;;; stdio.el -- stdio routines for emacs lisp  -*- lexical-binding: t; -*-
;;; Commentary:
;;; Code:

(require 'cl-lib)

(cl-defstruct (stdio-process (:constructor stdio-process-create)
                             (:copier nil))
  emacs-process buffer)

(defun stdio-make-filter (process)
  "Return a filter function for PROCESS."
  (lambda (_ input)
    (setf (stdio-process-buffer process)
          (concat (stdio-process-buffer process)
                  input))))

(defvar stdio--process-counter 0)
(defun stdio--make-process-name ()
  "Generate a new uniqe process name."
  (let* ((num stdio--process-counter)
        (name (format "stdio-subp-%d" num)))
    (setq stdio--process-counter (+ stdio--process-counter 1))
    name))

(defun stdio-call (command)
  "Call COMMAND, return stdio-process."
  (let* ((process (stdio-process-create))
         (emacs-process (make-process
                         :name (stdio--make-process-name)
                         :command command
                         :coding 'utf-8-unix
                         :noquery nil
                         :connection-type 'pipe
                         :filter (stdio-make-filter process)
                         )))
    (setf (stdio-process-emacs-process process) emacs-process)
    process))

(defun stdio-read-line (process)
  "Read next line from PROCESS."
  (if-let ((stdin-buf (stdio-process-buffer process))
           (newline-pos (string-search "\n" stdin-buf))
           (line (substring stdin-buf 0 newline-pos))
           (rest (substring stdin-buf (+ 1 newline-pos))))
      (progn
        (setf (stdio-process-buffer process) rest)
        line)
    ;; no newline character found
    (if (accept-process-output (stdio-process-emacs-process process))
        (stdio-read-line process)
      ;; no more output from process
      (when (> (length stdin-buf) 0)
          (progn (setf (stdio-process-buffer process) "")
                 stdin-buf)))))

(provide 'stdio)
;;; stdio.el ends here