// Copyright (C) 2015 The Android Open Source Project
//
// 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
//
//      http://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 database

import (
	"bytes"

	"android.googlesource.com/platform/tools/gpu/binary"
	"android.googlesource.com/platform/tools/gpu/log"
)

// Lazy is the interface for types that redirects database resolves to an
// object lazily built using BuildLazy(). The BuildLazy() method will be called
// the first time the object is resolved, and all subsequent resolves will
// return the same pre-built object.
// Lazy is commonly implemented by objects that generate data that is expensive
// to calculate but can be deterministically produced using the information
// stored in the Lazy.
type Lazy interface {
	binary.Object

	// BuildLazy constructs and returns the lazily-built object.
	// c is the build context that was passed to the database constructor.
	BuildLazy(c interface{}, d Database, l log.Logger) (interface{}, error)
}

// LazyOutputID returns the identifier of a LazyOutput object given the
// identifier of the Lazy. The database will not contain the LazyObject with the
// returned identifier until it is built.
func LazyOutputID(in binary.ID) binary.ID {
	b := bytes.Buffer{}
	b.WriteString("lazy:")
	b.WriteString(in.String())
	return binary.NewID(b.Bytes())
}