#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#include "util.h"

#define ERR_SYS(s)                                                             \
    do {                                                                       \
        perror(s);                                                             \
        exit(1);                                                               \
    } while (0)
#define ERR_EXIT(a)                                                            \
    do {                                                                       \
        fprintf(stderr, a);                                                    \
        fputc('\n', stderr);                                                   \
        exit(1);                                                               \
    } while (0)

#define INPUT_BUFFSIZE MAX_CMD_LEN
#define MAX_ARGC 3

typedef struct child {
    pid_t pid;
    int readfd;
    int writefd;
    struct child *next;
} Child, *ChildList;

typedef struct {
    char status;
    unsigned char number_of_descendents;
} KillMsg;

static unsigned long secret;
static char service_name[MAX_SERVICE_NAME_LEN];

char *inputbuf = NULL;
char buf[INPUT_BUFFSIZE];
size_t inputbufSize = INPUT_BUFFSIZE;
char *input_argv[MAX_ARGC];
ChildList childlist = NULL;
int childcount = 0;

static inline bool is_manager() { return strcmp(service_name, "Manager") == 0; }

void print_not_exist(char *service_name) {
    printf("%s doesn't exist\n", service_name);
}

void print_receive_command(char *service_name, char *cmd) {
    printf("%s has received %s\n", service_name, cmd);
}

void print_spawn(char *parent_name, char *child_name) {
    printf("%s has spawned a new service %s\n", parent_name, child_name);
}

void print_kill(char *target_name, int decendents_num) {
    printf("%s and %d child services are killed\n", target_name,
           decendents_num);
}

void print_acquire_secret(char *service_a, char *service_b,
                          unsigned long secret) {
    printf("%s has acquired a new secret from %s, value: %lu\n", service_a,
           service_b, secret);
}

void print_exchange(char *service_a, char *service_b) {
    printf("%s and %s have exchanged their secrets\n", service_a, service_b);
}

int readInput(int fd);
void check_argc(int _argc, int lowerbound) {
    if (_argc < lowerbound)
        ERR_EXIT("received command arguments are insufficient");
}

void spawn(char *parent, char *child);
void spawn_child(char *child);

void find_kill(char *name);
void let_child_suicide(Child *child);
void terminate();

void exchange(char *service_a, char *service_b, const int found);
void fifoname(char *s, char *from, char *to);

int main(int argc, char *argv[]) {
    pid_t pid = getpid();

    if (argc != 2) {
        fprintf(stderr, "Usage: ./service [service_name]\n");
        return 0;
    }

    srand(pid);
    secret = rand();
    /*
     * prevent buffered I/O
     * equivalent to fflush() after each stdout
     */
    setvbuf(stdout, NULL, _IONBF, 0);
    setvbuf(stderr, NULL, _IONBF, 0);

    strncpy(service_name, argv[1], MAX_SERVICE_NAME_LEN);

    printf("%s has been spawned, pid: %d, secret: %lu\n", service_name, pid,
           secret);

    inputbuf = (char *)malloc(inputbufSize);
    /*
    int parent_read_fd, parent_write_fd;
    if(is_manager()) parent_read_fd=STDIN_FILENO, parent_write_fd=STDOUT_FILENO;
    else parent_read_fd=3, parent_write_fd=4;
    */

    if (!is_manager()) {
        // send spawn msg back to parent
        char c = 1;
        if (write(PARENT_WRITE_FD, &c, 1) != 1)
            ERR_SYS("write error");
    }

    while (1) {
        int input_argc =
            readInput(is_manager() ? STDIN_FILENO : PARENT_READ_FD);
        check_argc(input_argc, 1);

        char *command = input_argv[0];
        if (strcmp(command, "spawn") == 0) {
            check_argc(input_argc, 3);
            sprintf(buf, "spawn %s %s", input_argv[1], input_argv[2]);
            print_receive_command(service_name, buf);
            spawn(input_argv[1], input_argv[2]);
        } else if (strcmp(command, "kill") == 0) {
            check_argc(input_argc, 2);
            sprintf(buf, "kill %s", input_argv[1]);
            print_receive_command(service_name, buf);
            find_kill(input_argv[1]);
        } else if (strcmp(command, "killall") == 0 && !is_manager()) {
            terminate();
        } else if (strcmp(command, "exchange") == 0) {
            check_argc(input_argc, 3);
            sprintf(buf, "exchange %s %s", input_argv[1], input_argv[2]);
            print_receive_command(service_name, buf);
            exchange(input_argv[1], input_argv[2], 0);
        } else if (strcmp(command, "exchange_foundone") == 0 && !is_manager()) {
            check_argc(input_argc, 3);
            sprintf(buf, "exchange %s %s", input_argv[1], input_argv[2]);
            print_receive_command(service_name, buf);
            exchange(input_argv[1], input_argv[2], 1);
        } else
            ERR_EXIT("invalid command");
    }
    return 0;
}

