package solver

import (
	"context"
	_ "crypto/sha256"
	"fmt"
	"math"
	"math/rand"
	"os"
	"sync/atomic"
	"testing"
	"time"

	"github.com/moby/buildkit/identity"
	digest "github.com/opencontainers/go-digest"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
	"github.com/stretchr/testify/require"
	"golang.org/x/sync/errgroup"
)

func init() {
	if debugScheduler {
		logrus.SetOutput(os.Stdout)
		logrus.SetLevel(logrus.DebugLevel)
	}
}

func TestSingleLevelActiveGraph(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	s := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
	})
	defer s.Close()

	j0, err := s.NewJob("job0")
	require.NoError(t, err)

	defer func() {
		if j0 != nil {
			j0.Discard()
		}
	}()

	g0 := Edge{
		Vertex: vtx(vtxOpt{
			name:  "v0",
			value: "result0",
		}),
	}
	g0.Vertex.(*vertex).setupCallCounters()

	res, err := j0.Build(ctx, g0)
	require.NoError(t, err)
	require.NotNil(t, res)
	require.Equal(t, unwrap(res), "result0")

	require.Equal(t, *g0.Vertex.(*vertex).cacheCallCount, int64(1))
	require.Equal(t, *g0.Vertex.(*vertex).execCallCount, int64(1))

	// calling again with same digest just uses the active queue
	j1, err := s.NewJob("job1")
	require.NoError(t, err)

	defer func() {
		if j1 != nil {
			j1.Discard()
		}
	}()

	g1 := Edge{
		Vertex: vtx(vtxOpt{
			name:  "v0",
			value: "result1",
		}),
	}
	g1.Vertex.(*vertex).setupCallCounters()

	res, err = j1.Build(ctx, g1)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result0")

	require.Equal(t, *g0.Vertex.(*vertex).cacheCallCount, int64(1))
	require.Equal(t, *g0.Vertex.(*vertex).execCallCount, int64(1))
	require.Equal(t, *g1.Vertex.(*vertex).cacheCallCount, int64(0))
	require.Equal(t, *g1.Vertex.(*vertex).execCallCount, int64(0))

	require.NoError(t, j0.Discard())
	j0 = nil

	// after discarding j0, j1 still holds the state

	j2, err := s.NewJob("job2")
	require.NoError(t, err)

	defer func() {
		if j2 != nil {
			j2.Discard()
		}
	}()

	g2 := Edge{
		Vertex: vtx(vtxOpt{
			name:  "v0",
			value: "result2",
		}),
	}
	g2.Vertex.(*vertex).setupCallCounters()

	res, err = j2.Build(ctx, g2)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result0")

	require.Equal(t, *g0.Vertex.(*vertex).cacheCallCount, int64(1))
	require.Equal(t, *g0.Vertex.(*vertex).execCallCount, int64(1))
	require.Equal(t, *g1.Vertex.(*vertex).cacheCallCount, int64(0))
	require.Equal(t, *g1.Vertex.(*vertex).execCallCount, int64(0))
	require.Equal(t, *g2.Vertex.(*vertex).cacheCallCount, int64(0))
	require.Equal(t, *g2.Vertex.(*vertex).execCallCount, int64(0))

	require.NoError(t, j1.Discard())
	j1 = nil
	require.NoError(t, j2.Discard())
	j2 = nil

	// everything should be released now

	j3, err := s.NewJob("job3")
	require.NoError(t, err)

	defer func() {
		if j3 != nil {
			j3.Discard()
		}
	}()

	g3 := Edge{
		Vertex: vtx(vtxOpt{
			name:  "v0",
			value: "result3",
		}),
	}
	g3.Vertex.(*vertex).setupCallCounters()

	res, err = j3.Build(ctx, g3)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result3")

	require.Equal(t, *g3.Vertex.(*vertex).cacheCallCount, int64(1))
	require.Equal(t, *g3.Vertex.(*vertex).execCallCount, int64(1))

	require.NoError(t, j3.Discard())
	j3 = nil

	// repeat the same test but make sure the build run in parallel now

	j4, err := s.NewJob("job4")
	require.NoError(t, err)

	defer func() {
		if j4 != nil {
			j4.Discard()
		}
	}()

	j5, err := s.NewJob("job5")
	require.NoError(t, err)

	defer func() {
		if j5 != nil {
			j5.Discard()
		}
	}()

