From 846e01166bc951b11be089c03d77879b1294265e Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Fri, 22 Dec 2023 13:36:29 -0800
Subject: [PATCH] Flatten fltr funcs into used methods

---
 attribute/set.go | 107 +++++++++++++++++++++--------------------------
 1 file changed, 48 insertions(+), 59 deletions(-)

diff --git a/attribute/set.go b/attribute/set.go
index 4734d4103a7..dd4a55e60e0 100644
--- a/attribute/set.go
+++ b/attribute/set.go
@@ -249,7 +249,7 @@ func NewSetWithFiltered(kvs []KeyValue, filter Filter) (Set, []KeyValue) {
 //
 // The second []KeyValue return value is a list of attributes that were
 // excluded by the Filter (if non-nil).
-func NewSetWithSortableFiltered(kvs []KeyValue, tmp *Sortable, filter Filter) (Set, []KeyValue) {
+func NewSetWithSortableFiltered(kvs []KeyValue, tmp *Sortable, keep Filter) (Set, []KeyValue) {
 	// Check for empty set.
 	if len(kvs) == 0 {
 		return empty(), nil
@@ -263,72 +263,55 @@ func NewSetWithSortableFiltered(kvs []KeyValue, tmp *Sortable, filter Filter) (S
 
 	*tmp = nil
 
-	// Use filteredToFront here for last-value-wins semantics.
-	uniq := filteredToFront(kvs, func() func(kv KeyValue) bool {
-		firstCall := true
-		var prev Key
-		return func(kv KeyValue) bool {
-			if firstCall {
-				firstCall, prev = false, kv.Key
-			} else {
-				if kv.Key == prev {
-					return false
-				}
-				prev = kv.Key
-			}
-			return true
-		}
-	}())
-	kvs = kvs[uniq:]
-
-	if filter != nil {
-		// Unique prior to filtering so the returned dropped attributes will
-		// not also include the deduplicated attributes.
-		k := filteredToBack(kvs, filter)
-		if k == len(kvs) {
-			return Set{equivalent: computeDistinct(kvs[:k])}, nil
-		}
-		return Set{equivalent: computeDistinct(kvs[:k])}, kvs[k:]
+	if keep == nil {
+		keep = func(KeyValue) bool { return true }
 	}
 
-	return Set{equivalent: computeDistinct(kvs)}, nil
-}
+	n := len(kvs)
+	prev := kvs[n-1]
 
-// filteredToBack filters slice in-place using f. All KeyValues that need to be
-// removed are moved to the end. All KeyValues that need to be kept are moved
-// (in-order) to the front. The index for the first KeyValue to be removed is
-// returned.
-func filteredToBack(slice []KeyValue, keep Filter) int {
-	var j int
-	for i := 0; i < len(slice); i++ {
-		if keep(slice[i]) {
-			slice[i], slice[j] = slice[j], slice[i]
-			j++
-		}
+	kept := n // Starting index of kept KeyValues.
+	if keep(prev) {
+		kept--
 	}
-	return j
-}
 
-// filteredToFront filters slice in-place using f. All KeyValues that need to
-// be removed are moved to the front. All KeyValues that need to be kept are
-// moved (in-order) to the back. The index for the first KeyValue to be kept is
-// returned.
-func filteredToFront(slice []KeyValue, keep Filter) int {
-	n := len(slice)
-	j := n
-	for i := n - 1; i >= 0; i-- {
-		if keep(slice[i]) {
-			j--
-			slice[i], slice[j] = slice[j], slice[i]
+	// Instead of iterating kvs once to de-duplicate and another time to
+	// filter, do both in a single pass.
+	//
+	// Iterate from back-to-front for last-value-wins semantics.
+	for i := n - 2; i >= 0; i-- {
+		kv := kvs[i]
+		if kv.Key == prev.Key {
+			// Delete duplicate from kvs while preserving order and keeping
+			// the deleted KeyValue in original slice.
+			copy(kvs[i:], kvs[i+1:])
+			kvs[len(kvs)-1] = kv
+			kvs = kvs[:len(kvs)-1]
+
+			// Update kept index for new kvs size.
+			kept--
+		} else {
+			prev = kv
+			if keep(kv) {
+				kept--
+				kvs[i], kvs[kept] = kvs[kept], kvs[i]
+			}
 		}
 	}
-	return j
+
+	switch kept {
+	case 0:
+		return Set{equivalent: computeDistinct(kvs)}, nil
+	case n:
+		return empty(), kvs
+	}
+	return Set{equivalent: computeDistinct(kvs[kept:])}, kvs[:kept]
 }
 
 // Filter returns a filtered copy of this Set. See the documentation for
 // NewSetWithSortableFiltered for more details.
-func (l *Set) Filter(re Filter) (Set, []KeyValue) {
-	if re == nil {
+func (l *Set) Filter(keep Filter) (Set, []KeyValue) {
+	if keep == nil {
 		return *l, nil
 	}
 
@@ -336,7 +319,7 @@ func (l *Set) Filter(re Filter) (Set, []KeyValue) {
 	start, n := 0, l.Len()
 	for ; start < n; start++ {
 		kv, _ := l.Get(start)
-		if !re(kv) {
+		if !keep(kv) {
 			break
 		}
 	}
@@ -352,7 +335,7 @@ func (l *Set) Filter(re Filter) (Set, []KeyValue) {
 	// immutable and filtering should not change this.
 	slice := l.ToSlice()
 
-	// Do not re-evaluate re(slice[i]).
+	// Do not re-evaluate keep(slice[i]).
 	end := len(slice) - 1
 	if start == end {
 		return Set{equivalent: computeDistinct(slice[:start])}, slice[start:]
@@ -362,7 +345,13 @@ func (l *Set) Filter(re Filter) (Set, []KeyValue) {
 	copy(slice[start:], slice[start+1:])
 	slice[end] = kv
 
-	div := filteredToBack(slice[start:end], re) + start
+	div := start // Index of the first KeyValue to be removed.
+	for i := start; i < end; i++ {
+		if keep(slice[i]) {
+			slice[i], slice[div] = slice[div], slice[i]
+			div++
+		}
+	}
 	return Set{equivalent: computeDistinct(slice[:div])}, slice[div:]
 }