nvim-tree.lua/lua/nvim-tree/renderer/decorator/init.lua

local HL_POSITION = require("nvim-tree.enum").HL_POSITION
local ICON_PLACEMENT = require("nvim-tree.enum").ICON_PLACEMENT

---Abstract Decorator
---Uses the factory pattern to instantiate child instances.
---@class (exact) Decorator
---@field private __index? table
---@field protected explorer Explorer
---@field protected enabled boolean
---@field protected hl_pos HL_POSITION
---@field protected icon_placement ICON_PLACEMENT
local Decorator = {}

---@param o Decorator|nil
---@return Decorator
function Decorator:new(o)
  o = o or {}

  setmetatable(o, self)
  self.__index = self

  return o
end

---Maybe highlight groups
---@param node Node
---@return string|nil icon highlight group
---@return string|nil name highlight group
function Decorator:groups_icon_name(node)
  local icon_hl, name_hl

  if self.enabled and self.hl_pos ~= HL_POSITION.none then
    local hl = self:calculate_highlight(node)

    if self.hl_pos == HL_POSITION.all or self.hl_pos == HL_POSITION.icon then
      icon_hl = hl
    end
    if self.hl_pos == HL_POSITION.all or self.hl_pos == HL_POSITION.name then
      name_hl = hl
    end
  end

  return icon_hl, name_hl
end

---Maybe icon sign
---@param node Node
---@return string|nil name
function Decorator:sign_name(node)
  if not self.enabled or self.icon_placement ~= ICON_PLACEMENT.signcolumn then
    return
  end

  local icons = self:calculate_icons(node)
  if icons and #icons > 0 then
    return icons[1].hl[1]
  end
end

---Icons when ICON_PLACEMENT.before
---@param node Node
---@return HighlightedString[]|nil icons
function Decorator:icons_before(node)
  if not self.enabled or self.icon_placement ~= ICON_PLACEMENT.before then
    return
  end

  return self:calculate_icons(node)
end

---Icons when ICON_PLACEMENT.after
---@param node Node
---@return HighlightedString[]|nil icons
function Decorator:icons_after(node)
  if not self.enabled or self.icon_placement ~= ICON_PLACEMENT.after then
    return
  end

  return self:calculate_icons(node)
end

---Icons when ICON_PLACEMENT.right_align
---@param node Node
---@return HighlightedString[]|nil icons
function Decorator:icons_right_align(node)
  if not self.enabled or self.icon_placement ~= ICON_PLACEMENT.right_align then
    return
  end

  return self:calculate_icons(node)
end

---Maybe icons, optionally implemented
---@protected
---@param _ Node
---@return HighlightedString[]|nil icons
function Decorator:calculate_icons(_)
  return nil
end

---Maybe highlight group, optionally implemented
---@protected
---@param _ Node
---@return string|nil group
function Decorator:calculate_highlight(_)
  return nil
end

---Define a sign
---@protected
---@param icon HighlightedString|nil
function Decorator:define_sign(icon)
  if icon and #icon.hl > 0 then
    local name = icon.hl[1]

    if not vim.tbl_isempty(vim.fn.sign_getdefined(name)) then
      vim.fn.sign_undefine(name)
    end

    -- don't use sign if not defined
    if #icon.str < 1 then
      self.icon_placement = ICON_PLACEMENT.none
      return
    end

    -- byte index of the next character, allowing for wide
    local bi = vim.fn.byteidx(icon.str, 1)

    -- first (wide) character, falls back to empty string
    local text = string.sub(icon.str, 1, bi)
    vim.fn.sign_define(name, {
      text = text,
      texthl = name,
    })
  end
end

return Decorator