[WIP] Kavadist Simulations (#435)

* feat: kavadist sims

* refactor genesis, add validation

* implement params

* rename simulation to genesis

Co-authored-by: Kevin Davis <kjydavis3@gmail.com>

x/kavadist/simulation/genesis.go

@@ -0,0 +1,84 @@
+package simulation
+
+import (
+	"fmt"
+	"math/rand"
+	"time"
+
+	"github.com/cosmos/cosmos-sdk/codec"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/types/module"
+	"github.com/cosmos/cosmos-sdk/x/simulation"
+
+	"github.com/kava-labs/kava/x/kavadist/types"
+)
+
+// SecondsPerYear is the number of seconds in a year
+const SecondsPerYear = 31536000
+
+// BaseAprPadding prevents the calculated SPR inflation rate from being 0.0
+const BaseAprPadding = "0.000000000100000000"
+
+// RandomizedGenState generates a random GenesisState for kavadist module
+func RandomizedGenState(simState *module.SimulationState) {
+	params := genRandomParams(simState)
+	if err := params.Validate(); err != nil {
+		panic(err)
+	}
+
+	kavadistGenesis := types.NewGenesisState(params, types.DefaultPreviousBlockTime)
+	if err := kavadistGenesis.Validate(); err != nil {
+		panic(err)
+	}
+
+	fmt.Printf("Selected randomly generated %s parameters:\n%s\n", types.ModuleName, codec.MustMarshalJSONIndent(simState.Cdc, kavadistGenesis))
+	simState.GenState[types.ModuleName] = simState.Cdc.MustMarshalJSON(kavadistGenesis)
+}
+
+func genRandomParams(simState *module.SimulationState) types.Params {
+	periods := genRandomPeriods(simState.Rand, simState.GenTimestamp)
+	params := types.NewParams(true, periods)
+	return params
+}
+
+func genRandomPeriods(r *rand.Rand, timestamp time.Time) types.Periods {
+	var periods types.Periods
+	numPeriods := simulation.RandIntBetween(r, 1, 10)
+	periodStart := timestamp
+	for i := 0; i < numPeriods; i++ {
+		// set periods to be between 2 weeks and 2 years
+		durationMultiplier := simulation.RandIntBetween(r, 14, 104)
+		duration := time.Duration(int64(24*durationMultiplier)) * time.Hour
+		periodEnd := periodStart.Add(duration)
+		inflation := genRandomInflation(r)
+		period := types.NewPeriod(periodStart, periodEnd, inflation)
+		periods = append(periods, period)
+		periodStart = periodEnd
+	}
+	return periods
+}
+
+func genRandomInflation(r *rand.Rand) sdk.Dec {
+	// If sim.RandomDecAmount returns 0 (happens frequently by design), add BaseAprPadding
+	extraAprInflation := simulation.RandomDecAmount(r, sdk.MustNewDecFromStr("0.25"))
+	for extraAprInflation.Equal(sdk.ZeroDec()) {
+		extraAprInflation = extraAprInflation.Add(sdk.MustNewDecFromStr(BaseAprPadding))
+	}
+
+	aprInflation := sdk.OneDec().Add(extraAprInflation)
+	// convert APR inflation to SPR (inflation per second)
+	inflationSpr, err := approxRoot(aprInflation, uint64(SecondsPerYear))
+	if err != nil {
+		panic(fmt.Sprintf("error generating random inflation %v", err))
+	}
+	return inflationSpr
+}
+
+func genRandomActive(r *rand.Rand) bool {
+	threshold := 50
+	value := simulation.RandIntBetween(r, 1, 100)
+	if value > threshold {
+		return true
+	}
+	return false
+}

x/kavadist/simulation/params.go

@@ -1,14 +1,34 @@
 package simulation
 
 import (
+	"fmt"
 	"math/rand"
 
 	"github.com/cosmos/cosmos-sdk/x/simulation"
+
+	"github.com/kava-labs/kava/x/kavadist/types"
 )
 
 // ParamChanges defines the parameters that can be modified by param change proposals
 // on the simulation
 func ParamChanges(r *rand.Rand) []simulation.ParamChange {
-	// TODO implement this
-	return []simulation.ParamChange{}
+	// Hacky way to validate periods since validation is wrapped in params
+	active := genRandomActive(r)
+	periods := genRandomPeriods(r, simulation.RandTimestamp(r))
+	if err := types.NewParams(active, periods).Validate(); err != nil {
+		panic(err)
+	}
+
+	return []simulation.ParamChange{
+		simulation.NewSimParamChange(types.ModuleName, string(types.KeyActive), "",
+			func(r *rand.Rand) string {
+				return fmt.Sprintf("\"%t\"", active)
+			},
+		),
+		simulation.NewSimParamChange(types.ModuleName, string(types.KeyPeriods), "",
+			func(r *rand.Rand) string {
+				return fmt.Sprintf("\"%v\"", periods)
+			},
+		),
+	}
 }