	g4 := Edge{
		Vertex: vtx(vtxOpt{
			name:       "v0",
			cacheDelay: 100 * time.Millisecond,
			value:      "result4",
		}),
	}
	g4.Vertex.(*vertex).setupCallCounters()

	eg, _ := errgroup.WithContext(ctx)

	eg.Go(func() error {
		res, err := j4.Build(ctx, g4)
		require.NoError(t, err)
		require.Equal(t, unwrap(res), "result4")
		return err
	})

	eg.Go(func() error {
		res, err := j5.Build(ctx, g4)
		require.NoError(t, err)
		require.Equal(t, unwrap(res), "result4")
		return err
	})

	require.NoError(t, eg.Wait())

	require.Equal(t, *g4.Vertex.(*vertex).cacheCallCount, int64(1))
	require.Equal(t, *g4.Vertex.(*vertex).execCallCount, int64(1))
}

func TestSingleLevelCache(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	s := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
	})
	defer s.Close()

	j0, err := s.NewJob("job0")
	require.NoError(t, err)

	defer func() {
		if j0 != nil {
			j0.Discard()
		}
	}()

	g0 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v0",
			cacheKeySeed: "seed0",
			value:        "result0",
		}),
	}
	g0.Vertex.(*vertex).setupCallCounters()

	res, err := j0.Build(ctx, g0)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result0")

	require.NoError(t, j0.Discard())
	j0 = nil

	// first try that there is no match for different cache
	j1, err := s.NewJob("job1")
	require.NoError(t, err)

	defer func() {
		if j1 != nil {
			j1.Discard()
		}
	}()

	g1 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v1",
			cacheKeySeed: "seed1",
			value:        "result1",
		}),
	}
	g1.Vertex.(*vertex).setupCallCounters()

	res, err = j1.Build(ctx, g1)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result1")

	require.Equal(t, *g1.Vertex.(*vertex).cacheCallCount, int64(1))
	require.Equal(t, *g1.Vertex.(*vertex).execCallCount, int64(1))

	require.NoError(t, j1.Discard())
	j1 = nil

	// expect cache match for first build

	j2, err := s.NewJob("job2")
	require.NoError(t, err)

	defer func() {
		if j2 != nil {
			j2.Discard()
		}
	}()

	g2 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v2",
			cacheKeySeed: "seed0", // same as first build
			value:        "result2",
		}),
	}
	g2.Vertex.(*vertex).setupCallCounters()

	res, err = j2.Build(ctx, g2)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result0")

	require.Equal(t, *g0.Vertex.(*vertex).cacheCallCount, int64(1))
	require.Equal(t, *g0.Vertex.(*vertex).execCallCount, int64(1))
	require.Equal(t, *g2.Vertex.(*vertex).cacheCallCount, int64(1))
	require.Equal(t, *g2.Vertex.(*vertex).execCallCount, int64(0))

	require.NoError(t, j2.Discard())
	j2 = nil

}

func TestSingleLevelCacheParallel(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	s := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
	})
	defer s.Close()

	// rebuild in parallel. only executed once.

	j0, err := s.NewJob("job0")
	require.NoError(t, err)

	defer func() {
		if j0 != nil {
			j0.Discard()
		}
	}()

	wait2Ready := blockingFuncion(2)

	g0 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v0",
			cacheKeySeed: "seed0",
			cachePreFunc: wait2Ready,
			value:        "result0",
		}),
	}
	g0.Vertex.(*vertex).setupCallCounters()

	j1, err := s.NewJob("job1")
	require.NoError(t, err)

	defer func() {
		if j1 != nil {
			j1.Discard()
		}
	}()

	g1 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v1",
			cacheKeySeed: "seed0", // same as g0
			cachePreFunc: wait2Ready,
			value:        "result0",
		}),
	}
	g1.Vertex.(*vertex).setupCallCounters()

	eg, _ := errgroup.WithContext(ctx)

	eg.Go(func() error {
		res, err := j0.Build(ctx, g0)
		require.NoError(t, err)
		require.Equal(t, unwrap(res), "result0")
		return err
	})

	eg.Go(func() error {
		res, err := j1.Build(ctx, g1)
		require.NoError(t, err)
		require.Equal(t, unwrap(res), "result0")
		return err
	})

	require.NoError(t, eg.Wait())

	require.Equal(t, int64(1), *g0.Vertex.(*vertex).cacheCallCount)
	require.Equal(t, int64(1), *g1.Vertex.(*vertex).cacheCallCount)
	// only one execution ran
	require.Equal(t, int64(1), *g0.Vertex.(*vertex).execCallCount+*g1.Vertex.(*vertex).execCallCount)

