From ebb81725514e6dfa089c245264eacdb6c1f26419 Mon Sep 17 00:00:00 2001
From: Kyle Isom <kyle@imap.cc>
Date: Tue, 23 Apr 2019 18:28:32 -0700
Subject: [PATCH] From scratch forth text editor.

---
 from_scratch/editor.rb | 203 +++++++++++++++++++++++++++++++++++++++++
 from_scratch/test.fs   |   1 +
 2 files changed, 204 insertions(+)
 create mode 100644 from_scratch/editor.rb
 create mode 100644 from_scratch/test.fs

diff --git a/from_scratch/editor.rb b/from_scratch/editor.rb
new file mode 100644
index 0000000..5ac417c
--- /dev/null
+++ b/from_scratch/editor.rb
@@ -0,0 +1,203 @@
+#!/usr/bin/env ruby
+# This is a simple forth editor written in Ruby, following along with
+# the DAS "from scratch" text editor tutorial.
+
+require "io/console"
+
+class Editor
+
+  def initialize(filename="")
+    if filename.length > 0
+      if File.exists? filename
+        lines = File.readlines(filename).map do |line|
+          line.sub(/\n$/, "")
+        end
+      else
+        lines = ['']        
+      end
+    else
+      filename = "untitled.txt"      
+      lines = ['']
+    end
+    @filename = filename
+    @buffer = Buffer.new(lines)
+    @cursor = Cursor.new
+    @history = []
+  end
+
+  def run
+    IO.console.raw do
+      loop do
+        render
+        handle_input
+      end
+    end
+
+  rescue
+    50.times { puts }
+    raise
+  end
+
+  def render
+    ANSI.clear_screen
+    ANSI.move_cursor(0, 0)
+    @buffer.render
+    ANSI.move_cursor(@cursor.row, @cursor.col)
+  end
+
+  def handle_input
+    char = $stdin.getc
+    case char
+    when "\C-q" then exit(0)
+    # operating on the cursor makes undo easier
+    when "\C-p" then @cursor = @cursor.up(@buffer)
+    when "\C-n" then @cursor = @cursor.down(@buffer)
+    when "\C-b" then @cursor = @cursor.left(@buffer)
+    when "\C-f" then @cursor = @cursor.right(@buffer)
+    when "\C-s" then @buffer.write(@filename)
+    when "\C-u" then restore_snapshot
+    when "\C-e" then
+      @cursor = @cursor.move_to_col(@buffer.line_length(@cursor.row))
+    when "\C-a" then @cursor = @cursor.move_to_col(0)
+    when "\C-r" then forth
+    when 127.chr
+      if @cursor.col > 0
+        save_snapshot
+        @buffer = @buffer.delete(@cursor.row, @cursor.col-1)
+        @cursor = @cursor.left(@buffer)
+      end
+    when "\r"
+      # in raw mode, enter sends \r
+      save_snapshot
+      @buffer = @buffer.split_line(@cursor.row, @cursor.col)
+      @cursor = @cursor.down(@buffer).move_to_col(0)
+    else
+      save_snapshot
+      # keep buffer immutable so we can do undo
+      @buffer = @buffer.insert(char, @cursor.row, @cursor.col)
+      # lot of the implemenation of basic actions is ensuring
+      # cursor consistency
+      @cursor = @cursor.right(@buffer)
+    end
+  end
+
+  def save_snapshot
+    @history <<[@buffer, @cursor]
+  end
+
+  def restore_snapshot
+    if @history.length > 0
+      @buffer, @cursor = @history.pop
+    end
+  end
+
+  def forth
+    ANSI.clear_screen
+    puts "gforth {@filename}\r\n"
+    puts "------\r\n"
+    output = `gforth #{@filename}`.split("\n")
+    Buffer.new(output).render
+    puts "-----\r\n"
+    puts "Press <enter> to exit...\r\n"
+    
+    loop do
+      char = $stdin.getc
+      case char
+      when "\r" then break
+      end
+    end
+  end
+end
+
+class Buffer
+  def initialize(lines)
+    @lines = lines
+  end
+
+  def render
+    @lines.each do |line|
+      $stdout.write(line + "\r\n")
+    end
+  end
+
+  def insert(char, row, col)
+    lines = @lines.map(&:dup)
+    lines.fetch(row).insert(col, char)
+    Buffer.new(lines)
+  end
+
+  def delete(row, col)
+    lines = @lines.map(&:dup)
+    lines.fetch(row).slice!(col)
+    Buffer.new(lines)
+  end
+
+  def split_line(row, col)
+    lines = @lines.map(&:dup)
+    line = lines.fetch(row)
+    lines[row..row] = [line[0...col], line[col..-1]]
+    Buffer.new(lines)
+  end
+
+  def line_count
+    @lines.count
+  end
+
+  def line_length(row)
+    @lines.fetch(row).length
+  end
+
+  def write(filename)
+    File.write(filename, @lines.join("\n"))
+  end
+end
+
+class Cursor
+  attr_reader :row, :col
+  def initialize(row=0, col=0)
+    @row = row
+    @col = col
+  end
+
+  def left(buffer)
+    Cursor.new(@row, @col-1).clamp(buffer)
+  end
+
+  def right(buffer)
+    Cursor.new(@row, @col+1).clamp(buffer)
+  end
+
+  def up(buffer)
+    Cursor.new(@row-1, @col).clamp(buffer)
+  end
+
+  def down(buffer)
+    Cursor.new(@row+1, @col).clamp(buffer)
+  end
+
+  def clamp(buffer)
+    row = @row.clamp(0, buffer.line_count - 1)
+    col = @col.clamp(0, buffer.line_length(row))
+    Cursor.new(row, col)
+  end
+
+  def move_to_col(col)
+    Cursor.new(row, col)
+  end
+end
+
+class ANSI
+  def self.clear_screen
+    $stdout.write("\e[2J")
+  end
+
+  def self.move_cursor(row, col)
+    $stdout.write("\e[#{row+1};#{col+1}H")
+  end
+end
+
+filename = ""
+if ARGV.length > 0
+  filename = ARGV[0]
+end
+Editor.new(filename).run
diff --git a/from_scratch/test.fs b/from_scratch/test.fs
new file mode 100644
index 0000000..1abff7d
--- /dev/null
+++ b/from_scratch/test.fs
@@ -0,0 +1 @@
+2 3 + . bye
\ No newline at end of file