From d99434ac43a61d618baf64f1c58b77acbfe94613 Mon Sep 17 00:00:00 2001
From: Felix Van der Jeugt <felix.vanderjeugt@posteo.net>
Date: Mon, 6 Dec 2021 21:37:34 +0100
Subject: [PATCH] will be needing a deque later

---
 deque.lua | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 deque.lua

diff --git a/deque.lua b/deque.lua
new file mode 100644
index 0000000..8d8a4c7
--- /dev/null
+++ b/deque.lua
@@ -0,0 +1,81 @@
+function deque()
+	local cap = 5
+	local elems = {}
+	for i = 0, cap - 1 do
+		elems[i] = nil
+	end
+	return {
+		start = 0,
+		size = 0,
+		cap = cap,
+		elems = elems,
+		pprint = pprint,
+		pop = pop,
+		prepend = prepend,
+		append = append,
+		popleft = popleft,
+	}
+end
+
+function pprint(self)
+	io.write(self.start .. "->" .. self.size .. ": ")
+	local i = self.start
+	for i = 0, self.cap - 1 do
+		io.write((self.elems[i] or "_") .. " ")
+	end
+	io.write("\n")
+end
+
+local function extend(self)
+	local copy = {}
+	for i = 0, self.size - 1 do
+		copy[i] = self.elems[(self.start + i) % self.size]
+	end
+	for i = self.size, 2 * self.size - 1 do
+		copy[i] = nil
+	end
+	self.elems = copy
+	self.start = 0
+	self.cap = self.cap * 2
+end
+
+function append(self, n)
+	if self.size == self.cap then
+		extend(self)
+	end
+	self.elems[(self.start + self.size) % self.cap] = n
+	self.size = self.size + 1
+end
+
+function pop(self)
+	if self.size > 0 then
+		local i = (self.start + self.size - 1) % self.cap
+		local v = self.elems[i]
+		self.elems[i] = nil
+		self.size = self.size - 1
+		return v
+	else
+		return nil
+	end
+end
+
+function prepend(self, n)
+	if self.size == self.cap then
+		extend(self)
+	end
+	self.size = self.size + 1
+	self.start = (self.start + self.cap - 1) % self.cap
+	self.elems[self.start] = n
+end
+
+function popleft(self)
+	if self.size > 0 then
+		local v = self.elems[self.start]
+		self.elems[self.start] = nil
+		self.start = (self.start + 1) % self.cap
+		self.size = self.size - 1
+		return v
+	else
+		return nil
+	end
+end