new error codes, code refactor, added getMessages function

database/contacts.go

@@ -313,7 +313,7 @@ func GetContacts(db *sql.DB, userID uuid.UUID) ([]*model.Contact, error) {
 	}
 
 	if err = rows.Err(); err != nil {
-		return nil, helpers.NewError(helpers.ErrInternal, "Failed to process contacts", err)
+		return nil, helpers.NewError(helpers.ErrInternal, "internal server error", fmt.Errorf("failed to process contacts: %w", err))
 	}
 
 	return contacts, nil
@@ -342,7 +342,7 @@ func ContactSuggestion(db *sql.DB, contactUsername string) ([]string, error) {
 		suggestions = append(suggestions, suggestion)
 	}
 	if err = rows.Err(); err != nil {
-		return nil, helpers.NewError(helpers.ErrInternal, "Error processing suggestions", err)
+		return nil, helpers.NewError(helpers.ErrInternal, "internal server error", fmt.Errorf("failed to process suggestions"))
 	}
 	return suggestions, nil
 }

database/messages.go

@@ -0,0 +1,109 @@
+package database
+
+import (
+	"database/sql"
+	"fmt"
+	"github.com/google/uuid"
+	"relay-server/helpers"
+	"relay-server/model"
+)
+
+func GetMessages(db *sql.DB, userID uuid.UUID, conversationID uuid.UUID, limit int, cursor int) ([]*model.Message, error) {
+	_, err := checkMembership(db, userID, conversationID)
+	if err != nil {
+		return nil, err
+	}
+	var query string
+	var messages []*model.Message
+
+	if cursor != 0 {
+		query = `
+        SELECT 
+            m.message_id, 
+            m.content AS message, 
+            m.sent_at, 
+            m.attachment_urls, 
+            a.username AS sender
+        FROM Messages m
+        JOIN Accounts a ON m.user_id = a.user_id
+        WHERE m.conversation_id = $1
+        AND m.message_id < $2
+        ORDER BY m.message_id DESC
+        LIMIT $3;
+      `
+		rows, err := db.Query(query, conversationID, cursor, limit)
+		if err != nil {
+			return nil, helpers.NewError(helpers.ErrInternal, "Failed to get messages", fmt.Errorf("failed to get messages: %w", err))
+		}
+
+		for rows.Next() {
+			message := &model.Message{}
+			err = rows.Scan(&message.MessageID, &message.Message, &message.SentAt, &message.AttachmentUrl, &message.Sender)
+			if err != nil {
+				return nil, helpers.NewError(helpers.ErrInternal, "Failed to get messages", fmt.Errorf("failed to scan message: %w", err))
+			}
+			messages = append(messages, message)
+		}
+		if err = rows.Err(); err != nil {
+			return nil, helpers.NewError(helpers.ErrInternal, "internal server error", fmt.Errorf("failed to process messages: %w", err))
+		}
+
+	} else {
+		query = `
+        SELECT 
+            m.message_id, 
+            m.content AS message, 
+            m.sent_at, 
+            m.attachment_urls, 
+            a.username AS sender
+        FROM Messages m
+        JOIN Accounts a ON m.user_id = a.user_id
+        WHERE m.conversation_id = $1
+        ORDER BY m.message_id DESC
+        LIMIT $2;
+      `
+		rows, err := db.Query(query, conversationID, cursor, limit)
+		if err != nil {
+			return nil, helpers.NewError(helpers.ErrInternal, "Failed to get messages", fmt.Errorf("failed to get messages: %w", err))
+		}
+
+		for rows.Next() {
+			message := &model.Message{}
+			err = rows.Scan(&message.MessageID, &message.Message, &message.SentAt, &message.AttachmentUrl, &message.Sender)
+			if err != nil {
+				return nil, helpers.NewError(helpers.ErrInternal, "Failed to get messages", fmt.Errorf("failed to scan message: %w", err))
+			}
+			messages = append(messages, message)
+		}
+		if err = rows.Err(); err != nil {
+			return nil, helpers.NewError(helpers.ErrInternal, "internal server error", fmt.Errorf("failed to process messages: %w", err))
+		}
+	}
+	if cursor != 0 {
+		// Reverse first messages
+		for i, j := 0, len(messages)-1; i < j; i, j = i+1, j-1 {
+			messages[i], messages[j] = messages[j], messages[i]
+		}
+	}
+	return messages, nil
+}
+
+func checkMembership(db *sql.DB, userID uuid.UUID, conversationID uuid.UUID) (bool, error) {
+	query := `
+    SELECT EXISTS (
+      SELECT 1 
+      FROM Memberships 
+      WHERE user_id = $1 
+      AND conversation_id = $2
+    ) AS is_member;
+  `
+	var isMember bool
+	err := db.QueryRow(query, userID, conversationID).Scan(&isMember)
+	if err != nil {
+		return false, helpers.NewError(helpers.ErrInternal, "internal server error", fmt.Errorf("failed to check membership: %w", err))
+	}
+	if !isMember {
+		return false, helpers.NewError(helpers.ErrForbidden, "You are member of the conversation", nil)
+	}
+	return isMember, nil
+}