lukesutton · December 12, 2016 05:45 · Dec 12, 2016
diff --git a/file-navigation.swift b/file-navigation.swift
@@ -0,0 +1,46 @@
+struct File {}
+
+struct Landscape {
+    let parents: FileList
+    let children: FileList
+}
+
+struct FileList {
+    fileprivate let all: Array<File>
+    fileprivate let before: ArraySlice<File>
+    fileprivate let after: ArraySlice<File>
+
+    var previous: FileList {
+        guard !before.isEmpty else { return self }
+        return shift(by: before.count - 1)
+    }
+
+    var next: FileList {
+        guard !after.isEmpty else { return self }
+        return shift(by: before.count + 1)
+    }
+
+    var current: File? {
+        return before.last
+    }
+
+    var isEmpty: Bool {
+        return all.isEmpty
+    }
+
+    fileprivate func shift(by prefixLength: Int) -> FileList {
+        return FileList(
+            all: all,
+            before: all.prefix(prefixLength), 
+            after: all.suffix(all.count - prefixLength)
+        )
+    }
+}
+
+extension FileList {
+    fileprivate init(_ elements: File...) {
+        self.all = elements
+        self.before = elements.prefix(1)
+        self.after = elements.suffix(elements.count - 1)
+    }
+}