From ea583f60b3cc7ad76abce94f80288205962db9f2 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Tue, 25 Oct 2022 12:18:25 +0530
Subject: [PATCH] Start work on kill ring

---
 tools/tui/readline/actions.go | 39 +++++++++++++++++++++++++++++
 tools/tui/readline/api.go     | 47 ++++++++++++++++++++++++++++++++++-
 tools/tui/readline/keys.go    |  4 +++
 3 files changed, 89 insertions(+), 1 deletion(-)

diff --git a/tools/tui/readline/actions.go b/tools/tui/readline/actions.go
index 7de119666..ad5306b80 100644
--- a/tools/tui/readline/actions.go
+++ b/tools/tui/readline/actions.go
@@ -51,6 +51,7 @@ func (self *Readline) all_text() string {
 }
 
 func (self *Readline) add_text(text string) {
+	defer func() { self.last_action = ActionAddText }()
 	new_lines := make([]string, 0, len(self.lines)+4)
 	new_lines = append(new_lines, self.lines[:self.cursor.Y]...)
 	var lines_after []string
@@ -355,7 +356,37 @@ func (self *Readline) move_to_start_of_word(amt uint, traverse_line_breaks bool)
 	return
 }
 
+func (self *Readline) kill_text(text string) {
+	if ActionStartKillActions < self.last_action && self.last_action < ActionEndKillActions {
+		self.kill_ring.append_to_existing_item(text)
+	} else {
+		self.kill_ring.add_new_item(text)
+	}
+}
+
+func (self *Readline) kill_to_end_of_line() bool {
+	line := self.lines[self.cursor.Y]
+	if self.cursor.X >= len(line) {
+		return false
+	}
+	self.lines[self.cursor.Y] = line[:self.cursor.X]
+	self.kill_text(line[self.cursor.X:])
+	return true
+}
+
+func (self *Readline) kill_to_start_of_line() bool {
+	line := self.lines[self.cursor.Y]
+	if self.cursor.X <= 0 {
+		return false
+	}
+	self.lines[self.cursor.Y] = line[self.cursor.X:]
+	self.kill_text(line[:self.cursor.X])
+	self.cursor.X = 0
+	return true
+}
+
 func (self *Readline) perform_action(ac Action, repeat_count uint) error {
+	defer func() { self.last_action = ac }()
 	switch ac {
 	case ActionBackspace:
 		if self.erase_chars_before_cursor(repeat_count, true) > 0 {
@@ -435,6 +466,14 @@ func (self *Readline) perform_action(ac Action, repeat_count uint) error {
 		self.RedrawNonAtomic()
 		self.loop.EndAtomicUpdate()
 		return nil
+	case ActionKillToEndOfLine:
+		if self.kill_to_end_of_line() {
+			return nil
+		}
+	case ActionKillToStartOfLine:
+		if self.kill_to_start_of_line() {
+			return nil
+		}
 	}
 	return ErrCouldNotPerformAction
 }
diff --git a/tools/tui/readline/api.go b/tools/tui/readline/api.go
index 9419ba715..0a0c1a914 100644
--- a/tools/tui/readline/api.go
+++ b/tools/tui/readline/api.go
@@ -3,6 +3,7 @@
 package readline
 
 import (
+	"container/list"
 	"fmt"
 	"strings"
 
@@ -56,8 +57,49 @@ const (
 	ActionHistoryNext
 	ActionHistoryPrevious
 	ActionClearScreen
+	ActionAddText
+
+	ActionStartKillActions
+	ActionKillToEndOfLine
+	ActionKillToStartOfLine
+	ActionEndKillActions
 )
 
+type kill_ring struct {
+	items *list.List
+}
+
+func (self *kill_ring) append_to_existing_item(text string) {
+	e := self.items.Front()
+	if e == nil {
+		self.add_new_item(text)
+	}
+	e.Value = e.Value.(string) + text
+}
+
+func (self *kill_ring) add_new_item(text string) {
+	if text != "" {
+		self.items.PushFront(text)
+	}
+}
+
+func (self *kill_ring) yank() string {
+	e := self.items.Front()
+	if e == nil {
+		return ""
+	}
+	return e.Value.(string)
+}
+
+func (self *kill_ring) pop_yank() string {
+	e := self.items.Front()
+	if e == nil {
+		return ""
+	}
+	self.items.MoveToBack(e)
+	return self.yank()
+}
+
 type Readline struct {
 	prompt                  string
 	prompt_len              int
@@ -66,6 +108,7 @@ type Readline struct {
 	mark_prompts            bool
 	loop                    *loop.Loop
 	history                 *History
+	kill_ring               kill_ring
 
 	// The number of lines after the initial line on the screen
 	cursor_y     int
@@ -75,6 +118,7 @@ type Readline struct {
 	// The cursor position in the text
 	cursor                 Position
 	bracketed_paste_buffer strings.Builder
+	last_action            Action
 }
 
 func New(loop *loop.Loop, r RlInit) *Readline {
@@ -84,7 +128,7 @@ func New(loop *loop.Loop, r RlInit) *Readline {
 	}
 	ans := &Readline{
 		prompt: r.Prompt, prompt_len: wcswidth.Stringwidth(r.Prompt), mark_prompts: !r.DontMarkPrompts,
-		loop: loop, lines: []string{""}, history: NewHistory(r.HistoryPath, hc),
+		loop: loop, lines: []string{""}, history: NewHistory(r.HistoryPath, hc), kill_ring: kill_ring{items: list.New().Init()},
 	}
 	if r.ContinuationPrompt != "" || !r.EmptyContinuationPrompt {
 		ans.continuation_prompt = r.ContinuationPrompt
@@ -112,6 +156,7 @@ func (self *Readline) ResetText() {
 	self.lines = []string{""}
 	self.cursor = Position{}
 	self.cursor_y = 0
+	self.last_action = ActionNil
 }
 
 func (self *Readline) ChangeLoopAndResetText(lp *loop.Loop) {
diff --git a/tools/tui/readline/keys.go b/tools/tui/readline/keys.go
index 923c685b2..0cca8010d 100644
--- a/tools/tui/readline/keys.go
+++ b/tools/tui/readline/keys.go
@@ -39,6 +39,10 @@ var default_shortcuts = map[string]Action{
 
 	"ctrl+d": ActionEndInput,
 	"enter":  ActionAcceptInput,
+
+	"ctrl+k": ActionKillToEndOfLine,
+	"ctrl+x": ActionKillToStartOfLine,
+	"ctrl+u": ActionKillToStartOfLine,
 }
 
 func action_for_key_event(event *loop.KeyEvent, shortcuts map[string]Action) Action {