From 83377c747018542157c17095c17cf04ac6f9e95b Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Fri, 24 Jun 2022 09:31:55 -0700
Subject: [PATCH] decaln

---
 conformance/esc_decaln.zig | 10 +++++++++
 src/Window.zig             |  4 ++++
 src/terminal/Terminal.zig  | 43 ++++++++++++++++++++++++++++++++++++++
 src/terminal/stream.zig    | 18 ++++++++++++++++
 4 files changed, 75 insertions(+)
 create mode 100644 conformance/esc_decaln.zig

diff --git a/conformance/esc_decaln.zig b/conformance/esc_decaln.zig
new file mode 100644
index 000000000..aeb1887a4
--- /dev/null
+++ b/conformance/esc_decaln.zig
@@ -0,0 +1,10 @@
+//! DECALN - ESC # 8
+const std = @import("std");
+
+pub fn main() !void {
+    const stdout = std.io.getStdOut().writer();
+    try stdout.print("\x1B#8", .{});
+
+    // const stdin = std.io.getStdIn().reader();
+    // _ = try stdin.readByte();
+}
diff --git a/src/Window.zig b/src/Window.zig
index bb905f664..aaa2c4dce 100644
--- a/src/Window.zig
+++ b/src/Window.zig
@@ -761,3 +761,7 @@ pub fn setCursorStyle(
     // it'll be updated the next time the window comes into focus.
     if (self.focused) try self.updateCursorStyle(grid_style, style.blinking());
 }
+
+pub fn decaln(self: *Window) !void {
+    self.terminal.decaln();
+}
diff --git a/src/terminal/Terminal.zig b/src/terminal/Terminal.zig
index fe1bbc2d3..6c93206ea 100644
--- a/src/terminal/Terminal.zig
+++ b/src/terminal/Terminal.zig
@@ -174,6 +174,27 @@ pub fn print(self: *Terminal, c: u21) !void {
     }
 }
 
+/// Resets all margins and fills the whole screen with the character 'E'
+///
+/// Sets the cursor to the top left corner.
+pub fn decaln(self: *Terminal) void {
+    // Reset margins, also sets cursor to top-left
+    self.setScrollingRegion(0, 0);
+
+    // Fill with Es, does not move cursor. We reset fg/bg so we can just
+    // optimize here by doing row copies.
+    const filled = self.screen.getRow(0);
+    var col: usize = 0;
+    while (col < self.cols) : (col += 1) {
+        filled[col] = .{ .char = 'E' };
+    }
+
+    var row: usize = 1;
+    while (row < self.rows) : (row += 1) {
+        std.mem.copy(Screen.Cell, self.screen.getRow(row), filled);
+    }
+}
+
 /// Move the cursor to the previous line in the scrolling region, possibly
 /// scrolling.
 ///
@@ -950,3 +971,25 @@ test "Terminal: reverseIndex from the top" {
         try testing.expectEqualStrings("E\nD\nA\nB", str);
     }
 }
+
+test "Terminal: DECALN" {
+    const alloc = testing.allocator;
+    var t = try init(alloc, 2, 2);
+    defer t.deinit(alloc);
+
+    // Initial value
+    try t.print('A');
+    t.carriageReturn();
+    t.linefeed();
+    try t.print('B');
+    t.decaln();
+
+    try testing.expectEqual(@as(usize, 0), t.cursor.y);
+    try testing.expectEqual(@as(usize, 0), t.cursor.x);
+
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("EE\nEE", str);
+    }
+}
diff --git a/src/terminal/stream.zig b/src/terminal/stream.zig
index 06c9ecd56..65c759ddc 100644
--- a/src/terminal/stream.zig
+++ b/src/terminal/stream.zig
@@ -345,6 +345,24 @@ pub fn Stream(comptime Handler: type) type {
             action: Parser.Action.ESC,
         ) !void {
             switch (action.final) {
+                '8' => blk: {
+                    switch (action.intermediates.len) {
+                        1 => switch (action.intermediates[0]) {
+                            // DECALN - Fill Screen with E
+                            '#' => if (@hasDecl(T, "decaln")) {
+                                try self.handler.decaln();
+                                break :blk {};
+                            } else log.warn("unimplemented ESC callback: {}", .{action}),
+
+                            else => {},
+                        },
+
+                        else => {}, // fall through
+                    }
+
+                    log.warn("unimplemented ESC action: {}", .{action});
+                },
+
                 // RI - Reverse Index
                 'M' => if (@hasDecl(T, "reverseIndex")) switch (action.intermediates.len) {
                     0 => try self.handler.reverseIndex(),