2 files changed, 38 insertions, 0 deletions
diff --git a/libs/utils/src/main/java/org/the_jk/cleversync/PathUtils.kt b/libs/utils/src/main/java/org/the_jk/cleversync/PathUtils.kt
index 4202b24..77037cd 100644
--- a/libs/utils/src/main/java/org/the_jk/cleversync/PathUtils.kt
+++ b/libs/utils/src/main/java/org/the_jk/cleversync/PathUtils.kt
@@ -1,5 +1,7 @@
 package org.the_jk.cleversync
 
+import kotlin.math.min
+
 object PathUtils {
     fun dirname(path: String): String {
         if (path.isEmpty()) return "."
@@ -46,4 +48,29 @@ object PathUtils {
         }
         return parts.joinToString("/", prefix = if (prefixed) "/" else "")
     }
+
+    // Return path relative to base. Returns path as-is if either path is not
+    // absolute.
+    fun relativeTo(base: String, path: String): String {
+        if (!base.startsWith('/') || !path.startsWith('/')) return path
+        val baseParts = base.split('/').filter { part ->
+            part.isNotEmpty() && part != "."
+        }
+        val pathParts = path.split('/').filter { part ->
+            part.isNotEmpty() && part != "."
+        }
+        var i = 0
+        while (i < min(baseParts.size, pathParts.size)) {
+            if (baseParts[i] != pathParts[i]) break
+            i++
+        }
+        if (i == baseParts.size) {
+            if (i == pathParts.size) return "."
+            return pathParts.subList(i, pathParts.size).joinToString("/")
+        }
+        return buildList {
+            repeat(baseParts.size - i) { add("..") }
+            addAll(pathParts.subList(i, pathParts.size))
+        }.joinToString("/")
+    }
 }
diff --git a/libs/utils/src/test/java/org/the_jk/cleversync/PathUtilsTest.kt b/libs/utils/src/test/java/org/the_jk/cleversync/PathUtilsTest.kt
index eb1d63f..1d411ea 100644
--- a/libs/utils/src/test/java/org/the_jk/cleversync/PathUtilsTest.kt
+++ b/libs/utils/src/test/java/org/the_jk/cleversync/PathUtilsTest.kt
@@ -55,4 +55,15 @@ class PathUtilsTest {
         assertThat(PathUtils.resolve("foo/../../../bar/")).isEqualTo("bar")
         assertThat(PathUtils.resolve("/foo/../../../bar/")).isEqualTo("/bar")
     }
+
+    @Test
+    fun relativeTo() {
+        assertThat(PathUtils.relativeTo("", "")).isEmpty()
+        assertThat(PathUtils.relativeTo("/", "/")).isEqualTo(".")
+        assertThat(PathUtils.relativeTo("/", "/foo")).isEqualTo("foo")
+        assertThat(PathUtils.relativeTo("/", "/foo/bar/")).isEqualTo("foo/bar")
+        assertThat(PathUtils.relativeTo("/foo", "/foo/bar/")).isEqualTo("bar")
+        assertThat(PathUtils.relativeTo("/foo", "/bar")).isEqualTo("../bar")
+        assertThat(PathUtils.relativeTo("/foo/bar", "/fum/bar")).isEqualTo("../../fum/bar")
+    }
 }