const (
	// Values for PreRelease.
	Alpha = prerelease("ALPHA")
	Beta  = prerelease("BETA")
	GA    = prerelease("")

	// Deprecated
	Deprecated = prerelease("DEPRECATED")
)

type Feature string

type FeatureGate interface {
	// Enabled returns true if the key is enabled.
	Enabled(key Feature) bool
	// KnownFeatures returns a slice of strings describing the FeatureGate's known features.
	KnownFeatures() []string
	// DeepCopy returns a deep copy of the FeatureGate object, such that gates can be
	// set on the copy without mutating the original. This is useful for validating
	// config against potential feature gate changes before committing those changes.
	DeepCopy() MutableFeatureGate
}

type FeatureSpec struct {
	// Default is the default enablement state for the feature
	Default bool
	// LockToDefault indicates that the feature is locked to its default and cannot be changed
	LockToDefault bool
	// PreRelease indicates the maturity level of the feature
	PreRelease prerelease
}

type MutableFeatureGate interface {
	FeatureGate

	// AddFlag adds a flag for setting global feature gates to the specified FlagSet.
	AddFlag(fs *pflag.FlagSet)
	// Set parses and stores flag gates for known features
	// from a string like feature1=true,feature2=false,...
	Set(value string) error
	// SetFromMap stores flag gates for known features from a map[string]bool or returns an error
	SetFromMap(m map[string]bool) error
	// Add adds features to the featureGate.
	Add(features map[Feature]FeatureSpec) error
	// GetAll returns a copy of the map of known feature names to feature specs.
	GetAll() map[Feature]FeatureSpec
	// AddMetrics adds feature enablement metrics
	AddMetrics()
	// OverrideDefault sets a local override for the registered default value of a named
	// feature. If the feature has not been previously registered (e.g. by a call to Add), has a
	// locked default, or if the gate has already registered itself with a FlagSet, a non-nil
	// error is returned.
	//
	// When two or more components consume a common feature, one component can override its
	// default at runtime in order to adopt new defaults before or after the other
	// components. For example, a new feature can be evaluated with a limited blast radius by
	// overriding its default to true for a limited number of components without simultaneously
	// changing its default for all consuming components.
	OverrideDefault(name Feature, override bool) error
}