}

func TestMultiLevelCacheParallel(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	s := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
	})
	defer s.Close()

	// rebuild in parallel. only executed once.

	j0, err := s.NewJob("job0")
	require.NoError(t, err)

	defer func() {
		if j0 != nil {
			j0.Discard()
		}
	}()

	wait2Ready := blockingFuncion(2)
	wait2Ready2 := blockingFuncion(2)

	g0 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v0",
			cacheKeySeed: "seed0",
			cachePreFunc: wait2Ready,
			value:        "result0",
			inputs: []Edge{{
				Vertex: vtx(vtxOpt{
					name:         "v0-c0",
					cacheKeySeed: "seed0-c0",
					cachePreFunc: wait2Ready2,
					value:        "result0-c0",
				})},
			},
		}),
	}
	g0.Vertex.(*vertex).setupCallCounters()

	j1, err := s.NewJob("job1")
	require.NoError(t, err)

	defer func() {
		if j1 != nil {
			j1.Discard()
		}
	}()

	g1 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v1",
			cacheKeySeed: "seed0", // same as g0
			cachePreFunc: wait2Ready,
			value:        "result0",
			inputs: []Edge{{
				Vertex: vtx(vtxOpt{
					name:         "v1-c0",
					cacheKeySeed: "seed0-c0", // same as g0
					cachePreFunc: wait2Ready2,
					value:        "result0-c",
				})},
			},
		}),
	}
	g1.Vertex.(*vertex).setupCallCounters()

	eg, _ := errgroup.WithContext(ctx)

	eg.Go(func() error {
		res, err := j0.Build(ctx, g0)
		require.NoError(t, err)
		require.Equal(t, unwrap(res), "result0")
		return err
	})

	eg.Go(func() error {
		res, err := j1.Build(ctx, g1)
		require.NoError(t, err)
		require.Equal(t, unwrap(res), "result0")
		return err
	})

	require.NoError(t, eg.Wait())

	require.Equal(t, int64(2), *g0.Vertex.(*vertex).cacheCallCount)
	require.Equal(t, int64(2), *g1.Vertex.(*vertex).cacheCallCount)
	require.Equal(t, int64(2), *g0.Vertex.(*vertex).execCallCount+*g1.Vertex.(*vertex).execCallCount)
}

func TestSingleCancelCache(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	s := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
	})
	defer s.Close()

	j0, err := s.NewJob("job0")
	require.NoError(t, err)

	defer func() {
		if j0 != nil {
			j0.Discard()
		}
	}()

	ctx, cancel := context.WithCancel(ctx)

	g0 := Edge{
		Vertex: vtx(vtxOpt{
			name: "v0",
			cachePreFunc: func(ctx context.Context) error {
				cancel()
				<-ctx.Done()
				return nil // error should still come from context
			},
		}),
	}
	g0.Vertex.(*vertex).setupCallCounters()

	_, err = j0.Build(ctx, g0)
	require.Error(t, err)
	require.Equal(t, errors.Cause(err), context.Canceled)

	require.Equal(t, *g0.Vertex.(*vertex).cacheCallCount, int64(1))
	require.Equal(t, *g0.Vertex.(*vertex).execCallCount, int64(0))

	require.NoError(t, j0.Discard())
	j0 = nil

}
func TestSingleCancelExec(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	s := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
	})
	defer s.Close()

	j1, err := s.NewJob("job1")
	require.NoError(t, err)

	defer func() {
		if j1 != nil {
			j1.Discard()
		}
	}()

	ctx, cancel := context.WithCancel(ctx)

	g1 := Edge{
		Vertex: vtx(vtxOpt{
			name: "v2",
			execPreFunc: func(ctx context.Context) error {
				cancel()
				<-ctx.Done()
				return nil // error should still come from context
			},
		}),
	}
	g1.Vertex.(*vertex).setupCallCounters()

	_, err = j1.Build(ctx, g1)
	require.Error(t, err)
	require.Equal(t, errors.Cause(err), context.Canceled)

	require.Equal(t, *g1.Vertex.(*vertex).cacheCallCount, int64(1))
	require.Equal(t, *g1.Vertex.(*vertex).execCallCount, int64(1))

	require.NoError(t, j1.Discard())
	j1 = nil
}

func TestSingleCancelParallel(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	s := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
	})
	defer s.Close()

