From dcd5d62501e61e0f6901d4d4687ab56430a4b8a7 Mon Sep 17 00:00:00 2001
From: Thijs Schreijer <thijs@thijsschreijer.nl>
Date: Mon, 6 May 2024 11:44:47 +0200
Subject: add example for reading a line from the terminal, non-blocking

Handles utf8, and character width
---
 examples/compat.lua   |   5 +-
 examples/readline.lua | 476 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 480 insertions(+), 1 deletion(-)
 create mode 100644 examples/readline.lua

(limited to 'examples')

diff --git a/examples/compat.lua b/examples/compat.lua
index c00d44a..a59d964 100644
--- a/examples/compat.lua
+++ b/examples/compat.lua
@@ -5,12 +5,15 @@ local sys = require "system"
 
 
 
-if sys.is_windows then
+if sys.windows then
   -- Windows holds multiple copies of environment variables, to ensure `getenv`
   -- returns what `setenv` sets we need to use the `system.getenv` instead of
   -- `os.getenv`.
   os.getenv = sys.getenv  -- luacheck: ignore
 
+  -- Set console output to UTF-8 encoding.
+  sys.setconsoleoutputcp(65001)
+
   -- Set up the terminal to handle ANSI escape sequences on Windows.
   if sys.isatty(io.stdout) then
     sys.setconsoleflags(io.stdout, sys.getconsoleflags(io.stdout) + sys.COF_VIRTUAL_TERMINAL_PROCESSING)
diff --git a/examples/readline.lua b/examples/readline.lua
new file mode 100644
index 0000000..f1e6258
--- /dev/null
+++ b/examples/readline.lua
@@ -0,0 +1,476 @@
+local sys = require("system")
+
+
+-- Mapping of key-sequences to key-names
+local key_names = {
+  ["\27[C"] = "right",
+  ["\27[D"] = "left",
+  ["\127"] = "backspace",
+  ["\27[3~"] = "delete",
+  ["\27[H"] = "home",
+  ["\27[F"] = "end",
+  ["\27"] = "escape",
+  ["\9"] = "tab",
+  ["\27[Z"] = "shift-tab",
+}
+
+if sys.windows then
+  key_names["\13"] = "enter"
+else
+  key_names["\10"] = "enter"
+end
+
+
+-- Mapping of key-names to key-sequences
+local key_sequences = {}
+for k, v in pairs(key_names) do
+  key_sequences[v] = k
+end
+
+
+-- bell character
+local function bell()
+  io.write("\7")
+  io.flush()
+end
+
+
+-- generate string to move cursor horizontally
+-- positive goes right, negative goes left
+local function cursor_move_horiz(n)
+  if n == 0 then
+    return ""
+  end
+  return "\27[" .. (n > 0 and n or -n) .. (n > 0 and "C" or "D")
+end
+
+
+-- -- generate string to move cursor vertically
+-- -- positive goes down, negative goes up
+-- local function cursor_move_vert(n)
+--   if n == 0 then
+--     return ""
+--   end
+--   return "\27[" .. (n > 0 and n or -n) .. (n > 0 and "B" or "A")
+-- end
+
+
+-- -- log to the line above the current line
+-- local function log(...)
+--   local arg = { n = select("#", ...), ...}
+--   for i = 1, arg.n do
+--     arg[i] = tostring(arg[i])
+--   end
+--   arg = " " .. table.concat(arg, " ") .. " "
+
+--   io.write(cursor_move_vert(-1), arg, cursor_move_vert(1), cursor_move_horiz(-#arg))
+-- end
+
+
+-- UTF8 character size in bytes
+-- @tparam number b the byte value of the first byte of a UTF8 character
+local function utf8size(b)
+  return b < 128 and 1 or b < 224 and 2 or b < 240 and 3 or b < 248 and 4
+end
+
+
+
+local utf8parse do
+  local utf8_value_mt = {
+    __tostring = function(self)
+      return table.concat(self, "")
+    end,
+  }
+
+  -- Parses a UTF8 string into list of individual characters.
+  -- key 'chars' gets the length in UTF8 characters, whilst # returns the length
+  -- for display (to handle double-width UTF8 chars).
+  -- in the list the double-width characters are followed by an empty string.
