1 files changed, 91 insertions, 0 deletions
diff --git a/shard/lib/data/store.ex b/shard/lib/data/store.ex
new file mode 100644
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+++ b/shard/lib/data/store.ex
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+defprotocol SData.Page do
+  @moduledoc"""
+  Protocol to be implemented by objects that are used as data pages
+  in a pagestore and that may reference other data pages by their hash.
+  """
+
+  @fallback_to_any true
+
+  @doc"""
+  Get hashes of all pages referenced by this page.
+  """
+  def refs(page)
+end
+
+defimpl SData.Page, for: Any do
+  def refs(_page), do: []
+end
+
+
+defprotocol SData.PageStore do
+  @moduledoc"""
+  Protocol to be implemented for page stores to allow their
+  manipulation.
+
+  This protocol may also be implemented by store proxies that track
+  operations and implement different synchronization or caching mechanisms.
+  """
+
+  @doc"""
+  Put a page. Argument is the content of the page, returns the
+  hash that the store has associated to it.
+
+  Returns {hash, store}
+  """
+  def put(store, page)
+
+  @doc"""
+  Get a page referenced by its hash.
+
+  Returns page
+  """
+  def get(store, hash)
+
+  @doc"""
+  Copy to the store a page and all its references from the other store.
+  In the case of pages on the network in a distributed store, this may
+  be lazy.
+
+  Returns store
+  """
+  def copy(store, other_store, hash)
+
+  @doc"""
+  Free a page referenced by its hash, marking it as no longer needed.
+
+  Returns store
+  """
+  def free(store, hash)
+end
+
+
+defmodule SData.LocalStore do
+  defstruct [:pages] 
+
+  def new() do
+    %SData.LocalStore{ pages: %{} }
+  end
+end
+
+defimpl SData.PageStore, for: SData.LocalStore do
+  def put(store, page) do
+    hash = SData.term_hash page
+    store = %{ store | pages: Map.put(store.pages, hash, page) }
+    { hash, store }
+  end
+
+  def get(store, hash) do
+    store.pages[hash]
+  end
+
+  def copy(store, other_store, hash) do
+    page = SData.PageStore.get(other_store, hash)
+    refs = SData.Page.refs(page)
+    store = Enum.reduce(refs, store, fn x, acc -> copy(acc, other_store, x) end)
+    %{ store | pages: Map.put(store.pages, hash, page) }
+  end
+
+  def free(store, hash) do
+    %{ store | pages: Map.delete(store.pages, hash) }
+  end
+end