feat(colorscheme): add recipe for persistent colorscheme changes

Author: mehalter

src/content/docs/recipes/colorscheme.mdx

@@ -89,3 +89,74 @@ return {
 This approach also handles the case when the colorscheme is not installed yet and AstroNvim will not try to set it.
 
 :::
+
+## Cache colorscheme
+
+:::tip
+
+This is available in the [AstroCommunity](https://github.com/AstroNvim/astrocommunity/tree/main/lua/astrocommunity/recipes/cache-colorscheme)
+
+```lua title="lua/community.lua" ins={3}
+return {
+  "AstroNvim/astrocommunity",
+  { import = "astrocommunity.recipes.cache-colorscheme" },
+}
+```
+
+:::
+
+Some users may want to persist the last chosen colorscheme rather than always using the value set in their user configuration on startup. This can be easily implemented within your plugin configuration with the following code:
+
+```lua title="lua/plugins/cache_colorscheme.lua"
+-- pick a location to cache colorscheme
+local colorscheme_cache = vim.fs.joinpath(vim.fn.stdpath "state" --[[@as string]], "last_colorscheme")
+
+--- Execute function with open file
+---@param file string path to file to interact with
+---@param mode openmode the mode in which to open the file
+---@param callback fun(fd:file*) the callback to execute with the opened file
+---@param on_error? fun(err:string) the callback to execute if unable to open the file
+local function with_file(file, mode, callback, on_error)
+  local fd, errmsg = io.open(file, mode)
+  if fd then
+    callback(fd)
+    fd:close()
+  elseif errmsg and on_error then
+    on_error(errmsg)
+  end
+end
+
+return {
+  {
+    "AstroNvim/astroui",
+    --@param opts AstroUIOpts
+    opts = function(_, opts)
+      -- read colorscheme cache on open
+      with_file(colorscheme_cache, "r", function(file)
+        opts.colorscheme = file:read "*a"
+      end)
+    end,
+  },
+  {
+    "AstroNvim/astrocore",
+    ---@type AstroCoreOpts
+    opts = {
+      autocmds = {
+        -- save colorscheme to cache on change
+        cache_colorscheme = {
+          {
+            event = "ColorScheme",
+            callback = function(args)
+              if args.match then
+                with_file(colorscheme_cache, "w+", function(file)
+                  file:write(args.match)
+                end)
+              end
+            end,
+          },
+        },
+      },
+    },
+  },
+}
+```