;;; test-music-config--append-track-to-m3u-file.el --- Tests for appending tracks to M3U files -*- coding: utf-8; lexical-binding: t; -*-
;;
;; Author: Craig Jennings <c@cjennings.net>
;;
;;; Commentary:
;; Unit tests for cj/music--append-track-to-m3u-file function.
;; Tests the pure, deterministic helper that appends track paths to M3U files.
;;
;; Test organization:
;; - Normal Cases: Standard append operations
;; - Boundary Cases: Edge conditions (unicode, long paths, special chars)
;; - Error Cases: File errors (missing, read-only, directory instead of file)
;;
;;; Code:

(require 'ert)
(require 'testutil-general)

;; Stub missing dependencies before loading music-config
(defvar-keymap cj/custom-keymap
  :doc "Stub keymap for testing")

;; Load production code
(require 'music-config)

;;; Setup & Teardown

(defun test-music-config--append-track-to-m3u-file-setup ()
  "Setup test environment."
  (cj/create-test-base-dir))

(defun test-music-config--append-track-to-m3u-file-teardown ()
  "Clean up test environment."
  (cj/delete-test-base-dir))

;;; Normal Cases

(ert-deftest test-music-config--append-track-to-m3u-file-normal-empty-file-appends-track ()
  "Append to brand new empty M3U file."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((cj/music-root (cj/create-test-base-dir))
             (m3u-file (cj/create-temp-test-file "test-playlist-"))
             (track-path (expand-file-name "artist/song.mp3" cj/music-root))
             (expected-relative "artist/song.mp3"))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (should (string= (buffer-string) (concat expected-relative "\n")))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-normal-existing-with-newline-appends-track ()
  "Append to file with existing content ending with newline."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((existing-content "first.mp3\n")
             (cj/music-root (cj/create-test-base-dir))
             (m3u-file (cj/create-temp-test-file-with-content existing-content "test-playlist-"))
             (track-path (expand-file-name "second.mp3" cj/music-root))
             (expected-relative "second.mp3"))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (should (string= (buffer-string)
                          (concat existing-content expected-relative "\n")))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-normal-existing-without-newline-appends-track ()
  "Append to file without trailing newline adds leading newline."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((existing-content "first.mp3")
             (cj/music-root (cj/create-test-base-dir))
             (m3u-file (cj/create-temp-test-file-with-content existing-content "test-playlist-"))
             (track-path (expand-file-name "second.mp3" cj/music-root))
             (expected-relative "second.mp3"))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (should (string= (buffer-string)
                          (concat existing-content "\n" expected-relative "\n")))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-normal-multiple-appends-all-succeed ()
  "Multiple appends to same file all succeed (allows duplicates)."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((cj/music-root (cj/create-test-base-dir))
             (m3u-file (cj/create-temp-test-file "test-playlist-"))
             (track1 (expand-file-name "track1.mp3" cj/music-root))
             (track2 (expand-file-name "track2.mp3" cj/music-root))
             (track1-duplicate (expand-file-name "track1.mp3" cj/music-root))
             (rel1 "track1.mp3")
             (rel2 "track2.mp3"))
        (cj/music--append-track-to-m3u-file track1 m3u-file)
        (cj/music--append-track-to-m3u-file track2 m3u-file)
        (cj/music--append-track-to-m3u-file track1-duplicate m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (let ((content (buffer-string)))
            (should (string= content
                            (concat rel1 "\n" rel2 "\n" rel1 "\n"))))))
    (test-music-config--append-track-to-m3u-file-teardown)))

