package core

import (
	"context"
	"github.com/matchsystems/werr"
	"mic-wallet/server/repository"
	"sync"
	"time"
)

type CommitBlockFunc func(ctx context.Context, block *Block) error

type IBlocksCommiter interface {
	// CommitBlock pushes blocks into the storage (db).
	// Block must be not null
	CommitBlock(ctx context.Context, block *Block)
}

type BlocksCommiter struct {
	BlocksQueue  []*Block
	Lock         *sync.RWMutex
	CountLim     int
	CountBusy    int
	TaskDeadline time.Duration
	ErrChan      chan error

	CommitBlockFunc CommitBlockFunc
}

func NewBlocksCommiter(repo *repository.Repository, errChan chan error, workersCountLim int) *BlocksCommiter {
	return &BlocksCommiter{
		BlocksQueue:  make([]*Block, 0),
		Lock:         &sync.RWMutex{},
		CountLim:     workersCountLim,
		CountBusy:    0,
		TaskDeadline: 0,
		ErrChan:      errChan,
		CommitBlockFunc: func(ctx context.Context, block *Block) error {
			return CommitBlock(ctx, repo, block)
		},
	}
}

// execute executes commiting block with deadline and cancelable by the context
// provided when calling CommitBlock.
// all the errors from it (including context) are sent to BlocksCommiter.ErrChan
func (bc *BlocksCommiter) execute(ctx context.Context, block *Block) {
	if bc.TaskDeadline > 0 {
		var cancel context.CancelFunc
		ctx, cancel = context.WithTimeout(ctx, bc.TaskDeadline)
		defer cancel()
	}
	errChan := make(chan error)
	go func() {
		if err := bc.CommitBlockFunc(ctx, block); err != nil {
			errChan <- err
		}
	}()
	select {
	case <-ctx.Done():
		bc.ErrChan <- werr.Wrapf(ctx.Err(), "ctx error while commiting block %d", block.Id)
	case err := <-errChan:
		bc.ErrChan <- werr.Wrapf(err, "error while commiting block %d", block.Id)
	}
}

func (bc *BlocksCommiter) CommitBlock(ctx context.Context, block *Block) {
	bc.Lock.Lock()
	if bc.CountBusy >= bc.CountLim {
		bc.BlocksQueue = append(bc.BlocksQueue, block)
		return
	}
	bc.CountBusy++
	bc.Lock.Unlock()
	for {
		bc.execute(ctx, block)
		bc.Lock.Lock()
		if len(bc.BlocksQueue) < 1 {
			bc.CountBusy--
			bc.Lock.Unlock()
			return
		}
		block = bc.BlocksQueue[0]
		bc.BlocksQueue = bc.BlocksQueue[1:]
		bc.Lock.Unlock()
	}
}