Refactor FileStore to JSONStore (#30)

Reviewed-on: #30
Co-authored-by: Natercio Moniz <[email protected]>

internal/state.go

@@ -2,12 +2,13 @@ package internal
 
 import (
 	"context"
+	"encoding/json"
 
 	"github.com/shopspring/decimal"
 )
 
 // StateVersion is the schema version of the persisted State struct.
-const StateVersion = "1"
+const StateVersion = "2"
 
 // State is the platform-agnostic representation of the buy-queue state that is
 // written to disk after a successful run and reloaded on the next run.
@@ -21,20 +22,20 @@ type State struct {
 // Record-specific data is kept as opaque bytes so the internal package does
 // not need to know about any broker package's concrete Record type.
 type persistedFiller struct {
-	RecordData []byte          `json:"record_data"`
+	RecordData json.RawMessage `json:"record_data"`
 	Quantity   decimal.Decimal `json:"quantity"`
 	Price      decimal.Decimal `json:"price"`
 	Filled     decimal.Decimal `json:"filled"`
 }
 
-// RecordEncoder encodes a Record into its broker-specific byte representation.
+// RecordEncoder encodes a Record into its broker-specific JSON representation.
 type RecordEncoder interface {
-	MarshalRecord(context.Context, Record) ([]byte, error)
+	MarshalRecord(context.Context, Record) (json.RawMessage, error)
 }
 
-// RecordDecoder decodes broker-specific bytes back into a Record.
+// RecordDecoder decodes broker-specific JSON back into a Record.
 type RecordDecoder interface {
-	UnmarshalRecord(context.Context, []byte) (Record, error)
+	UnmarshalRecord(context.Context, json.RawMessage) (Record, error)
 }
 
 // RecordSerializer composes encoding and decoding of Records. Broker packages