#define _GNU_SOURCE
#include <stdlib.h>
#include <string.h>
#include <inttypes.h>
#include <fcntl.h>
#include <unistd.h>
#include <termios.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <errno.h>

#include <patty/kiss.h>

enum kiss_flags {
    KISS_NONE    = 0,
    KISS_FRAME   = 1 << 0,
    KISS_COMMAND = 1 << 1,
    KISS_ESCAPE  = 1 << 2
};

enum tnc_opts {
    TNC_NONE             = 0,
    TNC_CLOSE_ON_DESTROY = 1 << 0
};

struct _patty_kiss_tnc {
    struct termios attrs,
                   attrs_old;

    int fd,
        opts;

    void *buf,
         *frame;

    size_t bufsz,
           offset,
           dropped;

    ssize_t readlen;
};

static inline ssize_t write_byte(int fd, uint8_t c) {
    return write(fd, &c, sizeof(c));
}

static inline ssize_t write_start(int fd,
                                  enum patty_kiss_command command,
                                  int port) {
    uint8_t start[2] = {
        PATTY_KISS_FEND,
        ((port & 0x0f) << 4) | (command & 0x0f)
    };

    return write(fd, start, sizeof(start));
}

static uint8_t escape_fend[2] = { PATTY_KISS_FESC, PATTY_KISS_TFEND };
static uint8_t escape_fesc[2] = { PATTY_KISS_FESC, PATTY_KISS_TFESC };

ssize_t patty_kiss_frame_send(int fd,
                             const void *buf,
                             size_t len,
                             int port) {
    size_t i, start = 0, end = 0;

    if (write_start(fd, PATTY_KISS_DATA, port) < 0) {
        goto error_io;
    }

    for (i=0; i<len; i++) {
        uint8_t c = ((uint8_t *)buf)[i];
        uint8_t *escape = NULL;

        switch (c) {
            case PATTY_KISS_FEND:
                escape = escape_fend;
                break;

            case PATTY_KISS_FESC:
                escape = escape_fesc;
                break;

            default:
                end = i + 1;

                break;
        }

        if (escape) {
            if (write(fd, ((uint8_t *)buf) + start, end - start) < 0) {
                goto error_io;
            }

            if (write(fd, escape, 2) < 0) {
                goto error_io;
            }

            escape = NULL;
            start  = i + 1;
            end    = start;
        }
    }

    if (end - start) {
        if (write(fd, ((uint8_t *)buf) + start, end - start) < 0) {
            goto error_io;
        }
    }

    if (write_byte(fd, PATTY_KISS_FEND) < 0) {
        goto error_io;
    }

    if (tcdrain(fd) < 0) {
        goto error_io;
    }

    return len;

error_io:
    return -1;
}

patty_kiss_tnc *patty_kiss_tnc_new_fd(int fd) {
    patty_kiss_tnc *tnc;

    if ((tnc = malloc(sizeof(*tnc))) == NULL) {
        goto error_malloc_tnc;
    }

    if ((tnc->buf = malloc(PATTY_KISS_BUFSZ)) == NULL) {
        goto error_malloc_buf;
    }

    if (isatty(fd) && ptsname(fd) == NULL) {
        if (tcgetattr(fd, &tnc->attrs) < 0) {
            goto error_tcgetattr;
        }

        memcpy(&tnc->attrs_old, &tnc->attrs, sizeof(tnc->attrs_old));

        cfmakeraw(&tnc->attrs);

        if (tcsetattr(fd, TCSANOW, &tnc->attrs) < 0) {
            goto error_tcsetattr;
        }
    }

    tnc->fd      =  fd;
    tnc->opts    =  TNC_NONE;
    tnc->bufsz   =  PATTY_KISS_BUFSZ;
    tnc->offset  =  0;
    tnc->dropped =  0;
    tnc->readlen = -1;

    return tnc;

error_tcsetattr:
error_tcgetattr:
error_malloc_buf:
    free(tnc);

error_malloc_tnc:
    return NULL;
}

patty_kiss_tnc *patty_kiss_tnc_new(const char *device) {
    patty_kiss_tnc *tnc;
    int fd;
    struct stat st;

    if (stat(device, &st) < 0) {
        goto error_stat;
    }

    if ((st.st_mode & S_IFMT) == S_IFSOCK) {
        struct sockaddr_un addr;

        if (strlen(device) > sizeof(addr.sun_path)) {
            errno = EOVERFLOW;

            goto error_overflow;
        }

        if ((fd = socket(PF_UNIX, SOCK_STREAM, 0)) < 0) {
            goto error_socket;
        }

