buildpack_plan.go

/*
 * Copyright 2018-2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package libpak

import (
	"fmt"
	"reflect"

	"github.com/buildpacks/libcnb"
	"github.com/imdario/mergo"
)

// PlanEntryResolver provides functionality for resolving a Buildpack Plan Entry given a name.
type PlanEntryResolver struct {

	// Plan is the BuildpackPlan to resolve against.
	Plan libcnb.BuildpackPlan
}

// MergeFunc takes two BuildpackPlanEntry's and returns a merged entry.
type MergeFunc func(a, b libcnb.BuildpackPlanEntry) (libcnb.BuildpackPlanEntry, error)

// ResolveWithMerge returns a single BuildpackPlanEntry that is a merged version of all entries that have a given name.
// A merge function is used to describe how two entries are merged together.
func (p *PlanEntryResolver) ResolveWithMerge(name string, f MergeFunc) (libcnb.BuildpackPlanEntry, bool, error) {
	m := libcnb.BuildpackPlanEntry{}

	var err error
	for _, e := range p.Plan.Entries {
		if e.Name == name {
			if m, err = f(m, e); err != nil {
				return libcnb.BuildpackPlanEntry{}, false, fmt.Errorf("error merging %+v and %+v\n%w", m, e, err)
			}
		}
	}

	if reflect.DeepEqual(m, libcnb.BuildpackPlanEntry{}) {
		return libcnb.BuildpackPlanEntry{}, false, nil
	}

	return m, true, nil
}

// ShallowMerge merges two BuildpackPlanEntry's together.  Declared versions are combined with a comma delimiter and
// metadata is combined with the values for b taking priority over the values of a when the keys are duplicated.
func ShallowMerge(a, b libcnb.BuildpackPlanEntry) (libcnb.BuildpackPlanEntry, error) {
	if err := mergo.Merge(&b, a); err != nil {
		return libcnb.BuildpackPlanEntry{}, fmt.Errorf("unable to merge %+v and %+v\n%w", a, b, err)
	}

	return b, nil
}

// Resolve calls ResolveWithMerge function passing in the ShallowMerge function as the merge strategy.
func (p *PlanEntryResolver) Resolve(name string) (libcnb.BuildpackPlanEntry, bool, error) {
	return p.ResolveWithMerge(name, ShallowMerge)
}