Add --tail=NUM to limit the number of items to keep in memory

src/merger.go

@@ -3,8 +3,8 @@ package fzf
 import "fmt"
 
 // EmptyMerger is a Merger with no data
-func EmptyMerger(revision int) *Merger {
-	return NewMerger(nil, [][]Result{}, false, false, revision)
+func EmptyMerger(revision revision) *Merger {
+	return NewMerger(nil, [][]Result{}, false, false, revision, 0)
 }
 
 // Merger holds a set of locally sorted lists of items and provides the view of
@@ -20,19 +20,25 @@ type Merger struct {
 	final    bool
 	count    int
 	pass     bool
-	revision int
+	revision revision
+	minIndex int32
 }
 
 // PassMerger returns a new Merger that simply returns the items in the
 // original order
-func PassMerger(chunks *[]*Chunk, tac bool, revision int) *Merger {
+func PassMerger(chunks *[]*Chunk, tac bool, revision revision) *Merger {
+	var minIndex int32
+	if len(*chunks) > 0 {
+		minIndex = (*chunks)[0].items[0].Index()
+	}
 	mg := Merger{
 		pattern:  nil,
 		chunks:   chunks,
 		tac:      tac,
 		count:    0,
 		pass:     true,
-		revision: revision}
+		revision: revision,
+		minIndex: minIndex}
 
 	for _, chunk := range *mg.chunks {
 		mg.count += chunk.count
@@ -41,7 +47,7 @@ func PassMerger(chunks *[]*Chunk, tac bool, revision int) *Merger {
 }
 
 // NewMerger returns a new Merger
-func NewMerger(pattern *Pattern, lists [][]Result, sorted bool, tac bool, revision int) *Merger {
+func NewMerger(pattern *Pattern, lists [][]Result, sorted bool, tac bool, revision revision, minIndex int32) *Merger {
 	mg := Merger{
 		pattern:  pattern,
 		lists:    lists,
@@ -52,7 +58,8 @@ func NewMerger(pattern *Pattern, lists [][]Result, sorted bool, tac bool, revisi
 		tac:      tac,
 		final:    false,
 		count:    0,
-		revision: revision}
+		revision: revision,
+		minIndex: minIndex}
 
 	for _, list := range mg.lists {
 		mg.count += len(list)
@@ -61,7 +68,7 @@ func NewMerger(pattern *Pattern, lists [][]Result, sorted bool, tac bool, revisi
 }
 
 // Revision returns revision number
-func (mg *Merger) Revision() int {
+func (mg *Merger) Revision() revision {
 	return mg.revision
 }
 
@@ -81,7 +88,7 @@ func (mg *Merger) First() Result {
 func (mg *Merger) FindIndex(itemIndex int32) int {
 	index := -1
 	if mg.pass {
-		index = int(itemIndex)
+		index = int(itemIndex - mg.minIndex)
 		if mg.tac {
 			index = mg.count - index - 1
 		}
@@ -102,6 +109,13 @@ func (mg *Merger) Get(idx int) Result {
 		if mg.tac {
 			idx = mg.count - idx - 1
 		}
+		firstChunk := (*mg.chunks)[0]
+		if firstChunk.count < chunkSize && idx >= firstChunk.count {
+			idx -= firstChunk.count
+
+			chunk := (*mg.chunks)[idx/chunkSize+1]
+			return Result{item: &chunk.items[idx%chunkSize]}
+		}
 		chunk := (*mg.chunks)[idx/chunkSize]
 		return Result{item: &chunk.items[idx%chunkSize]}
 	}