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https://github.com/livebook-dev/livebook.git
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70 lines
2.2 KiB
Elixir
70 lines
2.2 KiB
Elixir
defmodule Livebook.JSInterop do
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@moduledoc false
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alias Livebook.Delta
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@doc """
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Returns the result of applying `delta` to `string`.
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The delta operation lenghts (retain, delete) are treated
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such that they match the JavaScript strings behavior.
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JavaScript uses UTF-16 encoding, in which every character is stored
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as either one or two 16-bit code units. JS treats the number of units
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as string length and this also impacts position-based functions like `String.slice`.
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To match this behavior we first convert normal UTF-8 string
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into a list of UTF-16 code points, then apply the delta to this list
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and finally convert back to a UTF-8 string.
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"""
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@spec apply_delta_to_string(Delta.t(), String.t()) :: String.t()
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def apply_delta_to_string(delta, string) do
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code_units = string_to_utf16_code_units(string)
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delta.ops
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|> apply_to_code_units(code_units)
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|> utf16_code_units_to_string()
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end
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defp apply_to_code_units([], code_units), do: code_units
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defp apply_to_code_units([{:retain, n} | ops], code_units) do
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{left, right} = Enum.split(code_units, n)
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left ++ apply_to_code_units(ops, right)
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end
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defp apply_to_code_units([{:insert, inserted} | ops], code_units) do
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string_to_utf16_code_units(inserted) ++ apply_to_code_units(ops, code_units)
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end
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defp apply_to_code_units([{:delete, n} | ops], code_units) do
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apply_to_code_units(ops, Enum.slice(code_units, n..-1))
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end
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# ---
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defp string_to_utf16_code_units(string) do
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string
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|> :unicode.characters_to_binary(:utf8, :utf16)
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|> utf16_binary_to_code_units([])
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|> Enum.reverse()
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end
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defp utf16_binary_to_code_units(<<>>, code_units), do: code_units
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defp utf16_binary_to_code_units(<<code_unit::size(16), rest::binary>>, code_units) do
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utf16_binary_to_code_units(rest, [code_unit | code_units])
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end
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defp utf16_code_units_to_string(code_units) do
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code_units
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|> Enum.reverse()
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|> code_units_to_utf16_binary(<<>>)
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|> :unicode.characters_to_binary(:utf16, :utf8)
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end
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defp code_units_to_utf16_binary([], utf16_binary), do: utf16_binary
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defp code_units_to_utf16_binary([code_unit | code_units], utf16_binary) do
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code_units_to_utf16_binary(code_units, <<code_unit::size(16), utf16_binary::binary>>)
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end
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end
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