;;; Normal Cases: round-trip with the reader

(ert-deftest test-music-config--append-track-to-m3u-file-normal-round-trips-through-the-reader ()
  "Normal: the same-directory case round-trips through the reader.
A positive control only.  With the playlist and the music root in one
directory both candidate bases produce the same string, so this passes
against the old writer too — the discriminating cases are the two tests
below, which put the bases at different depths."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((base (cj/create-test-base-dir))
             (cj/music-root base)
             (m3u-file (cj/create-temp-test-file "test-playlist-"))
             (track-path (expand-file-name "artist/song.mp3" base)))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (should (equal (cj/music--m3u-file-tracks m3u-file)
                       (list track-path))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-normal-round-trips-outside-the-music-root ()
  "Normal/regression: a playlist living outside `cj/music-root' round-trips.
This is the case the old writer got wrong.  It based every relative path on
`cj/music-root' wherever the playlist sat, while the reader resolved against
the playlist's directory.  Inside the music root the two coincide, which is
why the defect stayed invisible until a playlist moved out of it."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      ;; The layout mirrors the real one: playlists/ and audio/ are siblings
      ;; under mpd/, and the music root is a separate tree at a different depth.
      ;; The depth difference is load-bearing -- put the music root alongside
      ;; playlists/ instead and both bases yield the same relative path, so the
      ;; test passes against the broken writer and proves nothing.
      (let* ((base (cj/create-test-base-dir))
             (playlists (expand-file-name "mpd/playlists/" base))
             (audio (expand-file-name "mpd/audio/" base))
             (cj/music-root (expand-file-name "music/" base))
             (m3u-file (expand-file-name "ambience.m3u" playlists))
             (track-path (expand-file-name "rain-loop.mp3" audio)))
        (make-directory playlists t)
        (make-directory audio t)
        (make-directory cj/music-root t)
        (with-temp-buffer (write-file m3u-file))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (should (equal (cj/music--m3u-file-tracks m3u-file)
                       (list track-path))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-normal-under-playlist-dir-is-relative ()
  "Normal: a track under the playlist's directory is written relative to it.
The music root sits at a different depth on purpose.  Put it alongside the
playlist directory instead and both candidate bases produce the same string,
so the assertion would hold against a writer using either one."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((base (cj/create-test-base-dir))
             (playlists (expand-file-name "mpd/playlists/" base))
             (cj/music-root (expand-file-name "music/" base))
             (m3u-file (expand-file-name "album.m3u" playlists))
             (track-path (expand-file-name "sub/song.mp3" playlists)))
        (make-directory (expand-file-name "sub/" playlists) t)
        (make-directory cj/music-root t)
        (with-temp-buffer (write-file m3u-file))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (should (string= (buffer-string) "sub/song.mp3\n")))
        (should (equal (cj/music--m3u-file-tracks m3u-file) (list track-path))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-normal-sibling-dir-is-absolute ()
  "Normal: a track outside the playlist's directory is written absolute.
A sibling would otherwise come out as \"../audio/x.mp3\".  Absolute is the
convention for cross-tree references here, and it survives the playlist being
moved again later, which a ../ chain does not."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((base (cj/create-test-base-dir))
             (playlists (expand-file-name "mpd/playlists/" base))
             (audio (expand-file-name "mpd/audio/" base))
             (cj/music-root (expand-file-name "music/" base))
             (m3u-file (expand-file-name "ambience.m3u" playlists))
             (track-path (expand-file-name "rain-loop.mp3" audio)))
        (make-directory playlists t)
        (make-directory audio t)
        (make-directory cj/music-root t)
        (with-temp-buffer (write-file m3u-file))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (should (string= (buffer-string) (concat track-path "\n"))))
        (should (equal (cj/music--m3u-file-tracks m3u-file) (list track-path))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-normal-deep-parent-chain-goes-absolute ()
  "Normal: a track several levels away is written absolute, not as a ../ chain.
This is the case the absolute fallback exists for.  A four-level chain is
unreadable and breaks the moment the playlist moves, so distance from the
playlist is exactly when an absolute path earns its keep."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((base (cj/create-test-base-dir))
             (playlists (expand-file-name "a/b/c/playlists/" base))
             (cj/music-root (expand-file-name "music/" base))
             (m3u-file (expand-file-name "deep.m3u" playlists))
             (track-path (expand-file-name "faraway/song.mp3" base)))
        (make-directory playlists t)
        (make-directory (expand-file-name "faraway/" base) t)
        (make-directory cj/music-root t)
        (with-temp-buffer (write-file m3u-file))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          ;; Four hops up (playlists -> c -> b -> a -> base) would be the
          ;; relative form; the writer declines it and emits the absolute path.
          (should (string= (buffer-string) (concat track-path "\n"))))
        (should (equal (cj/music--m3u-file-tracks m3u-file)
                       (list track-path))))
    (test-music-config--append-track-to-m3u-file-teardown)))

