From c7693191d45cc931d8c70e56977be6f4bf3b3c0c Mon Sep 17 00:00:00 2001
From: Lucas Sta Maria <lucas@priime.dev>
Date: Sat, 23 Aug 2025 00:31:04 +0800
Subject: [PATCH] feat: add `ghpr-review-mode`

---
 ghpr-api.el    | 20 +++++++++++++++
 ghpr-review.el | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)

diff --git a/ghpr-api.el b/ghpr-api.el
index 7f67a03..41c9acf 100644
--- a/ghpr-api.el
+++ b/ghpr-api.el
@@ -75,6 +75,26 @@ Returns a list of pull request objects on success, nil on failure."
                   (message "Error fetching pull requests: %s" error-thrown)))))
     result))
 
+(defun ghpr--get-patch-content (repo-name pr-number)
+  "Retrieve the diff contents for PR-NUMBER in REPO-NAME."
+  (let ((token (ghpr--get-token))
+        (url (format "https://api.github.com/repos/%s/pulls/%s" repo-name pr-number))
+        (result nil))
+    (when token
+      (request url
+        :type "GET"
+        :headers `(("Accept" . "application/vnd.github.diff")
+                   ("Authorization" . ,(format "Bearer %s" token))
+                   ("X-GitHub-Api-Version" . "2022-11-28"))
+        :sync t
+        :success (cl-function
+                  (lambda (&key data &allow-other-keys)
+                    (setq result data)))
+        :error (cl-function
+                (lambda (&key error-thrown &allow-other-keys)
+                  (message "Error fetching diff: %s" error-thrown)))))
+    result))
+
 (provide 'ghpr-api)
 
 ;;; ghpr-api.el ends here
diff --git a/ghpr-review.el b/ghpr-review.el
index 8ef9608..169a06e 100644
--- a/ghpr-review.el
+++ b/ghpr-review.el
@@ -31,6 +31,76 @@
 
 ;;; Code:
 
+(require 'request)
+
+(require 'ghpr-api)
+(require 'ghpr-utils)
+
+(defface ghpr-review-added-line
+  '((t (:background "green" :foreground "black")))
+  "Face for added lines in PR diff."
+  :group 'ghpr)
+
+(defface ghpr-review-removed-line
+  '((t (:background "red" :foreground "black")))
+  "Face for removed lines in PR diff."
+  :group 'ghpr)
+
+(defvar ghpr-review-font-lock-keywords
+  '(("^\\(> \\+[^+]\\)\\(.*\\)$"
+     (0 'ghpr-review-added-line t))
+    ("^\\(> \\+\\)$"  ; Handle line with just "> +"
+     (0 'ghpr-review-added-line t))
+    ("^\\(> -[^-]\\)\\(.*\\)$"
+     (0 'ghpr-review-removed-line t))
+    ("^\\(> -\\)$"  ; Handle line with just "> -"
+     (0 'ghpr-review-removed-line t)))
+  "Font lock keywords for ghpr-review-mode.")
+
+(define-derived-mode ghpr-review-mode special-mode "GHPR Review"
+  "Major mode for reviewing GitHub pull requests."
+  :group 'ghpr
+  (setq truncate-lines t)
+  (setq font-lock-defaults '(ghpr-review-font-lock-keywords t nil nil nil))
+  (font-lock-ensure))
+(defun ghpr--prefix-line (line)
+  "Prefix the LINE with `> '."
+  (concat "> " line))
+
+(defun ghpr--prefix-lines (text)
+  "Prefix every line in TEXT with `> '."
+  (let ((lines (split-string text "\n")))
+    (mapconcat #'ghpr--prefix-line lines "\n")))
+
+(defun ghpr--open-pr/collect-contents (pr repo-name)
+  "Return a string of the title, body, and patch content separated by newlines."
+  (let* ((body (or (alist-get 'body pr) ""))
+         (number (alist-get 'number pr))
+         (content-parts (list (ghpr--pr-summary pr))))
+    (when (not (string-empty-p body))
+      (push body content-parts))
+    (let ((patch-content (ghpr--get-patch-content repo-name number)))
+      (when patch-content
+        (push patch-content content-parts)))
+    (mapconcat 'identity (reverse content-parts) "\n\n")))
+
+(defun ghpr--open-pr/insert-contents (pr repo-name)
+  "Insert the contents of the pr into the current buffer."
+  (erase-buffer)
+  (let ((contents (ghpr--open-pr/collect-contents pr repo-name)))
+    (insert (ghpr--prefix-lines contents))))
+
+(defun ghpr--open-pr (pr repo-name)
+  "Open a new buffer containing the body of the PR."
+  (let* ((number (alist-get 'number pr))
+         (buffer-name (format "*ghpr-pr-%s*" number))
+         (buffer (get-buffer-create buffer-name)))
+    (with-current-buffer buffer
+      (ghpr-review-mode)
+      (ghpr--open-pr/insert-contents pr repo-name)
+      (goto-char (point-min)))
+    (display-buffer buffer)))
+
 (provide 'ghpr-review)
 
 ;;; ghpr-review.el ends here