Add ls method to prevfile

spec/prevfile_spec.lua

@@ -1,9 +1,75 @@
-describe("prevfile", function()
+function get_directory_iterator_from_table(table)
+	return function(directory) 
+		local index = 0
+		local filenames = table
+
+		return function()
+			index = index + 1
+			return filenames[index]
+		end
+	end
+end
+
+describe("ls", function()
+	local lfs = require "lfs"
 	local prevfile = require "prevfile"
 
-	it("returns nil when target directory is empty", function()
-		previous = prevfile.prevfile("dummy/")
+	insulate("if directory does not exist", function()
+		lfs.dir = function(directory) error("No such file or directory") end
 
-		assert.are.equals(nil, previous)
+		it("should return nil", function()
+			local files = prevfile.ls("/testdir")
+
+			assert.equals(nil, files)
+		end)
+	end)
+
+	insulate("if directory is empty", function()
+		lfs.dir = get_directory_iterator_from_table({})
+
+		it("should return empty table", function()
+			local files = prevfile.ls("/testdir")
+
+			assert.are.same({}, files)
+		end)
+
+		it("should call lfs.dir with target directory", function()
+			spy.on(lfs, "dir")
+			local test_directory = "/testdir"
+
+			prevfile.ls(test_directory)
+
+			assert.stub(lfs.dir).was_called_with(test_directory)
+		end)
+	end)
+
+	insulate("if directory contains files", function()
+		lfs.dir = get_directory_iterator_from_table({"a.txt", "b.txt", "z.txt", "c.txt"})
+
+		it("should return the files in lexographical order", function()
+			local files = prevfile.ls("/testdir")
+
+			assert.are.same({"a.txt", "b.txt", "c.txt", "z.txt"}, files)
+		end)
+	end)
+
+	insulate("if directory contains numerically-named files", function()
+		lfs.dir = get_directory_iterator_from_table({"/testdir/709.txt", "/testdir/71.txt", "/testdir/710.txt"})
+
+		it("should return the files in numerical order", function()
+			local files = prevfile.ls("/testdir")
+
+			assert.are.same({"/testdir/71.txt", "/testdir/709.txt", "/testdir/710.txt"}, files)
+		end)
+	end)
+
+	insulate("if directory contains hidden files", function()
+		lfs.dir = get_directory_iterator_from_table({"a.txt", ".b.txt.swp", "c.txt"})
+
+		it("should exclude them from the listing", function()
+			local files = prevfile.ls("/testdir")
+
+			assert.are.same({"a.txt", "c.txt"}, files)
+		end)
 	end)
 end)

src/prevfile.lua

@@ -1,7 +1,30 @@
+local lfs = require "lfs"
+
 local prevfile = {}
  
-function prevfile.prevfile(target_directory)
-	return nil
+local function padnum(d)
+	local dec, n = string.match(d, "(%.?)0*(.+)")
+	return #dec > 0 and ("%.12f"):format(d) or ("%s%03d%s"):format(dec, #n, n)
+end
+
+local function humansort(a, b)
+    return tostring(a):gsub("%.?%d+", padnum) < tostring(b):gsub("%.?%d+", padnum)
+ end
+
+function prevfile.ls(directory)
+	if not pcall(lfs.dir, directory) then
+		return nil
+	end
+
+	local files = {}
+	for file in lfs.dir(directory) do
+		if string.sub(file, 1, 1) ~= "." then
+			table.insert(files, file)
+		end
+	end
+
+	table.sort(files, humansort)
+	return files
 end
 
 return prevfile