Encodes ExRatatui.CellSession.Diff payloads for transmission to the browser via Phoenix.LiveView.push_event/3.

LiveView's push_event/3 only accepts JSON-serializable terms — atoms encode as strings (via Jason), but tuples like {:rgb, r, g, b} do not encode cleanly. This module bridges the gap: convert each %CellSession.Cell{} into a fixed-shape array that the JS hook on the other side can read positionally without allocating an object per cell.

Wire shape

A diff payload becomes a map ready for push_event/3:

%{
  "width" => 80,
  "height" => 24,
  "ops" => [
    [row, col, symbol, fg, bg, modifiers, skip],
    ...
  ]
}

Where each value follows these encodings:

• row, col — integers, zero-indexed
• symbol — UTF-8 string (single character or grapheme cluster)
• fg, bg — color encoding:
  • :reset → "reset"
  • named atoms (:red, :dark_gray, ...) → matching string ("red")
  • {:rgb, r, g, b} → ["rgb", r, g, b]
  • {:indexed, n} → ["indexed", n]
• modifiers — list of strings in canonical bitflag order (["bold", "italic"]); empty list when no modifiers are set
• skip — boolean; true means "leave whatever was here"

Why arrays not objects per op

A 200×60 full diff is 12_000 cells. Encoded as objects with named keys ({"row": 0, "col": 0, "symbol": " ", "fg": "reset", ...}) each cell is roughly 80 bytes; encoded as a 7-element array each cell is roughly 30 bytes. At websocket frame scale that's the difference between ~1MB and ~360KB on a single full-paint, before gzip. Since every browser implements Array#0 access in a single CPU instruction, the JS side pays nothing for the positional read.

Defaults are not omitted

Every cell in the diff carries a full 7-element op even when most of its fields are at their default values ("reset", [], false). Omitting defaults would shrink the payload further but would push schema knowledge into the JS hook, and the diff path already filters cells aggressively — frames that "shouldn't" carry a cell at all don't appear in :ops to begin with. We can revisit if profiling flags it.