perf(windows): use a single powershell process for trash operations (#271)

* perf(trash_windows): use a single powershell instance for operations

* refactor(trash_windows): encapsulate powershell connection logic

* refactor(windows_trash): better name for functions

* fix(windows_trash): set connection error on initializatino if needed

* refactor(windows_trash): simplify initialization code

* refactor: extract some powershell logic into separate file

---------

Co-authored-by: Steven Arcangeli <stevearc@stevearc.com>

lua/oil/adapters/trash/windows/powershell-connection.lua

@@ -0,0 +1,114 @@
+---@class (exact) oil.PowershellCommand
+---@field cmd string
+---@field cb fun(err?: string, output?: string)
+---@field running? boolean
+
+---@class oil.PowershellConnection
+---@field private jid integer
+---@field private execution_error? string
+---@field private commands oil.PowershellCommand[]
+---@field private stdout string[]
+---@field private is_reading_data boolean
+local PowershellConnection = {}
+
+---@param init_command? string
+---@return oil.PowershellConnection
+function PowershellConnection.new(init_command)
+  local self = setmetatable({
+    commands = {},
+    stdout = {},
+    is_reading_data = false,
+  }, { __index = PowershellConnection })
+
+  self:_init(init_command)
+
+  return self
+end
+
+---@param init_command? string
+function PowershellConnection:_init(init_command)
+  local jid = vim.fn.jobstart({
+    "powershell",
+    "-NoProfile",
+    "-NoLogo",
+    "-ExecutionPolicy",
+    "Bypass",
+    "-NoExit",
+    "-Command",
+    "-",
+  }, {
+    ---@param data string[]
+    on_stdout = function(_, data)
+      for _, fragment in ipairs(data) do
+        if fragment:find("===DONE%((%a+)%)===") then
+          self.is_reading_data = false
+          local output = table.concat(self.stdout, "")
+          local cb = self.commands[1].cb
+          table.remove(self.commands, 1)
+          local success = fragment:match("===DONE%((%a+)%)===")
+          if success == "True" then
+            cb(nil, output)
+          elseif success == "False" then
+            cb(success .. ": " .. output, output)
+          end
+          self.stdout = {}
+          self:_consume()
+        elseif self.is_reading_data then
+          table.insert(self.stdout, fragment)
+        end
+      end
+    end,
+  })
+
+  if jid == 0 then
+    self:_set_error("passed invalid arguments to 'powershell'")
+  elseif jid == -1 then
+    self:_set_error("'powershell' is not executable")
+  else
+    self.jid = jid
+  end
+
+  if init_command then
+    table.insert(self.commands, { cmd = init_command, cb = function() end })
+    self:_consume()
+  end
+end
+
+---@param command string
+---@param cb fun(err?: string, output?: string[])
+function PowershellConnection:run(command, cb)
+  if self.execution_error then
+    cb(self.execution_error)
+  else
+    table.insert(self.commands, { cmd = command, cb = cb })
+    self:_consume()
+  end
+end
+
+function PowershellConnection:_consume()
+  if not vim.tbl_isempty(self.commands) then
+    local cmd = self.commands[1]
+    if not cmd.running then
+      cmd.running = true
+      self.is_reading_data = true
+      -- $? contains the execution status of the last command.
+      -- see https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_automatic_variables?view=powershell-7.4#section-1
+      vim.api.nvim_chan_send(self.jid, cmd.cmd .. '\nWrite-Host "===DONE($?)==="\n')
+    end
+  end
+end
+
+---@param err string
+function PowershellConnection:_set_error(err)
+  if self.execution_error then
+    return
+  end
+  self.execution_error = err
+  local commands = self.commands
+  self.commands = {}
+  for _, cmd in ipairs(commands) do
+    cmd.cb(err)
+  end
+end
+
+return PowershellConnection