package config

import (
	"os"
	"strings"
	"testing"
)

// ClearEnvForTest unsets every variable in the process environment
// for the rest of the test, so a test sees only the variables it sets
// itself, not whatever the developer's shell exports. When the test
// ends it leaves the environment exactly as it found it: each variable
// it unset is put back, and any variable added since is removed.
func ClearEnvForTest(t *testing.T) {
	t.Helper()

	present := make(map[string]bool)

	for _, entry := range os.Environ() {
		key, _, _ := strings.Cut(entry, "=")
		present[key] = true

		// t.Setenv registers the restore; the Unsetenv after it is
		// what makes the key absent, since a key set to the empty
		// string is still present, and godotenv will not overwrite a
		// present key.
		t.Setenv(key, "")

		err := os.Unsetenv(key)
		if err != nil {
			t.Fatalf("unsetting %s: %v", key, err)
		}
	}

	// A variable the test adds other than through t.Setenv, as loading
	// a .env file does, has no restore of its own.
	t.Cleanup(func() {
		for _, entry := range os.Environ() {
			key, _, _ := strings.Cut(entry, "=")
			if present[key] {
				continue
			}

			err := os.Unsetenv(key)
			if err != nil {
				t.Errorf("unsetting %s: %v", key, err)
			}
		}
	})
}