Add active hook system to settings

core/settings.lua

@@ -10,6 +10,7 @@ function settings:_init()
   self.declarations = {}
   self.stateQueue = {}
   self.defaults = {}
+  self.hooks = {}
 
   self:declare({
     parameter = "document.language",
@@ -105,7 +106,16 @@ end
 
 function settings:popState ()
   if not self then return deprecator() end
+  local previous = self.state
   self.state = table.remove(self.stateQueue)
+  for parameter, oldvalue in pairs(previous) do
+    if self.hooks[parameter] then
+      local newvalue = self.state[parameter]
+      if oldvalue ~= newvalue then
+        self:runHooks(parameter, newvalue)
+      end
+    end
+  end
 end
 
 function settings:declare (spec)
@@ -118,6 +128,10 @@ function settings:declare (spec)
     return
   end
   self.declarations[spec.parameter] = spec
+  self.hooks[spec.parameter] = {}
+  if spec.hook then
+     self:registerHook(spec.parameter, spec.hook)
+  end
   self:set(spec.parameter, spec.default, true)
 end
 
@@ -202,6 +216,20 @@ function settings:set (parameter, value, makedefault, reset)
   if makedefault then
     self.defaults[parameter] = value
   end
+  self:runHooks(parameter, value)
+end
+
+function settings:registerHook (parameter, func)
+   table.insert(self.hooks[parameter], func)
+end
+
+function settings:runHooks (parameter, value)
+  if self.hooks[parameter] then
+    for _, func in ipairs(self.hooks[parameter]) do
+      SU.debug("classhooks", "Running seting hook for", parameter)
+      func(value)
+    end
+  end
 end
 
 function settings:temporarily (func)

core/settings_spec.lua

@@ -0,0 +1,42 @@
+SILE = require("core.sile")
+
+describe("The settings handler", function()
+
+  it("should trigger callbacks on set", function()
+    local private = "foo"
+    local function callback (value)
+       private = value .. " hooked"
+    end
+    SILE.settings:declare({
+       parameter = "test.callback",
+       type = "string",
+       default = "bar",
+       hook = callback
+    })
+    SILE.settings:set("test.callback", "baz")
+    assert.is.equal("baz hooked", private)
+  end)
+
+  it("should trigger callbacks on push/pop events", function()
+    local mystate = "foo"
+    local function callback2 (value)
+       mystate = value .. " stack"
+    end
+    SILE.settings:declare({
+       parameter = "test.callback2",
+       type = "string",
+       default = "bar",
+       hook = callback2
+    })
+    SILE.settings:pushState()
+    SILE.settings:set("test.callback2", "baz1")
+    SILE.settings:pushState()
+    SILE.settings:set("test.callback2", "baz2")
+    assert.is.equal("baz2 stack", mystate)
+    SILE.settings:popState()
+    assert.is.equal("baz1 stack", mystate)
+    SILE.settings:popState()
+    assert.is.equal("bar stack", mystate)
+  end)
+
+end)