffer - (size_t) length,
                               "%s%*s\x1b[2m%*d.\x1b[22m %s %s%s%s\x1b[K%s\r\n",
                               background, base_indent, "", number_width, number,
                               task_box, dim, name, dim_reset, background_reset);
        }

        emitted++;
        index++;
    }

    while (emitted < visible)
    {
        length += snprintf(buffer + length, sizeof buffer - (size_t) length, "\x1b[K\r\n");
        emitted++;
    }

    if (mode == MODE_COMMAND || mode == MODE_SEARCH)
        length += snprintf(buffer + length, sizeof buffer - (size_t) length,
                           "\x1b[%d;1H%*s%c%s\x1b[K",
                           rows, LEFT_MARGIN, "", mode == MODE_SEARCH ? '/' : ':', command);
    else if (mode == MODE_CONFIRM)
        length += snprintf(buffer + length, sizeof buffer - (size_t) length,
                           "\x1b[%d;1H%*s%s [y/n]\x1b[K",
                           rows, LEFT_MARGIN, "",
                           pending_action == PENDING_CLEAR ? "clear the whole list?" : "reset all items to todo?");
    else
        length += snprintf(buffer + length, sizeof buffer - (size_t) length,
                           "\x1b[%d;1H%*s\x1b[2m[%s]  %d/%d done\x1b[0m\x1b[K",
                           rows, LEFT_MARGIN, "", mode_name(mode), done, total_items);

    if (mode == MODE_COMMAND || mode == MODE_SEARCH)
    {
        int cursor_column = LEFT_MARGIN + 2 + (int) strlen(command);

        length += snprintf(buffer + length, sizeof buffer - (size_t) length,
                           "\x1b[%d;%dH\x1b[6 q\x1b[?25h", rows, cursor_column);
    }
    else if (mode != MODE_CONFIRM && cursor >= 0 && cursor < list->count && cursor_row >= 0)
    {
        int cursor_column;

        if (is_section(&list->items[cursor]))
        {
            int level = section_level(&list->items[cursor]);
            int section_indent = LEFT_MARGIN + (level - 1) * SECTION_INDENT;
            cursor_column = is_editing(mode) ? section_indent + 1 + edit_pos : section_indent + 1;
        }
        else
        {
            int heading_level = 0;

            for (int k = cursor - 1; k >= 0; k--)
                if (is_section(&list->items[k]))
                {
                    heading_level = section_level(&list->items[k]);
                    break;
                }

            int base_indent = LEFT_MARGIN + heading_level * SECTION_INDENT;
            int text_start;

            if (is_subtask(&list->items[cursor]))
                text_start = base_indent + number_width + SUBTASK_INDENT + 5;
            else
                text_start = base_indent + number_width + 7;

            cursor_column = text_start + edit_pos;
        }

        const char* shape = mode == MODE_REPLACE ? "\x1b[4 q"
                          : mode == MODE_INSERT ? "\x1b[6 q"
                                                : "\x1b[2 q";

        length += snprintf(buffer + length, sizeof buffer - (size_t) length,
                           "\x1b[%d;%dH%s\x1b[?25h", cursor_row, cursor_column, shape);
    }
    else
    {
        length += snprintf(buffer + length, sizeof buffer - (size_t) length, "\x1b[?25l");
    }

    (void) write(STDOUT_FILENO, buffer, (size_t) length);
}

static int read_key(void)
{
    static int pending = -1;

    if (pending != -1)
    {
        int key = pending;
        pending = -1;
        return key;
    }

    char character;

    if (read(STDIN_FILENO, &character, 1) != 1)
        return -1;

    if (character != 27)
        return (unsigned char) character;