+  -- @tparam string s the UTF8 string to parse
+  -- @treturn table the list of characters
+  function utf8parse(s)
+    local t = setmetatable({ chars = 0 }, utf8_value_mt)
+    local i = 1
+    while i <= #s do
+      local b = s:byte(i)
+      local w = utf8size(b)
+      local char = s:sub(i, i + w - 1)
+      t[#t + 1] = char
+      t.chars = t.chars + 1
+      if sys.utf8cwidth(char) == 2 then
+        -- double width character, add empty string to keep the length of the
+        -- list the same as the character width on screen
+        t[#t + 1] = ""
+      end
+      i = i + w
+    end
+    return t
+  end
+end
+
+
+
+-- inline tests for utf8parse
+-- do
+--   local t = utf8parse("a你b好c")
+--   assert(t[1] == "a")
+--   assert(t[2] == "你")  -- double width
+--   assert(t[3] == "")
+--   assert(t[4] == "b")
+--   assert(t[5] == "好")  -- double width
+--   assert(t[6] == "")
+--   assert(t[7] == "c")
+--   assert(#t == 7)       -- size as displayed
+-- end
+
+
+
+-- readline class
+
+local readline = {}
+readline.__index = readline
+
+
+--- Create a new readline object.
+-- @tparam table opts the options for the readline object
+-- @tparam[opt=""] string opts.prompt the prompt to display
+-- @tparam[opt=80] number opts.max_length the maximum length of the input
+-- @tparam[opt=""] string opts.value the default value
+-- @tparam[opt=`#value`] number opts.position of the cursor in the input
+-- @tparam[opt={"\10"/"\13"}] table opts.exit_keys an array of keys that will cause the readline to exit
+-- @treturn readline the new readline object
+function readline.new(opts)
+  local value = utf8parse(opts.value or "")
+  local prompt = utf8parse(opts.prompt or "")
+  local pos = math.floor(opts.position or (#value + 1))
+  pos = math.max(math.min(pos, (#value + 1)), 1)
+  local len = math.floor(opts.max_length or 80)
+  if len < 1 then
+    error("max_length must be at least 1", 2)
+  end
+
+  if value.chars > len then
+    error("value is longer than max_length", 2)
+  end
+
+  local exit_keys = {}
+  for _, key in ipairs(opts.exit_keys or {}) do
+    exit_keys[key] = true
+  end
+  if exit_keys[1] == nil then
+    -- nothing provided, default to Enter-key
+    exit_keys[1] = key_sequences.enter
+  end
+
+  local self = {
+    value = value,          -- the default value
+    max_length = len,       -- the maximum length of the input
+    prompt = prompt,        -- the prompt to display
+    position = pos,         -- the current position in the input
+    drawn_before = false,   -- if the prompt has been drawn
+    exit_keys = exit_keys,  -- the keys that will cause the readline to exit
+  }
+
+  setmetatable(self, readline)
+  return self
+end
+
+
+
+-- draw the prompt and the input value, and position the cursor.
+local function draw(self, redraw)
+  if redraw or not self.drawn_before then
+    -- we are at start of prompt
+    self.drawn_before = true
+  else
+    -- we are at current cursor position, move to start of prompt
+    io.write(cursor_move_horiz(-(#self.prompt + self.position)))
+  end
+  -- write prompt & value
+  io.write(tostring(self.prompt) .. tostring(self.value))
+  -- clear remainder of input size
+  io.write(string.rep(" ", self.max_length - self.value.chars))
+  io.write(cursor_move_horiz(-(self.max_length - self.value.chars)))
+  -- move to cursor position
+  io.write(cursor_move_horiz(-(#self.value + 1 - self.position)))
+  io.flush()
+end
+
+
+local handle_key do -- keyboard input handler
+
+  local key_handlers
+  key_handlers = {
+    left = function(self)
+      if self.position == 1 then
+        bell()
+        return
+      end
+
+      local new_pos = self.position - 1
+      while self.value[new_pos] == "" do -- skip empty strings; double width chars
+        new_pos = new_pos - 1
+      end
+
+      io.write(cursor_move_horiz(-(self.position - new_pos)))
+      io.flush()
+      self.position = new_pos
+    end,
+
+    right = function(self)
+      if self.position == #self.value + 1 then
+        bell()
+        return
+      end
+
