add config package

2 files changed, 142 insertions, 0 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
new file mode 100644
index 0000000..ab9ee7a
--- /dev/null
+++ b/internal/config/config.go
@@ -0,0 +1,90 @@
+package config
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"strings"
+	"unicode"
+)
+
+type config struct {
+	EmailTo    string `json:"EmailTo,omitempty"`
+	EmailFrom  string `json:"EmailFrom,omitempty"`
+	SMTPServer string `json:"SMTPServer,omitempty"`
+	DataDir    string `json:"StateDir,omitempty"`
+	Partner    string `json:"Partner,omitempty"`
+}
+
+func newConfig(configFile string) (config, error) {
+	conf := config{
+		EmailTo:    fromEnv("EmailTo"),
+		EmailFrom:  fromEnv("EmailFrom"),
+		SMTPServer: fromEnv("SMTPServer"),
+		DataDir:    fromEnv("DataDir", "data"),
+		Partner:    fromEnv("Partner"),
+	}
+
+	file, err := os.Open(configFile)
+	if err != nil {
+		return conf, err
+	}
+	defer file.Close()
+
+	bytes, err := io.ReadAll(file)
+	if err != nil {
+		return conf, err
+	}
+
+	err = json.Unmarshal(bytes, &conf)
+	if err != nil {
+		return conf, err
+	}
+
+	if conf.SMTPServer == "" {
+		hostname, err := os.Hostname()
+		if err != nil {
+			log.Fatal(err)
+		}
+		conf.SMTPServer = fmt.Sprintf("%s:25", hostname)
+		log.Println("Set SMTPServer to " + conf.SMTPServer)
+	}
+
+	if conf.DataDir == "" {
+		conf.DataDir = "data"
+		log.Println("Set data dir to " + conf.DataDir)
+	}
+
+	return conf, nil
+}
+
+// Set config from envoronment variable if present, e.g. hansWurst from GOS_HANS_WURST
+func fromEnv(configKey string, defaultValue ...string) string {
+	envKey := camelToSnakeWithPrefix("GOS", configKey)
+	if value := os.Getenv(envKey); value != "" {
+		return value
+	}
+
+	if len(defaultValue) > 0 {
+		return defaultValue[0]
+	}
+	return ""
+}
+
+// camelToSnaeWithPrefix converts camelCase strings to UPPER_SNAKE_CASE with a prefix.
+func camelToSnakeWithPrefix(prefix, s string) string {
+	var builder strings.Builder
+	builder.WriteString(strings.ToUpper(prefix))
+	builder.WriteRune('_')
+
+	for i, r := range s {
+		if unicode.IsUpper(r) && i > 0 {
+			builder.WriteRune('_')
+		}
+		builder.WriteRune(unicode.ToUpper(r))
+	}
+
+	return builder.String()
+}
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
new file mode 100644
index 0000000..5c429c9
--- /dev/null
+++ b/internal/config/config_test.go
@@ -0,0 +1,52 @@
+package config
+
+import (
+	"os"
+	"testing"
+)
+
+func TestCamelToSnake(t *testing.T) {
+	t.Parallel()
+
+	var (
+		expected = "GOS_FOO_BAR_BAZ"
+		got      = camelToSnakeWithPrefix("GOS", "fooBarBaz")
+	)
+
+	if got != expected {
+		t.Errorf("got '%s' but expected '%s'", got, expected)
+		return
+	}
+	t.Logf("got '%s' as expected", expected)
+}
+
+func TestFromEnv(t *testing.T) {
+	t.Parallel()
+
+	os.Setenv("GOS_TEST_FROM_ENV", "foobarbaz")
+
+	var (
+		expected = "foobarbaz"
+		got      = fromEnv("testFromEnv")
+	)
+
+	if got != expected {
+		t.Errorf("got '%s' but expected '%s'", got, expected)
+		return
+	}
+	t.Logf("got '%s' as expected", expected)
+
+	expected = "default value"
+	got = fromEnv("jajaja", expected)
+	if got != expected {
+		t.Errorf("got '%s' but expected '%s'", got, expected)
+		return
+	}
+	t.Logf("got '%s' as expected", expected)
+
+	if got = fromEnv("jujuju"); got != "" {
+		t.Errorf("got '%s' but expected empty string", got)
+		return
+	}
+	t.Logf("got empty string as expected")
+}