x/kavadist/simulation/simulation.go

@@ -1,22 +0,0 @@
-package simulation
-
-import (
-	"fmt"
-
-	"github.com/cosmos/cosmos-sdk/codec"
-	"github.com/cosmos/cosmos-sdk/types/module"
-
-	"github.com/kava-labs/kava/x/kavadist/types"
-)
-
-// RandomizedGenState generates a random GenesisState for cdp
-func RandomizedGenState(simState *module.SimulationState) {
-
-	// TODO implement this fully
-	// - randomly generating the genesis params
-	// - overwriting with genesis provided to simulation
-	genesis := types.DefaultGenesisState()
-
-	fmt.Printf("Selected randomly generated %s parameters:\n%s\n", types.ModuleName, codec.MustMarshalJSONIndent(simState.Cdc, genesis))
-	simState.GenState[types.ModuleName] = simState.Cdc.MustMarshalJSON(genesis)
-}

x/kavadist/simulation/utils.go

@@ -0,0 +1,64 @@
+package simulation
+
+import (
+	"errors"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+)
+
+// TODO use the official version available in v0.38.2 of the sdk
+// https://github.com/cosmos/cosmos-sdk/blob/e8d89a2fe26175b73545a3e79ae783032b4e975e/types/decimal.go#L328
+func approxRoot(d sdk.Dec, root uint64) (guess sdk.Dec, err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			var ok bool
+			err, ok = r.(error)
+			if !ok {
+				err = errors.New("out of bounds")
+			}
+		}
+	}()
+
+	if d.IsNegative() {
+		absRoot, err := approxRoot(d.MulInt64(-1), root)
+		return absRoot.MulInt64(-1), err
+	}
+	if root == 1 || d.IsZero() || d.Equal(sdk.OneDec()) {
+		return d, nil
+	}
+	if root == 0 {
+		return sdk.OneDec(), nil
+	}
+	rootInt := sdk.NewInt(int64(root))
+	guess, delta := sdk.OneDec(), sdk.OneDec()
+	for delta.Abs().GT(sdk.SmallestDec()) {
+		prev := power(guess, (root - 1))
+		if prev.IsZero() {
+			prev = sdk.SmallestDec()
+		}
+		delta = d.Quo(prev)
+		delta = delta.Sub(guess)
+		delta = delta.QuoInt(rootInt)
+
+		guess = guess.Add(delta)
+	}
+	return guess, nil
+}
+
+// Power returns a the result of raising to a positive integer power
+func power(d sdk.Dec, power uint64) sdk.Dec {
+	if power == 0 {
+		return sdk.OneDec()
+	}
+	tmp := sdk.OneDec()
+	for i := power; i > 1; {
+		if i%2 == 0 {
+			i /= 2
+		} else {
+			tmp = tmp.Mul(d)
+			i = (i - 1) / 2
+		}
+		d = d.Mul(d)
+	}
+	return d.Mul(tmp)
+}

x/kavadist/simulation/utils_test.go

@@ -0,0 +1,30 @@
+package simulation
+
+import (
+	"testing"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/stretchr/testify/require"
+)
+
+func TestApproxRoot(t *testing.T) {
+	testCases := []struct {
+		input    sdk.Dec
+		root     uint64
+		expected sdk.Dec
+	}{
+		{sdk.OneDec(), 10, sdk.OneDec()},                                                       // 1.0 ^ (0.1) => 1.0
+		{sdk.NewDecWithPrec(25, 2), 2, sdk.NewDecWithPrec(5, 1)},                               // 0.25 ^ (0.5) => 0.5
+		{sdk.NewDecWithPrec(4, 2), 2, sdk.NewDecWithPrec(2, 1)},                                // 0.04 => 0.2
+		{sdk.NewDecFromInt(sdk.NewInt(27)), 3, sdk.NewDecFromInt(sdk.NewInt(3))},               // 27 ^ (1/3) => 3
+		{sdk.NewDecFromInt(sdk.NewInt(-81)), 4, sdk.NewDecFromInt(sdk.NewInt(-3))},             // -81 ^ (0.25) => -3
+		{sdk.NewDecFromInt(sdk.NewInt(2)), 2, sdk.NewDecWithPrec(1414213562373095049, 18)},     // 2 ^ (0.5) => 1.414213562373095049
+		{sdk.NewDecWithPrec(1005, 3), 31536000, sdk.MustNewDecFromStr("1.000000000158153904")}, // 1.005 ^ (1/31536000) = 1.000000000158153904
+	}
+
+	for i, tc := range testCases {
+		res, err := approxRoot(tc.input, tc.root)
+		require.NoError(t, err)
+		require.True(t, tc.expected.Sub(res).Abs().LTE(sdk.SmallestDec()), "unexpected result for test case %d, input: %v", i, tc.input)
+	}
+}

x/kavadist/types/params.go

@@ -33,6 +33,15 @@ type Period struct {
 	Inflation sdk.Dec   `json:"inflation" yaml:"inflation"` // example "1.000000003022265980"  - 10% inflation
 }
 
+// NewPeriod returns a new instance of Period
+func NewPeriod(start time.Time, end time.Time, inflation sdk.Dec) Period {
+	return Period{
+		Start:     start,
+		End:       end,
+		Inflation: inflation,
+	}
+}
+
 // String implements fmt.Stringer
 func (pr Period) String() string {
 	return fmt.Sprintf(`Period: