feat: simulateStateChanges GraphQL query — Phase 0 scaffolding + walking skeleton

internal/serve/graphql/resolvers/resolver.go

@@ -50,21 +50,23 @@ var ErrNotStateChange = errors.New("object is not a StateChange")
 // Resolver is the main resolver struct for gqlgen.
 // It holds dependencies needed by all resolver functions.
 type Resolver struct {
-	models        *data.Models
-	rpcService    services.RPCService
-	balanceReader BalanceReader
-	metrics       *metrics.Metrics
-	config        ResolverConfig
+	models            *data.Models
+	rpcService        services.RPCService
+	balanceReader     BalanceReader
+	metrics           *metrics.Metrics
+	config            ResolverConfig
+	simulationService services.TransactionSimulationService
 }
 
 // NewResolver creates a new resolver instance with required dependencies.
-func NewResolver(models *data.Models, rpcService services.RPCService, balanceReader BalanceReader, m *metrics.Metrics, config ResolverConfig) *Resolver {
+func NewResolver(models *data.Models, rpcService services.RPCService, balanceReader BalanceReader, m *metrics.Metrics, config ResolverConfig, simulationService services.TransactionSimulationService) *Resolver {
 	return &Resolver{
-		models:        models,
-		rpcService:    rpcService,
-		balanceReader: balanceReader,
-		metrics:       m,
-		config:        config,
+		models:            models,
+		rpcService:        rpcService,
+		balanceReader:     balanceReader,
+		metrics:           m,
+		config:            config,
+		simulationService: simulationService,
 	}
 }
 