void spawn(char *parent, char *child) {
    if (strcmp(service_name, parent) == 0) {
        spawn_child(child);
        if (is_manager())
            print_spawn(parent, child);
        else {
            char msg = 1;
            if (write(PARENT_WRITE_FD, &msg, 1) != 1)
                ERR_SYS("error telling parent spawn is complete");
        }
    } else {
        Child *p = childlist;
        char msg;
        while (p != NULL) {
            sprintf(buf, "spawn %s %s", parent, child);
            if (write(p->writefd, buf, strlen(buf)) != strlen(buf))
                ERR_SYS("error passing spawn to child");

            // wait for child
            if (read(p->readfd, &msg, 1) != 1)
                ERR_SYS("error receiving spawn status from child");
            if (msg == 1)
                break;
            p = p->next;
        }
        if (p == NULL) {
            // spawn failed since parent was not found
            if (is_manager()) {
                print_not_exist(parent);
            } else {
                msg = 0;
                if (write(PARENT_WRITE_FD, &msg, 1) != 1)
                    ERR_SYS("error telling parent spawn failed");
            }
        } else {
            // spawn succeeded
            if (is_manager()) {
                print_spawn(parent, child);
            } else {
                msg = 1;
                if (write(PARENT_WRITE_FD, &msg, 1) != 1)
                    ERR_SYS("error telling parent spawn succeeded");
            }
        }
    }
}

void spawn_child(char *child) {
    Child *p = (Child *)malloc(sizeof(Child));
    p->next = NULL;

    int p2cfd[2], c2pfd[2]; // parent-to-child, child-to-parent
    if (pipe2(p2cfd, O_CLOEXEC) < 0 || pipe2(c2pfd, O_CLOEXEC) < 0)
        ERR_SYS("pipe error");
    // fprintf(stderr, "%d, %d, %d, %d\n", p2cfd[0], p2cfd[1], c2pfd[0],
    // c2pfd[1]);

    p->readfd = c2pfd[0];
    p->writefd = p2cfd[1];

    pid_t pid;
    if ((pid = fork()) < 0)
        ERR_SYS("fork error");
    else if (pid == 0) {
        // child process
        // DO NOT DO THIS: if(!is_manager()) close(PARENT_READ_FD),
        // close(PARENT_WRITE_FD);

        int tmp_write_fd = dup(c2pfd[1]), tmp_read_fd = dup(p2cfd[0]);
        close(c2pfd[1]), close(p2cfd[0]), close(c2pfd[0]), close(p2cfd[1]);
        dup2(tmp_write_fd, PARENT_WRITE_FD);
        dup2(tmp_read_fd, PARENT_READ_FD);
        close(tmp_read_fd), close(tmp_write_fd);

        // fprintf(stderr, "%d, %d, %d, %d,,, %d, %d\n", p2cfd[0], p2cfd[1],
        // c2pfd[0], c2pfd[1], tmp_read_fd, tmp_write_fd);

        /*
        int flag=fcntl(PARENT_READ_FD, F_GETFD);
        fcntl(PARENT_READ_FD, F_SETFD, flag&(~FD_CLOEXEC));
        flag=fcntl(PARENT_WRITE_FD, F_GETFD);
        fcntl(PARENT_WRITE_FD, F_SETFD, flag&(~FD_CLOEXEC));
        */

        if (execl("./service", "service", child, NULL) < 0)
            ERR_SYS("exec error");
    } else {
        // parent process
        close(c2pfd[1]), close(p2cfd[0]);
        p->pid = pid;

        char c;
        if (read(p->readfd, &c, 1) != 1 || c != 1)
            ERR_SYS("read error");
    }

    if (childlist == NULL)
        childlist = p;
    else {
        Child *head = childlist;
        while (head->next != NULL)
            head = head->next;
        head->next = p;
    }
    childcount++;
}

void find_kill(char *name) {
    if (strcmp(name, service_name) == 0)
        terminate();

