@spec calculate_delta(current_context :: map(), new_context :: map()) :: map()

Calculates the delta between two contexts.

Given a current_context and a new_context, this function determines the differences:

• Keys present in new_context but not in current_context are marked as :added.
• Keys present in both but with differing values are marked as :modified.
• Keys present in current_context but absent in new_context are marked as :removed.

Parameters

• current_context (map): The original context.
• new_context (map): The updated context.

Returns

• (map): A map representing the delta, where each key maps to a change descriptor.

Example

iex> current_context = %{a: 1, b: 2, c: 3}
iex> new_context = %{a: 1, b: 5, d: 4}
iex> Chord.Delta.calculate_delta(current_context, new_context)
%{
  b: %{action: :modified, old_value: 2, value: 5},
  c: %{action: :removed},
  d: %{action: :added, value: 4}
}

@spec format_delta(delta :: map(), context_id :: any()) :: list()

Formats a delta map for external communication or storage.

Uses the configured delta formatter to transform the delta map into a desired format. By default, it uses Chord.Delta.Formatter.Default.

Parameters

• delta (map): The delta to format.
• context_id (any): The context associated with the delta.

Returns

• (list): The formatted delta, as determined by the formatter module.

Example

iex> delta = %{a: %{action: :added, value: 1}, b: %{action: :removed}}
iex> Chord.Delta.format_delta(delta, "game:1")
[
  %{key: :a, action: :added, value: 1, context: "game:1"},
  %{key: :b, action: :removed, context: "game:1"}
]

@spec merge_deltas(delta_list :: [map()]) :: map()

Merges a list of deltas into a single delta.

Combines multiple delta maps to produce a unified view of changes. The merging logic ensures:

• If any delta marks a key as :removed, it takes precedence.
• If multiple deltas modify the same key, the old_value is taken from the first modification, and the value from the last.
• Otherwise, the latest change is retained.

Parameters

• delta_list (list of maps): A list of deltas to merge.

Returns

• (map): A single delta representing the merged changes.

Example

iex> delta1 = %{a: %{action: :added, value: 1}, b: %{action: :modified, old_value: 2, value: 3}}
iex> delta2 = %{b: %{action: :removed}, c: %{action: :added, value: 4}}
iex> Chord.Delta.merge_deltas([delta1, delta2])
%{
  a: %{action: :added, value: 1},
  b: %{action: :removed},
  c: %{action: :added, value: 4}
}