From 1bb8c867610d1a19352bae723687a4df21a59c24 Mon Sep 17 00:00:00 2001
From: itchyny <itchyny@hatena.ne.jp>
Date: Wed, 8 Jan 2020 10:27:20 +0900
Subject: [PATCH] add comments to the main logic

---
 mmv.go | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/mmv.go b/mmv.go
index ea0f3e6..4f12baf 100644
--- a/mmv.go
+++ b/mmv.go
@@ -40,12 +40,15 @@ func (err *sameDestinationError) Error() string {
 }
 
 func buildRenames(files map[string]string) ([]rename, error) {
-	rs := make([]rename, 0, 2*len(files))
-	revs := make(map[string]string, len(files))
+	revs := make(map[string]string, len(files)) // reverse of files
+
+	// list the current rename sources
 	srcs := make([]string, 0, len(files))
 	for src := range files {
 		srcs = append(srcs, src)
 	}
+
+	// clean the paths and check duplication
 	for _, src := range srcs {
 		dst := files[src]
 		if src == "" || dst == "" {
@@ -65,19 +68,26 @@ func buildRenames(files map[string]string) ([]rename, error) {
 		}
 		revs[dst] = src
 	}
+
+	// remove source == destination
 	for src, dst := range files {
 		if src == dst {
 			delete(files, src)
 			delete(revs, dst)
 		}
 	}
+
+	// list the renames
 	var i int
+	rs := make([]rename, 0, 2*len(files))
 	vs := make(map[string]int, len(files))
 	for _, dst := range files {
 		if vs[dst] > 0 {
 			continue
 		}
-		i++
+		i++ // connected component identifier
+
+		// mark the nodes in the connected component and check cycle
 		var cycle bool
 		for {
 			vs[dst] = i
@@ -91,12 +101,16 @@ func buildRenames(files map[string]string) ([]rename, error) {
 				break
 			}
 		}
+
+		// if there is a cycle, rename to a temporary file
 		var tmp string
 		if cycle {
 			tmp = randomPath(filepath.Dir(dst))
 			rs = append(rs, rename{dst, tmp})
 			vs[dst]--
 		}
+
+		// rename from the leaf node
 		for {
 			if src, ok := revs[dst]; ok && (!cycle || vs[src] == i) {
 				rs = append(rs, rename{src, dst})
@@ -108,6 +122,8 @@ func buildRenames(files map[string]string) ([]rename, error) {
 				break
 			}
 		}
+
+		// if there is a cycle, rename the remporary file
 		if cycle {
 			rs = append(rs, rename{tmp, dst})
 		}