package toolkit

import (
	"context"
	"sync"
	"testing"

	"github.com/stretchr/testify/assert"
)

// ExpectedBlockpoint represents the expectation that Blockpoint will be called
// on a TestBlocker. It is possible to both wait for the Blockpoint call to
// occur and to unblock it once it has occured.
type ExpectedBlockpoint struct {
	waitCh    chan struct{}
	unblockCh chan struct{}
}

// Wait will block until blockpoint has been hit and is itself blocking, or will
// return the context error.
func (eb ExpectedBlockpoint) Wait(ctx context.Context) error {
	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-eb.waitCh:
		return nil
	}
}

// Unblock unblocks the Blockpoint call which is/was expected. If Unblock can be
// called prior to Wait being called (and therefore prior to the Blockpoint
// being hit).
func (eb ExpectedBlockpoint) Unblock() {
	close(eb.unblockCh)
}

// On is a helper which will spawn a go-routine, call Wait on the
// ExpectedBlockpoint, call the given callback, and then Unblock the
// ExpectedBlockpoint.
//
// If Wait returns an error (due to context cancellation) then this fails the
// test and returns without calling the callback.
func (eb ExpectedBlockpoint) On(t *testing.T, ctx context.Context, cb func()) {
	go func() {
		defer eb.Unblock()
		if !assert.NoError(t, eb.Wait(ctx)) {
			return
		}
		cb()
	}()
}

// TestBlocker is used as an injected dependency into components, so that tests
// can cause those components to block at specific execution points internally.
// This is useful for testing race conditions between multiple components.
//
// A TestBlocker is initialized using `new`. A nil TestBlocker will never block.
type TestBlocker struct {
	l               sync.Mutex
	blockpointsByID map[string][]ExpectedBlockpoint
	blocksByID      map[string]int
}

// NewTestBlocker initializes a TestBlocker and registers a Cleanup callback on
// the T which will call AssertExpectations.
func NewTestBlocker(t *testing.T) *TestBlocker {
	b := new(TestBlocker)
	t.Cleanup(func() { b.AssertExpectations(t) })
	return b
}

// Blockpoint will block if and only if TestBlocker is non-nil and
// ExpectBlockpoint has been called with the same ID previously. If the context
// is canceled while blocking then this call will return.
func (b *TestBlocker) Blockpoint(ctx context.Context, id string) {
	if b == nil {
		return
	}

	b.l.Lock()

	blockpoints := b.blockpointsByID[id]
	if len(blockpoints) == 0 {
		b.l.Unlock()
		return
	}

	blockpoint, blockpoints := blockpoints[0], blockpoints[1:]
	b.blockpointsByID[id] = blockpoints
	b.blocksByID[id]++

	b.l.Unlock()

	close(blockpoint.waitCh)

	select {
	case <-ctx.Done():
	case <-blockpoint.unblockCh:
	}
}

// ExpectBlockpoint will cause the TestBlocker to block upon the next call to
// Blockpoint using the same id. The returned ExpectBlockpoint can be used to
// wait until Blockpoint is called, as well as to unblock it.
func (b *TestBlocker) ExpectBlockpoint(id string) ExpectedBlockpoint {
	b.l.Lock()
	defer b.l.Unlock()

	if b.blockpointsByID == nil {
		b.blockpointsByID = map[string][]ExpectedBlockpoint{}
	}

	if b.blocksByID == nil {
		b.blocksByID = map[string]int{}
	}

	blockpoint := ExpectedBlockpoint{
		waitCh:    make(chan struct{}),
		unblockCh: make(chan struct{}),
	}

	b.blockpointsByID[id] = append(b.blockpointsByID[id], blockpoint)

	return blockpoint
}

// AssertExpectations will Fail the test and return false if any calls to
// ExpectBlockpoint have not had a corresponding Blockpoint call made.
func (b *TestBlocker) AssertExpectations(t *testing.T) bool {
	b.l.Lock()
	defer b.l.Unlock()

	var failed bool
	for id, blockpoints := range b.blockpointsByID {
		if len(blockpoints) == 0 {
			continue
		}

		failed = true
		t.Errorf(
			"Blockpoint(%q) called %d times, expected %d more",
			id, b.blocksByID[id], len(blockpoints),
		)
	}

	return !failed
}