nok.go

// Copyright 2016 Andreas Pannewitz. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package do

// ===========================================================================

// Nok represents some condition
// which is false by default.
//
// The null value is useful: its Do() never returns true.
type Nok func() bool

// Do applies Ok iff Ok is not nil
// and returns its value - usually false,
func (nok *Nok) Do() bool {
	if *nok != nil {
		return (*nok)()
	}
	return false
}

// Not returns the negation - usually true.
func (nok *Nok) Not() bool {
	if *nok != nil {
		return !(*nok)()
	}
	return true
}

// ===========================================================================

// NokJoin returns a closure around given fs.
//
// Iff there are no fs, nil is returned, and
// iff there is only one fs, this single fs is returned.
//
// Evaluate the returned function
// by invoking its Do() or
// by invoking it directly, iff not nil.
//
// Note: Order matters - evaluation terminates on first exceptional (non-default) result.
func NokJoin(fs ...Nok) Nok {
	switch len(fs) {
	case 0:
		return nil
	case 1:
		return fs[0]
	default:
		return func() bool {
			for _, f := range fs {
				if (&f).Do() {
					return true
				}
			}
			return false
		}
	}
}

// ===========================================================================

// Set sets all noks as the new nok
// when the returned Option is applied.
func (nok *Nok) Set(noks ...Nok) Option {
	return func(any interface{}) Opt {
		prev := *nok
		*nok = NokJoin(noks...)
		return func() Opt {
			return (*nok).Set(prev)(any)
		}
	}
}

// Add appends all noks to the existing nok
// when the returned Option is applied.
func (nok *Nok) Add(noks ...Nok) Option {
	if nok == nil || *nok == nil {
		return (*nok).Set(noks...)
	}
	return func(any interface{}) Opt {
		prev := *nok
		*nok = NokJoin(append([]Nok{prev}, noks...)...)
		return func() Opt {
			return (*nok).Set(prev)(any)
		}
	}
}

// ===========================================================================

// NokIt returns a Nok function
// which Do()es the Join of the given its
// and returns the default, namely: `false`,
// upon evaluation.
//
// Evaluate the returned function
// by invoking it's Do() or
// by invoking it directly, iff not nil.
//
// NokIt is a convenient wrapper.
func NokIt(its ...It) Nok {
	return func() bool {
		it := ItJoin(its...)
		(&it).Do()
		return false
	}
}

// ===========================================================================