Add persistence.

Adds some basic persistence using a yml file for now. Eventually I'll
swap this out for "proper" KV storage connection.

.gitignore

@@ -21,4 +21,7 @@
 go.work
 
 # Sensitive config
-config.yml
+config.yml
+
+# Simple local KV store
+storage.yml

main.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"os"
 
+	"github.com/samshadwell/split-ynab/storage"
 	"github.com/samshadwell/split-ynab/ynab"
 )
 
@@ -24,13 +25,30 @@ func main() {
 		os.Exit(1)
 	}
 
-	budgetsResponse, err := client.GetBudgetsWithResponse(context.TODO(), &ynab.GetBudgetsParams{})
+	storage := storage.NewLocalStorageAdapter()
+	// Ignore error return, we can use the default value of 0 in case of error.
+	serverKnowledge, _ := storage.GetLastServerKnowledge(config.BudgetId)
+
+	transactionsResponse, err := client.GetTransactionsByAccountWithResponse(
+		context.TODO(),
+		config.BudgetId,
+		config.SplitAccountIds[0],
+		&ynab.GetTransactionsByAccountParams{
+			LastKnowledgeOfServer: &serverKnowledge,
+		},
+	)
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "Error while getting budgets: %v\n", err)
+		fmt.Fprintf(os.Stderr, "Error while getting transactions: %v\n", err)
 		os.Exit(1)
 	}
 
-	fmt.Printf("Budgets: %v\n", budgetsResponse.JSON200.Data.Budgets)
+	newKnowledge := transactionsResponse.JSON200.Data.ServerKnowledge
+	fmt.Printf("Transaction count: %v, New server knowledge: %v\n", len(transactionsResponse.JSON200.Data.Transactions), newKnowledge)
+	err = storage.SetLastServerKnowledge(config.BudgetId, newKnowledge)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error while setting new server knowledge: %v\n", err)
+		os.Exit(1)
+	}
 }
 
 func constructClient(authToken string) (*ynab.ClientWithResponses, error) {

storage/file_storage_adapter.go

@@ -0,0 +1,92 @@
+package storage
+
+import (
+	"fmt"
+	"os"
+
+	"gopkg.in/yaml.v3"
+)
+
+type localStorageAdapter struct{}
+
+const storageFile = "storage.yml"
+
+type budgetData struct {
+	BudgetId            string `yaml:"budgetId"`
+	LastServerKnowledge int64  `yaml:"lastServerKnowledge"`
+}
+
+// Creates a StorageAdapter which stores data in a yaml file. Intended mostly for prototyping or running in environments
+// without "proper" KV storage mechanisms.
+func NewLocalStorageAdapter() StorageAdapter {
+	return &localStorageAdapter{}
+}
+
+func (l *localStorageAdapter) GetLastServerKnowledge(budgetId string) (int64, error) {
+	data, err := l.readData(budgetId)
+	if err != nil {
+		return 0, err
+	}
+
+	for _, d := range data {
+		if d.BudgetId == budgetId {
+			return d.LastServerKnowledge, nil
+		}
+	}
+
+	return 0, fmt.Errorf("No budget found with id %v", budgetId)
+}
+
+func (l *localStorageAdapter) SetLastServerKnowledge(budgetId string, serverKnowledge int64) error {
+	var data []budgetData
+
+	if _, err := os.Stat(storageFile); err == nil {
+		data, err = l.readData(budgetId)
+		if err != nil {
+			return err
+		}
+	}
+
+	found := false
+	for i, d := range data {
+		if d.BudgetId == budgetId {
+			data[i].LastServerKnowledge = serverKnowledge
+			found = true
+			break
+		}
+	}
+	if !found {
+		data = append(data, budgetData{
+			BudgetId:            budgetId,
+			LastServerKnowledge: serverKnowledge,
+		})
+	}
+
+	f, err := os.Create(storageFile)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	encoder := yaml.NewEncoder(f)
+	defer encoder.Close()
+
+	return encoder.Encode(data)
+}
+
+func (l *localStorageAdapter) readData(budgetId string) ([]budgetData, error) {
+	f, err := os.Open(storageFile)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var data []budgetData
+	decoder := yaml.NewDecoder(f)
+	err = decoder.Decode(&data)
+	if err != nil {
+		return nil, err
+	}
+
+	return data, nil
+}

storage/storage_adapter.go

@@ -0,0 +1,6 @@
+package storage
+
+type StorageAdapter interface {
+	GetLastServerKnowledge(budgetId string) (int64, error)
+	SetLastServerKnowledge(budgetId string, serverKnowledge int64) error
+}