    /* an escape: peek for an arrow sequence without blocking. a byte that is
     * not part of a sequence is pushed back so a lone escape followed by a
     * command (e.g. :wq) never swallows the following keys. */
    int flags = fcntl(STDIN_FILENO, F_GETFL);
    (void) fcntl(STDIN_FILENO, F_SETFL, flags | O_NONBLOCK);

    char first;

    if (read(STDIN_FILENO, &first, 1) != 1)
    {
        (void) fcntl(STDIN_FILENO, F_SETFL, flags);
        return 27;
    }

    if (first == '[')
    {
        char second;
        ssize_t got = read(STDIN_FILENO, &second, 1);
        (void) fcntl(STDIN_FILENO, F_SETFL, flags);

        if (got == 1)
            switch (second)
            {
                case 'A': return KEY_UP;
                case 'B': return KEY_DOWN;
                case 'C': return KEY_RIGHT;
                case 'D': return KEY_LEFT;
            }

        return 27;
    }

    (void) fcntl(STDIN_FILENO, F_SETFL, flags);
    pending = (unsigned char) first;
    return 27;
}

static int normal_key(struct List* list, int* cursor, enum Mode* mode, int* edit_pos,
                      char* command, const char* search, int count, int key)
{
    switch (key)
    {
        case ':':
            command[0] = '\0';
            *mode = MODE_COMMAND;
            break;

        case '/':
            command[0] = '\0';
            *mode = MODE_SEARCH;
            break;

        case 'n':
        {
            int match = find_match(list, *cursor, 1, search);

            if (match >= 0)
                *cursor = match;

            break;
        }

        case 'N':
        {
            int match = find_match(list, *cursor, -1, search);

            if (match >= 0)
                *cursor = match;

            break;
        }

        case 'y':
        {
            char next;

            if (read(STDIN_FILENO, &next, 1) == 1 && next == 'y'
                && *cursor >= 0 && *cursor < list->count)
            {
                yank_register = list->items[*cursor];
                yank_full = 1;
            }

            break;
        }

        case 'p':
            paste_item(list, *cursor + 1, cursor);
            break;

        case 'P':
            paste_item(list, *cursor, cursor);
            break;

        case 'j':
        case KEY_DOWN:
            *cursor += count;
            break;

        case 'k':
        case KEY_UP:
            *cursor -= count;
            break;

        case 'h':
        case KEY_LEFT:
            *edit_pos -= count;
            break;

        case 'l':
        case KEY_RIGHT:
            *edit_pos += count;
            break;

        case 'w':
            if (*cursor >= 0 && *cursor < list->count)
            {
                const char* text = list->items[*cursor].text;
                int length = (int) strlen(text);
                int position = *edit_pos;

                for (int repeat = 0; repeat < count; repeat++)
                {
                    while (position < length && text[position] != ' ')
                        position++;

                    while (position < length && text[position] == ' ')
                        position++;
                }

                *edit_pos = position;
            }

            break;

        case 'b':
            if (*cursor >= 0 && *cursor < list->count)
            {
                const char* text = list->items[*cursor].text;
                int position = *edit_pos;

                for (int repeat = 0; repeat < count; repeat++)
                {
                    if (position > 0)
                        position--;

                    while (position > 0 && text[position] == ' ')
                        position--;

                    while (position > 0 && text[position - 1] != ' ')
                        position--;
                }

                *edit_pos = position;
            }

            break;

        case 'u':
            history_undo(list);
            break;

        case 18:
            history_redo(list);
            break;

        case ' ':
            if (*cursor >= 0 && *cursor < list->count && !is_section(&list->items[*cursor]))
            {
                history_record(list);
                struct Item* item = &list->items[*cursor];
                item->state = (enum State) ((item->state + 1) % 3);
                commit(list);
            }

            break;

        case 'x':
            if (*cursor >= 0 && *cursor < list->count && !is_section(&list->items[*cursor]))
            {
                history_record(list);
                struct Item* item = &list->items[*cursor];
                item->state = item->state == STATE_DONE ? STATE_TODO : STATE_DONE;
                commit(list);
            }

            break;

        case 'o':
            history_record(list);
            insert_item(list, *cursor + 1);
            *cursor = *cursor + 1 < list->count ? *cursor + 1 : list->count - 1;
            *edit_pos = 0;
            *mode = MODE_INSERT;
            break;

        case 'A':
            history_record(list);

            if (list->count == 0)
            {
                insert_item(list, 0);
                *cursor = 0;
            }

            if (*cursor >= 0 && *cursor < list->count)
            {
                *edit_pos = (int) strlen(list->items[*cursor].text);
                *mode = MODE_INSERT;
            }

            break;

        case 'i':
            if (*cursor >= 0 && *cursor < list->count)
            {
                history_record(list);

                if (is_section(&list->items[*cursor]))
                {
                    int position = 1;

                    while (list->items[*cursor].text[position] == ' ')
                        position++;

