From cbd6505d25b0ce8f5ebda6b8be7a97749db4df18 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Thu, 28 Apr 2022 21:18:27 -0700
Subject: [PATCH] terminal: scrolling

---
 src/main.zig              |  1 +
 src/terminal/Terminal.zig | 31 ++++++++++++++++++++++++++++---
 src/terminal/main.zig     | 11 +++++++++++
 3 files changed, 40 insertions(+), 3 deletions(-)
 create mode 100644 src/terminal/main.zig

diff --git a/src/main.zig b/src/main.zig
index 557aa85fb..2c0aaa023 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -30,4 +30,5 @@ test {
     // Libraries
     _ = @import("segmented_pool.zig");
     _ = @import("libuv/main.zig");
+    _ = @import("terminal/main.zig");
 }
diff --git a/src/terminal/Terminal.zig b/src/terminal/Terminal.zig
index e0525cd73..5f282dd86 100644
--- a/src/terminal/Terminal.zig
+++ b/src/terminal/Terminal.zig
@@ -140,7 +140,7 @@ fn execute(self: *Terminal, alloc: Allocator, c: u8) !void {
         .BEL => self.bell(),
         .BS => self.backspace(),
         .HT => try self.horizontal_tab(alloc),
-        .LF => self.linefeed(),
+        .LF => self.linefeed(alloc),
         .CR => self.carriage_return(),
     }
 }
@@ -176,11 +176,36 @@ pub fn carriage_return(self: *Terminal) void {
 }
 
 /// Linefeed moves the cursor to the next line.
-pub fn linefeed(self: *Terminal) void {
-    // TODO: end of screen
+pub fn linefeed(self: *Terminal, alloc: Allocator) void {
+    // If we're at the end of the screen, scroll up. This is surprisingly
+    // common because most terminals live with a full screen so we do this
+    // check first.
+    if (self.cursor.y == self.rows - 1) {
+        self.scroll_up(alloc);
+        return;
+    }
+
+    // Increase cursor by 1
     self.cursor.y += 1;
 }
 
+/// Scroll the text up by one row.
+pub fn scroll_up(self: *Terminal, alloc: Allocator) void {
+    // TODO: this is horribly expensive. we need to optimize the screen repr
+
+    // If we have no items, scrolling does nothing.
+    if (self.screen.items.len == 0) return;
+
+    // Clear the first line
+    self.screen.items[0].deinit(alloc);
+
+    var i: usize = 0;
+    while (i < self.screen.items.len - 1) : (i += 1) {
+        self.screen.items[i] = self.screen.items[i + 1];
+    }
+    self.screen.items.len -= 1;
+}
+
 fn getOrPutCell(self: *Terminal, alloc: Allocator, x: usize, y: usize) !*Cell {
     // If we don't have enough lines to get to y, then add it.
     if (self.screen.items.len < y + 1) {
diff --git a/src/terminal/main.zig b/src/terminal/main.zig
new file mode 100644
index 000000000..43ea9fd83
--- /dev/null
+++ b/src/terminal/main.zig
@@ -0,0 +1,11 @@
+pub const Terminal = @import("Terminal.zig");
+
+// Not exported because they're just used for tests.
+
+test {
+    _ = Terminal;
+
+    _ = @import("parse_table.zig");
+    _ = @import("Parser.zig");
+    _ = @import("Tabstops.zig");
+}