Implement notifications service with shared messaging and email drivers (#36)

backend/notifications/app/config.go

@@ -0,0 +1,53 @@
+package app
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"strings"
+
+	"git.sendico.io/tech/sxchnge/notifications/email"
+	db "git.sendico.io/tech/sxchnge/shared/database"
+	merrors "git.sendico.io/tech/sxchnge/shared/errors"
+	"git.sendico.io/tech/sxchnge/shared/messaging"
+	"gopkg.in/yaml.v3"
+)
+
+type Config struct {
+	Messaging messaging.Config  `yaml:"messaging"`
+	Listen    string            `yaml:"listen"`
+	TLSCert   string            `yaml:"tls_cert"`
+	TLSKey    string            `yaml:"tls_key"`
+	Database  db.Config         `yaml:"database"`
+	Templates string            `yaml:"templates"`
+	Callers   map[string]string `yaml:"callers"` // caller -> token environment variable
+	Email     email.Config      `yaml:"email"`
+}
+
+func Load(path string) (Config, error) {
+	var c Config
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return c, merrors.OpaqueWrap(merrors.ErrInvalidArg, err, "cannot read configuration")
+	}
+	decoder := yaml.NewDecoder(bytes.NewReader(data))
+	decoder.KnownFields(true)
+	if err = decoder.Decode(&c); err != nil {
+		return c, merrors.InvalidArgument("invalid configuration")
+	}
+	if err = decoder.Decode(new(any)); err != io.EOF {
+		return c, merrors.InvalidArgument("unexpected configuration content")
+	}
+	if c.Listen == "" || c.TLSCert == "" || c.TLSKey == "" || c.Database.Driver != db.Mongo || c.Messaging.Driver != messaging.BBNats || c.Templates == "" || len(c.Callers) == 0 {
+		return c, merrors.InvalidArgument("missing notification configuration")
+	}
+	seen := map[string]bool{}
+	for caller, env := range c.Callers {
+		token := os.Getenv(env)
+		if strings.TrimSpace(caller) == "" || len(strings.TrimSpace(token)) < 32 || seen[token] {
+			return c, merrors.InvalidArgument("caller credentials must be unique and at least 32 bytes")
+		}
+		seen[token] = true
+	}
+	return c, nil
+}