Initial implementation of the hunk header.

Author: Lethja

demo/xtra/DIFF.LUA

@@ -1,20 +1,35 @@
 local function diff_u(fn1,fn2)
 	local function open(fn) local f, e = io.open(fn) if not f then print(e) os.exit(1) end return f end
 	local f1, f2, pre, add, del, post, x, y, h, l1, l2 = open(fn1), open(fn2), {}, {}, {}, 0, 0, 0
+	local buf = {add = 0, del = 0, line = {}}
 	local function flush_pre()
 		if not h then print("--- " .. fn1 .. "\n+++ " .. fn2) h = true end
-		for _, v in ipairs(pre) do print(" " .. v) end
-		pre = {}
+		for _, v in ipairs(pre) do table.insert(buf.line, " " .. v) end
+		buf.ls, buf.rs, pre = x, y, {}
 	end
-	local function flush_hunks()
-		for _, v in ipairs(del) do print("-" .. v) end
-		for _, v in ipairs(add) do print("+" .. v) end
-		del, add = {}, {}
+	local function flush_hunk()
+		for _, v in ipairs(del) do table.insert(buf.line, "-" .. v) end
+		for _, v in ipairs(add) do table.insert(buf.line, "+" .. v) end
+		buf.add, buf.del = buf.add + #add, buf.del + #del del, add = {}, {}
+	end
+	local function flush_buf()
+		if #buf.line then
+			local header = "@@ -" .. (buf.ls or "0") .. (buf.del == 1 and "" or "," .. buf.del) ..
+					" +" .. (buf.rs or "0") .. (buf.add == 1 and "" or "," .. buf.add) .. " @@"
+			table.insert(buf.line, 1, header)
+			for _, v in ipairs(buf.line) do print(v) end
+		end
+		buf.line, buf.add, buf.del, buf.ls, buf.rs = {}, 0, 0, nil, nil
 	end
 	local function diagonal()
-		flush_hunks()
+		flush_hunk()
 		if #pre >= 3 then table.remove(pre, 1) end
-		if #pre <= 0 and post > 0 then print(" " .. l2) post = post - 1 else table.insert(pre, l2) end
+		if #pre <= 0 and post > 0 then
+			table.insert(buf.line, " " .. l2) post = post - 1
+			if post == 0 then flush_buf() end
+		else
+			table.insert(pre, l2)
+		end
 		x, y, l1, l2 = x + 1, y + 1, f1:read("*l"), f2:read("*l")
 	end
 	local function right()
@@ -36,7 +51,7 @@ local function diff_u(fn1,fn2)
 
 	until not l1 and not l2
 	f1:close() f2:close()
-	if #add > 0 or #del > 0 then flush_pre() flush_hunks() end
+	if #add > 0 or #del > 0 then flush_pre() flush_hunk() flush_buf() end
 end
 
 if #arg < 2 then return end