From f57fd99d3e0d8aa650c5926a4ed27251b7d25c21 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Wed, 16 Aug 2023 08:52:53 -0700
Subject: [PATCH] input: starting to work on KeyEncoder, got ctrl sequences

---
 src/input.zig            |   1 +
 src/input/KeyEncoder.zig | 131 +++++++++++++++++++++++++++++++++++++++
 src/input/key.zig        |  56 ++++++++++++++++-
 3 files changed, 186 insertions(+), 2 deletions(-)
 create mode 100644 src/input/KeyEncoder.zig

diff --git a/src/input.zig b/src/input.zig
index e2deed0e2..f382386c6 100644
--- a/src/input.zig
+++ b/src/input.zig
@@ -6,6 +6,7 @@ pub usingnamespace @import("input/key.zig");
 pub const function_keys = @import("input/function_keys.zig");
 pub const keycodes = @import("input/keycodes.zig");
 pub const Binding = @import("input/Binding.zig");
+pub const KeyEncoder = @import("input/KeyEncoder.zig");
 pub const SplitDirection = Binding.Action.SplitDirection;
 pub const SplitFocusDirection = Binding.Action.SplitFocusDirection;
 
diff --git a/src/input/KeyEncoder.zig b/src/input/KeyEncoder.zig
new file mode 100644
index 000000000..65a80c1f7
--- /dev/null
+++ b/src/input/KeyEncoder.zig
@@ -0,0 +1,131 @@
+/// KeyEncoder is responsible for processing keyboard input and generating
+/// the proper VT sequence for any events.
+///
+/// A new KeyEncoder should be created for each individual key press.
+/// These encoders are not meant to be reused.
+const KeyEncoder = @This();
+
+const std = @import("std");
+const testing = std.testing;
+
+const key = @import("key.zig");
+
+key: key.Key,
+binding_mods: key.Mods,
+
+/// Initialize
+fn init(event: key.Event) KeyEncoder {
+    const effective_mods = event.effectiveMods();
+    const binding_mods = effective_mods.binding();
+
+    return .{
+        .key = event.key,
+        .binding_mods = binding_mods,
+    };
+}
+
+/// Returns the C0 byte for the key event if it should be used.
+/// This converts a key event into the expected terminal behavior
+/// such as Ctrl+C turning into 0x03, amongst many other translations.
+///
+/// This will return null if the key event should not be converted
+/// into a C0 byte. There are many cases for this and you should read
+/// the source code to understand them.
+fn ctrlSeq(self: *const KeyEncoder) ?u8 {
+    // Remove alt from our modifiers because it does not impact whether
+    // we are generating a ctrl sequence.
+    const unalt_mods = unalt_mods: {
+        var unalt_mods = self.binding_mods;
+        unalt_mods.alt = false;
+        break :unalt_mods unalt_mods;
+    };
+
+    // If we have any other modifier key set, then we do not generate
+    // a C0 sequence.
+    const ctrl_only = comptime (key.Mods{ .ctrl = true }).int();
+    if (unalt_mods.int() != ctrl_only) return null;
+
+    // The normal approach to get this value is to make the ascii byte
+    // with 0x1F. However, not all apprt key translation will properly
+    // generate the correct value so we just hardcode this based on
+    // logical key.
+    return switch (self.key) {
+        .space => 0,
+        .slash => 0x1F,
+        .zero => 0x30,
+        .one => 0x31,
+        .two => 0x00,
+        .three => 0x1B,
+        .four => 0x1C,
+        .five => 0x1D,
+        .six => 0x1E,
+        .seven => 0x1F,
+        .eight => 0x7F,
+        .nine => 0x39,
+        .backslash => 0x1C,
+        .left_bracket => 0x1B,
+        .right_bracket => 0x1D,
+        .a => 0x01,
+        .b => 0x02,
+        .c => 0x03,
+        .d => 0x04,
+        .e => 0x05,
+        .f => 0x06,
+        .g => 0x07,
+        .h => 0x08,
+        .i => 0x09,
+        .j => 0x0A,
+        .k => 0x0B,
+        .l => 0x0C,
+        .m => 0x0D,
+        .n => 0x0E,
+        .o => 0x0F,
+        .p => 0x10,
+        .q => 0x11,
+        .r => 0x12,
+        .s => 0x13,
+        .t => 0x14,
+        .u => 0x15,
+        .v => 0x16,
+        .w => 0x17,
+        .x => 0x18,
+        .y => 0x19,
+        .z => 0x1A,
+        else => null,
+    };
+}
+
+test "ctrlseq: normal ctrl c" {
+    const enc = init(.{ .key = .c, .mods = .{ .ctrl = true } });
+    const seq = enc.ctrlSeq();
+    try testing.expectEqual(@as(u8, 0x03), seq.?);
+}
+
+test "ctrlseq: alt should be allowed" {
+    const enc = init(.{ .key = .c, .mods = .{ .alt = true, .ctrl = true } });
+    const seq = enc.ctrlSeq();
+    try testing.expectEqual(@as(u8, 0x03), seq.?);
+}
+
+test "ctrlseq: no ctrl does nothing" {
+    const enc = init(.{ .key = .c, .mods = .{} });
+    try testing.expect(enc.ctrlSeq() == null);
+}
+
+test "ctrlseq: shift does not generate ctrl seq" {
+    {
+        const enc = init(.{
+            .key = .c,
+            .mods = .{ .shift = true },
+        });
+        try testing.expect(enc.ctrlSeq() == null);
+    }
+
+    {
+        const enc = init(.{
+            .key = .c,
+            .mods = .{ .shift = true, .ctrl = true },
+        });
+        try testing.expect(enc.ctrlSeq() == null);
+    }
+}
diff --git a/src/input/key.zig b/src/input/key.zig
index 8ec485c9a..92db8009e 100644
--- a/src/input/key.zig
+++ b/src/input/key.zig
@@ -1,8 +1,55 @@
 const std = @import("std");
 const Allocator = std.mem.Allocator;
 