	// run 2 in parallel cancel first, second one continues without errors
	eg, ctx := errgroup.WithContext(ctx)

	firstReady := make(chan struct{})
	firstErrored := make(chan struct{})

	eg.Go(func() error {
		j, err := s.NewJob("job2")
		require.NoError(t, err)

		defer func() {
			if j != nil {
				j.Discard()
			}
		}()

		ctx, cancel := context.WithCancel(ctx)
		defer cancel()

		g := Edge{
			Vertex: vtx(vtxOpt{
				name:  "v2",
				value: "result2",
				cachePreFunc: func(ctx context.Context) error {
					close(firstReady)
					time.Sleep(200 * time.Millisecond)
					cancel()
					<-firstErrored
					return nil
				},
			}),
		}

		_, err = j.Build(ctx, g)
		close(firstErrored)
		require.Error(t, err)
		require.Equal(t, errors.Cause(err), context.Canceled)
		return nil
	})

	eg.Go(func() error {
		j, err := s.NewJob("job3")
		require.NoError(t, err)

		defer func() {
			if j != nil {
				j.Discard()
			}
		}()

		g := Edge{
			Vertex: vtx(vtxOpt{
				name: "v2",
			}),
		}
		<-firstReady

		res, err := j.Build(ctx, g)
		require.NoError(t, err)
		require.Equal(t, unwrap(res), "result2")
		return err
	})

	require.NoError(t, eg.Wait())
}

func TestMultiLevelCalculation(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	l := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
	})
	defer l.Close()

	j0, err := l.NewJob("j0")
	require.NoError(t, err)

	defer func() {
		if j0 != nil {
			j0.Discard()
		}
	}()

	g := Edge{
		Vertex: vtxSum(1, vtxOpt{
			inputs: []Edge{
				{Vertex: vtxSum(0, vtxOpt{
					inputs: []Edge{
						{Vertex: vtxConst(7, vtxOpt{})},
						{Vertex: vtxConst(2, vtxOpt{})},
					},
				})},
				{Vertex: vtxSum(0, vtxOpt{
					inputs: []Edge{
						{Vertex: vtxConst(7, vtxOpt{})},
						{Vertex: vtxConst(2, vtxOpt{})},
					},
				})},
				{Vertex: vtxConst(2, vtxOpt{})},
				{Vertex: vtxConst(2, vtxOpt{})},
				{Vertex: vtxConst(19, vtxOpt{})},
			},
		}),
	}

	res, err := j0.Build(ctx, g)
	require.NoError(t, err)
	require.Equal(t, unwrapInt(res), 42) // 1 + 2*(7 + 2) + 2 + 2 + 19

	require.NoError(t, j0.Discard())
	j0 = nil

	// repeating same build with cache should behave the same
	j1, err := l.NewJob("j1")
	require.NoError(t, err)

	defer func() {
		if j1 != nil {
			j1.Discard()
		}
	}()

	g2 := Edge{
		Vertex: vtxSum(1, vtxOpt{
			inputs: []Edge{
				{Vertex: vtxSum(0, vtxOpt{
					inputs: []Edge{
						{Vertex: vtxConst(7, vtxOpt{})},
						{Vertex: vtxConst(2, vtxOpt{})},
					},
				})},
				{Vertex: vtxSum(0, vtxOpt{
					inputs: []Edge{
						{Vertex: vtxConst(7, vtxOpt{})},
						{Vertex: vtxConst(2, vtxOpt{})},
					},
				})},
				{Vertex: vtxConst(2, vtxOpt{})},
				{Vertex: vtxConst(2, vtxOpt{})},
				{Vertex: vtxConst(19, vtxOpt{})},
			},
		}),
	}
	res, err = j1.Build(ctx, g2)
	require.NoError(t, err)
	require.Equal(t, unwrapInt(res), 42)

}

func TestHugeGraph(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	rand.Seed(time.Now().UnixNano())

	cacheManager := newTrackingCacheManager(NewInMemoryCacheManager())

	l := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
		DefaultCache:  cacheManager,
	})
	defer l.Close()

	j0, err := l.NewJob("j0")
	require.NoError(t, err)

	defer func() {
		if j0 != nil {
			j0.Discard()
		}
	}()

	nodes := 1000

	g, v := generateSubGraph(nodes)
	// printGraph(g, "")
	g.Vertex.(*vertexSum).setupCallCounters()

