once more unto the breach

lib/hexpds/mststorage.ex

@@ -0,0 +1,9 @@
+defmodule Hexpds.MST.MSTStorage do
+  @moduledoc """
+  Simplified storage module for MST.
+  """
+  def read_obj(_pointer) do
+    # TODO
+    %{}
+  end
+end

lib/hexpds/mstutil.ex

@@ -0,0 +1,51 @@
+defmodule Hexpds.MST.MSTUtil do
+  @moduledoc """
+  Utility functions for MST operations.
+  """
+
+  @spec ensure_valid_key(String.t()) :: :ok | no_return()
+  def ensure_valid_key(key) do
+    if String.length(key) > 0 do
+      :ok
+    else
+      raise "Invalid key: Key must be a non-empty string."
+    end
+  end
+
+  @spec leading_zeros_on_hash(String.t()) :: integer()
+  def leading_zeros_on_hash(key) do
+    hash = :crypto.hash(:sha256, key)
+    hash
+    |> :binary.bin_to_list()
+    |> Enum.reduce_while(0, fn byte, acc ->
+      case byte do
+        0 -> {:cont, acc + 8}
+        _ -> {:halt, acc + leading_zeros(byte)}
+      end
+    end)
+  end
+
+  @spec leading_zeros(integer()) :: integer()
+  defp leading_zeros(byte) do
+    bits = :erlang.integer_to_binary(byte, 2)
+    String.length(String.trim_leading(bits, "0"))
+  end
+
+  @spec cid_for_entries(list()) :: binary()
+  def cid_for_entries(entries) do
+    data = serialize_node_data(entries)
+    :crypto.hash(:sha256, data)
+  end
+
+  @spec serialize_node_data(list()) :: binary()
+  def serialize_node_data(entries) do
+    # CBOR serialization
+    :erlang.term_to_binary(entries)
+  end
+
+  @spec deserialize_node_data(module(), binary()) :: list()
+  def deserialize_node_data(_storage, data) do
+    # CBOR deserialization
+    :erlang.binary_to_term(data)
+  end
+end