/*
Copyright 2018 The Kubernetes Authors.
Copyright 2018-2023 The Volcano Authors.

Modifications made by Volcano authors:
- Enhanced preemption logic with support for both inter-job and intra-job priority-based preemption
- Added job starving detection functionality to improve resource allocation efficiency

Licensed 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.
*/

package priority

import (
	"k8s.io/klog/v2"

	"volcano.sh/volcano/pkg/scheduler/api"
	"volcano.sh/volcano/pkg/scheduler/framework"
	"volcano.sh/volcano/pkg/scheduler/plugins/util"
)

// PluginName indicates name of volcano scheduler plugin.
const PluginName = "priority"

type priorityPlugin struct {
	// Arguments given for the plugin
	pluginArguments framework.Arguments
}

// New return priority plugin
func New(arguments framework.Arguments) framework.Plugin {
	return &priorityPlugin{pluginArguments: arguments}
}

func (pp *priorityPlugin) Name() string {
	return PluginName
}

func (pp *priorityPlugin) OnSessionOpen(ssn *framework.Session) {
	taskOrderFn := func(l interface{}, r interface{}) int {
		lv := l.(*api.TaskInfo)
		rv := r.(*api.TaskInfo)

		klog.V(4).Infof("Priority TaskOrder: <%v/%v> priority is %v, <%v/%v> priority is %v",
			lv.Namespace, lv.Name, lv.Priority, rv.Namespace, rv.Name, rv.Priority)

		if lv.Priority == rv.Priority {
			return 0
		}

		if lv.Priority > rv.Priority {
			return -1
		}

		return 1
	}

	// Add Task Order function
	ssn.AddTaskOrderFn(pp.Name(), taskOrderFn)

	jobOrderFn := func(l, r interface{}) int {
		lv := l.(*api.JobInfo)
		rv := r.(*api.JobInfo)

		klog.V(4).Infof("Priority JobOrderFn: <%v/%v> priority: %d, <%v/%v> priority: %d",
			lv.Namespace, lv.Name, lv.Priority, rv.Namespace, rv.Name, rv.Priority)

		if lv.Priority > rv.Priority {
			return -1
		}

		if lv.Priority < rv.Priority {
			return 1
		}

		return 0
	}

	ssn.AddJobOrderFn(pp.Name(), jobOrderFn)

	subJobOrderFn := func(l, r interface{}) int {
		lv := l.(*api.SubJobInfo)
		rv := r.(*api.SubJobInfo)

		klog.V(4).Infof("Priority SubJobOrderFn: <%v> priority: %d, <%v> priority: %d",
			lv.UID, lv.Priority, rv.UID, rv.Priority)

		if lv.Priority > rv.Priority {
			return -1
		}

		if lv.Priority < rv.Priority {
			return 1
		}

		return 0
	}

	ssn.AddSubJobOrderFn(pp.Name(), subJobOrderFn)

	preemptableFn := func(preemptor *api.TaskInfo, preemptees []*api.TaskInfo) ([]*api.TaskInfo, int) {
		preemptorJob := ssn.Jobs[preemptor.Job]
		if preemptorJob == nil {
			klog.Warningf("[priority] Skip preemption: preemptor job <%s> not found in session (orphaned task from deleted PodGroup)",
				preemptor.Job)
			return nil, util.Permit
		}

		var victims []*api.TaskInfo
		for _, preemptee := range preemptees {
			preempteeJob := ssn.Jobs[preemptee.Job]
			if preempteeJob == nil {
				klog.Warningf("[priority] Skip preemptee <%s/%s>: job <%s> not found in session (orphaned task from deleted PodGroup)",
					preemptee.Namespace, preemptee.Name, preemptee.Job)
				continue
			}
			if preempteeJob.UID != preemptorJob.UID {
				if preempteeJob.Priority >= preemptorJob.Priority { // Preemption between Jobs within Queue
					klog.V(4).Infof("[priority] Can not preempt task <%v/%v> "+
						"because preemptee job has greater or equal job priority (%d) than preemptor (%d)",
						preemptee.Namespace, preemptee.Name, preempteeJob.Priority, preemptorJob.Priority)
				} else {
					victims = append(victims, preemptee)
				}
			} else { // same job's different tasks should compare task's priority
				if preemptee.Priority >= preemptor.Priority {
					klog.V(4).Infof("[priority] Can not preempt task <%v/%v> "+
						"because preemptee task has greater or equal task priority (%d) than preemptor (%d)",
						preemptee.Namespace, preemptee.Name, preemptee.Priority, preemptor.Priority)
				} else {
					victims = append(victims, preemptee)
				}
			}
		}

		klog.V(4).Infof("[priority] Victims from Priority plugin are %+v", victims)
		return victims, util.Permit
	}
	ssn.AddPreemptableFn(pp.Name(), preemptableFn)

	// Currently handles GangReclaim and GangPreempt only.
	// Support for legacy task-level preempt/reclaim will be added in the future.
	ssn.AddUnifiedEvictableFn(pp.Name(), func(evictCtx *api.EvictionContext, candidates []*api.TaskInfo) ([]*api.TaskInfo, int) {
		if evictCtx.Kind == api.EvictionKindGangReclaim {
			// Reclaim is fairness-driven (cross-queue); priority does not gate
			// reclaimability — consistent with legacy reclaim where priority
			// registers no ReclaimableFn.
			return candidates, util.Permit
		}
		var victims []*api.TaskInfo
		for _, candidate := range candidates {
			candidateJob := ssn.Jobs[candidate.Job]
			if candidateJob.Priority >= evictCtx.Job.Priority {
				klog.V(4).Infof("Can not evict task <%v/%v> because victim job priority (%d) >= preemptor job priority (%d)",
					candidate.Namespace, candidate.Name, candidateJob.Priority, evictCtx.Job.Priority)
			} else {
				victims = append(victims, candidate)
			}
		}
		klog.V(4).Infof("Victims from Priority UnifiedEvictableFn are %+v", victims)
		return victims, util.Permit
	})

	jobStarvingFn := func(obj interface{}) bool {
		ji := obj.(*api.JobInfo)
		return ji.ReadyTaskNum()+ji.WaitingTaskNum() < int32(len(ji.Tasks))
	}
	ssn.AddJobStarvingFns(pp.Name(), jobStarvingFn)
}

func (pp *priorityPlugin) OnSessionClose(ssn *framework.Session) {}
