util.smqueue: Abstract queue with acknowledgements and overflow

Meant to be used in mod_smacks for XEP-0198

Meant to have a larger virtual size than actual number of items stored,
on the theory that in most cases, the excess will be acked before needed
for a resumption event.

spec/util_smqueue_spec.lua

@@ -0,0 +1,55 @@
+describe("util.smqueue", function()
+
+	local smqueue
+	setup(function() smqueue = require "util.smqueue"; end)
+
+	describe("#new()", function()
+		it("should work", function()
+			local q = smqueue.new(10);
+			assert.truthy(q);
+		end)
+	end)
+
+	describe("#push()", function()
+		it("should allow pushing many items", function()
+			local q = smqueue.new(10);
+			for i = 1, 20 do q:push(i); end
+			assert.equal(20, q:count_unacked());
+		end)
+	end)
+
+	describe("#resumable()", function()
+		it("returns true while the queue is small", function()
+			local q = smqueue.new(10);
+			for i = 1, 10 do q:push(i); end
+			assert.truthy(q:resumable());
+			q:push(11);
+			assert.falsy(q:resumable());
+		end)
+	end)
+
+	describe("#ack", function()
+		it("allows removing items", function()
+			local q = smqueue.new(10);
+			for i = 1, 10 do q:push(i); end
+			assert.same({ 1; 2; 3 }, q:ack(3));
+			assert.same({ 4; 5; 6 }, q:ack(6));
+			assert.falsy(q:ack(3), "can't go backwards")
+			assert.falsy(q:ack(100), "can't ack too many")
+			for i = 11, 20 do q:push(i); end
+			assert.same({ 11; 12 }, q:ack(12), "items are dropped");
+		end)
+	end)
+
+	describe("#resume", function()
+		it("iterates over current items", function()
+			local q = smqueue.new(10);
+			for i = 1, 12 do q:push(i); end
+			assert.same({ 3; 4; 5; 6 }, q:ack(6));
+			assert.truthy(q:resumable());
+			local resume = {}
+			for _, i in q:resume() do resume[i] = true end
+			assert.same({ [7] = true; [8] = true; [9] = true; [10] = true; [11] = true; [12] = true }, resume);
+		end)
+	end)
+end);