package worker

import (
	"context"
	"errors"
	"log/slog"
	"sync"
)

type (

	// A simple task to deal with list.
	ChanProcessor[T any] interface {
		Query(context.Context) (<-chan T, error)
		Process(context.Context, T) error
	}

	OnFail[T any] interface {
		OnFail(context.Context, T, error)
	}

	ListProcessor[T any] interface {
		Query(context.Context) ([]T, error)
		Process(context.Context, T) error
	}

	chanProcessorTask[T any] struct {
		chanProcessor ChanProcessor[T]
		logger        *slog.Logger
		scheduler     *Scheduler
	}

	batchProcessorTask[T any] struct {
		batchProcessor ListProcessor[T]
		logger         *slog.Logger
		scheduler      *Scheduler
	}

	serialProcessorTask[T any] struct {
		batchProcessor ListProcessor[T]
		logger         *slog.Logger
		scheduler      *Scheduler
	}
)

func NewTaskFromBatchProcessor[T any](
	batchProcessor ListProcessor[T],
	scheduler *Scheduler,
	logger *slog.Logger,
) Task {
	return &batchProcessorTask[T]{
		batchProcessor: batchProcessor,
		scheduler:      scheduler,
		logger:         logger,
	}
}

func NewTaskFromSerialProcessor[T any](
	batchProcessor ListProcessor[T],
	scheduler *Scheduler,
	logger *slog.Logger,
) Task {
	return &serialProcessorTask[T]{
		batchProcessor: batchProcessor,
		scheduler:      scheduler,
		logger:         logger,
	}
}

func NewTaskFromChanProcessor[T any](
	chanProcessor ChanProcessor[T],
	scheduler *Scheduler,
	logger *slog.Logger,
) Task {
	return &chanProcessorTask[T]{
		chanProcessor: chanProcessor,
		scheduler:     scheduler,
		logger:        logger,
	}
}

func (l *batchProcessorTask[T]) Start(ctx context.Context) error {
	for {
		values, err := l.batchProcessor.Query(ctx)
		if err != nil {
			return err
		}

		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		if len(values) == 0 {
			return nil
		}
		var wg sync.WaitGroup

		for _, v := range values {
			select {
			case <-ctx.Done():
				return ctx.Err()
			default:
			}

			wg.Add(1)
			l.scheduler.Take()
			go func(v T) {
				defer l.scheduler.Return()
				defer wg.Done()
				if err := l.batchProcessor.Process(ctx, v); err != nil && !errors.Is(err, context.Canceled) {
					l.logger.Error(
						"Error processing batch",
						slog.String("error", err.Error()),
					)
					if failure, ok := l.batchProcessor.(OnFail[T]); ok {
						failure.OnFail(ctx, v, err)
					}
				}
			}(v)
		}

		wg.Wait()
	}
}

func (l *serialProcessorTask[T]) Start(ctx context.Context) error {
	for {
		values, err := l.batchProcessor.Query(ctx)
		if err != nil {
			return err
		}

		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		if len(values) == 0 {
			return nil
		}
		for _, v := range values {
			select {
			case <-ctx.Done():
				return ctx.Err()
			default:
			}

			l.scheduler.Take()
			if err := l.batchProcessor.Process(ctx, v); err != nil && !errors.Is(err, context.Canceled) {
				l.logger.Error(
					"Error processing batch",
					slog.String("error", err.Error()),
				)
				if failure, ok := l.batchProcessor.(OnFail[T]); ok {
					failure.OnFail(ctx, v, err)
				}
			}
			l.scheduler.Return()
		}
	}
}

func (l *chanProcessorTask[T]) Start(ctx context.Context) error {
	c, err := l.chanProcessor.Query(ctx)
	if err != nil {
		return err
	}

	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case v, ok := <-c:
			if !ok {
				return nil
			}

			l.scheduler.Take()
			go func(v T) {
				defer l.scheduler.Return()
				if err := l.chanProcessor.Process(ctx, v); err != nil {
					l.logger.Error(
						"Error processing batch",
						slog.String("error", err.Error()),
					)
					if failure, ok := l.chanProcessor.(OnFail[T]); ok {
						failure.OnFail(ctx, v, err)
					}
				}
			}(v)
		}
	}
}