Add --tiebreak option for customizing sort criteria

Close #191

4 files changed, 67 insertions, 8 deletions

diff --git a/src/core.go b/src/core.go
index 9f33b41d..4a834240 100644
--- a/src/core.go
+++ b/src/core.go
@@ -55,6 +55,7 @@ func Run(options *Options) {
 
 	opts := ParseOptions()
 	sort := opts.Sort > 0
+	rankTiebreak = opts.Tiebreak
 
 	if opts.Version {
 		fmt.Println(Version)
diff --git a/src/item.go b/src/item.go
index 9e2e1e7e..996c5e19 100644
--- a/src/item.go
+++ b/src/item.go
@@ -1,6 +1,8 @@
 package fzf
 
 import (
+	"math"
+
 	"github.com/junegunn/fzf/src/curses"
 )
 
@@ -27,17 +29,21 @@ type Item struct {
 // Rank is used to sort the search result
 type Rank struct {
 	matchlen uint16
-	strlen   uint16
+	tiebreak uint16
 	index    uint32
 }
 
+// Tiebreak criterion to use. Never changes once fzf is started.
+var rankTiebreak tiebreak
+
 // Rank calculates rank of the Item
 func (i *Item) Rank(cache bool) Rank {
-	if cache && (i.rank.matchlen > 0 || i.rank.strlen > 0) {
+	if cache && (i.rank.matchlen > 0 || i.rank.tiebreak > 0) {
 		return i.rank
 	}
 	matchlen := 0
 	prevEnd := 0
+	minBegin := math.MaxUint16
 	for _, offset := range i.offsets {
 		begin := int(offset[0])
 		end := int(offset[1])
@@ -48,10 +54,30 @@ func (i *Item) Rank(cache bool) Rank {
 			prevEnd = end
 		}
 		if end > begin {
+			if begin < minBegin {
+				minBegin = begin
+			}
 			matchlen += end - begin
 		}
 	}
-	rank := Rank{uint16(matchlen), uint16(len(*i.text)), i.index}
+	var tiebreak uint16
+	switch rankTiebreak {
+	case byLength:
+		tiebreak = uint16(len(*i.text))
+	case byBegin:
+		// We can't just look at i.offsets[0][0] because it can be an inverse term
+		tiebreak = uint16(minBegin)
+	case byEnd:
+		if prevEnd > 0 {
+			tiebreak = uint16(1 + len(*i.text) - prevEnd)
+		} else {
+			// Empty offsets due to inverse terms.
+			tiebreak = 1
+		}
+	case byIndex:
+		tiebreak = 1
+	}
+	rank := Rank{uint16(matchlen), tiebreak, i.index}
 	if cache {
 		i.rank = rank
 	}
@@ -199,9 +225,9 @@ func compareRanks(irank Rank, jrank Rank, tac bool) bool {
 		return false
 	}
 
-	if irank.strlen < jrank.strlen {
+	if irank.tiebreak < jrank.tiebreak {
 		return true
-	} else if irank.strlen > jrank.strlen {
+	} else if irank.tiebreak > jrank.tiebreak {
 		return false
 	}
 
diff --git a/src/item_test.go b/src/item_test.go
index 4eea8c15..2d375e47 100644
--- a/src/item_test.go
+++ b/src/item_test.go
@@ -42,7 +42,7 @@ func TestItemRank(t *testing.T) {
 	strs := []string{"foo", "foobar", "bar", "baz"}
 	item1 := Item{text: &strs[0], index: 1, offsets: []Offset{}}
 	rank1 := item1.Rank(true)
-	if rank1.matchlen != 0 || rank1.strlen != 3 || rank1.index != 1 {
+	if rank1.matchlen != 0 || rank1.tiebreak != 3 || rank1.index != 1 {
 		t.Error(item1.Rank(true))
 	}
 	// Only differ in index
diff --git a/src/options.go b/src/options.go
index c186542d..d13a53b8 100644
--- a/src/options.go
+++ b/src/options.go
@@ -28,7 +28,8 @@ const usage = `usage: fzf [options]
   Search result
     +s, --no-sort         Do not sort the result
         --tac             Reverse the order of the input
-                          (e.g. 'history | fzf --tac --no-sort')
+        --tiebreak=CRI    Sort criterion when the scores are tied;
+                          [length|begin|end|index] (default: length)
 
   Interface
     -m, --multi           Enable multi-select with tab/shift-tab
@@ -50,7 +51,6 @@ const usage = `usage: fzf [options]
         --expect=KEYS     Comma-separated list of keys to complete fzf
         --toggle-sort=KEY Key to toggle sort
         --sync            Synchronous search for multi-staged filtering
-                          (e.g. 'fzf --multi | fzf --sync')
 
   Environment variables
     FZF_DEFAULT_COMMAND   Default command to use when input is tty
@@ -78,6 +78,16 @@ const (
 	CaseRespect
 )
 
+// Sort criteria
+type tiebreak int
+
+const (
+	byLength tiebreak = iota
+	byBegin
+	byEnd
+	byIndex
+)
+
 // Options stores the values of command-line options
 type Options struct {
 	Mode       Mode
@@ -87,6 +97,7 @@ type Options struct {
 	Delimiter  *regexp.Regexp
 	Sort       int
 	Tac        bool
+	Tiebreak   tiebreak
 	Multi      bool
 	Ansi       bool
 	Mouse      bool
@@ -116,6 +127,7 @@ func defaultOptions() *Options {
 		Delimiter:  nil,
 		Sort:       1000,
 		Tac:        false,
+		Tiebreak:   byLength,
 		Multi:      false,
 		Ansi:       false,
 		Mouse:      true,
@@ -238,6 +250,22 @@ func parseKeyChords(str string, message string) []int {
 	return chords
 }
 
+func parseTiebreak(str string) tiebreak {
+	switch strings.ToLower(str) {
+	case "length":
+		return byLength
+	case "index":
+		return byIndex
+	case "begin":
+		return byBegin
+	case "end":
+		return byEnd
+	default:
+		errorExit("invalid sort criterion: " + str)
+	}
+	return byLength
+}
+
 func checkToggleSort(str string) int {
 	keys := parseKeyChords(str, "key name required")
 	if len(keys) != 1 {
@@ -265,6 +293,8 @@ func parseOptions(opts *Options, allArgs []string) {
 			opts.Filter = &filter
 		case "--expect":
 			opts.Expect = parseKeyChords(nextString(allArgs, &i, "key names required"), "key names required")
+		case "--tiebreak":
+			opts.Tiebreak = parseTiebreak(nextString(allArgs, &i, "sort criterion required"))
 		case "--toggle-sort":
 			opts.ToggleSort = checkToggleSort(nextString(allArgs, &i, "key name required"))
 		case "-d", "--delimiter":
@@ -352,6 +382,8 @@ func parseOptions(opts *Options, allArgs []string) {
 				opts.ToggleSort = checkToggleSort(value)
 			} else if match, value := optString(arg, "--expect="); match {
 				opts.Expect = parseKeyChords(value, "key names required")
+			} else if match, value := optString(arg, "--tiebreak="); match {
+				opts.Tiebreak = parseTiebreak(value)
 			} else {
 				errorExit("unknown option: " + arg)
 			}