	res, err := j0.Build(ctx, g)
	require.NoError(t, err)
	require.Equal(t, unwrapInt(res), v)
	require.Equal(t, int64(nodes), *g.Vertex.(*vertexSum).cacheCallCount)
	// execCount := *g.Vertex.(*vertexSum).execCallCount
	// require.True(t, execCount < 1000)
	// require.True(t, execCount > 600)
	require.Equal(t, int64(0), cacheManager.loadCounter)

	require.NoError(t, j0.Discard())
	j0 = nil

	j1, err := l.NewJob("j1")
	require.NoError(t, err)

	defer func() {
		if j1 != nil {
			j1.Discard()
		}
	}()

	g.Vertex.(*vertexSum).setupCallCounters()
	res, err = j1.Build(ctx, g)
	require.NoError(t, err)
	require.Equal(t, unwrapInt(res), v)

	require.Equal(t, int64(nodes), *g.Vertex.(*vertexSum).cacheCallCount)
	require.Equal(t, int64(0), *g.Vertex.(*vertexSum).execCallCount)
	require.Equal(t, int64(1), cacheManager.loadCounter)
}

// TestOptimizedCacheAccess tests that inputs are not loaded from cache unless
// they are really needed
func TestOptimizedCacheAccess(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	cacheManager := newTrackingCacheManager(NewInMemoryCacheManager())

	l := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
		DefaultCache:  cacheManager,
	})
	defer l.Close()

	j0, err := l.NewJob("j0")
	require.NoError(t, err)

	defer func() {
		if j0 != nil {
			j0.Discard()
		}
	}()

	g0 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v0",
			cacheKeySeed: "seed0",
			value:        "result0",
			inputs: []Edge{
				{Vertex: vtx(vtxOpt{
					name:         "v1",
					cacheKeySeed: "seed1",
					value:        "result1",
				})},
				{Vertex: vtx(vtxOpt{
					name:         "v2",
					cacheKeySeed: "seed2",
					value:        "result2",
				})},
			},
			slowCacheCompute: map[int]ResultBasedCacheFunc{
				1: digestFromResult,
			},
		}),
	}
	g0.Vertex.(*vertex).setupCallCounters()

	res, err := j0.Build(ctx, g0)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result0")

	require.Equal(t, int64(3), *g0.Vertex.(*vertex).cacheCallCount)
	require.Equal(t, int64(3), *g0.Vertex.(*vertex).execCallCount)
	require.Equal(t, int64(0), cacheManager.loadCounter)

	require.NoError(t, j0.Discard())
	j0 = nil

	// changing cache seed for the input with slow cache should not pull result1

	j1, err := l.NewJob("j1")
	require.NoError(t, err)

	defer func() {
		if j1 != nil {
			j1.Discard()
		}
	}()

	g1 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v0",
			cacheKeySeed: "seed0",
			value:        "result0-nocache",
			inputs: []Edge{
				{Vertex: vtx(vtxOpt{
					name:         "v1",
					cacheKeySeed: "seed1",
					value:        "result1-nocache",
				})},
				{Vertex: vtx(vtxOpt{
					name:         "v2-changed",
					cacheKeySeed: "seed2-changed",
					value:        "result2", // produces same slow key as g0
				})},
			},
			slowCacheCompute: map[int]ResultBasedCacheFunc{
				1: digestFromResult,
			},
		}),
	}
	g1.Vertex.(*vertex).setupCallCounters()

	res, err = j1.Build(ctx, g1)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result0")

	require.Equal(t, int64(3), *g1.Vertex.(*vertex).cacheCallCount)
	require.Equal(t, int64(1), *g1.Vertex.(*vertex).execCallCount)
	require.Equal(t, int64(1), cacheManager.loadCounter)

	require.NoError(t, j1.Discard())
	j1 = nil
}

// TestOptimizedCacheAccess2 is a more narrow case that tests that inputs are
// not loaded from cache unless they are really needed. Inputs that match by
// definition should be less prioritized for slow cache calculation than the
// inputs that didn't.
func TestOptimizedCacheAccess2(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	cacheManager := newTrackingCacheManager(NewInMemoryCacheManager())

	l := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
		DefaultCache:  cacheManager,
	})
	defer l.Close()

	j0, err := l.NewJob("j0")
	require.NoError(t, err)

	defer func() {
		if j0 != nil {
			j0.Discard()
		}
	}()

