Chording support for vim mode (#53)

* initial experimental success

* refined chording

* add default value

* refactor chording from switch to if

* revert change introduced when debugging

* remove unnecessary try

* added configuration option

src/config.zig

@@ -8,6 +8,7 @@ gutter_line_numbers_relative: bool = false,
 vim_normal_gutter_line_numbers_relative: bool = true,
 vim_visual_gutter_line_numbers_relative: bool = true,
 vim_insert_gutter_line_numbers_relative: bool = false,
+vim_insert_chording_keybindings: bool = true,
 enable_terminal_cursor: bool = false,
 enable_terminal_color_scheme: bool = builtin.os.tag != .windows,
 highlight_current_line: bool = true,

src/tui/mode/input/vim/insert.zig

@@ -1,4 +1,5 @@
 const tp = @import("thespian");
+const std = @import("std");
 
 const key = @import("renderer").input.key;
 const mod = @import("renderer").input.modifier;
@@ -21,6 +22,14 @@ input: ArrayList(u8),
 last_cmd: []const u8 = "",
 leader: ?struct { keypress: u32, modifiers: u32 } = null,
 commands: Commands = undefined,
+last_key: KeyPressEvent = .{},
+
+pub const KeyPressEvent = struct {
+    keypress: u32 = 0,
+    modifiers: u32 = std.math.maxInt(u32),
+    egc: u32 = 0,
+    timestamp_ms: i64 = 0,
+};
 
 pub fn create(allocator: Allocator) !tui.Mode {
     const self: *Self = try allocator.create(Self);
@@ -82,6 +91,46 @@ fn mapPress(self: *Self, keypress: u32, egc: u32, modifiers: u32) !void {
         key.LALT, key.RALT => return self.cmd("enable_jump_mode", .{}),
         else => {},
     }
+
+    if (tui.current().config.vim_insert_chording_keybindings) {
+
+        //reset chord if enough time has passed
+        const chord_time_window_ms = 750;
+        if (std.time.milliTimestamp() - self.last_key.timestamp_ms > chord_time_window_ms) {
+            self.last_key = .{};
+        }
+
+        //chording
+        if (self.last_key.keypress == 'j' and self.last_key.modifiers == 0 and keypress == 'k' and modifiers == 0) {
+            try self.cmd("delete_backward", .{});
+            try self.cmd("enter_mode", command.fmt(.{"vim/normal"}));
+            return;
+        }
+        if (self.last_key.keypress == 'k' and self.last_key.modifiers == 0 and keypress == 'j' and modifiers == 0) {
+            try self.cmd("delete_backward", .{});
+            try self.cmd("enter_mode", command.fmt(.{"vim/normal"}));
+            return;
+        }
+        if (self.last_key.keypress == 'f' and self.last_key.modifiers == 0 and keypress == 'j' and modifiers == 0) {
+            try self.cmd("delete_backward", .{});
+            try self.cmd("enter_mode", command.fmt(.{"vim/normal"}));
+            return;
+        }
+        if (self.last_key.keypress == 'j' and self.last_key.modifiers == 0 and keypress == 'f' and modifiers == 0) {
+            try self.cmd("delete_backward", .{});
+            try self.cmd("enter_mode", command.fmt(.{"vim/normal"}));
+            return;
+        }
+
+        //record current key event
+        self.last_key = .{
+            .keypress = keypress,
+            .modifiers = modifiers,
+            .egc = egc,
+            .timestamp_ms = std.time.milliTimestamp(),
+        };
+    }
+
     return switch (modifiers) {
         mod.CTRL => switch (keynormal) {
             'E' => self.cmd("open_recent", .{}),