package models

// DeferralClause returns the SQL deferral clause for a foreign key constraint
// ("DEFERRABLE", "DEFERRABLE INITIALLY DEFERRED" or "NOT DEFERRABLE"), or ""
// when the model does not specify one. InitiallyDeferred without Deferrable
// implies DEFERRABLE; InitiallyDeferred=false alone specifies nothing.
func (d *Constraint) DeferralClause() string {
	deferrable, initially, set := d.effectiveDeferral()
	switch {
	case !set:
		return ""
	case !deferrable:
		return "NOT DEFERRABLE"
	case initially != nil && *initially:
		return "DEFERRABLE INITIALLY DEFERRED"
	default:
		return "DEFERRABLE"
	}
}

// effectiveDeferral resolves the optional flags. set is false when the model says nothing
// about deferral; initially is nil when the initial mode is unspecified.
func (d *Constraint) effectiveDeferral() (deferrable bool, initially *bool, set bool) {
	switch {
	case d.Deferrable != nil:
		return *d.Deferrable, d.InitiallyDeferred, true
	case d.InitiallyDeferred != nil && *d.InitiallyDeferred:
		return true, d.InitiallyDeferred, true
	}
	return false, nil, false
}

// DeferralMatches reports whether two constraints agree on deferral. An unspecified side
// matches anything, and the initial mode is only compared when both sides specify it.
func DeferralMatches(a, b *Constraint) bool {
	da, ia, aSet := a.effectiveDeferral()
	db, ib, bSet := b.effectiveDeferral()
	if !aSet || !bSet {
		return true
	}
	if da != db {
		return false
	}
	if !da || ia == nil || ib == nil {
		return true
	}
	return *ia == *ib
}