	g0 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v0",
			cacheKeySeed: "seed0",
			value:        "result0",
			inputs: []Edge{
				{Vertex: vtx(vtxOpt{
					name:         "v1",
					cacheKeySeed: "seed1",
					value:        "result1",
				})},
				{Vertex: vtx(vtxOpt{
					name:         "v2",
					cacheKeySeed: "seed2",
					value:        "result2",
				})},
			},
			slowCacheCompute: map[int]ResultBasedCacheFunc{
				0: digestFromResult,
				1: digestFromResult,
			},
		}),
	}
	g0.Vertex.(*vertex).setupCallCounters()

	res, err := j0.Build(ctx, g0)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result0")

	require.Equal(t, int64(3), *g0.Vertex.(*vertex).cacheCallCount)
	require.Equal(t, int64(3), *g0.Vertex.(*vertex).execCallCount)
	require.Equal(t, int64(0), cacheManager.loadCounter)

	require.NoError(t, j0.Discard())
	j0 = nil

	// changing cache seed for the input with slow cache should not pull result1

	j1, err := l.NewJob("j1")
	require.NoError(t, err)

	defer func() {
		if j1 != nil {
			j1.Discard()
		}
	}()

	g1 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v0",
			cacheKeySeed: "seed0",
			value:        "result0-nocache",
			inputs: []Edge{
				{Vertex: vtx(vtxOpt{
					name:         "v1",
					cacheKeySeed: "seed1",
					value:        "result1",
				})},
				{Vertex: vtx(vtxOpt{
					name:         "v2-changed",
					cacheKeySeed: "seed2-changed",
					value:        "result2", // produces same slow key as g0
				})},
			},
			slowCacheCompute: map[int]ResultBasedCacheFunc{
				0: digestFromResult,
				1: digestFromResult,
			},
		}),
	}
	g1.Vertex.(*vertex).setupCallCounters()

	res, err = j1.Build(ctx, g1)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result0")

	require.Equal(t, int64(3), *g1.Vertex.(*vertex).cacheCallCount)
	require.Equal(t, int64(1), *g1.Vertex.(*vertex).execCallCount)
	require.Equal(t, int64(1), cacheManager.loadCounter) // v1 is never loaded nor executed

	require.NoError(t, j1.Discard())
	j1 = nil

	// make sure that both inputs are still used for slow cache hit
	j2, err := l.NewJob("j2")
	require.NoError(t, err)

	defer func() {
		if j2 != nil {
			j2.Discard()
		}
	}()

	g2 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v0",
			cacheKeySeed: "seed0",
			value:        "result0-nocache",
			inputs: []Edge{
				{Vertex: vtx(vtxOpt{
					name:         "v1",
					cacheKeySeed: "seed1-changed2",
					value:        "result1",
				})},
				{Vertex: vtx(vtxOpt{
					name:         "v2-changed",
					cacheKeySeed: "seed2-changed2",
					value:        "result2", // produces same slow key as g0
				})},
			},
			slowCacheCompute: map[int]ResultBasedCacheFunc{
				0: digestFromResult,
				1: digestFromResult,
			},
		}),
	}
	g2.Vertex.(*vertex).setupCallCounters()

	res, err = j2.Build(ctx, g2)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result0")

	require.Equal(t, int64(3), *g2.Vertex.(*vertex).cacheCallCount)
	require.Equal(t, int64(2), *g2.Vertex.(*vertex).execCallCount)
	require.Equal(t, int64(2), cacheManager.loadCounter)

	require.NoError(t, j2.Discard())
	j1 = nil
}

func TestSlowCache(t *testing.T) {
	t.Parallel()
	ctx := context.TODO()

	rand.Seed(time.Now().UnixNano())

	l := NewJobList(SolverOpt{
		ResolveOpFunc: testOpResolver,
	})
	defer l.Close()

	j0, err := l.NewJob("j0")
	require.NoError(t, err)

	defer func() {
		if j0 != nil {
			j0.Discard()
		}
	}()

	g0 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v0",
			cacheKeySeed: "seed0",
			value:        "result0",
			inputs: []Edge{
				{Vertex: vtx(vtxOpt{
					name:         "v1",
					cacheKeySeed: "seed1",
					value:        "result1",
				})},
			},
			slowCacheCompute: map[int]ResultBasedCacheFunc{
				0: digestFromResult,
			},
		}),
	}

	res, err := j0.Build(ctx, g0)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result0")

	require.NoError(t, j0.Discard())
	j0 = nil

	j1, err := l.NewJob("j1")
	require.NoError(t, err)

	defer func() {
		if j1 != nil {
			j1.Discard()
		}
	}()