internal/serve/graphql/resolvers/simulation.go

@@ -0,0 +1,140 @@
+package resolvers
+
+import (
+	"fmt"
+	"math"
+
+	"github.com/stellar/wallet-backend/internal/indexer/types"
+	graphql1 "github.com/stellar/wallet-backend/internal/serve/graphql/generated"
+)
+
+// convertToSimulatedStateChanges resolves the concrete simulated GraphQL type for
+// each state change produced by the simulation pipeline. Unlike the history types
+// (convertStateChangeTypes), simulated types are plain structs built eagerly: the
+// data never touches the DB, so there are no lazy column-backed resolvers.
+func (r *Resolver) convertToSimulatedStateChanges(stateChanges []types.StateChange) ([]graphql1.BaseSimulatedStateChange, error) {
+	converted := make([]graphql1.BaseSimulatedStateChange, len(stateChanges))
+	for i, stateChange := range stateChanges {
+		c, err := r.convertToSimulatedStateChange(stateChange)
+		if err != nil {
+			return nil, err
+		}
+		converted[i] = c
+	}
+	return converted, nil
+}
+
+// convertToSimulatedStateChange dispatches on (category, reason), mirroring
+// convertStateChangeTypes. A change matching no arm means the simulation pipeline
+// emitted a variant the simulated schema does not expose yet, and surfaces as an
+// error rather than a silently dropped row.
+func (r *Resolver) convertToSimulatedStateChange(sc types.StateChange) (graphql1.BaseSimulatedStateChange, error) {
+	accountAddress := string(sc.AccountID)
+
+	switch sc.StateChangeCategory {
+	case types.StateChangeCategoryBalance:
+		switch sc.StateChangeReason {
+		case types.StateChangeReasonDebit, types.StateChangeReasonCredit, types.StateChangeReasonMint, types.StateChangeReasonBurn:
+			tokenID, err := r.resolveRequiredAddress(sc.TokenID, "tokenId")
+			if err != nil {
+				return nil, err
+			}
+			amount, err := r.resolveRequiredString(sc.Amount, "amount")
+			if err != nil {
+				return nil, err
+			}
+			return graphql1.SimulatedBalanceChange{
+				Category:       sc.StateChangeCategory,
+				Reason:         sc.StateChangeReason,
+				AccountAddress: accountAddress,
+				TokenID:        tokenID,
+				Amount:         amount,
+				ToMuxedID:      r.resolveNullableString(sc.ToMuxedID),
+			}, nil
+		default: // invalid reason for BALANCE; falls through to the error below
+		}
+	case types.StateChangeCategoryAccount:
+		switch sc.StateChangeReason {
+		case types.StateChangeReasonCreate:
+			creatorAddress, err := r.resolveRequiredAddress(sc.CreatorAccountID, "creatorAddress")
+			if err != nil {
+				return nil, err
+			}
+			return graphql1.SimulatedAccountCreatedChange{
+				Category:       sc.StateChangeCategory,
+				Reason:         sc.StateChangeReason,
+				AccountAddress: accountAddress,
+				CreatorAddress: creatorAddress,
+			}, nil
+		default: // invalid reason for ACCOUNT; falls through to the error below
+		}
+	case types.StateChangeCategoryAllowance:
+		switch sc.StateChangeReason {
+		case types.StateChangeReasonUpdate:
+			tokenID, err := r.resolveRequiredAddress(sc.TokenID, "tokenId")
+			if err != nil {
+				return nil, err
+			}
+			spender, err := r.resolveRequiredAddress(sc.SpenderAccountID, "spender")
+			if err != nil {
+				return nil, err
+			}
+			amount, err := r.resolveRequiredString(sc.Amount, "amount")
+			if err != nil {
+				return nil, err
+			}
+			expirationLedger, ok := keyValueUint32(sc.KeyValue, "live_until_ledger")
+			if !ok {
+				return nil, fmt.Errorf("state change is missing required expirationLedger")
+			}
+			return graphql1.SimulatedAllowanceChange{
+				Category:         sc.StateChangeCategory,
+				Reason:           sc.StateChangeReason,
+				AccountAddress:   accountAddress,
+				TokenID:          tokenID,
+				Spender:          spender,
+				Amount:           amount,
+				ExpirationLedger: expirationLedger,
+			}, nil
+		default: // invalid reason for ALLOWANCE; falls through to the error below
+		}
+	case types.StateChangeCategoryBalanceAuthorization:
+		switch sc.StateChangeReason {
+		case types.StateChangeReasonSet, types.StateChangeReasonClear:
+			var flags []types.TrustlineFlag
+			if sc.Flags.Valid {
+				flags = types.DecodeTrustlineFlags(sc.Flags.Int16)
+			}
+			return graphql1.SimulatedBalanceAuthorizationChange{
+				Category:        sc.StateChangeCategory,
+				Reason:          sc.StateChangeReason,
+				AccountAddress:  accountAddress,
+				TokenID:         r.resolveNullableAddress(sc.TokenID),
+				LiquidityPoolID: r.resolveNullableString(sc.LiquidityPoolID),
+				Flags:           flags,
+			}, nil
+		default: // invalid reason for BALANCE_AUTHORIZATION; falls through to the error below
+		}
+	case types.StateChangeCategorySigner, types.StateChangeCategorySignatureThreshold,
+		types.StateChangeCategoryDataEntry, types.StateChangeCategoryHomeDomain,
+		types.StateChangeCategoryFlags, types.StateChangeCategoryTrustline:
+		// Classic-source variants: the simulated schema doesn't expose them yet.
+		// They land with the classic derivation source; falls through to the error below.
+	}
+	return nil, fmt.Errorf("state change has no simulated GraphQL type for (category=%s, reason=%s)",
+		sc.StateChangeCategory, sc.StateChangeReason)
+}
+
+// keyValueUint32 reads a uint32 from a KeyValue JSONB payload, where JSON
+// unmarshal exposes numbers as float64.
+func keyValueUint32(kv types.NullableJSONB, key string) (uint32, bool) {
+	raw, ok := kv[key]
+	if !ok {
+		return 0, false
+	}
+	f, ok := raw.(float64)
+	if !ok || f < 0 || f > math.MaxUint32 {
+		return 0, false
+	}
+	return uint32(f), true
+}