From f97bea78eb81f71c609f57101cd1645799154646 Mon Sep 17 00:00:00 2001
From: Fred Boniface <fred@fjla.uk>
Date: Sun, 14 Apr 2024 21:21:13 +0100
Subject: [PATCH] Added multiple attempts with backoff delay to datebase
 connection

---
 dbAccess/client.go | 48 ++++++++++++++++++++++++++++++++++------------
 helpers/backoff.go | 18 +++++++++++++++++
 2 files changed, 54 insertions(+), 12 deletions(-)
 create mode 100644 helpers/backoff.go

diff --git a/dbAccess/client.go b/dbAccess/client.go
index 3f566f4..56a8aac 100644
--- a/dbAccess/client.go
+++ b/dbAccess/client.go
@@ -3,9 +3,9 @@ package dbAccess
 import (
 	"git.fjla.uk/owlboard/timetable-mgr/helpers"
 	"git.fjla.uk/owlboard/timetable-mgr/log"
+	"go.uber.org/zap"
 
 	"context"
-	"fmt"
 	"time"
 
 	"go.mongodb.org/mongo-driver/mongo"
@@ -26,19 +26,43 @@ var bsonOpts = &options.BSONOptions{
 	UseJSONStructTags: true,
 }
 
-// Initialise the DB Connection
 func InitDataAccess(cfg *helpers.Configuration) {
-	uri := getDbUri(cfg)
-	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
-	defer cancel()
-	client, err := mongo.Connect(ctx, options.Client().ApplyURI(uri).SetBSONOptions(bsonOpts))
-	if err != nil {
-		fmt.Println(err)
-		log.Fatal("Error connecting to database: " + err.Error())
-	} else {
-		log.Info("Database connection initialising")
+	log.Debug("Starting database connection")
+	url := getDbUri(cfg)
+
+	const maxRetries = 8
+
+	for attempt := 1; attempt <= maxRetries; attempt++ {
+		log.Info("Attempting to connect to database", zap.Int("attempt", attempt), zap.Int("max-tries", maxRetries))
+		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+		defer cancel()
+
+		client, err := mongo.Connect(ctx, options.Client().ApplyURI(url).SetBSONOptions(bsonOpts))
+		if err != nil {
+			log.Warn("Error connecting to database", zap.Int("attempt", attempt), zap.Int("max-tries", maxRetries))
+			cancel()
+			if attempt != maxRetries {
+				helpers.BackoffDelay(attempt)
+			}
+			continue
+		}
+
+		err = client.Ping(ctx, nil)
+		if err != nil {
+			log.Warn("Error pinging database", zap.Int("attempt", attempt), zap.Int("max-tries", maxRetries))
+			cancel()
+			if attempt != maxRetries {
+				helpers.BackoffDelay(attempt)
+			}
+			continue
+		}
+
+		MongoClient = client
+		log.Info("Database connection successful")
+		return
 	}
-	MongoClient = client
+
+	log.Fatal("Failed to connect to database on multiple attempts", zap.Int("attempts", maxRetries))
 }
 
 // Closes the connection to the database - used for cleanup functions
diff --git a/helpers/backoff.go b/helpers/backoff.go
new file mode 100644
index 0000000..403bddd
--- /dev/null
+++ b/helpers/backoff.go
@@ -0,0 +1,18 @@
+package helpers
+
+import (
+	"math"
+	"time"
+
+	"git.fjla.uk/owlboard/timetable-mgr/log"
+	"go.uber.org/zap"
+)
+
+// Implements an exponential backoff strategy and sleeps for a duration calculated as 1 second to the power of (attempt - 1).
+// The backoff time doubles with each attempt, starting from 1 second for the first attempt.
+func BackoffDelay(attempt int) {
+	base := time.Second
+	backoff := base * time.Duration(math.Pow(2, float64(attempt-1)))
+	log.Info("Retry backoff", zap.Duration("delay", backoff))
+	time.Sleep(backoff)
+}