	g1 := Edge{
		Vertex: vtx(vtxOpt{
			name:         "v2",
			cacheKeySeed: "seed0",
			value:        "not-cached",
			inputs: []Edge{
				{Vertex: vtx(vtxOpt{
					name:         "v3",
					cacheKeySeed: "seed3",
					value:        "result1", // used for slow key
				})},
			},
			slowCacheCompute: map[int]ResultBasedCacheFunc{
				0: digestFromResult,
			},
		}),
	}

	res, err = j1.Build(ctx, g1)
	require.NoError(t, err)
	require.Equal(t, unwrap(res), "result0")

	require.NoError(t, j1.Discard())
	j1 = nil

}

func generateSubGraph(nodes int) (Edge, int) {
	if nodes == 1 {
		value := rand.Int() % 500
		return Edge{Vertex: vtxConst(value, vtxOpt{})}, value
	}
	spread := rand.Int()%5 + 2
	inc := int(math.Ceil(float64(nodes) / float64(spread)))
	if inc > nodes {
		inc = nodes
	}
	added := 1
	value := 0
	inputs := []Edge{}
	i := 0
	for {
		i++
		if added >= nodes {
			break
		}
		if added+inc > nodes {
			inc = nodes - added
		}
		e, v := generateSubGraph(inc)
		inputs = append(inputs, e)
		value += v
		added += inc
	}
	extra := rand.Int() % 500
	value += extra
	return Edge{Vertex: vtxSum(extra, vtxOpt{inputs: inputs})}, value
}

type vtxOpt struct {
	name             string
	cacheKeySeed     string
	execDelay        time.Duration
	cacheDelay       time.Duration
	cachePreFunc     func(context.Context) error
	execPreFunc      func(context.Context) error
	inputs           []Edge
	value            string
	slowCacheCompute map[int]ResultBasedCacheFunc
}

func vtx(opt vtxOpt) *vertex {
	if opt.name == "" {
		opt.name = identity.NewID()
	}
	if opt.cacheKeySeed == "" {
		opt.cacheKeySeed = identity.NewID()
	}
	return &vertex{opt: opt}
}

type vertex struct {
	opt vtxOpt

	cacheCallCount *int64
	execCallCount  *int64
}

func (v *vertex) Digest() digest.Digest {
	return digest.FromBytes([]byte(v.opt.name))
}
func (v *vertex) Sys() interface{} {
	return v
}
func (v *vertex) Inputs() []Edge {
	return v.opt.inputs
}
func (v *vertex) Name() string {
	return v.opt.name
}

func (v *vertex) setupCallCounters() {
	var cacheCount int64
	var execCount int64

	v.setCallCounters(&cacheCount, &execCount)
}

func (v *vertex) setCallCounters(cacheCount, execCount *int64) {
	v.cacheCallCount = cacheCount
	v.execCallCount = execCount

	for _, inp := range v.opt.inputs {
		var v *vertex
		switch vv := inp.Vertex.(type) {
		case *vertex:
			v = vv
		case *vertexSum:
			v = vv.vertex
		case *vertexConst:
			v = vv.vertex
		}
		v.setCallCounters(cacheCount, execCount)
	}
}

func (v *vertex) cacheMap(ctx context.Context) error {
	if f := v.opt.cachePreFunc; f != nil {
		if err := f(ctx); err != nil {
			return err
		}
	}
	if v.cacheCallCount != nil {
		atomic.AddInt64(v.cacheCallCount, 1)
	}
	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
	}
	select {
	case <-time.After(v.opt.cacheDelay):
	case <-ctx.Done():
		return ctx.Err()
	}
	return nil
}

func (v *vertex) CacheMap(ctx context.Context) (*CacheMap, error) {
	if err := v.cacheMap(ctx); err != nil {
		return nil, err
	}
	return v.makeCacheMap(), nil
}

func (v *vertex) exec(ctx context.Context, inputs []Result) error {
	if len(inputs) != len(v.Inputs()) {
		return errors.Errorf("invalid number of inputs")
	}
	if f := v.opt.execPreFunc; f != nil {
		if err := f(ctx); err != nil {
			return err
		}
	}
	if v.execCallCount != nil {
		atomic.AddInt64(v.execCallCount, 1)
	}
	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
	}
	select {
	case <-time.After(v.opt.execDelay):
	case <-ctx.Done():
		return ctx.Err()
	}
	return nil
}

func (v *vertex) Exec(ctx context.Context, inputs []Result) (outputs []Result, err error) {
	if err := v.exec(ctx, inputs); err != nil {
		return nil, err
	}
	return []Result{&dummyResult{id: identity.NewID(), value: v.opt.value}}, nil
}

func (v *vertex) makeCacheMap() *CacheMap {
	m := &CacheMap{
		Digest: digest.FromBytes([]byte(fmt.Sprintf("seed:%s", v.opt.cacheKeySeed))),
		Deps: make([]struct {
			Selector          digest.Digest
			ComputeDigestFunc ResultBasedCacheFunc
		}, len(v.Inputs())),
	}
	for i, f := range v.opt.slowCacheCompute {
		m.Deps[i].ComputeDigestFunc = f
	}
	return m
}