;;; Boundary Cases

(ert-deftest test-music-config--append-track-to-m3u-file-boundary-dotdot-named-dir-stays-relative ()
  "Boundary: a directory whose name merely begins with two dots stays relative.
This is the input the relative-vs-absolute test actually turns on.  The check
looks for a leading \"../\", so a real subdirectory named \"..hidden\" is under
the playlist and must not be mistaken for an escape.  Loosening the check to
\"..\" would break exactly this case and nothing else in the suite would catch
it."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((base (cj/create-test-base-dir))
             (playlists (expand-file-name "mpd/playlists/" base))
             (cj/music-root (expand-file-name "music/" base))
             (m3u-file (expand-file-name "p.m3u" playlists))
             (track-path (expand-file-name "..hidden/song.mp3" playlists)))
        (make-directory (expand-file-name "..hidden/" playlists) t)
        (make-directory cj/music-root t)
        (with-temp-buffer (write-file m3u-file))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (should (string= (buffer-string) "..hidden/song.mp3\n")))
        (should (equal (cj/music--m3u-file-tracks m3u-file) (list track-path))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-boundary-very-long-path-appends-successfully ()
  "Append very long track path without truncation."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((cj/music-root (cj/create-test-base-dir))
             (m3u-file (cj/create-temp-test-file "test-playlist-"))
             ;; Create a relative path that's ~450 chars long
             (relative-path (concat (make-string 440 ?a) "/song.mp3"))
             (track-path (expand-file-name relative-path cj/music-root)))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (should (string= (buffer-string) (concat relative-path "\n")))
          (should (= (length (buffer-string)) (1+ (length relative-path))))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-boundary-path-with-unicode-appends-successfully ()
  "Append path with unicode characters preserves UTF-8 encoding."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((cj/music-root (cj/create-test-base-dir))
             (m3u-file (cj/create-temp-test-file "test-playlist-"))
             (relative-path "中文/artist-名前/song🎵.mp3")
             (track-path (expand-file-name relative-path cj/music-root)))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (should (string= (buffer-string) (concat relative-path "\n")))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-boundary-path-with-spaces-appends-successfully ()
  "Append path with spaces and special characters."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((cj/music-root (cj/create-test-base-dir))
             (m3u-file (cj/create-temp-test-file "test-playlist-"))
             (relative-path "Artist Name/Album (2024)/01 - Song's Title [Remix].mp3")
             (track-path (expand-file-name relative-path cj/music-root)))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (should (string= (buffer-string) (concat relative-path "\n")))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-boundary-m3u-with-comments-appends-after ()
  "Append to M3U file containing comments and metadata."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((existing-content "#EXTM3U\n#EXTINF:-1,Radio Station\nhttp://stream.url/radio\n")
             (cj/music-root (cj/create-test-base-dir))
             (m3u-file (cj/create-temp-test-file-with-content existing-content "test-playlist-"))
             (relative-path "local-track.mp3")
             (track-path (expand-file-name relative-path cj/music-root)))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (should (string= (buffer-string)
                          (concat existing-content relative-path "\n")))))
    (test-music-config--append-track-to-m3u-file-teardown)))

;;; Boundary Cases: symlinked playlists

(defun test-music-config--append--make-symlinked-playlist (base content link-depth)
  "Create a playlist whose deployed path is a symlink, and return that path.
CONTENT is written to the real file.  LINK-DEPTH controls how long the link
string is, which is the whole point: `file-attributes' does not follow
symlinks, so a writer sizing the file that way reads the length of the link
rather than the content."
  (let* ((deployed (expand-file-name "deployed/" base))
         (deep (expand-file-name (mapconcat #'identity
                                            (make-list link-depth "longdirname")
                                            "/")
                                 base))
         (real (expand-file-name "p.m3u" deep))
         (link (expand-file-name "p.m3u" deployed)))
    (make-directory deep t)
    (make-directory deployed t)
    (with-temp-buffer (insert content) (write-file real))
    (make-symbolic-link (file-relative-name real deployed) link t)
    link))

