diff --git a/lib/excache/stream.ex b/lib/excache/stream.ex
new file mode 100644
index 0000000..16237c9
--- /dev/null
+++ b/lib/excache/stream.ex
@@ -0,0 +1,309 @@
+defmodule Excache.Stream do
+  @moduledoc false
+
+  alias Excache.Stream.Group
+
+  defstruct entries: :gb_trees.empty(),
+            lastId: {0, 0},
+            maxDeletedId: {0, 0},
+            length: 0,
+            entriesAdded: 0,
+            groups: %{}
+
+  def new, do: %__MODULE__{}
+
+  def length(%__MODULE__{length: length}), do: length
+
+  def formatId({ms, seq}), do: "#{ms}-#{seq}"
+
+  def parseId(raw, defaultSeq) do
+    case String.split(raw, "-", parts: 2) do
+      [ms] ->
+        withInteger(ms, fn value -> {:ok, {value, defaultSeq}} end)
+
+      [ms, "*"] ->
+        withInteger(ms, fn value -> {:ok, {:autoSeq, value}} end)
+
+      [ms, seq] ->
+        withInteger(ms, fn msValue ->
+          withInteger(seq, fn seqValue -> {:ok, {msValue, seqValue}} end)
+        end)
+    end
+  end
+
+  def parseAddId("*", _now), do: {:ok, :auto}
+
+  def parseAddId(raw, _now) do
+    case String.split(raw, "-", parts: 2) do
+      [ms] ->
+        withInteger(ms, fn value -> {:ok, {:autoSeq, value}} end)
+
+      [ms, "*"] ->
+        withInteger(ms, fn value -> {:ok, {:autoSeq, value}} end)
+
+      [ms, seq] ->
+        withInteger(ms, fn msValue ->
+          withInteger(seq, fn seqValue -> {:ok, {:full, msValue, seqValue}} end)
+        end)
+    end
+  end
+
+  def parseRangeStart("-"), do: {:ok, {:incl, {0, 0}}}
+  def parseRangeStart("+"), do: {:ok, {:incl, {maxMs(), maxSeq()}}}
+  def parseRangeStart("(" <> rest), do: rangeBound(rest, 0, :excl)
+  def parseRangeStart(raw), do: rangeBound(raw, 0, :incl)
+
+  def parseRangeEnd("-"), do: {:ok, {:incl, {0, 0}}}
+  def parseRangeEnd("+"), do: {:ok, {:incl, {maxMs(), maxSeq()}}}
+  def parseRangeEnd("(" <> rest), do: rangeBound(rest, maxSeq(), :excl)
+  def parseRangeEnd(raw), do: rangeBound(raw, maxSeq(), :incl)
+
+  def add(stream, idSpec, fields, now) do
+    case resolveId(stream, idSpec, now) do
+      {:ok, id} ->
+        entries = :gb_trees.insert(id, fields, stream.entries)
+
+        updated = %{
+          stream
+          | entries: entries,
+            lastId: id,
+            length: stream.length + 1,
+            entriesAdded: stream.entriesAdded + 1
+        }
+
+        {:ok, updated, id}
+
+      {:error, reason} ->
+        {:error, reason}
+    end
+  end
+
+  def get(stream, id) do
+    case :gb_trees.lookup(id, stream.entries) do
+      {:value, fields} -> {:ok, fields}
+      :none -> :miss
+    end
+  end
+
+  def member?(stream, id), do: :gb_trees.is_defined(id, stream.entries)
+
+  def range(stream, {startKind, startId}, {endKind, endId}, count) do
+    lower = if startKind == :excl, do: successor(startId), else: startId
+
+    upperOk = fn id ->
+      case endKind do
+        :incl -> id <= endId
+        :excl -> id < endId
+      end
+    end
+
+    if stream.length == 0 or lower > endId do
+      []
+    else
+      iterator = :gb_trees.iterator_from(lower, stream.entries)
+      collectForward(iterator, upperOk, count, [])
+    end
+  end
+
+  def reverseRange(stream, endBound, startBound, count) do
+    stream
+    |> range(startBound, endBound, :all)
+    |> Enum.reverse()
+    |> take(count)
+  end
+
+  def afterId(stream, id, count) do
+    range(stream, {:excl, id}, {:incl, {maxMs(), maxSeq()}}, count)
+  end
+
+  def delete(stream, ids) do
+    Enum.reduce(ids, {stream, 0}, fn id, {acc, removed} ->
+      if :gb_trees.is_defined(id, acc.entries) do
+        entries = :gb_trees.delete(id, acc.entries)
+        maxDeleted = max(acc.maxDeletedId, id)
+        {%{acc | entries: entries, length: acc.length - 1, maxDeletedId: maxDeleted}, removed + 1}
+      else
+        {acc, removed}
+      end
+    end)
+  end
+
+  def trimMaxlen(stream, maxlen) when maxlen < 0, do: {stream, 0}
+
+  def trimMaxlen(stream, maxlen) do
+    dropSmallest(stream, max(stream.length - maxlen, 0), 0)
+  end
+
+  def trimMinId(stream, minId) do
+    dropBelow(stream, minId, 0)
+  end
+
+  def setLastId(stream, id), do: %{stream | lastId: id}
+
+  def lastEntryId(%__MODULE__{lastId: lastId}), do: lastId
+
+  def info(stream) do
+    %{
+      length: stream.length,
+      lastGeneratedId: stream.lastId,
+      maxDeletedId: stream.maxDeletedId,
+      entriesAdded: stream.entriesAdded,
+      groups: map_size(stream.groups),
+      firstEntry: firstEntryPair(stream),
+      lastEntry: lastEntry(stream)
+    }
+  end
+
+  defp firstEntryPair(stream) do
+    case :gb_trees.is_empty(stream.entries) do
+      true -> nil