    Child *head = childlist, *prev = NULL;
    KillMsg killmsg;
    unsigned char number_of_descendents;
    while (head != NULL) {
        sprintf(buf, "kill %s", name);
        if (write(head->writefd, buf, strlen(buf)) != strlen(buf))
            ERR_SYS("error passing kill to child");

        // wait for child
        if (read(head->readfd, &killmsg, sizeof(killmsg)) != sizeof(killmsg))
            ERR_SYS("error receiving kill status from child");
        // fprintf(stderr, "kill.status==%d\n", killmsg.status);
        if (killmsg.status == 1) {
            // kill succeeded and "name" is not child, then return
            number_of_descendents = killmsg.number_of_descendents;
            break;
        } else if (killmsg.status == 2) {
            // victim is child
            if (prev != NULL)
                prev->next = head->next;
            else
                childlist = head->next;
            number_of_descendents = killmsg.number_of_descendents;

            let_child_suicide(head);

            break;
        } else if (killmsg.status != 0)
            ERR_EXIT("kill status invalid");
        prev = head;
        head = head->next;
    }
    if (head == NULL) {
        // not exist
        if (is_manager()) {
            print_not_exist(name);
        } else {
            killmsg.status = 0;
            if (write(PARENT_WRITE_FD, &killmsg, sizeof(killmsg)) !=
                sizeof(killmsg))
                ERR_SYS("error telling parent kill failed");
        }
    } else {
        // kill succeeded
        if (is_manager())
            print_kill(name, number_of_descendents);
        else {
            killmsg.status = 1;
            killmsg.number_of_descendents = number_of_descendents;
            if (write(PARENT_WRITE_FD, &killmsg, sizeof(killmsg)) !=
                sizeof(killmsg))
                ERR_SYS("error telling parent kill succeeded");
        }
    }
}

void let_child_suicide(Child *child) {
    /* You must send kill or killall command to child first! */
    KillMsg killmsg;
    // tell child to kill itself (yes, suicide)
    killmsg.status = 3;
    // fprintf(stderr, "not done telling suicide\n");
    if (write(child->writefd, &killmsg, sizeof(killmsg)) != sizeof(killmsg))
        ERR_SYS("error telling child to suicide");

    // fprintf(stderr, "done telling suicide\n");
    //  wait for child to terminate
    if (waitpid(child->pid, NULL, 0) < 0)
        ERR_SYS("waitpid error");

    close(child->readfd), close(child->writefd);
    free(child);
    childcount--;
}

void terminate() {
    // kill all childs first
    // fprintf(stderr, "terminating %s...\n", service_name);
    Child *head = childlist, *next;
    KillMsg killmsg;
    unsigned char number_of_descendents = 0;
    while (head != NULL) {
        next = head->next;
        if (write(head->writefd, "killall", 7) != 7)
            ERR_SYS("error passing killall to child");

        // wait for child
        if (read(head->readfd, &killmsg, sizeof(killmsg)) != sizeof(killmsg))
            ERR_SYS("error receiving kill status from child");
        if (killmsg.status != 2)
            ERR_EXIT("kill status invalid");
        number_of_descendents += killmsg.number_of_descendents + 1;

        let_child_suicide(head);

        head = next;
    }

    if (is_manager()) {
        print_kill(service_name, number_of_descendents);
    } else {
        // int n;
        killmsg.number_of_descendents = number_of_descendents;
        killmsg.status = 2;
        if ((write(PARENT_WRITE_FD, &killmsg, sizeof(killmsg))) !=
            sizeof(killmsg))
            ERR_SYS("error sending number of decendents to parent");

        if ((read(PARENT_READ_FD, &killmsg, sizeof(killmsg))) !=
            sizeof(killmsg))
            ERR_SYS("error waiting for parent to agree suicide");
        if (killmsg.status != 3)
            ERR_EXIT("kill status invalid");

        close(PARENT_READ_FD), close(PARENT_WRITE_FD);
    }

    free(inputbuf);

    exit(0);
}

void exchange(char *service_a, char *service_b, const int found) {
    int found_here = 0;
    char *peer = NULL;
    int to_wait[2] = {-1, -1};
    bool is_service_a = false;
    if (strcmp(service_name, service_a) == 0)
        peer = service_b, found_here++, is_service_a = true;
    else if (strcmp(service_name, service_b) == 0)
        peer = service_a, found_here++;