                    *edit_pos = position;
                }

                *mode = MODE_INSERT;
            }

            break;

        case 'R':
            history_record(list);

            if (list->count == 0)
            {
                insert_item(list, 0);
                *cursor = 0;
                *edit_pos = 0;
            }

            if (*cursor >= 0 && *cursor < list->count)
            {
                (void) snprintf(replace_original, sizeof replace_original, "%s", list->items[*cursor].text);
                replace_start = *edit_pos;
                *mode = MODE_REPLACE;
            }

            break;

        case 'g':
        {
            char next;

            if (read(STDIN_FILENO, &next, 1) == 1 && next == 'g')
                *cursor = 0;

            break;
        }

        case 'G':
            *cursor = list->count - 1;
            break;

        case '}':
        {
            int next = *cursor + 1;

            while (next < list->count && !is_section(&list->items[next]))
                next++;

            *cursor = next < list->count ? next : list->count - 1;
            break;
        }

        case '{':
        {
            int previous = *cursor - 1;

            while (previous >= 0 && !is_section(&list->items[previous]))
                previous--;

            *cursor = previous >= 0 ? previous : 0;
            break;
        }

        case 'd':
        {
            char next;

            if (read(STDIN_FILENO, &next, 1) == 1 && next == 'd'
                && *cursor >= 0 && *cursor < list->count)
            {
                history_record(list);
                yank_register = list->items[*cursor];
                yank_full = 1;

                for (int repeat = 0; repeat < count && *cursor < list->count; repeat++)
                    delete_item(list, *cursor);

                commit(list);
            }

            break;
        }

        case 'J':
            if (*cursor < 0 || *cursor >= list->count)
                break;

            history_record(list);

            if (is_section(&list->items[*cursor]))
            {
                int start = *cursor;
                int end = block_end(list, start);

                if (end < list->count)
                {
                    int next_end = block_end(list, end);
                    reverse_items(list, start, end);
                    reverse_items(list, end, next_end);
                    reverse_items(list, start, next_end);
                    *cursor = start + (next_end - end);
                }
            }
            else if (*cursor + 1 < list->count && !is_section(&list->items[*cursor + 1]))
            {
                struct Item moved = list->items[*cursor];
                list->items[*cursor] = list->items[*cursor + 1];
                list->items[*cursor + 1] = moved;
                (*cursor)++;
            }

            break;

        case 'K':
            if (*cursor < 0 || *cursor >= list->count)
                break;

            history_record(list);

            if (is_section(&list->items[*cursor]))
            {
                int start = *cursor;

                if (start > 0)
                {
                    int previous = start - 1;

                    while (previous >= 0 && !is_section(&list->items[previous]))
                        previous--;

                    int previous_start = previous >= 0 ? previous : 0;
                    int end = block_end(list, start);
                    reverse_items(list, previous_start, start);
                    reverse_items(list, start, end);
                    reverse_items(list, previous_start, end);
                    *cursor = previous_start;
                }
            }
            else if (*cursor > 0 && !is_section(&list->items[*cursor - 1]))
            {
                struct Item moved = list->items[*cursor];
                list->items[*cursor] = list->items[*cursor - 1];
                list->items[*cursor - 1] = moved;
                (*cursor)--;
            }

            break;

        case 'D':
        {
            history_record(list);
            int kept = 0;

            for (int i = 0; i < list->count; i++)
                if (list->items[i].state != STATE_DONE)
                    list->items[kept++] = list->items[i];

            list->count = kept;
            commit(list);
            break;
        }

        default:
            break;
    }

    return 1;
}

static void insert_key(struct List* list, int* cursor, enum Mode* mode, int* edit_pos, int key)
{
    struct Item* item = &list->items[*cursor];
    size_t length = strlen(item->text);

    if (key == 27 || ((key == '\r' || key == '\n') && item->text[0] == '\0'))
    {
        if (item->text[0] == '\0')
        {
            delete_item(list, *cursor);