+      local new_pos = self.position + 1
+      while self.value[new_pos] == "" do -- skip empty strings; double width chars
+        new_pos = new_pos + 1
+      end
+
+      io.write(cursor_move_horiz(new_pos - self.position))
+      io.flush()
+      self.position = new_pos
+    end,
+
+    backspace = function(self)
+      if self.position == 1 then
+        bell()
+        return
+      end
+
+      while self.value[self.position - 1] == "" do -- remove empty strings; double width chars
+        io.write(cursor_move_horiz(-1))
+        self.position = self.position - 1
+        table.remove(self.value, self.position)
+      end
+      -- remove char itself
+      io.write(cursor_move_horiz(-1))
+      self.position = self.position - 1
+      table.remove(self.value, self.position)
+      self.value.chars = self.value.chars - 1
+      draw(self)
+    end,
+
+    home = function(self)
+      local new_pos = 1
+      io.write(cursor_move_horiz(new_pos - self.position))
+      self.position = new_pos
+    end,
+
+    ["end"] = function(self)
+      local new_pos = #self.value + 1
+      io.write(cursor_move_horiz(new_pos - self.position))
+      self.position = new_pos
+    end,
+
+    delete = function(self)
+      if self.position > #self.value then
+        bell()
+        return
+      end
+
+      key_handlers.right(self)
+      key_handlers.backspace(self)
+    end,
+  }
+
+
+  -- handles a single input key/ansi-sequence.
+  -- @tparam string key the key or ansi-sequence (from `system.readansi`)
+  -- @tparam string keytype the type of the key, either "char" or "ansi" (from `system.readansi`)
+  -- @treturn string status the status of the key handling, either "ok", "exit_key" or an error message
+  function handle_key(self, key, keytype)
+    if self.exit_keys[key] then
+      -- registered exit key
+      return "exit_key"
+    end
+
+    local handler = key_handlers[key_names[key] or true ]
+    if handler then
+      handler(self)
+      return "ok"
+    end
+
+    if keytype == "ansi" then
+      -- we got an ansi sequence, but dunno how to handle it, ignore
+      -- print("unhandled ansi: ", key:sub(2,-1), string.byte(key, 1, -1))
+      bell()
+      return "ok"
+    end
+
+    -- just a single key
+    if key < " " then
+      -- control character
+      bell()
+      return "ok"
+    end
+
+    if self.value.chars >= self.max_length then
+      bell()
+      return "ok"
+    end
+
+    -- insert the key into the value
+    if sys.utf8cwidth(key) == 2 then
+      -- double width character, insert empty string after it
+      table.insert(self.value, self.position, "")
+      table.insert(self.value, self.position, key)
+      self.position = self.position + 2
+      io.write(cursor_move_horiz(2))
+    else
+      table.insert(self.value, self.position, key)
+      self.position = self.position + 1
+      io.write(cursor_move_horiz(1))
+    end
+    self.value.chars = self.value.chars + 1
+    draw(self)
+    return "ok"
+  end
+end
+
+
+
+--- Get_size returns the maximum size of the input box (prompt + input).
+-- The size is in rows and columns. Columns is determined by
+-- the prompt and the `max_length * 2` (characters can be double-width).
+-- @treturn number the number of rows (always 1)
+-- @treturn number the number of columns
+function readline:get_size()
+  return 1, #self.prompt + self.max_length * 2
+end
+
+
+
+--- Get coordinates of the cursor in the input box (prompt + input).
+-- The coordinates are 1-based. They are returned as row and column, within the
+-- size as reported by `get_size`.
+-- @treturn number the row of the cursor (always 1)
+-- @treturn number the column of the cursor
+function readline:get_cursor()
+  return 1, #self.prompt + self.position
+end
+
+
+
+--- Set the coordinates of the cursor in the input box (prompt + input).
+-- The coordinates are 1-based. They are expected to be within the
+-- size as reported by `get_size`, and beyond the prompt.
+-- If the position is invalid, it will be corrected.
+-- Use the results to check if the position was adjusted.
