chore(iterators): create Iterator module and migrate iterators to use it (#1392)

lua/nvim-tree/iterators/node-iterator.lua

@@ -0,0 +1,67 @@
+local NodeIterator = {}
+NodeIterator.__index = NodeIterator
+
+function NodeIterator.builder(nodes)
+  return setmetatable({
+    nodes = nodes,
+    _filter_hidden = function(node)
+      return not node.hidden
+    end,
+    _apply_fn_on_node = function(_) end,
+    _match = function(_) end,
+    _recurse_with = function(node)
+      return node.nodes
+    end,
+  }, NodeIterator)
+end
+
+function NodeIterator:hidden()
+  self._filter_hidden = function(_)
+    return true
+  end
+  return self
+end
+
+function NodeIterator:matcher(f)
+  self._match = f
+  return self
+end
+
+function NodeIterator:applier(f)
+  self._apply_fn_on_node = f
+  return self
+end
+
+function NodeIterator:recursor(f)
+  self._recurse_with = f
+  return self
+end
+
+function NodeIterator:iterate()
+  local function iter(nodes)
+    local i = 1
+    for _, node in ipairs(nodes) do
+      if self._filter_hidden(node) then
+        if self._match(node) then
+          return node, i
+        end
+        self._apply_fn_on_node(node)
+        local children = self._recurse_with(node)
+        if children then
+          local n, idx = iter(children)
+          i = i + idx
+          if n then
+            return n, i
+          else
+            i = i + 1
+          end
+        end
+      end
+    end
+    return nil, i
+  end
+
+  return iter(self.nodes)
+end
+
+return NodeIterator