Gave all modules own directory; added test CI pipeline

src/env/env.v

@@ -0,0 +1,82 @@
+module env
+
+import os
+import toml
+
+// The prefix that every environment variable should have
+const prefix = 'VIETER_'
+
+// The suffix an environment variable in order for it to be loaded from a file
+// instead
+const file_suffix = '_FILE'
+
+fn get_env_var(field_name string) ?string {
+	env_var_name := '$env.prefix$field_name.to_upper()'
+	env_file_name := '$env.prefix$field_name.to_upper()$env.file_suffix'
+	env_var := os.getenv(env_var_name)
+	env_file := os.getenv(env_file_name)
+
+	// If both are missing, we return an empty string
+	if env_var == '' && env_file == '' {
+		return ''
+	}
+
+	// If they're both set, we report a conflict
+	if env_var != '' && env_file != '' {
+		return error('Only one of $env_var_name or $env_file_name can be defined.')
+	}
+
+	// If it's the env var itself, we return it.
+	// I'm pretty sure this also prevents variable ending in _FILE (e.g.
+	// VIETER_LOG_FILE) from being mistakingely read as an _FILE suffixed env
+	// var.
+	if env_var != '' {
+		return env_var
+	}
+
+	// Otherwise, we process the file
+	return os.read_file(env_file) or {
+		error('Failed to read file defined in $env_file_name: ${err.msg}.')
+	}
+}
+
+// load<T> attempts to create an object of type T from the given path to a toml
+// file & environment variables. For each field, it will select either a value
+// given from an environment variable, a value defined in the config file or a
+// configured default if present, in that order.
+pub fn load<T>(path string) ?T {
+	mut res := T{}
+
+	if os.exists(path) {
+		// We don't use reflect here because reflect also sets any fields not
+		// in the toml back to their zero value, which we don't want
+		doc := toml.parse_file(path) ?
+
+		$for field in T.fields {
+			s := doc.value(field.name)
+
+			// We currently only support strings
+			if s.type_name() == 'string' {
+				res.$(field.name) = s.string()
+			}
+		}
+	}
+
+	$for field in T.fields {
+		$if field.typ is string {
+			env_value := get_env_var(field.name) ?
+
+			// The value of the env var will always be chosen over the config
+			// file
+			if env_value != '' {
+				res.$(field.name) = env_value
+			}
+			// If there's no value from the toml file either, we try to find a
+			// default value
+			else if res.$(field.name) == '' {
+				return error("Missing config variable '$field.name' with no provided default. Either add it to the config file or provide it using an environment variable.")
+			}
+		}
+	}
+	return res
+}