View Source Chord.Delta (Chord v0.1.1)

Provides utilities for calculating, merging, and formatting context deltas.

This module contains functions to:

  • Compute the differences (deltas) between two contexts.
  • Merge multiple deltas into a single representation.
  • Format deltas for communication or storage purposes.

The formatting of deltas is customizable. Developers can define their own formatter module implementing the Chord.Delta.Formatter.Behaviour and configure it in their application. By default, the library uses Chord.Delta.Formatter.Default.

Summary

Functions

Calculates the delta between two contexts.

Formats a delta map for external communication or storage.

Merges a list of deltas into a single delta.

Functions

calculate_delta(current_context, new_context)

@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}
}

format_delta(delta, context_id)

@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"}
]

merge_deltas(delta_list)

@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}
}