From 40d24a500b6a9062122147be332a41fe48a8371a Mon Sep 17 00:00:00 2001
From: Yuchen Pei <id@ypei.org>
Date: Sun, 15 Oct 2023 00:18:54 +1100
Subject: Unify emacs packages with webapps: use bom as an example

Emacs commands:

bom; bom-state

Paths in webapps:

/bom; /bom-state/<state>

Next step: generalise the transformation with macros etc.
---
 bom.el | 105 +++++++++++++++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 89 insertions(+), 16 deletions(-)

(limited to 'bom.el')

diff --git a/bom.el b/bom.el
index 06b9784..d70226d 100644
--- a/bom.el
+++ b/bom.el
@@ -125,25 +125,62 @@ Used as parentfn for hierarchy."
     ""))
 
 (defun bom-format-areas-org (areas)
-  "Format hierarchy of AREAS with forecasts.
+  "Format hierarchy of AREAS with forecasts into an org string.
 
-We use the description of the first root as the state name."
+We use the description of the first root as the state name.
+
+The org string is ready to be inserted into an empty buffer for
+display or export."
   (let ((state-name (dom-attr (car (hierarchy-roots areas)) 'description)))
-    (format "#+title: %s weather forecast\n\n%s"
+    (format "#+title: %s weather forecast
+
+[[elisp:(bom)][Back]]
+
+%s"
             state-name
             (string-join
              (hierarchy-map 'bom-format-area areas 1)
              "\n"))))
 
+(defun bom-to-path (sexp)
+  "Given an SEXP, return the corresponding path.
+
+For example, (foo \"bar\" \"baz\") is converted to /foo/bar/baz."
+  (pcase-let ((`(,func . ,args) (read sexp)))
+    (unless (and (symbolp func)
+                 (memq func '(bom bom-state))
+                 (every 'stringp args))
+      (user-error "Invalid sexp: %s" sexp))
+    (format "/%s"
+            (string-join (cons (format "%s" func) args) "/"))))
+
+(defun bom-elisp-link-export (link desc format)
+  "An :export function for elisp: links.
+
+Takes a LINK with description DESC, assuming FORMAT is html,
+output the http path."
+  (cl-assert (eq format 'html))
+  (format "<a href=\"%s\">%s</a>"
+          (bom-to-path link)
+          (or desc link)))
+
 (defun bom-org-to-html (s)
   "Export org string S to html and return the html string."
   (with-temp-buffer
     (insert s)
-    (let ((org-html-postamble))
-      (org-export-as 'html))))
+    (let ((org-html-postamble)
+          (org-link-parameters
+           (cons '("elisp" :export bom-elisp-link-export)
+                 org-link-parameters)))
+      (let ((result
+             (org-export-as 'html)))
+        (pop org-link-parameters)
+        result))))
 
 (defun bom-format-areas-html (areas)
-  "Format hierarchy of AREAS with forecasts to html."
+  "Format hierarchy of AREAS with forecasts to an html string.
+
+The html string can be sent as a web server response."
   (bom-org-to-html (bom-format-areas-org areas)))
 
 (defun bom-get-forecasts (state)
@@ -156,26 +193,62 @@ We use the description of the first root as the state name."
     (hierarchy-sort areas 'bom-area-lessp)
     areas))
 
-(defun bom-format-state-lists-org ()
+(defun bom-state-org (state)
+  (bom-format-areas-org
+   (bom-get-forecasts state)))
+
+(defun bom-org ()
+  "Format the \"landing page\" org string.
+
+The string is ready for display or export."
   (format
-   "#+title: Australia weather forecast\n%s"
+   "#+title: Australia weather forecast
+
+%s"
    (mapconcat
-    (lambda (pair) (format "[[file:%s][%s]]"
+    (lambda (pair) (format "[[elisp:(bom-state \"%s\")][%s]]"
                            (car pair)
                            (upcase (format "%s" (car pair)))))
     bom-state-files
     " ")))
 
-(defun bom-format-state-lists-html ()
-  (bom-org-to-html (bom-format-state-lists-org)))
+;;;###autoload
+(defun bom-state (state)
+  "Open bom forecast for STATE."
+  (interactive "sState: ")
+  (with-current-buffer (get-buffer-create "*bom*")
+    (erase-buffer)
+    (insert (bom-states-org state))
+    (goto-char (point-min))
+    (org-mode))
+  (display-buffer "*bom*"))
+
+;;;###autoload
+(defun bom ()
+  "Entrypoint - open bom landing page."
+  (interactive)
+  (with-current-buffer (get-buffer-create "*bom*")
+    (erase-buffer)
+    (insert (bom-org))
+    (goto-char (point-min))
+    (org-mode))
+  (display-buffer "*bom*"))
+
+(defun bom-from-path (path)
+  "Translate a GET PATH to a pair of function and string args.
+
+For example, if path is /foo/bar/baz, then we return
+(foo . (\"bar\" \"baz\"))"
+  (unless (string-prefix-p "/" path)
+    (user-error "Invalid path: %s" path))
+  (pcase-let ((`(,func-name . ,args) (cdr (split-string path "/"))))
+    (unless (memq (intern func-name) '(bom bom-state))
+      (user-error "Invalid path: %s" path))
+    (cons (intern (format "%s-org" func-name)) args)))
 
 (defun bom-serve (path)
   "Serve based on PATH."
-  (setq path (substring path 1))
-  (if (string-empty-p path)
-      (bom-format-state-lists-html)
-    (bom-format-areas-html
-     (bom-get-forecasts path))))
+  (bom-org-to-html (apply (bom-from-path path))))
 
 ;;;###autoload
 (defun bom-start ()
-- 
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