// Copyright 2024 PingCAP, Inc.
//
// 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,
// See the License for the specific language governing permissions and
// limitations under the License.

package scheduler

import (
	"github.com/pingcap/log"
	"github.com/pingcap/ticdc/pkg/node"
	"github.com/pingcap/ticdc/pkg/scheduler/replica"
	"github.com/pingcap/ticdc/utils/heap"
)

// BasicSchedule schedules the absent tasks to the available nodes
func BasicSchedule[T replica.ReplicationID, R replica.Replication[T]](
	availableSize int,
	absent []R,
	nodeTasks map[node.ID]int,
	schedule func(R, node.ID) bool,
) {
	if len(nodeTasks) == 0 {
		log.Warn("scheduler: no node available, skip")
		return
	}
	minPriorityQueue := priorityQueue[T, R]{
		h:    heap.NewHeap[*item[T, R]](),
		less: func(a, b int) bool { return a < b },
	}
	for key, size := range nodeTasks {
		minPriorityQueue.InitItem(key, size, nil)
	}

	taskSize := 0
	for _, cf := range absent {
		item, _ := minPriorityQueue.PeekTop()
		// the operator is pushed successfully
		if schedule(cf, item.Node) {
			// update the task size priority queue
			item.Load++
			taskSize++
		}
		if taskSize >= availableSize {
			break
		}
		minPriorityQueue.AddOrUpdate(item)
	}
}