refactor(ynabber): channels for fan out to writers

Use channels to batch transactions and fan out to writers. This is
prep work for allowing multiple "pipelines" of readers and writers and
potentially multiple instances of Ynabber running concurrently.

commit-id:d118ecdf

cmd/ynabber/main.go

@@ -1,11 +1,9 @@
 package main
 
 import (
-	"fmt"
 	"log"
 	"log/slog"
 	"os"
-	"time"
 
 	"github.com/carlmjohnson/versioninfo"
 	"github.com/kelseyhightower/envconfig"
@@ -38,61 +36,26 @@ func main() {
 	setupLogging(cfg.Debug)
 	slog.Info("starting...", "version", versioninfo.Short())
 
-	ynabber := ynabber.Ynabber{}
+	y := ynabber.NewYnabber(&cfg)
 	for _, reader := range cfg.Readers {
 		switch reader {
 		case "nordigen":
-			ynabber.Readers = append(ynabber.Readers, nordigen.NewReader(&cfg))
+			y.Readers = append(y.Readers, nordigen.NewReader(&cfg))
 		default:
 			log.Fatalf("Unknown reader: %s", reader)
 		}
 	}
 	for _, writer := range cfg.Writers {
 		switch writer {
 		case "ynab":
-			ynabber.Writers = append(ynabber.Writers, ynab.NewWriter(&cfg))
+			y.Writers = append(y.Writers, ynab.NewWriter(&cfg))
 		case "json":
-			ynabber.Writers = append(ynabber.Writers, json.Writer{})
+			y.Writers = append(y.Writers, json.Writer{})
 		default:
 			log.Fatalf("Unknown writer: %s", writer)
 		}
 	}
 
-	for {
-		start := time.Now()
-		err = run(ynabber)
-		if err != nil {
-			panic(err)
-		} else {
-			slog.Info("run succeeded", "in", time.Since(start))
-			if cfg.Interval > 0 {
-				slog.Info("waiting for next run", "in", cfg.Interval)
-				time.Sleep(cfg.Interval)
-			} else {
-				os.Exit(0)
-			}
-		}
-	}
-}
-
-func run(y ynabber.Ynabber) error {
-	var transactions []ynabber.Transaction
-
-	// Read transactions from all readers
-	for _, reader := range y.Readers {
-		t, err := reader.Bulk()
-		if err != nil {
-			return fmt.Errorf("reading: %w", err)
-		}
-		transactions = append(transactions, t...)
-	}
-
-	// Write transactions to all writers
-	for _, writer := range y.Writers {
-		err := writer.Bulk(transactions)
-		if err != nil {
-			return fmt.Errorf("writing: %w", err)
-		}
-	}
-	return nil
+	// Run Ynabber
+	y.Run()
 }

ynabber.go

@@ -1,13 +1,25 @@
 package ynabber
 
 import (
+	"log/slog"
 	"strconv"
 	"time"
 )
 
 type Ynabber struct {
 	Readers []Reader
 	Writers []Writer
+
+	config *Config
+	logger slog.Logger
+}
+
+// NewYnabber creates a new Ynabber instance
+func NewYnabber(config *Config) *Ynabber {
+	return &Ynabber{
+		config: config,
+		logger: *slog.Default(),
+	}
 }
 
 type Reader interface {
@@ -53,3 +65,62 @@ func (m Milliunits) String() string {
 func MilliunitsFromAmount(amount float64) Milliunits {
 	return Milliunits(amount * 1000)
 }
+
+// Run starts Ynabber by reading transactions from all readers into a channel to
+// fan out to all writers
+func (y *Ynabber) Run() {
+	batches := make(chan []Transaction)
+
+	// Create a channel for each writer and fan out transactions to each one
+	channels := make([]chan []Transaction, len(y.Writers))
+	for c := range channels {
+		channels[c] = make(chan []Transaction)
+	}
+	go func() {
+		for batch := range batches {
+			for _, c := range channels {
+				c <- batch
+			}
+		}
+	}()
+
+	for c, writer := range y.Writers {
+		go func(writer Writer, batches <-chan []Transaction) {
+			for batch := range batches {
+				err := writer.Bulk(batch)
+				if err != nil {
+					y.logger.Error("writing", "error", err, "writer", writer)
+				}
+			}
+		}(writer, channels[c])
+	}
+
+	for _, r := range y.Readers {
+		go func(reader Reader) {
+			for {
+				start := time.Now()
+				batch, err := reader.Bulk()
+				if err != nil {
+					y.logger.Error("reading", "error", err, "reader", reader)
+					continue
+				}
+				batches <- batch
+				y.logger.Info("run succeeded", "in", time.Since(start))
+
+				// TODO(Martin): The interval should be controlled by the
+				// reader. We are only pausing the entire reader goroutine
+				// because thats how the config option is implemented now.
+				// Eventually we should move this option into the reader
+				// allowing for multiple readers with different intervals.
+				if y.config.Interval > 0 {
+					y.logger.Info("waiting for next run", "in", y.config.Interval)
+					time.Sleep(y.config.Interval)
+				} else {
+					break
+				}
+			}
+		}(r)
+	}
+
+	select {}
+}