#!/bin/sh
#| -*- scheme -*-
exec guile -e main -s "$0" "$@"

Flat Fuck Format
--- a new configuration format, because who doesn't need that?

Copyright (C) 2023 Case Duckworth <acdw@acdw.net>

Everyone is permitted to do whatever with this software, without
limitation.  This software comes without any warranty whatsoever,
but with two pieces of advice:

- Don't hurt yourself.
- Make good choices.

Commentary:

This script will convert files defined in the Flat Fuck Format (fff) into json.
It will not convert anything back to fff.  fff is explicitly made to be as
simple as possible, and exclusively human-written.  If a machine writes your
configuration, ... use a better configuration format.  Or make your program
scriptable!

FLAT FUCK FORMAT : Specification
|#
!#

(define-module (fff)
  #:use-module (ice-9 peg)
  #:use-module (ice-9 match)
  #:use-module (srfi srfi-11)
  #:version (0 1 0)
  #:export (fff
            fff?
            fff/comments?
            fff->scm))


;;; PEG Grammar

(define-peg-pattern fff all
  (and (* (or WHITESPACE NEWLINE))
       (* (or comment
              object
              array
              item
              blanks))
       (* NEWLINE)
       (not-followed-by peg-any)))

(define-peg-pattern comment all
  (and (+ HASH) (* WHITESPACE)
       (* (and (not-followed-by NEWLINE)
               peg-any))))

(define-peg-pattern object all
  (and name
       (+ object-item)))

(define-peg-pattern array all
  (and name
       (+ array-item)))

(define-peg-pattern item all
  (and object-item
       (* NEWLINE)))

(define-peg-pattern object-item body
  (and key (* WHITESPACE)
       COLON (* WHITESPACE)
       (or ref val)
       (? NEWLINE)))

(define-peg-pattern array-item body
  (and (* WHITESPACE)
       COLON (* WHITESPACE)
       (or ref val)
       (? NEWLINE)))

(define-peg-pattern name all
  (and key COLON COLON (* WHITESPACE) NEWLINE))

(define-peg-pattern key body
  (+ (and (not-followed-by COLON)
          nonl)))

(define-peg-pattern val all
  (and (* nonl)))

(define-peg-pattern ref all
  (and AT key))

(define-peg-pattern escaped body
  (and BACKSLASH (or (and NEWLINE (* WHITESPACE))
                     peg-any)))

(define-peg-pattern blanks none
  (+ NEWLINE))

(define-peg-pattern nonl body
  (or escaped
      (and (not-followed-by NEWLINE)
           peg-any)))

(define-peg-pattern NEWLINE none
  (or "\r\n" "\r" "\n"))

(define-peg-pattern WHITESPACE none
  (or " " "\t"))

(define-peg-pattern BACKSLASH none "\\")

(define-peg-pattern COLON none ":")

(define-peg-pattern HASH none "#")

(define-peg-pattern AT none "@")


;;; Utility functions

(define (ensure-nested-list x)
  (if (list? (car x))
      x
      (list x)))

(define (atom? x)
  (and (not (null? x))
       (not (pair? x))
       (not (vector? x))))

(define (car-safe x)
  (if (pair? x)
      (car x)
      #f))


;;; Parameters

(define fff/comments?
  (make-parameter #f))

(define fff/dupes?
  (make-parameter #f))


;;; FFF -> Scheme structures

(define (fff? x)
  (and (pair? x)
       (eq? (car x) 'fff)))

(define (fff->scm str)
  (let ((tree (peg:tree (match-pattern fff str))))
    (if (fff? tree)
        (fff-ref-resolve (fff-tree->ref-tree tree))
        #f)))

(define (fff-tree->ref-tree tree)
  (let loop ((xs (cdr tree))
             (it '()))
    (if (null? xs)
        (reverse it)
        (loop (cdr xs)
              (match (car xs)
                (`(object (name ,name) ,pairs)
                 (cons (cons name
                             (map fff-pair->scm
                                  (ensure-nested-list pairs)))
                       it))
                (`(array (name ,name) ,values)
                 (cons (cons name
                             (list->vector (map fff-value->scm
                                                (ensure-nested-list values))))
                       it))
                (`(item . ,pair)
                 (cons (fff-pair->scm pair)
                       it))
                (`(comment ,comment)
                 (if (fff/comments?)
                     (cons (car xs) it)
                     it))
                (_ it))))))

(define* (fff-ref-resolve tree #:optional environment keep-dupes?)
  (define dupes '())
  (define env (append (or environment '())
                      '(("true" . #t)
                        ("false" . #f)
                        ("null" . null))))
  (filter (lambda (x)
            (if (or keep-dupes?
                    (fff/dupes?))
                #t
                (not (member (or (car-safe x) x)
                             dupes))))
          (let loop ((xs tree)
                     (v? #f)
                     (it '()))
            (if (null? xs)
                ((if v? list->vector identity)
                 (reverse it))
                (begin
                  (loop (cdr xs)
                        v?
                        (cons (let ((x (car xs)))
                                (cond
                                 ((procedure? x)
                                  (let-values (((resval reskey)
                                                (x (append env tree))))
                                    (set! env (cons reskey env))
                                    (set! dupes (cons reskey dupes))
                                    (list (cons reskey resval))))
                                 ((atom? x)
                                  (set! env (cons x env))
                                  x)
                                 ((procedure? (cdr x))
                                  (set! dupes (cons (car x) dupes))
                                  (let ((resolved
                                         (cons (car x)
                                               (cdr ((cdr x)
                                                     (append env tree))))))
                                    (set! env (cons resolved env))
                                    resolved))
                                 ((atom? (cdr x))
                                  (set! env (cons x env))
                                  x)
                                 ((vector? (cdr x))
                                  (let ((vl (vector->list (cdr x))))
                                    (set! env (cons (fff-ref-resolve vl env #f)
                                                    env))
                                    (cons (car x)
                                          (loop vl #t '()))))
                                 (else   ; object
                                  (set! env (cons (fff-ref-resolve x env #t)
                                                  env))
                                  (cons (car x) ; not tail-recursive!
                                        (loop (cdr x) #f '())))))
                              it)))))))

(define (fff-pair->scm pair)
  (cons (car pair) (fff-value->scm (cadr pair))))

(define (fff-value->scm val)
  (match val
    (`(val ,v) v)
    (`(ref ,r) (lambda (alist)
                 (values (assoc-ref alist r)
                         r)))))