From cef12c9e02eafd8e01bbd740e83f62470cb83614 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Sat, 13 Jun 2020 22:57:59 +0200
Subject: Add duration parser.

---
 module/vcomponent/duration.scm | 75 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 module/vcomponent/duration.scm

(limited to 'module/vcomponent/duration.scm')

diff --git a/module/vcomponent/duration.scm b/module/vcomponent/duration.scm
new file mode 100644
index 00000000..049c8821
--- /dev/null
+++ b/module/vcomponent/duration.scm
@@ -0,0 +1,75 @@
+(define-module (vcomponent duration)
+  :use-module (util)
+  :use-module (util exceptions)
+  :use-module (datetime)
+  :use-module (ice-9 peg)
+  :use-module (ice-9 match)
+  :use-module (srfi srfi-9 gnu)
+  :use-module (srfi srfi-1)
+  :export (duration parse-duration))
+
+(define-immutable-record-type <duration>
+  (make-duration sign week day dur-time)
+  duration?
+  (sign duration-sign)
+  (week duration-week)
+  (day duration-day)
+  (dur-time duration-time))
+
+(define* (duration
+          key: (sign '+)
+          week day time)
+  (when (and week (or day time))
+    (error "Can't give week together with day or time"))
+  (make-duration sign week day time))
+
+(define-peg-pattern number all (+ (range #\0 #\9)))
+
+(define-peg-pattern time-pattern body
+  (and (ignore "T")
+       (and (capture (and number "H"))
+            (? (and (capture (and number "M"))
+                    (? (capture (and number "S"))))))))
+
+(define-peg-pattern dur-pattern body
+  (and (capture (? (or "+" "-")))
+       (and "P"
+            (or (capture (and number "W"))
+                (or (capture (and (and number "D")
+                                  (? time-pattern)))
+                    (capture time-pattern))))))
+
+(define (parse-duration str)
+  (let ((m (match-pattern dur-pattern str)))
+    (unless m
+      (error "~a doesn't appar to be a duration" str))
+
+    (unless (= (peg:end m) (string-length str))
+      (warning "Garbage at end of duration"))
+
+    (let* ((tree (peg:tree m))
+           (sign (case (string->symbol (car tree))
+                   [(+ -) => identity]
+                   [(P) '+]))
+           (lst (concatenate
+                 (map (match-lambda
+                        [(('number num) type)
+                         (let ((n (string->number num)))
+                           (case (string->symbol type)
+                             [(W) `(week: ,n)]
+                             [(D) `(day:  ,n)]
+                             [(H) `(hour: ,n)]
+                             [(M) `(minute: ,n)]
+                             [(S) `(second: ,n)]
+                             [else (error "Invalid key")]))]
+                        [#\T '()])
+                      (cadr (member "P" tree))))))
+      (apply duration
+             (cons* sign: sign
+                    (let loop ((rem lst))
+                      (if (null? rem)
+                          '()
+                          (if (eqv? hour: (car rem))
+                              (list time: (apply time rem))
+                              (cons* (car rem) (cadr rem)
+                                     (loop (cddr rem)))))))))))
-- 
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