/** Includes */
#define _DEFAULT_SOURCE
#define _BSD_SOURCE
#define _GNU_SOURCE

#include <ctype.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <termios.h>
#include <unistd.h>

/** defines */
#define TYREL_VERSION "0.0.1"
#define CTRL_KEY(k) ((k) & 0x1f)

enum editorKey {
    ARROW_LEFT = 1000,
    ARROW_RIGHT,
    ARROW_UP,
    ARROW_DOWN,
    DEL_KEY,
    HOME_KEY,
    END_KEY,
    PAGE_UP,
    PAGE_DOWN
};


/** data */
typedef struct erow {
    int size;
    char *chars;
} erow;

struct editorConfig {
    int cx, cy;
    int screenrows;
    int screencols;
    int numrows;
    erow *row;
    struct termios orig_termios;
};
struct editorConfig E;

/** terminal */
void die(const char *s) {
    write(STDOUT_FILENO, "\x1b[2J", 4);
    write(STDOUT_FILENO, "\x1b[H", 3);

    perror(s);
    exit(1);
}

void disableRawMode() {
    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &E.orig_termios) == -1) {
        die("tcsetattr");
    }
}

void enableRawMode() {
    if (tcgetattr(STDIN_FILENO, &E.orig_termios) == -1) die("tcgetattr");

    atexit(disableRawMode);

    struct termios raw = E.orig_termios;
    raw.c_iflag &= ~(BRKINT | ICRNL | INPCK | ISTRIP | IXON);
    raw.c_oflag &= ~(OPOST);
    raw.c_cflag |= (CS8);
    raw.c_lflag &= ~(ECHO | ICANON | IEXTEN | ISIG);
    raw.c_cc[VMIN] = 0;
    raw.c_cc[VTIME] = 1;
    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &raw) == -1) die("tcsetattr");
}

int editorReadKey() {
    int nread;
    char c;
    while ((nread = read(STDIN_FILENO, &c, 1)) != 1) {
        if (nread == -1 && errno != EAGAIN) die("read");
    }

    if (c == '\x1b') {
        char seq[3];
        if (read(STDIN_FILENO, &seq[0], 1) != 1) return '\x1b';
        if (read(STDIN_FILENO, &seq[1], 1) != 1) return '\x1b';
        if (seq[0] == '[') {
            if (seq[1] >= '0' && seq[1] <= '9') {
                if (read(STDIN_FILENO, &seq[2], 1) != 1) return '\x1b';
                if (seq[2] == '~') {
                    switch (seq[1]) {
                        case '1':
                            return HOME_KEY;
                        case '3':
                            return DEL_KEY;
                        case '4':
                            return END_KEY;
                        case '5':
                            return PAGE_UP;
                        case '6':
                            return PAGE_DOWN;
                        case '7':
                            return HOME_KEY;
                        case '8':
                            return END_KEY;
                    }
                }
            } else {
                switch (seq[1]) {
                    case 'A':
                        return ARROW_UP;
                    case 'B':
                        return ARROW_DOWN;
                    case 'C':
                        return ARROW_RIGHT;
                    case 'D':
                        return ARROW_LEFT;
                    case 'H':
                        return HOME_KEY;
                    case 'F':
                        return END_KEY;
                }
            }
        } else if (seq[0] == 'O') {
            switch (seq[1]) {
                case 'H':
                    return HOME_KEY;
                case 'F':
                    return END_KEY;
            }
        }
        return '\x1b';
    } else {
        return c;
    }
}

int getCursorPosition(int *rows, int *cols) {
    char buf[32];
    unsigned int i = 0;
    if (write(STDOUT_FILENO, "\x1b[6n", 4) != 4) return -1;

    while (i < sizeof(buf) - 1) {
        if (read(STDIN_FILENO, &buf[i], 1) != 1) break;
        if (buf[i] == 'R') break;
        i++;
    }
    buf[i] = '\0'; //assign null to final byte
    if (buf[0] != '\x1b' || buf[1] != '[') return -1;
    if (sscanf(&buf[2], "%d;%d", rows, cols) != 2) return -1;
    return 0;
}

int getWindowSize(int *rows, int *cols) {
    struct winsize ws;
    if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) == -1 || ws.ws_col == 0) {
        if (write(STDOUT_FILENO, "\x1b[999C\x1b[999B", 12) != 12) return -1;
        return getCursorPosition(rows, cols);
    } else {
        *cols = ws.ws_col;
        *rows = ws.ws_row;
        return 0;
    }
}
/** Row operations */
void editorAppendRow(char *s, size_t len) {
    E.row = realloc(E.row, sizeof(erow) * (E.numrows+1));
    int at = E.numrows;
    E.row[at].size = len;
    E.row[at].chars = malloc(len+1);
    memcpy(E.row[at].chars, s, len);
    E.row[at].chars[len] = '\0';
    E.numrows++;
}

