// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package semaphore_test

import (
	"context"
	"fmt"
	"testing"

	"golang.org/x/sync/semaphore"
)

// weighted is an interface matching a subset of *Weighted.  It allows
// alternate implementations for testing and benchmarking.
type weighted interface {
	Acquire(context.Context, int64) error
	TryAcquire(int64) bool
	Release(int64)
}

// semChan implements Weighted using a channel for
// comparing against the condition variable-based implementation.
type semChan chan struct{}

func newSemChan(n int64) semChan {
	return semChan(make(chan struct{}, n))
}

func (s semChan) Acquire(_ context.Context, n int64) error {
	for i := int64(0); i < n; i++ {
		s <- struct{}{}
	}
	return nil
}

func (s semChan) TryAcquire(n int64) bool {
	if int64(len(s))+n > int64(cap(s)) {
		return false
	}

	for i := int64(0); i < n; i++ {
		s <- struct{}{}
	}
	return true
}

func (s semChan) Release(n int64) {
	for i := int64(0); i < n; i++ {
		<-s
	}
}

// acquireN calls Acquire(size) on sem N times and then calls Release(size) N times.
func acquireN(b *testing.B, sem weighted, size int64, N int) {
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		for j := 0; j < N; j++ {
			sem.Acquire(context.Background(), size)
		}
		for j := 0; j < N; j++ {
			sem.Release(size)
		}
	}
}

// tryAcquireN calls TryAcquire(size) on sem N times and then calls Release(size) N times.
func tryAcquireN(b *testing.B, sem weighted, size int64, N int) {
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		for j := 0; j < N; j++ {
			if !sem.TryAcquire(size) {
				b.Fatalf("TryAcquire(%v) = false, want true", size)
			}
		}
		for j := 0; j < N; j++ {
			sem.Release(size)
		}
	}
}

func BenchmarkNewSeq(b *testing.B) {
	for _, cap := range []int64{1, 128} {
		b.Run(fmt.Sprintf("Weighted-%d", cap), func(b *testing.B) {
			for i := 0; i < b.N; i++ {
				_ = semaphore.NewWeighted(cap)
			}
		})
		b.Run(fmt.Sprintf("semChan-%d", cap), func(b *testing.B) {
			for i := 0; i < b.N; i++ {
				_ = newSemChan(cap)
			}
		})
	}
}

func BenchmarkAcquireSeq(b *testing.B) {
	for _, c := range []struct {
		cap, size int64
		N         int
	}{
		{1, 1, 1},
		{2, 1, 1},
		{16, 1, 1},
		{128, 1, 1},
		{2, 2, 1},
		{16, 2, 8},
		{128, 2, 64},
		{2, 1, 2},
		{16, 8, 2},
		{128, 64, 2},
	} {
		for _, w := range []struct {
			name string
			w    weighted
		}{
			{"Weighted", semaphore.NewWeighted(c.cap)},
			{"semChan", newSemChan(c.cap)},
		} {
			b.Run(fmt.Sprintf("%s-acquire-%d-%d-%d", w.name, c.cap, c.size, c.N), func(b *testing.B) {
				acquireN(b, w.w, c.size, c.N)
			})
			b.Run(fmt.Sprintf("%s-tryAcquire-%d-%d-%d", w.name, c.cap, c.size, c.N), func(b *testing.B) {
				tryAcquireN(b, w.w, c.size, c.N)
			})
		}
	}
}