// vtxConst returns a vertex that outputs a constant integer
func vtxConst(v int, opt vtxOpt) *vertexConst {
	if opt.cacheKeySeed == "" {
		opt.cacheKeySeed = fmt.Sprintf("const-%d", v)
	}
	if opt.name == "" {
		opt.name = opt.cacheKeySeed + "-" + identity.NewID()
	}
	return &vertexConst{vertex: vtx(opt), value: v}
}

type vertexConst struct {
	*vertex
	value int
}

func (v *vertexConst) Sys() interface{} {
	return v
}

func (v *vertexConst) Exec(ctx context.Context, inputs []Result) (outputs []Result, err error) {
	if err := v.exec(ctx, inputs); err != nil {
		return nil, err
	}
	return []Result{&dummyResult{id: identity.NewID(), intValue: v.value}}, nil
}

// vtxSum returns a vertex that ourputs sum of its inputs plus a constant
func vtxSum(v int, opt vtxOpt) *vertexSum {
	if opt.cacheKeySeed == "" {
		opt.cacheKeySeed = fmt.Sprintf("sum-%d", v)
	}
	if opt.name == "" {
		opt.name = opt.cacheKeySeed + "-" + identity.NewID()
	}
	return &vertexSum{vertex: vtx(opt), value: v}
}

type vertexSum struct {
	*vertex
	value int
}

func (v *vertexSum) Sys() interface{} {
	return v
}

func (v *vertexSum) Exec(ctx context.Context, inputs []Result) (outputs []Result, err error) {
	if err := v.exec(ctx, inputs); err != nil {
		return nil, err
	}
	s := v.value
	for _, inp := range inputs {
		r, ok := inp.Sys().(*dummyResult)
		if !ok {
			return nil, errors.Errorf("invalid input type: %T", inp.Sys())
		}
		s += r.intValue
	}
	return []Result{&dummyResult{id: identity.NewID(), intValue: s}}, nil
}

func printGraph(e Edge, pfx string) {
	name := e.Vertex.Name()
	fmt.Printf("%s %d %s\n", pfx, e.Index, name)
	for _, inp := range e.Vertex.Inputs() {
		printGraph(inp, pfx+"-->")
	}
}

type dummyResult struct {
	id       string
	value    string
	intValue int
}

func (r *dummyResult) ID() string                    { return r.id }
func (r *dummyResult) Release(context.Context) error { return nil }
func (r *dummyResult) Sys() interface{}              { return r }

func testOpResolver(v Vertex) (Op, error) {
	if op, ok := v.Sys().(Op); ok {
		return op, nil
	}
	return nil, errors.Errorf("invalid vertex")
}

func unwrap(res Result) string {
	r, ok := res.Sys().(*dummyResult)
	if !ok {
		return "unwrap-error"
	}
	return r.value
}

func unwrapInt(res Result) int {
	r, ok := res.Sys().(*dummyResult)
	if !ok {
		return -1e6
	}
	return r.intValue
}

func blockingFuncion(i int) func(context.Context) error {
	limit := int64(i)
	block := make(chan struct{})
	return func(context.Context) error {
		if atomic.AddInt64(&limit, -1) == 0 {
			close(block)
		}
		<-block
		return nil
	}
}

func newTrackingCacheManager(cm CacheManager) *trackingCacheManager {
	return &trackingCacheManager{CacheManager: cm}
}

type trackingCacheManager struct {
	CacheManager
	loadCounter int64
}

func (cm *trackingCacheManager) Load(ctx context.Context, rec *CacheRecord) (Result, error) {
	atomic.AddInt64(&cm.loadCounter, 1)
	return cm.CacheManager.Load(ctx, rec)
}

func digestFromResult(ctx context.Context, res Result) (digest.Digest, error) {
	return digest.FromBytes([]byte(unwrap(res))), nil
}