From c4403522df754627d698f0806d3920764e3d1291 Mon Sep 17 00:00:00 2001
From: Yuchen Pei <hi@ypei.me>
Date: Wed, 5 Oct 2022 11:28:34 +1100
Subject: Adding ability to navigate within help buffer

---
 hcel-client.el  | 38 ++++++++++++++++++++++++++++++++++++++
 hcel-minor.el   |  4 ++--
 hcel-results.el | 17 ++++++++++-------
 hcel-utils.el   | 10 ++++++++++
 4 files changed, 60 insertions(+), 9 deletions(-)

diff --git a/hcel-client.el b/hcel-client.el
index d5f7abd..fef8bf6 100644
--- a/hcel-client.el
+++ b/hcel-client.el
@@ -159,6 +159,44 @@ Example of approximate location:
            (hcel-format-pagination-query page per-page))
    nil with-header))
 
+(defun hcel-api-global-identifier-a (package-id component-id module-name entity
+                                            name)
+  (hcel-url-fetch-json
+   (concat hcel-host "/api/globalIdentifierA/"
+           (hcel-format-package-id package-id "-") "/" component-id "/"
+           module-name "/" entity "/" name)))
+
+(defun hcel-api-global-identifier-e (package-id module-path start-line start-column
+                                                end-line end-column name)
+  (hcel-url-fetch-json
+   (concat hcel-host "/api/globalIdentifierE/"
+           (hcel-format-package-id package-id "-") "/"
+           (replace-regexp-in-string "/" "%2F" module-path) "/"
+           (number-to-string start-line) "/"
+           (number-to-string start-column) "/"
+           (number-to-string end-line) "/"
+           (number-to-string end-column) "/" name)))
+
+(defun hcel-global-identifier (location-info &optional name)
+  (let ((tag (hcel-location-tag location-info)))
+    (cond ((equal tag "ApproximateLocation")
+           (hcel-api-global-identifier-a
+            (alist-get 'packageId location-info)
+            (alist-get 'componentId location-info)
+            (alist-get 'moduleName location-info)
+            (alist-get 'entity location-info)
+            (alist-get 'name location-info)))
+          ((equal tag "ExactLocation")
+           (hcel-api-global-identifier-e
+            (alist-get 'packageId location-info)
+            (alist-get 'modulePath location-info)
+            (alist-get 'startLine location-info)
+            (alist-get 'startColumn location-info)
+            (alist-get 'endLine location-info)
+            (alist-get 'endColumn location-info)
+            name))
+          (t (error "Location info %S not supported." location-info)))))
+
 (defun hcel-api-global-references (name)
   (hcel-url-fetch-json (concat hcel-host "/api/globalReferences/" name)))
 
diff --git a/hcel-minor.el b/hcel-minor.el
index 687c596..26badbb 100644
--- a/hcel-minor.el
+++ b/hcel-minor.el
@@ -73,11 +73,11 @@
                         (buffer-substring-no-properties
                          (progn
                            (text-property-search-backward
-                            'internal-id internal-id 'string=)
+                            'internal-id internal-id 'equal)
                            (point))
                          (progn
                            (text-property-search-forward
-                            'internal-id internal-id 'string=)
+                            'internal-id internal-id 'equal)
                            (point)))))
               (docstring
                (cond ((derived-mode-p 'hcel-outline-mode)
diff --git a/hcel-results.el b/hcel-results.el
index 6cac9de..3a676b9 100644
--- a/hcel-results.el
+++ b/hcel-results.el
@@ -436,17 +436,20 @@ Start by choosing a package."
   (hcel-ids 'package query hcel-package-id))
 (define-key hcel-mode-map "i" #'hcel-package-ids)
 
-;; TODO: it is impossible with the current API to follow link within the help
-;; buffer, as definitionSite does not contain signature, and ExactLocation does
-;; not contain component name or even name
+(defun hcel-tag-span-button-help (marker)
+  (hcel-help-internal
+   (hcel-global-identifier
+    (get-text-property marker 'location-info)
+    (hcel-string-with-text-property-at-point 'location-info))))
+
 (defun hcel-help-internal (identifier)
   (help-setup-xref (list #'hcel-help-internal identifier)
                    (called-interactively-p 'interactive))
   (with-help-window (help-buffer)
-      (with-current-buffer standard-output
-        (insert
-         (hcel-ids-render-identifier
-          identifier 'hcel-tag-span-button-load-source)))))
+    (with-current-buffer standard-output
+      (insert
+       (hcel-ids-render-identifier
+        identifier 'hcel-tag-span-button-help)))))
 
 (defun hcel-help (query)
   (interactive
diff --git a/hcel-utils.el b/hcel-utils.el
index d5b75cf..be152f5 100644
--- a/hcel-utils.el
+++ b/hcel-utils.el
@@ -191,5 +191,15 @@ Example of an idSrcSpan:
   (or (get-text-property (point) prop)
       (get-text-property (max (point-min) (1- (point))) prop)))
 
+(defun hcel-string-with-text-property-at-point (prop)
+  "Find the string with property PROP at point.
+
+Does not check whether point does indeed has property PROP."
+  (save-excursion
+    (let ((beg) (end))
+      (setq end (next-single-char-property-change (point) prop))
+      (setq beg (previous-single-char-property-change end prop))
+      (buffer-substring-no-properties beg end))))
+
 (provide 'hcel-utils)
 ;;; hcel-utils.el ends here.
-- 
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