+      false -> :gb_trees.smallest(stream.entries) |> pairFromKV()
+    end
+  end
+
+  def createGroup(stream, name, startId) do
+    if Map.has_key?(stream.groups, name) do
+      {:error, :busygroup}
+    else
+      group = %Group{lastDeliveredId: startId, entriesRead: 0}
+      {:ok, %{stream | groups: Map.put(stream.groups, name, group)}}
+    end
+  end
+
+  def destroyGroup(stream, name) do
+    if Map.has_key?(stream.groups, name) do
+      {%{stream | groups: Map.delete(stream.groups, name)}, 1}
+    else
+      {stream, 0}
+    end
+  end
+
+  def fetchGroup(stream, name), do: Map.fetch(stream.groups, name)
+
+  def putGroup(stream, name, group), do: %{stream | groups: Map.put(stream.groups, name, group)}
+
+  def firstId(stream) do
+    case :gb_trees.is_empty(stream.entries) do
+      true -> nil
+      false -> :gb_trees.smallest(stream.entries) |> elem(0)
+    end
+  end
+
+  def lastEntry(stream) do
+    case :gb_trees.is_empty(stream.entries) do
+      true -> nil
+      false -> :gb_trees.largest(stream.entries) |> pairFromKV()
+    end
+  end
+
+  def toList(stream) do
+    stream.entries |> :gb_trees.to_list() |> Enum.map(&pairFromKV/1)
+  end
+
+  def successor({ms, seq}) when seq >= 0, do: {ms, seq + 1}
+
+  defp pairFromKV({id, fields}), do: {id, fields}
+
+  defp resolveId(stream, :auto, now) do
+    {lastMs, lastSeq} = stream.lastId
+    ms = max(now, lastMs)
+    seq = if ms == lastMs, do: lastSeq + 1, else: 0
+    validate(stream, {ms, seq})
+  end
+
+  defp resolveId(stream, {:autoSeq, ms}, _now) do
+    {lastMs, lastSeq} = stream.lastId
+
+    cond do
+      ms < lastMs -> {:error, :smaller}
+      ms == lastMs -> validate(stream, {ms, lastSeq + 1})
+      true -> validate(stream, {ms, 0})
+    end
+  end
+
+  defp resolveId(stream, {:full, ms, seq}, _now) do
+    validate(stream, {ms, seq})
+  end
+
+  defp validate(stream, {0, 0}), do: validateAgainst(stream, {0, 0}, :zero)
+  defp validate(stream, id), do: validateAgainst(stream, id, :normal)
+
+  defp validateAgainst(_stream, {0, 0}, :zero), do: {:error, :zero}
+
+  defp validateAgainst(stream, id, _kind) do
+    if id > stream.lastId, do: {:ok, id}, else: {:error, :smaller}
+  end
+
+  defp collectForward(_iterator, _upperOk, 0, acc), do: Enum.reverse(acc)
+
+  defp collectForward(iterator, upperOk, count, acc) do
+    case :gb_trees.next(iterator) do
+      :none ->
+        Enum.reverse(acc)
+
+      {id, fields, nextIterator} ->
+        if upperOk.(id) do
+          remaining = if count == :all, do: :all, else: count - 1
+          collectForward(nextIterator, upperOk, remaining, [{id, fields} | acc])
+        else
+          Enum.reverse(acc)
+        end
+    end
+  end
+
+  defp take(list, :all), do: list
+  defp take(list, count), do: Enum.take(list, count)
+
+  defp dropSmallest(stream, 0, removed), do: {stream, removed}
+
+  defp dropSmallest(stream, remaining, removed) do
+    {id, _fields, entries} = :gb_trees.take_smallest(stream.entries)
+    maxDeleted = max(stream.maxDeletedId, id)
+    updated = %{stream | entries: entries, length: stream.length - 1, maxDeletedId: maxDeleted}
+    dropSmallest(updated, remaining - 1, removed + 1)
+  end
+
+  defp dropBelow(stream, minId, removed) do
+    case :gb_trees.is_empty(stream.entries) do
+      true ->
+        {stream, removed}
+
+      false ->
+        {id, _fields} = :gb_trees.smallest(stream.entries)
+
+        if id < minId do
+          {_, _, entries} = :gb_trees.take_smallest(stream.entries)
+          maxDeleted = max(stream.maxDeletedId, id)
+
+          updated = %{
+            stream
+            | entries: entries,
+              length: stream.length - 1,
+              maxDeletedId: maxDeleted
+          }
+
+          dropBelow(updated, minId, removed + 1)
+        else
+          {stream, removed}
+        end
+    end
+  end
+
+  defp rangeBound(raw, defaultSeq, kind) do
+    case parseId(raw, defaultSeq) do
+      {:ok, {:autoSeq, _ms}} -> :error
+      {:ok, id} -> {:ok, {kind, id}}
+      :error -> :error
+    end
+  end
+
+  defp withInteger(raw, continue) do
+    case Integer.parse(raw) do
+      {value, ""} when value >= 0 -> continue.(value)
+      _ -> :error
+    end
+  end
+
+  defp maxMs, do: 0xFFFFFFFFFFFFFFFF
+  defp maxSeq, do: 0xFFFFFFFFFFFFFFFF
+end
diff --git a/lib/excache/stream/group.ex b/lib/excache/stream/group.ex
new file mode 100644
index 0000000..054cbe9
--- /dev/null
+++ b/lib/excache/stream/group.ex
@@ -0,0 +1,5 @@
+defmodule Excache.Stream.Group do
+  @moduledoc false
+
+  defstruct lastDeliveredId: {0, 0}, pending: %{}, consumers: %{}, entriesRead: 0
+end