(ert-deftest test-music-config--append-track-to-m3u-file-boundary-symlink-longer-than-content ()
  "Boundary: appending to a symlinked playlist whose link string is longer than
its content must not signal.  Sizing the file with `file-attributes' returns
the link's length, so the read range falls outside the file, nothing is
inserted, and `char-after' hands nil to a numeric comparison.  Measured on the
real deployed set: 31 of 100 symlinked playlists are in this state."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((base (cj/create-test-base-dir))
             (m3u-file (test-music-config--append--make-symlinked-playlist
                        base "https://example.com/s.mp3\n" 8))
             (track-path (expand-file-name "song.mp3" (file-name-directory m3u-file))))
        (should (> (file-attribute-size (file-attributes m3u-file))
                   (file-attribute-size (file-attributes (file-truename m3u-file)))))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        ;; The seeded line is a stream URL, which the reader passes through, so
        ;; both entries come back.
        (should (equal (cj/music--m3u-file-tracks m3u-file)
                       (list "https://example.com/s.mp3" track-path))))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-boundary-symlink-no-spurious-blank-line ()
  "Boundary: a symlinked playlist already ending in a newline gains no blank line.
The trailing-newline probe reads a byte chosen from the wrong size, so it
misreads a terminated file as unterminated and prepends a newline.  All 100
symlinked playlists in the deployed set read the wrong byte this way."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      ;; Content deliberately longer than the link string, so the misread byte
      ;; still lands inside the file.  That separates this from the sibling test
      ;; above: here the probe reads a valid but wrong byte and silently
      ;; misjudges, rather than reading past the end and signalling.
      (let* ((base (cj/create-test-base-dir))
             (content (mapconcat (lambda (i) (format "track-%03d-with-a-longish-name.mp3" i))
                                 (number-sequence 1 12) "\n"))
             (m3u-file (test-music-config--append--make-symlinked-playlist
                        base (concat content "\n") 2))
             (track-path (expand-file-name "second.mp3" (file-name-directory m3u-file))))
        (should (< (file-attribute-size (file-attributes m3u-file))
                   (file-attribute-size (file-attributes (file-truename m3u-file)))))
        (cj/music--append-track-to-m3u-file track-path m3u-file)
        (with-temp-buffer
          (insert-file-contents m3u-file)
          (should (string= (buffer-string) (concat content "\nsecond.mp3\n")))))
    (test-music-config--append-track-to-m3u-file-teardown)))

;;; Error Cases

(ert-deftest test-music-config--append-track-to-m3u-file-error-nonexistent-file-signals-error ()
  "Signal error when M3U file doesn't exist."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((m3u-file "/nonexistent/path/to/playlist.m3u")
             (track-path "/home/user/music/song.mp3"))
        (should-error (cj/music--append-track-to-m3u-file track-path m3u-file)
                     :type 'error))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-error-readonly-file-signals-error ()
  "Signal error when M3U file is read-only."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      ;; No `cj/music-root' rebinding here: the writable-p guard signals before
      ;; any path computation runs, so binding it would imply a dependency the
      ;; read-only path does not have.
      (let* ((m3u-file (cj/create-temp-test-file "test-playlist-"))
             (track-path "/home/user/music/song.mp3"))
        ;; Make file read-only
        (set-file-modes m3u-file #o444)
        (should-error (cj/music--append-track-to-m3u-file track-path m3u-file)
                     :type 'error))
    (test-music-config--append-track-to-m3u-file-teardown)))

(ert-deftest test-music-config--append-track-to-m3u-file-error-directory-not-file-signals-error ()
  "Signal error when path points to directory instead of file."
  (test-music-config--append-track-to-m3u-file-setup)
  (unwind-protect
      (let* ((m3u-dir (cj/create-test-subdirectory "test-playlist-dir"))
             (track-path "/home/user/music/song.mp3"))
        (should-error (cj/music--append-track-to-m3u-file track-path m3u-dir)
                     :type 'error))
    (test-music-config--append-track-to-m3u-file-teardown)))

(provide 'test-music-config--append-track-to-m3u-file)
;;; test-music-config--append-track-to-m3u-file.el ends here