// Package idear is the roster for a Rastrillo instance: who is in it,
// at what role, and who may change that. It never mints a session,
// hashes a password, or renders a sign-in form — it sits on top of
// sessions and whichever identity plugin the app already chose.
package idear

// Role is a member's rank within one instance. It is a string, not an
// int, because it round-trips through form posts and database columns
// without a mapping table to keep in sync — but that means any string
// decodes without error, so every caller that receives one from outside
// the package (a form, a query) must run it through ParseRole rather
// than trust the cast.
type Role string

const (
	RoleOwner  Role = "owner"
	RoleAdmin  Role = "admin"
	RoleMember Role = "member"
)

// rank orders the three roles for comparison; 0 means "not a role; see
// Valid" rather than "below Member" so it never wins a comparison it
// has no business winning.
func rank(r Role) int {
	switch r {
	case RoleOwner:
		return 3
	case RoleAdmin:
		return 2
	case RoleMember:
		return 1
	default:
		return 0
	}
}

// Valid reports whether r is one of the three known roles.
func (r Role) Valid() bool {
	return rank(r) > 0
}

// AtLeast reports whether r's rank is at or above min's. Both sides
// must be valid roles — an invalid r is never at least anything, not
// even an equally invalid min, and an invalid min is never a threshold
// anything can clear. Without that second half, two unknown strings
// would compare equal by falling through to the same rank(0), and
// AtLeast would call garbage "at least" garbage.
func (r Role) AtLeast(min Role) bool {
	if !r.Valid() || !min.Valid() {
		return false
	}
	return rank(r) >= rank(min)
}

// Title is the display form of r — "Owner", "Admin", "Member" — and
// the empty string for anything that isn't a role, so a template that
// prints it renders nothing rather than a raw lowercase form value.
func (r Role) Title() string {
	switch r {
	case RoleOwner:
		return "Owner"
	case RoleAdmin:
		return "Admin"
	case RoleMember:
		return "Member"
	default:
		return ""
	}
}

// ParseRole accepts only the three known lowercase spellings. It is the
// one place a string from outside the package (a posted form field, a
// query parameter) becomes a Role; everywhere else in idear a Role is
// assumed already valid.
func ParseRole(s string) (Role, bool) {
	r := Role(s)
	if !r.Valid() {
		return "", false
	}
	return r, true
}