Make Nationwide statement processing data-driven.

Instead of different scripts for credit card and current account
statements, define a profile for each that specifies the date
and amount columns, and have this control the processing.

guile/fix-nationwide-statement.scm

@@ -1,11 +1,17 @@
 #!/usr/bin/env -S guile -e main -s
 !#
 
-(use-modules (ice-9 match)
+;; Script for updating current account and credit card statements
-             (ice-9 getopt-long)
+;; downloaded from Nationwide, who use a date and currency format
+;; that Gnucash does not support.
+
+(use-modules (ice-9 getopt-long)
+             ((srfi srfi-1) #:select (drop))
              (dsv))
 
-
+;; Date appears in Nationwide statements in the format
+;; "10 Jan 2024", but this is not understood by Gnucash
+;; so we convert it to YYYY-MM-DD format.
 (define date-input-format "%d %b %Y")
 (define date-output-format "%Y-%m-%d")
 
@@ -13,31 +19,84 @@
   (strftime date-output-format
             (car (strptime date-input-format d))))
 
-(define (read-statement path)
+;; Characters we expect to see in a numeric amount field. The
-  (call-with-input-file path
+;; Nationwide statements contain a non-ASCII currency character
-    (lambda (port)
+;; that we want to delete.
-      (dsv->scm port #:format 'rfc4180))))
-
 (define currency-charset (string->char-set "0123456789.-"))
 
 (define (format-amount s)
   (string-filter currency-charset s))
 
-(define (process-row row)
+;; Profiles for the different statemnets.
-  (match-let (((date description location paid-out paid-in) row))
+;; skip: the number of leading rows to skip
-    (list (format-date date)
+;; header: boolean indicating whether or not the first unskipped
-          description
+;;         row is a header
-          location
+;; date-cols: list of columns containing dates
-          (format-amount paid-out)
+;; amount-cols: list columns containing amounts
-          (format-amount paid-in))))
+(define profiles
+  '(("credit-card" . ((skip . 4)
+                      (header . #t)
+                      (date-cols . (0))
+                      (amount-cols . (3 4))))
+    ("current-account" . ((skip . 4)
+                          (header . #t)
+                          (date-cols . (0))
+                          (amount-cols . (3 4 5))))))
 
-(define (process-statement input-path output-path)
+;; Predicate for validating the profile option.
-  (match-let (((_ _ _ _ header . data) (read-statement input-path)))
+(define (valid-profile? p)
-    (let ((updated (cons header (map process-row data))))
+  (if (assoc p profiles) #t #f))
-      (call-with-output-file output-path
-        (lambda (port)
-          (scm->dsv updated port #:format 'rfc4180))))))
 
+;; Update a list by applying the given function to each of the
+;; listed columns.
+(define (update-list lst cols f)
+  (for-each (lambda (k)
+              (let ((v (list-ref lst k)))
+                (list-set! lst k (f v))))
+            cols))
+
+;; Given a spec listing the date and amount columns, return a
+;; function that will apply the corresponding formats to a row.
+(define (process-row spec)
+  (let ((date-cols (assq-ref spec 'date-cols))
+        (amount-cols (assq-ref spec 'amount-cols)))
+    (lambda (row)
+      (when date-cols
+        (update-list row date-cols format-date))
+      (when amount-cols
+        (update-list row amount-cols format-amount)))))
+
+;; Read a CSV from the given path.
+(define (read-statement path)
+  (call-with-input-file path
+    (lambda (port)
+      (dsv->scm port #:format 'rfc4180))))
+
+;; Write data to the given path in CSV format.
+(define (write-statement data path)
+  (call-with-output-file path
+    (lambda (port)
+      (scm->dsv data port #:format 'rfc4180))))
+
+
+(define (update-data spec data)
+  (let* ((data (drop data (or (assq-ref spec 'skip) 0)))
+         (header (if (assq-ref spec 'header) (car data) #f))
+         (data (if header (cdr data) data)))
+    (for-each (process-row spec) data)
+    (if header
+        (cons header data)
+        data)))
+
+;; Apply the updates defined in `spec` to the statement read
+;; from input-path and write the updated data to output-path.
+(define (process-statement spec input-path output-path)
+  (let ((data (read-statement input-path)))
+    (write-statement (update-data spec data) output-path)))
+
+;; Display a usage message and (optional) error message to STDERR
+;; and exit. If an error message is given the exit code will be
+;; non-zero.
 (define* (usage #:optional errmsg)
   (with-output-to-port (current-error-port)
     (lambda ()
@@ -51,22 +110,28 @@ Usage: fix-credit-card-statement [options]
     -i, --input=FILENAME   Input file path.
     -o, --output=FILENAME  Output file path. Required unless --overwrite is given.
     -w, --overwrite        Overwrite the input file with the updated data.
+    -p, --profile=PROFILE  Profile name [credit-card|current-account].
 ")
       (exit (if errmsg EXIT_FAILURE EXIT_SUCCESS)))))
 
+;; Process command-line arguments and validate options.
+;; If valid, run process-statement with the given options.
 (define (main args)
-  (let* ((option-spec '((help      (single-char #\h) (value #f))
+  (let* ((option-spec `((help      (single-char #\h) (value #f))
                         (input     (single-char #\i) (value #t))
                         (output    (single-char #\o) (value #t))
-                        (overwrite (single-char #\w) (value #f))))
+                        (overwrite (single-char #\w) (value #f))
+                        (profile   (single-char #\p) (value #t) (predicate ,valid-profile?))))
          (options (getopt-long args option-spec))
          (help-wanted (option-ref options 'help #f))
+         (profile (option-ref options 'profile #f))
          (input (option-ref options 'input #f))
          (output (option-ref options 'output #f))
          (overwrite (option-ref options 'overwrite #f)))
     (cond
      (help-wanted (usage))
+     ((not profile) (usage "profile is required"))
      ((not input) (usage "input filename is required"))
      ((and overwrite output) (usage "output filename cannot be given with --overwrite"))
      ((not (or overwrite output)) (usage "output filename is required without --overwrite")))
-    (process-statement input (or output input))))
+    (process-statement (assoc-ref profiles profile) input (or output input))))