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

            if (*cursor < 0)
                *cursor = 0;
        }

        normalize_tasks(list);
        *mode = MODE_NORMAL;
        return;
    }

    if (key == '\r' || key == '\n')
    {
        insert_item(list, *cursor + 1);
        (*cursor)++;
        *edit_pos = 0;
        return;
    }

    if (key == KEY_LEFT)
    {
        if (*edit_pos > 0)
            (*edit_pos)--;

        return;
    }

    if (key == KEY_RIGHT)
    {
        if (*edit_pos < (int) length)
            (*edit_pos)++;

        return;
    }

    if (key == 127 || key == 8)
    {
        if (*mode == MODE_REPLACE)
        {
            if (*edit_pos > replace_start)
            {
                (*edit_pos)--;

                if (*edit_pos < (int) strlen(replace_original))
                    item->text[*edit_pos] = replace_original[*edit_pos];
                else
                    item->text[*edit_pos] = '\0';
            }
        }
        else if (*edit_pos > 0)
        {
            memmove(&item->text[*edit_pos - 1], &item->text[*edit_pos], length - (size_t) *edit_pos + 1);
            (*edit_pos)--;
        }

        return;
    }

    if (key >= 32 && key != 127 && key < 256 && length + 1 < sizeof item->text)
    {
        if (*mode == MODE_REPLACE && *edit_pos < (int) length)
        {
            item->text[*edit_pos] = (char) key;
        }
        else
        {
            memmove(&item->text[*edit_pos + 1], &item->text[*edit_pos], length - (size_t) *edit_pos + 1);
            item->text[*edit_pos] = (char) key;
        }

        (*edit_pos)++;
    }
}

static int command_key(struct List* list, const char* path, enum Mode* mode, char* command, int key)
{
    size_t length = strlen(command);

    if (key == 27)
    {
        command[0] = '\0';
        *mode = MODE_NORMAL;
        return 1;
    }

    if (key == '\r' || key == '\n')
    {
        if (strcmp(command, "reset") == 0 || strcmp(command, "clear") == 0)
        {
            pending_action = strcmp(command, "clear") == 0 ? PENDING_CLEAR : PENDING_RESET;
            command[0] = '\0';
            *mode = MODE_CONFIRM;
            return 1;
        }

        int write = strchr(command, 'w') != NULL || strcmp(command, "x") == 0;
        int quit = strchr(command, 'q') != NULL || strcmp(command, "x") == 0;

        *mode = MODE_NORMAL;

        if (write)
            save(list, path);

        command[0] = '\0';

        if (quit)
            return 0;

        return 1;
    }

    if (key == 127 || key == 8)
    {
        if (length > 0)
            command[length - 1] = '\0';
        else
            *mode = MODE_NORMAL;

        return 1;
    }

    if (key >= 32 && key != 127 && key < 256 && length + 1 < MAX_COMMAND)
    {
        command[length] = (char) key;
        command[length + 1] = '\0';
    }

    return 1;
}

static void search_key(const struct List* list, int* cursor, enum Mode* mode, char* command, char* search, int key)
{
    size_t length = strlen(command);

    if (key == 27)
    {
        command[0] = '\0';
        *mode = MODE_NORMAL;
        return;
    }

    if (key == '\r' || key == '\n')
    {
        (void) snprintf(search, MAX_COMMAND, "%s", command);
        command[0] = '\0';
        *mode = MODE_NORMAL;

        int match = find_match(list, *cursor, 1, search);

        if (match >= 0)
            *cursor = match;

        return;
    }

    if (key == 127 || key == 8)
    {
        if (length > 0)
            command[length - 1] = '\0';
        else
            *mode = MODE_NORMAL;

        return;
    }

    if (key >= 32 && key != 127 && key < 256 && length + 1 < MAX_COMMAND)
    {
        command[length] = (char) key;
        command[length + 1] = '\0';
    }
}