    Child *head = childlist;
    unsigned char msg;
    while (head != NULL && found + found_here < 2) {
        sprintf(buf, "%s %s %s",
                (found + found_here == 1) ? "exchange_foundone" : "exchange",
                service_a, service_b);
        if (write(head->writefd, buf, strlen(buf)) != strlen(buf))
            ERR_SYS("error passing exchange to child");

        // wait for child
        if (read(head->readfd, &msg, 1) != 1)
            ERR_SYS("error receiving exchange status from child");
        if (msg == 2) {
            to_wait[0] = head->readfd;
            found_here = 2;
        } else if (msg == 1)
            to_wait[found_here++] = head->readfd;
        head = head->next;
    }
    if (is_manager()) {
        if (found + found_here < 2)
            fprintf(stderr, "%s or %s does not exist", service_a, service_b);
    } else {
        msg = (unsigned char)(found_here);
        if (write(PARENT_WRITE_FD, &msg, 1) != 1)
            ERR_SYS("error telling parent exchange found count");
    }

    if (found_here == 0)
        return;
    if (peer != NULL) {
        char read_fifo[MAX_FIFO_NAME_LEN], write_fifo[MAX_FIFO_NAME_LEN];
        fifoname(read_fifo, peer, service_name),
            fifoname(write_fifo, service_name, peer);

        if (mkfifo(read_fifo, 0666) == -1 && errno != EEXIST)
            ERR_SYS("mkfifo error");
        if (mkfifo(write_fifo, 0666) == -1 && errno != EEXIST)
            ERR_SYS("mkfifo error");

        int read_fd, write_fd;
        unsigned long new_secret;

        if (is_service_a) {
            if ((read_fd = open(read_fifo, O_RDONLY)) < 0)
                ERR_SYS("open fifo error");
            if (read(read_fd, &new_secret, sizeof(new_secret)) !=
                sizeof(new_secret))
                ERR_SYS("error reading secret of peer");
            print_acquire_secret(service_name, peer, new_secret);
            close(read_fd);
            if (unlink(read_fifo) < 0)
                ERR_SYS("unlink fifo error");

            if ((write_fd = open(write_fifo, O_WRONLY)) < 0)
                ERR_SYS("open fifo error");
            if (write(write_fd, &secret, sizeof(secret)) != sizeof(secret))
                ERR_SYS("error sending secret of self");
            close(write_fd);
        } else {
            if ((write_fd = open(write_fifo, O_WRONLY)) < 0)
                ERR_SYS("open fifo error");
            if (write(write_fd, &secret, sizeof(secret)) != sizeof(secret))
                ERR_SYS("error sending secret of self");
            close(write_fd);

            if ((read_fd = open(read_fifo, O_RDONLY)) < 0)
                ERR_SYS("open fifo error");
            if (read(read_fd, &new_secret, sizeof(new_secret)) !=
                sizeof(new_secret))
                ERR_SYS("error reading secret of peer");
            print_acquire_secret(service_name, peer, new_secret);
            close(read_fd);
            if (unlink(read_fifo) < 0)
                ERR_SYS("unlink fifo error");
        }
        secret = new_secret;
    }

    char c = 0;
    for (int j = 0; j <= 1; j++) {
        if (to_wait[j] != -1) {
            if (read(to_wait[j], &c, 1) != 1)
                ERR_SYS("error waiting for child to finish doing fifo");
            if (c != 0)
                ERR_EXIT("invalid fifo status");
        }
    }
    if (is_manager())
        print_exchange(service_a, service_b);
    else if (write(PARENT_WRITE_FD, &c, 1) != 1)
        ERR_SYS("error telling parent fifo is finished");
}

void fifoname(char *s, char *from, char *to) {
    sprintf(s, "%s_to_%s.fifo", from, to);
}

int readInput(int fd) {
    /* fd==0: read from stdin */
    ssize_t bytesRead;
    if (fd == STDIN_FILENO) {
        bytesRead = getline(&inputbuf, &inputbufSize, stdin);
        if (bytesRead == -1)
            ERR_SYS("error reading input from stdin");
        else if (bytesRead > 0)
            inputbuf[bytesRead - 1] = '\0';
    } else {
        bytesRead = read(fd, inputbuf, inputbufSize);
        if (bytesRead <= 0)
            ERR_SYS("error reading from pipe");
        inputbuf[bytesRead] = '\0';
    }

    int argc = 0;
    char *ptr = strtok(inputbuf, " ");
    while (ptr != NULL && argc < MAX_ARGC) {
        input_argv[argc++] = ptr;
        ptr = strtok(NULL, " ");
    }
    return argc;
}