+-- @tparam number row the row of the cursor (always 1)
+-- @tparam number col the column of the cursor
+-- @return results of get_cursor
+function readline:set_cursor(row, col)
+  local l_prompt = #self.prompt
+  local l_value = #self.value
+
+  if col < l_prompt + 1 then
+    col = l_prompt + 1
+  elseif col > l_prompt + l_value + 1 then
+    col = l_prompt + l_value + 1
+  end
+
+  while self.value[col - l_prompt] == "" do
+    col = col - 1 -- on an empty string, so move back to start of double-width char
+  end
+
+  local new_pos = col - l_prompt
+
+  cursor_move_horiz(self.position - new_pos)
+  io.flush()
+
+  self.position = new_pos
+  return self:get_cursor()
+end
+
+
+
+--- Read a line of input from the user.
+-- It will first print the `prompt` and then wait for input. Ensure the cursor
+-- is at the correct position before calling this function. This function will
+-- do all cursor movements in a relative way.
+-- Can be called again after an exit-key or timeout has occurred. Just make sure
+-- the cursor is at the same position where is was when it returned the last time.
+-- Alternatively the cursor can be set to the position of the prompt (the position
+-- the cursor was in before the first call), and the parameter `redraw` can be set
+-- to `true`.
+-- @tparam[opt=math.huge] number timeout the maximum time to wait for input in seconds
+-- @tparam[opt=false] boolean redraw if `true` the prompt will be redrawn (cursor must be at prompt position!)
+-- @treturn[1] string the input string as entered the user
+-- @treturn[1] string the exit-key used to exit the readline (see `new`)
+-- @treturn[2] nil when input is incomplete
+-- @treturn[2] string error message, the reason why the input is incomplete, `"timeout"`, or an error reading a key
+function readline:__call(timeout, redraw)
+  draw(self, redraw)
+  timeout = timeout or math.huge
+  local timeout_end = sys.gettime() + timeout
+
+  while true do
+    local key, keytype = sys.readansi(timeout_end - sys.gettime())
+    if not key then
+      -- error or timeout
+      return nil, keytype
+    end
+
+    local status = handle_key(self, key, keytype)
+    if status == "exit_key" then
+      return tostring(self.value), key
+
+    elseif status ~= "ok" then
+      error("unknown status received: " .. tostring(status))
+    end
+  end
+end
+
+
+
+-- return readline
+
+
+
+
+-- setup Windows console to handle ANSI processing
+local of_in = sys.getconsoleflags(io.stdin)
+local cp_in = sys.getconsolecp()
+-- sys.setconsolecp(65001)
+sys.setconsolecp(850)
+local of_out = sys.getconsoleflags(io.stdout)
+local cp_out = sys.getconsoleoutputcp()
+sys.setconsoleoutputcp(65001)
+sys.setconsoleflags(io.stdout, sys.getconsoleflags(io.stdout) + sys.COF_VIRTUAL_TERMINAL_PROCESSING)
+sys.setconsoleflags(io.stdin, sys.getconsoleflags(io.stdin) + sys.CIF_VIRTUAL_TERMINAL_INPUT)
+
+-- setup Posix terminal to use non-blocking mode, and disable line-mode
+local of_attr = sys.tcgetattr(io.stdin)
+local of_block = sys.getnonblock(io.stdin)
+sys.setnonblock(io.stdin, true)
+sys.tcsetattr(io.stdin, sys.TCSANOW, {
+  lflag = of_attr.lflag - sys.L_ICANON - sys.L_ECHO, -- disable canonical mode and echo
+})
+
+
+local rl = readline.new{
+  prompt = "Enter something: ",
+  max_length = 60,
+  value = "Hello, 你-好 World 🚀!",
+  -- position = 2,
+  exit_keys = {key_sequences.enter, "\27", "\t", "\27[Z"}, -- enter, escape, tab, shift-tab
+}
+
+
+local result, key = rl()
+print("")  -- newline after input, to move cursor down from the input line
+print("Result (string): '" .. result .. "'")
+print("Result (bytes):", result:byte(1,-1))
+print("Exit-Key (bytes):", key:byte(1,-1))
+
+
+-- Clean up afterwards
+sys.setnonblock(io.stdin, false)
+sys.setconsoleflags(io.stdout, of_out)
+sys.setconsoleflags(io.stdin, of_in)
+sys.tcsetattr(io.stdin, sys.TCSANOW, of_attr)
+sys.setnonblock(io.stdin, of_block)
+sys.setconsolecp(cp_in)
+sys.setconsoleoutputcp(cp_out)
-- 
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