From 2157ead39273691013c38529b14953ea839c2a58 Mon Sep 17 00:00:00 2001
From: Yuchen Pei <id@ypei.org>
Date: Mon, 21 Aug 2023 22:40:09 +1000
Subject: Adding transformers.

Transformers convert from one type to another, thus generalises web
search engines.

Example: a function returning a url for a git commit hash is a
query-to-url transformer
---
 hmm.el | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 63 insertions(+), 14 deletions(-)

diff --git a/hmm.el b/hmm.el
index f3cd7e0..25ca4a0 100644
--- a/hmm.el
+++ b/hmm.el
@@ -52,6 +52,12 @@
      (:command hmm-file-mime-type)))
   "hmm handlers.")
 
+(defvar hmm-transformers
+  nil
+  "hmm transformers.
+
+Transforms from one type to another type.")
+
 (defvar hmm-external-handlers
   '((:name mpv
            :external-command "mpv %U"
@@ -90,18 +96,44 @@
     ((expand-file-name default-directory) . hmm-file))
   "Matchers for 'hmm-thing-at-point'.")
 
-(defmacro hmm-define-web-search-engine (engine browser)
+(defmacro hmm-define-web-search-engine (engine)
+  "Defines a simple transformer from a search engine.
+
+A search engine is basically a format string with one single %s
+to be substitutes by the search query."
   (let* ((engine-name (plist-get engine :name))
-         (browser-name (plist-get browser :name))
          (function-name (intern
-                         (format "hmm-search-%s-%s" engine-name browser-name))))
+                         (format "hmm-%s-format-url" engine-name))))
     `(progn
        (defun ,function-name (query)
-         ,(format "Search %s in %s." engine-name browser-name)
-         (interactive ,(format "sSearch %s in %s for: " engine-name browser-name))
-         (,(plist-get browser :command)
-          (format ,(plist-get engine :format) query)))
-       (hmm-add-handler '(:command ,function-name) :query))))
+         ,(format "Format %s url from QUERY." engine-name)
+         (format ,(plist-get engine :format) query))
+       (hmm-add-transformer
+        '( :function ,function-name :name ,engine-name
+           :from :query :to :url)))))
+
+;; TODO: Validate the output type of the transformer agrees with the
+;; input type of the handler.
+(defmacro hmm-define-compound-handler (transformer handler)
+  "Define a compound handler that feeds the output of TRANSFORMER into HANDLER.
+
+Say transformer is ddg (query->url) and handler is firefox (url),
+then the resulting function is hmm-ddg-firefox, which takes a
+input and open the ddg search url in firefox."
+  (when-let* ((trans-name (or (plist-get transformer :name)
+                              (plist-get transformer :function)))
+              (handler-name (plist-get handler :name))
+              (function-name (intern
+                              (format "hmm-%s-%s" trans-name handler-name)))
+              (from (plist-get transformer :from)))
+    `(progn
+       (defun ,function-name (input)
+         ,(format "Handle the output of %s with %s."
+                  trans-name handler-name)
+         (interactive ,(format "sHandle %s with %s for: " trans-name handler-name))
+         (,(plist-get handler :command)
+          (,(plist-get transformer :function) input)))
+       (hmm-add-handler '(:command ,function-name) ,from))))
 
 (defmacro hmm-define-external-handler (handler type)
   (let* ((name (plist-get handler :name))
@@ -142,7 +174,15 @@
 (defun hmm-add-handler (handler handling)
   (let ((handlers (plist-get hmm-handlers handling)))
     (cl-pushnew handler handlers)
-    (plist-put hmm-handlers handling handlers)))
+    (setq hmm-handlers (plist-put hmm-handlers handling handlers))))
+
+(defun hmm-add-transformer (transformer)
+  (let* ((sig (intern (format "%s->%s"
+                              (plist-get transformer :from)
+                              (plist-get transformer :to))))
+         (transformers (plist-get hmm-transformers sig)))
+    (cl-pushnew transformer transformers)
+    (setq hmm-transformers (plist-put hmm-transformers sig transformers))))
 
 (defun hmm-thing-in-region (from to)
   (interactive "r")
@@ -211,7 +251,7 @@
         (and
          (hmm-thing-match thing type handler)
          (or (null (plist-get handler :mimetypes))
-             (member mimetype 
+             (member mimetype
                      (plist-get handler :mimetypes)))))
       (plist-get hmm-handlers type)))))
 
@@ -240,8 +280,7 @@
 (defun hmm-update-handlers ()
   (interactive)
   (dolist (engine hmm-web-search-engines)
-    (dolist (browser hmm-web-browsers)
-      (eval `(hmm-define-web-search-engine ,engine ,browser))))
+    (eval `(hmm-define-web-search-engine ,engine)))
   (dolist (xdg-handler (hmm-get-xdg-handlers))
     (eval `(hmm-define-external-handler ,xdg-handler :file)))
   (dolist (handler hmm-external-handlers)
@@ -249,14 +288,24 @@
   (dolist (browser hmm-web-browsers)
     (hmm-add-handler
      (list :command (plist-get browser :command)
+           :name (plist-get browser :name)
            :schemes (list "http" "https"))
-     :url)))
+     :url))
+  (print (length  (plist-get hmm-transformers :query->:url)))
+  (print (length  (plist-get hmm-handlers :url)))
+  (let ((pairs))
+    (dolist (transformer (plist-get hmm-transformers :query->:url))
+      (dolist (handler (plist-get hmm-handlers :url))
+        (pushnew (cons transformer handler) pairs)))
+    (dolist (pair pairs)
+      (eval `(hmm-define-compound-handler ,(car pair) ,(cdr pair)))))
+  )
 
 (defun hmm-update ()
   (interactive)
   (hmm-update-handlers)
   (hmm-define-hmm-thing-at-point)
-  (message "Updated."))
+  (message "hmm: updated."))
 
 (defun hmm-get-xdg-handlers ()
   (seq-filter
-- 
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