/****************************************************************************
 * sched/task/task_reparent.c
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <assert.h>
#include <errno.h>

#include <nuttx/irq.h>
#include <nuttx/sched.h>

#include "sched/sched.h"
#include "group/group.h"
#include "task/task.h"

#ifdef CONFIG_SCHED_HAVE_PARENT

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: task_reparent
 *
 * Description:
 *   Change the parent of a task.
 *
 * Input Parameters:
 *   ppid - PID of the new parent task (0 for grandparent, i.e. the parent
 *     of the current parent task)
 *   chpid  - PID of the child to be reparented.
 *
 * Returned Value:
 *   0 (OK) on success; A negated errno value on failure.
 *
 ****************************************************************************/

#ifdef HAVE_GROUP_MEMBERS
int task_reparent(pid_t ppid, pid_t chpid)
{
#ifdef CONFIG_SCHED_CHILD_STATUS
  FAR struct child_status_s *child;
#endif
  FAR struct task_group_s *chgrp;
  FAR struct task_group_s *ogrp;
  FAR struct task_group_s *pgrp;
  FAR struct tcb_s *chtcb;
  FAR struct tcb_s *otcb;
  FAR struct tcb_s *ptcb;
  pid_t opid;
  int ret = -ECHILD;

  /* Get the child tasks task group */

  chtcb = nxsched_get_tcb(chpid);
  if (chtcb)
    {
      chgrp = chtcb->group;
      DEBUGASSERT(chgrp);

      /* Get the PID of the old parent task's task group (opid) */

      opid = chgrp->tg_ppid;

      /* Get the old parent task's task group (ogrp) */

      otcb = nxsched_get_tcb(opid);
      if (otcb)
        {
          ogrp = otcb->group;
          DEBUGASSERT(ogrp);

          /* If new parent task's PID (ppid) is zero, then new parent
           * is the grandparent will be the new parent, i.e.,
           * the parent of the current parent task.
           */

          if (ppid == 0)
            {
              /* Get the grandparent task's task group (pgrp) */

              ppid = ogrp->tg_ppid;
              ptcb = nxsched_get_tcb(ppid);
              if (ptcb)
                {
                  ret = OK;
                  pgrp = ptcb->group;
                }
            }
          else
            {
              /* Get the new parent task's task group (pgrp) */

              ptcb = nxsched_get_tcb(ppid);
              if (ptcb)
                {
                  ret = OK;
                  pgrp = chtcb->group;
                  ppid = pgrp->tg_pid;
                }
              else
                {
                  ret = -ESRCH;
                }
            }

          if (ret == OK)
            {
              /* Then reparent the child. Notice that we don't actually
               * change the parent of the task. Rather, we change the parent
               * task group for all members of the child's task group.
               */

              chgrp->tg_ppid = ppid;

#ifdef CONFIG_SCHED_CHILD_STATUS
              /* Remove the child status entry from old parent task group */

              child = group_remove_child(ogrp, chpid);
              if (child)
                {
                  /* Has the new parent's task group suppressed child exit
                   * status?
                   */

                  if (!(atomic_read(&pgrp->tg_flags) & GROUP_FLAG_NOCLDWAIT))
                    {
                      /* No.. Add the child status entry to the new parent's
                       * task group
                       */

                      group_add_child(pgrp, child);
                    }
                  else
                    {
                      /* Yes.. Discard the child status entry */

                      group_free_child(child);
                    }

                  /* Either case is a success */
                }
              else
                {
                  /* This would not be an error if the original parent's task
                   * group has suppressed child exit status.
                   */

                  ret = ((atomic_read(&ogrp->tg_flags) &
                          GROUP_FLAG_NOCLDWAIT) == 0) ? -ENOENT : OK;
                }

#else /* CONFIG_SCHED_CHILD_STATUS */
              /* Child task exit status is not retained */

              DEBUGASSERT(atomic_read(&ogrp->tg_nchildren) > 0);

              /* The original parent now has one few children */

              atomic_sub(&ogrp->tg_nchildren, 1);

              /* The new parent has one additional child */

              atomic_add(&pgrp->tg_nchildren, 1);

#endif /* CONFIG_SCHED_CHILD_STATUS */

              nxsched_put_tcb(ptcb);
            }

          nxsched_put_tcb(otcb);
        }

      nxsched_put_tcb(chtcb);
    }

  return ret;
}
#else
int task_reparent(pid_t ppid, pid_t chpid)
{
#ifdef CONFIG_SCHED_CHILD_STATUS
  FAR struct child_status_s *child;
#endif
  FAR struct tcb_s *ptcb = NULL;
  FAR struct tcb_s *chtcb = NULL;
  FAR struct tcb_s *otcb = NULL;
  pid_t opid;
  int ret = -ECHILD;

  /* Get the child tasks TCB (chtcb) */

  chtcb = nxsched_get_tcb(chpid);
  if (chtcb)
    {
      /* Get the PID of the child task's parent (opid) */

      opid = chtcb->group->tg_ppid;

      /* Get the TCB of the child task's parent (otcb) */

      otcb = nxsched_get_tcb(opid);
      if (!otcb)
        {
          ret = -ESRCH;
        }
      else
        {
          /* If new parent task's PID (tg_ppid) is zero, then new parent
           * is the grandparent will be the new parent, i.e., the parent
           * of the current parent task.
           */

          if (ppid == 0)
            {
              ppid = otcb->group->tg_ppid;
            }

          /* Get the new parent task's TCB (ptcb) */

          ptcb = nxsched_get_tcb(ppid);
          if (!ptcb)
            {
              ret = -ESRCH;
            }
          else
            {
              /* Then reparent the child.  The task specified by ppid is
               * the new parent.
               */

              chtcb->group->tg_ppid = ppid;

#ifdef CONFIG_SCHED_CHILD_STATUS
              /* Remove the child status entry from old parent TCB */

              child = group_remove_child(otcb->group, chpid);
              if (child)
                {
                  /* Has the new parent's task group suppressed child
                   * exit status?
                   * */

                  if (!(atomic_read(&ptcb->group->tg_flags) &
                        GROUP_FLAG_NOCLDWAIT))
                    {
                      /* No.. Add the child status entry to the new parent's
                       * task group
                       */

                      group_add_child(ptcb->group, child);
                    }
                  else
                    {
                      /* Yes.. Discard the child status entry */

                      group_free_child(child);
                    }

                  /* Either case is a success */

                  ret = OK;
                }
              else
                {
                  /* This would not be an error if the original parent's task
                   * group has suppressed child exit status.
                   */

                  ret = ((atomic_read(&otcb->group->tg_flags) &
                          GROUP_FLAG_NOCLDWAIT) == 0) ? -ENOENT : OK;
                }

#else /* CONFIG_SCHED_CHILD_STATUS */
              /* Child task exit status is not retained */

              DEBUGASSERT(otcb->group != NULL &&
                          atomic_read(&otcb->group->tg_nchildren) > 0);

              /* The original parent now has one few children */

              atomic_sub(&otcb->group->tg_nchildren, 1);

              /* The new parent has one additional child */

              atomic_add(&ptcb->group->tg_nchildren, 1);
              ret = OK;

#endif /* CONFIG_SCHED_CHILD_STATUS */

              nxsched_put_tcb(ptcb);
            }

          nxsched_put_tcb(otcb);
        }

      nxsched_put_tcb(chtcb);
    }

  return ret;
}
#endif
#endif /* CONFIG_SCHED_HAVE_PARENT */