WIP cache

common/cache.go

@@ -0,0 +1,65 @@
+package common
+
+import "github.com/pkg/errors"
+
+type BlockCache struct {
+	MaxEntries int
+
+	FirstBlock int
+	LastBlock  int
+
+	m map[int][]byte
+}
+
+func New(maxEntries int) *BlockCache {
+	return &BlockCache{
+		MaxEntries: maxEntries,
+		FirstBlock: -1,
+		LastBlock:  -1,
+		m:          make(map[int][]byte),
+	}
+}
+
+func (c *BlockCache) Add(height int, bytes []byte) error {
+
+	if c.FirstBlock == -1 && c.LastBlock == -1 {
+		// If this is the first block, prep the data structure
+		c.FirstBlock = height
+		c.LastBlock = height - 1
+	} else if height >= c.FirstBlock && height <= c.LastBlock {
+		// Overwriting an existing entry. If so, then remove all
+		// subsequent blocks, since this might be a reorg
+		for i := height; i <= c.LastBlock; i++ {
+			delete(c.m, i)
+		}
+	}
+
+	if height != c.LastBlock+1 {
+		return errors.New("Blocks need to be added sequentially")
+	}
+
+	// Add the entry and update the counters
+	c.m[height] = bytes
+	c.LastBlock = height
+
+	// If the cache is full, remove the oldest block
+	if c.LastBlock-c.FirstBlock+1 > c.MaxEntries {
+		delete(c.m, c.FirstBlock)
+		c.FirstBlock = c.FirstBlock + 1
+	}
+
+	return nil
+}
+
+func (c *BlockCache) Get(height int) ([]byte, error) {
+
+	if c.LastBlock == -1 || c.FirstBlock == -1 {
+		return nil, errors.New("Map is empty")
+	}
+
+	if height < c.FirstBlock || height > c.LastBlock {
+		return nil, errors.New("Index out of range")
+	}
+
+	return c.m[height], nil
+}