From 25b2858452df8935fa8d6b80264236c7bcfe5c50 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@hornquist.se>
Date: Wed, 24 Oct 2018 16:55:19 +0200
Subject: Adding cache.

---
 parse.scm | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 67 insertions(+), 9 deletions(-)

diff --git a/parse.scm b/parse.scm
index c17da40..33f0e72 100755
--- a/parse.scm
+++ b/parse.scm
@@ -9,14 +9,20 @@
 (use-modules (srfi srfi-1)
              (srfi srfi-8)
              (srfi srfi-9)
+             (srfi srfi-9 gnu)
              (srfi srfi-26)
 
              (ice-9 rdelim)
              (ice-9 peg)
+             (ice-9 popen)
 
              (patterns)
              (macros arrow))
 
+(define (md5-file file)
+  (-> (string-append "md5sum " file)
+      open-input-pipe
+      read))
 
 ;; var is the field to test
 ;; symb is the expected value
@@ -66,13 +72,19 @@ otherwise return the full list"
        tree))
 
 (define-record-type csv
-  (make-csv data)
+  (make-csv data
+            input-file input-hash
+            cache-hash)
   csv?
-  (data get-data))
+  (data get-data)
+  (input-file get-file)
+  (input-hash get-hash)
+  (cache-hash get-cache-hash))
 
-(use-modules (srfi srfi-9 gnu))
 (define (csv-printer record port)
-  (format port "#<csv data ...>"))
+  (format port "#<csv file: ~s, hash ~s, data ...>"
+          (get-file record)
+          (symbol->string (get-hash record))))
 (set-record-type-printer! csv csv-printer)
 
 (define (tree->vector tree)
@@ -82,12 +94,58 @@ otherwise return the full list"
      ;; TODO this assoc list ought to be a hash map
      (map (cut map cons fields <>) data))))
 
-;;; This creates some form of weird object 
-(define (load-csv filename)
-  (-> (call-with-input-file filename read-csv)
+;;; Primitive load csv
+(define (load-csv port)
+  (-> port
+      read-csv
       clean-peg-tree
-      tree->vector
-      make-csv))
+      tree->vector))
+
+(define (get-cache-file csv-file)
+  (let ((path-word (string-join (string-split csv-file #\/)
+                                "%")))
+    (string-append (getenv "HOME")
+                   "/.cache/csv-cache/" path-word)))
+
+(define (write-cache csv-file csv-hash cache-hash)
+  (with-output-to-file (string-append (get-cache-file csv-file) ".status")
+    (lambda ()
+      (write (list csv-hash cache-hash)))))
+
+;;; TODO rewrite this 
+(define (load-csv* filename)
+  "Loads the csv file from disk, or from cache"
+  (let* ((cache-file (get-cache-file filename))
+         (cache-status-file (string-append cache-file ".status"))
+         (cache-status (if (file-exists? cache-status-file)
+                           (call-with-input-file cache-status-file read)
+                           (list '#{0}# '#{0}#)))
+         (csv-sum-expected (list-ref cache-status 0))
+         (cache-sum-expected (list-ref cache-status 1))
+         (csv-sum (md5-file filename))
+         (cache-sum (md5-file cache-file)))
+    (cond ((not (eqv? csv-sum csv-sum-expected))
+           ;; file changed, rebuild cache
+           (display "file changed, rebuild cache\n")
+           (let ((data (call-with-input-file filename load-csv)))
+             (write data (open-output-file cache-file))
+             (write-cache filename csv-sum cache-sum)
+             (make-csv data filename csv-sum cache-sum))
+           )
+          ((eqv? cache-sum cache-sum-expected)
+           ;; use cache
+           (display "use cache\n")
+           (make-csv (call-with-input-file cache-file read)
+                     filename
+                     csv-sum cache-sum)
+           )
+          (else ; rebuild cache
+           (display "rebuild cache\n")
+           (let ((data (call-with-input-file filename load-csv)))
+             (write data (open-output-file cache-file))
+             (write-cache filename csv-sum cache-sum)
+             (make-csv data filename csv-sum cache-sum))
+           ))))
 
 (define-syntax-rule (ensure-csv csv)
  (unless (csv? csv)
-- 
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