-/// A bitmask for all key modifiers. This is taken directly from the
-/// GLFW representation, but we use this generically.
+/// A generic key input event. This is the information that is necessary
+/// regardless of apprt in order to generate the proper terminal
+/// control sequences for a given key press.
+///
+/// Some apprts may not be able to provide all of this information, such
+/// as GLFW. In this case, the apprt should provide as much information
+/// as it can and it should be expected that the terminal behavior
+/// will not be totally correct.
+pub const Event = struct {
+    /// The action: press, release, etc.
+    action: Action = .press,
+
+    /// "key" is the logical key that was pressed. For example, if
+    /// a Dvorak keyboard layout is being used on a US keyboard,
+    /// the "i" physical key will be reported as "c". The physical
+    /// key is the key that was physically pressed on the keyboard.
+    key: Key,
+    physical_key: Key = .invalid,
+
+    /// Mods are the modifiers that are pressed.
+    mods: Mods = .{},
+
+    /// The mods that were consumed in order to generate the text
+    /// in utf8. This has the mods set that were consumed, so to
+    /// get the set of mods that are effective you must negate
+    /// mods with this.
+    ///
+    /// This field is meaningless if utf8 is empty.
+    consumed_mods: Mods = .{},
+
+    /// Composing is true when this key event is part of a dead key
+    /// composition sequence and we're in the middle of it.
+    composing: bool = false,
+
+    /// The utf8 sequence that was generated by this key event.
+    /// This will be an empty string if there is no text generated.
+    /// If composing is true and this is non-empty, this is preedit
+    /// text.
+    utf8: []const u8 = "",
+
+    /// Returns the effective modifiers for this event. The effective
+    /// modifiers are the mods that should be considered for keybindings.
+    pub fn effectiveMods(self: Event) Mods {
+        if (self.utf8.len == 0) return self.mods;
+        return self.mods.unset(self.consumed_mods);
+    }
+};
+
+/// A bitmask for all key modifiers.
 ///
 /// IMPORTANT: Any changes here update include/ghostty.h
 pub const Mods = packed struct(Mods.Backing) {
@@ -56,6 +103,11 @@ pub const Mods = packed struct(Mods.Backing) {
         };
     }
 
+    /// Perform `self &~ other` to remove the other mods from self.
+    pub fn unset(self: Mods, other: Mods) Mods {
+        return @bitCast(self.int() & ~other.int());
+    }
+
     /// Returns the mods without locks set.
     pub fn withoutLocks(self: Mods) Mods {
         var copy = self;