/** file i/o */

void editorOpen(char *filename) {
    FILE *fp = fopen(filename, "r");
    if (!fp) die("fopen");

    char *line = NULL;
    size_t linecap = 0;
    ssize_t linelen;
    linelen = getline(&line, &linecap, fp);
    while((linelen = getline(&line, &linecap, fp)) != -1) {
        while (linelen > 0 && (line[linelen - 1] == '\n' ||
                               line[linelen - 1] == '\r'))
            linelen--;
        editorAppendRow(line, linelen);
    }
    free(line);
    fclose(fp);
}



/** append buffer */
struct abuf {
    char *b;
    int len;
};
#define ABUF_INIT {NULL, 0}

void abAppend(struct abuf *ab, const char *s, int len) {
    char *new = realloc(ab->b, ab->len + len);

    if (new == NULL) return;
    memcpy(&new[ab->len], s, len);
    ab->b = new;
    ab->len += len;
}

void abFree(struct abuf *ab) {
    free(ab->b);
}


/** output */
void editorDrawRows(struct abuf *ab) {
    int y;
    for (y = 0; y < E.screenrows; y++) {
        if (y >= E.numrows) { // Draw rows after buffer
            if (E.numrows == 0 && y == E.screenrows / 3) {
                char welcome[80];
                int welcomelen = snprintf(welcome, sizeof welcome, "Tyrel Editor -- version %s", TYREL_VERSION);
                int padding = (E.screencols - welcomelen) / 2;
                if (padding) {
                    abAppend(ab, "~", 1);
                    padding--;
                }
                while (padding--) abAppend(ab, " ", 1);
                if (welcomelen > E.screencols) welcomelen = E.screencols;
                abAppend(ab, welcome, welcomelen);
            } else {
                abAppend(ab, "~", 1);
            }
        } else { // draw buffer
            int len = E.row[y].size;
            if (len > E.screencols) len = E.screencols; // truncate if further than columns
            abAppend(ab, E.row[y].chars, len);
        }

        abAppend(ab, "\x1b[K", 3);
        if (y < E.screenrows - 1) {
            abAppend(ab, "\r\n", 2);
        }
    }
}

void editorRefreshScreen() {
    struct abuf ab = ABUF_INIT;
    abAppend(&ab, "\x1b[?25l", 6);
    abAppend(&ab, "\x1b[H", 3); // Cursor Position home
    editorDrawRows(&ab);

    char buf[32];
    snprintf(buf, sizeof(buf), "\x1b[%d;%dH", E.cy + 1, E.cx + 1);
    abAppend(&ab, buf, strlen(buf));
    abAppend(&ab, "\x1b[?25h", 6);

    write(STDOUT_FILENO, ab.b, ab.len);
    abFree(&ab);
}


/** input */
void editorMoveCursor(int key) {
    switch (key) {
        case ARROW_LEFT:
            if (E.cx != 0) {
                E.cx--;
            }
            break;
        case ARROW_RIGHT:
            if (E.cx != E.screencols - 1) {
                E.cx++;
            }
            break;
        case ARROW_UP:
            if (E.cy != 0) {
                E.cy--;
            }
            break;
        case ARROW_DOWN:
            if (E.cy != E.screenrows - 1) {
                E.cy++;
            }
            break;
    }
}

void editorProcessKeypress() {
    int c = editorReadKey();
    switch (c) {
        case CTRL_KEY('q'):
            write(STDOUT_FILENO, "\x1b[2J", 4);
            write(STDOUT_FILENO, "\x1b[H", 3);
            exit(0);
            break;

        case HOME_KEY:
            E.cx = 0;
            break;

        case END_KEY:
            E.cx = E.screencols - 1;
            break;

        case PAGE_UP:
        case PAGE_DOWN: {
            int times = E.screenrows;
            while (times--)
                editorMoveCursor(c == PAGE_UP ? ARROW_UP : ARROW_DOWN);
        }
            break;
        case ARROW_UP:
        case ARROW_DOWN:
        case ARROW_LEFT:
        case ARROW_RIGHT:
            editorMoveCursor(c);
            break;
    }
}

/** init */
void initEditor() {
    E.cx = 0;
    E.cy = 0;
    E.numrows = 0;
    E.row = NULL;
    if (getWindowSize(&E.screenrows, &E.screencols) == -1) die("getWindowSize");
}

int main(int argc, char *argv[]) {
    enableRawMode();
    initEditor();
    if (argc >= 2) {
        editorOpen(argv[1]);
    }

    while (1) {
        editorRefreshScreen();
        editorProcessKeypress();
    }
    return 0;
}