static void confirm_key(struct List* list, enum Mode* mode, int key)
{
    if (key == 'y' || key == 'Y')
    {
        history_record(list);

        if (pending_action == PENDING_RESET)
        {
            for (int i = 0; i < list->count; i++)
                if (!is_section(&list->items[i]))
                    list->items[i].state = STATE_TODO;
        }
        else if (pending_action == PENDING_CLEAR)
        {
            list->count = 0;
        }

        commit(list);
    }

    pending_action = PENDING_NONE;
    *mode = MODE_NORMAL;
}

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

    normalize_tasks(list);
    sort_list(list);

    enum Mode mode = MODE_NORMAL;
    int cursor = 0;
    int scroll = 0;
    int edit_pos = 0;
    int count = 0;
    char command[MAX_COMMAND] = "";
    char search[MAX_COMMAND] = "";

    for (;;)
    {
        int visible = content_rows();

        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;

        if (list->count > 0)
        {
            int text_length = (int) strlen(list->items[cursor].text);
            int caret_max = is_editing(mode) ? text_length : (text_length > 0 ? text_length - 1 : 0);

            if (edit_pos > caret_max)
                edit_pos = caret_max;

            if (edit_pos < 0)
                edit_pos = 0;
        }

        render(list, cursor, scroll, mode, edit_pos, command);

        int key = read_key();

        if (key == -1)
            break;

        switch (mode)
        {
            case MODE_NORMAL:
                if ((key >= '1' && key <= '9') || (key == '0' && count > 0))
                {
                    count = count * 10 + (key - '0');

                    if (count > 9999)
                        count = 9999;

                    break;
                }

                normal_key(list, &cursor, &mode, &edit_pos, command, search, count > 0 ? count : 1, key);
                count = 0;
                break;

            case MODE_INSERT:
            case MODE_REPLACE:
                insert_key(list, &cursor, &mode, &edit_pos, key);
                break;

            case MODE_COMMAND:
                if (command_key(list, path, &mode, command, key) == 0)
                    return;

                break;

            case MODE_SEARCH:
                search_key(list, &cursor, &mode, command, search, key);
                break;

            case MODE_CONFIRM:
                confirm_key(list, &mode, key);
                break;
        }
    }
}

static void print_version(void)
{
    (void) printf("%s %s\n", TODO_PROGRAM, TODO_VERSION);
}

static void print_help(void)
{
    (void) printf(
        "%s %s - a little modal todo list\n"
        "\n"
        "usage: %s              open the list ($TODO_FILE, or ~/.todo.txt)\n"
        "       %s -h | --help\n"
        "       %s -v | --version\n"
        "\n"
        "keys:\n"
        "  h j k l / arrows  move        w / b  words        { / }  sections\n"
        "  gg / G  top/bottom            o  new item         i  insert at cursor\n"
        "  A  append text                R  overtype (replace)   3j 2dd  counts\n"
        "  x  toggle done                space  cycle state\n"
        "  dd  cut item                  D  clear done        yy p P  yank/paste\n"
        "  J / K  move item or section   / n N  search        u  ctrl-r  undo/redo\n"
        "  :w :q :wq :x  write / quit    :reset  all back to todo   :clear  empty\n"
        "\n"
        "items: '=' section, '==' subsection, '-' subtask, '*' optional, else a task.\n"
        "\n"
        "by hachem <im@hachem.wtf>\n",
        TODO_PROGRAM, TODO_VERSION, TODO_PROGRAM, TODO_PROGRAM, TODO_PROGRAM);
}

int main(int argc, char** argv)
{
    if (argc >= 2 && (strcmp(argv[1], "-h") == 0 || strcmp(argv[1], "--help") == 0))
    {
        print_help();
        return EXIT_SUCCESS;
    }

    if (argc >= 2 && (strcmp(argv[1], "-v") == 0 || strcmp(argv[1], "--version") == 0))
    {
        print_version();
        return EXIT_SUCCESS;
    }

    (void) setlocale(LC_ALL, "");

    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;
}