        memset(&addr, '\0', sizeof(addr));
        addr.sun_family = AF_UNIX;
        strncpy(addr.sun_path, device, sizeof(addr.sun_path));

        if (connect(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
            goto error_connect;
        }
    } else {
        if ((fd = open(device, O_RDWR)) < 0) {
            goto error_open;
        }
    }

    if ((tnc = patty_kiss_tnc_new_fd(fd)) == NULL) {
        goto error_tnc_new_fd;
    }

    tnc->opts |= TNC_CLOSE_ON_DESTROY;

    return tnc;

error_tnc_new_fd:
error_connect:
    close(fd);

error_socket:
error_overflow:
error_open:
error_stat:
    return NULL;
}

int patty_kiss_tnc_fd(patty_kiss_tnc *tnc) {
    return tnc->fd;
}

void patty_kiss_tnc_destroy(patty_kiss_tnc *tnc) {
    if (isatty(tnc->fd) && ptsname(tnc->fd) == NULL) {
        (void)tcsetattr(tnc->fd, TCSANOW, &tnc->attrs_old);
    }

    if (tnc->opts & TNC_CLOSE_ON_DESTROY) {
        close(tnc->fd);
    }

    free(tnc->buf);
    free(tnc);
}

static void tnc_drop(patty_kiss_tnc *tnc) {
    tnc->offset  =  0;
    tnc->readlen = -1;
    tnc->dropped++;
}

size_t patty_kiss_tnc_dropped(patty_kiss_tnc *tnc) {
    return tnc->dropped;
}

ssize_t patty_kiss_tnc_pending(patty_kiss_tnc *tnc) {
    if (tnc->readlen < 0) {
        return -1;
    }

    if (tnc->offset == 0) {
        return 0;
    }

    return tnc->readlen - tnc->offset;
}

ssize_t patty_kiss_tnc_recv(patty_kiss_tnc *tnc,
                            void *buf,
                            size_t len,
                            int *port) {
    size_t r = 0, /* Number of bytes read */
           w = 0; /* Number of bytes written to buf */

    enum kiss_flags flags = KISS_NONE;

    if (tnc->offset == tnc->readlen) {
        errno = 0;

        return 0;
    }

    while (1) {
        uint8_t c;

        r++;

        if (w == len) {
            tnc_drop(tnc);

            flags &= ~KISS_FRAME;
                w  = 0;
        }

        if (tnc->offset == 0) {
            if ((tnc->readlen = read(tnc->fd, tnc->buf, tnc->bufsz)) < 0) {
                goto error_io;
            } else if (tnc->readlen == 0) {
                if (errno) {
                    goto error_io;
                }

                goto done;
            }
        }

        c = ((uint8_t *)tnc->buf)[tnc->offset++];

        if (tnc->offset == tnc->readlen) {
            tnc->offset = 0;
        }

        if (!(flags & KISS_FRAME)) {
            if (c == PATTY_KISS_FEND) {
                flags |= KISS_FRAME;

                continue;
            } else {
                errno = EIO;

                goto error_io;
            }
        } else {
            if (c == PATTY_KISS_FEND) {
                if (w > 0) {
                    flags &= ~KISS_FRAME;

                    goto done;
                }

                continue;
            }
        }

        if (!(flags & KISS_COMMAND)) {
            if (PATTY_KISS_COMMAND(c) != PATTY_KISS_DATA) {
                errno = EIO;

                goto error_io;
            }

            if (port) {
                *port = PATTY_KISS_COMMAND_PORT(c);
            }

            flags |= KISS_COMMAND;

            continue;
        }

        if (!(flags & KISS_ESCAPE)) {
            if (c == PATTY_KISS_FESC) {
                flags |= KISS_ESCAPE;

                continue;
            }
        } else {
            switch (c) {
                case PATTY_KISS_TFEND:
                    ((uint8_t *)buf)[w++] = PATTY_KISS_FEND;
                    flags &= ~KISS_ESCAPE;
                    continue;

                case PATTY_KISS_TFESC:
                    ((uint8_t *)buf)[w++] = PATTY_KISS_FESC;
                    flags &= ~KISS_ESCAPE;
                    continue;

                default:
                    errno = EIO;

                    goto error_io;
            }
        }

        ((uint8_t *)buf)[w++] = c;
    }

done:
    if (flags & KISS_FRAME) {
        tnc_drop(tnc);

        errno = 0;

        return 0;
    }

    return (ssize_t)w;

error_io:
    return -1;
}

ssize_t patty_kiss_tnc_send(patty_kiss_tnc *tnc,
                            const void *buf,
                            size_t len,
                            int port) {
    return patty_kiss_frame_send(tnc->fd, buf, len, port);
}