From 5a7f7a00ece49b51ace7e645ebe78f1b2c7938df Mon Sep 17 00:00:00 2001
From: Rich-Harris <richard.a.harris@gmail.com>
Date: Wed, 21 Mar 2018 11:31:45 -0400
Subject: [PATCH] reinstate previous code from before i ballsed it up

---
 src/shared/keyed-each.js | 69 +++++++++++++++++++++++++---------------
 1 file changed, 43 insertions(+), 26 deletions(-)

diff --git a/src/shared/keyed-each.js b/src/shared/keyed-each.js
index 384a96f6ed..40ad3f302c 100644
--- a/src/shared/keyed-each.js
+++ b/src/shared/keyed-each.js
@@ -20,22 +20,36 @@ export function outroAndDestroyIteration(iteration, lookup) {
 // TODO is it possible to avoid mounting iterations that are
 // already in the right place?
 export function updateKeyedEach(component, key, changed, key_prop, dynamic, list, head, lookup, node, has_outro, create_each_block, intro_method, get_context) {
+	var expected = head;
+
 	var keep = {};
+	var mounts = {};
 
-	var i = list.length;
-	while (i--) {
+	for (var i = 0; i < list.length; i += 1) {
 		var key = list[i][key_prop];
 		var iteration = lookup[key];
+		var next_data = list[i+1];
+		var next = next_data && lookup[next_data[key_prop]];
+
+		if (dynamic && iteration) iteration.p(changed, get_context(i)); // TODO should this be deferred? could it be redundant?
 
-		if (iteration) {
-			if (dynamic) iteration.p(changed, get_context(i));
+		if (expected && (key === expected.key)) {
+			var first = iteration && iteration.first;
+			var parentNode = first && first.parentNode
+			if (!parentNode || (iteration && iteration.next) != next) mounts[key] = iteration;
+			expected = iteration.next;
+		} else if (iteration) {
+			mounts[key] = iteration;
+			expected = iteration.next;
 		} else {
+			// key is being inserted
 			iteration = lookup[key] = create_each_block(component, key, get_context(i));
 			iteration.c();
+			mounts[key] = iteration;
 		}
-
 		lookup[key] = iteration;
-		keep[key] = 1;
+		keep[iteration.key] = iteration;
+		// last = iteration;
 	}
 
 	var destroy = has_outro
@@ -49,32 +63,35 @@ export function updateKeyedEach(component, key, changed, key_prop, dynamic, list
 	}
 
 	var next = null;
+	var next_iteration = null;
 
-	i = list.length;
-	while (i--) {
-		key = list[i][key_prop];
+	for (i = list.length - 1; i >= 0; i -= 1) {
+		var data = list[i];
+		var key = data[key_prop];
 		iteration = lookup[key];
 
-		var anchor;
-
-		if (has_outro) {
-			var next_key = next && next.key;
-			var neighbour = iteration.next;
-			var anchor_key;
+		var block = mounts[key];
+		if (block) {
+			var anchor;
 
-			while (neighbour && anchor_key != next_key && !keep[anchor_key]) {
-				anchor = neighbour && neighbour.first;
-				neighbour = neighbour.next;
-				anchor_key = neighbour && neighbour.key;
+			if (has_outro) {
+				var key_next_iteration = next_iteration && next_iteration.key;
+				var iteration_anchor = iteration.next;
+				var key_anchor;
+				do {
+					anchor = iteration_anchor && iteration_anchor.first;
+					iteration_anchor = iteration_anchor && iteration_anchor.next;
+					key_anchor = iteration_anchor && iteration_anchor.key;
+				} while(iteration_anchor && key_anchor != key_next_iteration && !keep[key_anchor])
+			} else {
+				anchor = next_iteration && next_iteration.first;
 			}
-		} else {
-			anchor = next && next.first;
-		}
 
-		iteration[intro_method](node, anchor);
+			block[intro_method](node, anchor);
+		}
 
-		iteration.next = next;
-		if (next) next.last = iteration;
-		next = iteration;
+		iteration.next = next_iteration;
+		if (next_iteration) next_iteration.last = iteration;
+		next_iteration = iteration;
 	}
 }
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