1 files changed, 80 insertions, 0 deletions
diff --git a/cache/partitioned_lazy_cache.go b/cache/partitioned_lazy_cache.go
new file mode 100644
index 000000000..9baf0377d
--- /dev/null
+++ b/cache/partitioned_lazy_cache.go
@@ -0,0 +1,80 @@
+// Copyright 2017-present The Hugo Authors. All rights reserved.
+//
+// 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 cache
+
+import (
+	"sync"
+)
+
+// Partition represents a cache partition where Load is the callback
+// for when the partition is needed.
+type Partition struct {
+	Key  string
+	Load func() (map[string]interface{}, error)
+}
+
+type lazyPartition struct {
+	initSync sync.Once
+	cache    map[string]interface{}
+	load     func() (map[string]interface{}, error)
+}
+
+func (l *lazyPartition) init() error {
+	var err error
+	l.initSync.Do(func() {
+		var c map[string]interface{}
+		c, err = l.load()
+		l.cache = c
+	})
+
+	return err
+}
+
+// PartitionedLazyCache is a lazily loaded cache paritioned by a supplied string key.
+type PartitionedLazyCache struct {
+	partitions map[string]*lazyPartition
+}
+
+// NewPartitionedLazyCache creates a new NewPartitionedLazyCache with the supplied
+// partitions.
+func NewPartitionedLazyCache(partitions ...Partition) *PartitionedLazyCache {
+	lazyPartitions := make(map[string]*lazyPartition, len(partitions))
+	for _, partition := range partitions {
+		lazyPartitions[partition.Key] = &lazyPartition{load: partition.Load}
+	}
+	cache := &PartitionedLazyCache{partitions: lazyPartitions}
+
+	return cache
+}
+
+// Get initializes the partition if not already done so, then looks up the given
+// key in the given partition, returns nil if no value found.
+func (c *PartitionedLazyCache) Get(partition, key string) (interface{}, error) {
+	p, found := c.partitions[partition]
+
+	if !found {
+		return nil, nil
+	}
+
+	if err := p.init(); err != nil {
+		return nil, err
+	}
+
+	if v, found := p.cache[key]; found {
+		return v, nil
+	}
+
+	return nil, nil
+
+}