package channel

import (
	"time"
)

// GroupByTime groups all incoming values from source using the grouper function
// and sends them to the returned channel after the given amount of time.
// This can useful for summing or averaging values from a channel on a fixed interval
func GroupByTime[T, G any](source <-chan T, duration time.Duration, grouper func(current G, value T) G) <-chan G {
	out := make(chan G, cap(source))

	go func() {
		defer close(out)

		ticker := time.NewTicker(duration)
		defer ticker.Stop()

		current := *new(G)
		changed := false
		for {
			select {
			case value, ok := <-source:
				if !ok {
					if changed {
						out <- current
					}
					return
				}
				current = grouper(current, value)
				changed = true
			case <-ticker.C:
				group := current
				out <- group
				current = *new(G)
				changed = false
			}
		}
	}()

	return out
}

// GroupByAmount groups all incoming values from source using the grouper function
// and sends them to the returned channel after the given amount of values were grouped.
// This can useful for summing or averaging values from a channel for a given amount of values
func GroupByAmount[T, G any](source <-chan T, amount int, grouper func(current G, value T) G) <-chan G {
	out := make(chan G, cap(source))

	go func() {
		defer close(out)

		current := *new(G)
		currentAmount := 0
		for value := range source {
			currentAmount++
			current = grouper(current, value)

			if currentAmount%amount == 0 {
				group := current
				out <- group
				current = *new(G)
			}
		}
	}()

	return out
}

// GroupByValue groups all incoming values from source using the grouper function
// and sends them to the returned channel after valueFunc returns true for a given value.
// This can useful for summing or averaging values from a channel for a given amount of values
func GroupByValue[T, G any](source <-chan T, valueFunc func(T) bool, grouper func(current G, value T) G) <-chan G {
	out := make(chan G, cap(source))

	go func() {
		defer close(out)

		current := *new(G)
		currentAmount := 0
		for value := range source {
			currentAmount++
			current = grouper(current, value)

			if valueFunc(value) {
				group := current
				out <- group
				current = *new(G)
			}
		}
	}()

	return out
}