Make better preview displays in terminals (#758)

* Implement markdown renderer for terminal
* Implement preview command for file|mime types
* Introduce preview command into walk command
* Drop to support KDL for now
* Replace renmark with mdcat in preview command to support darwin
* I might add poppler in another PR for yazi PDF preview

flake.nix

@@ -132,6 +132,8 @@
               "nix-hash-url"
               "trim-github-user-prefix-for-reponame"
               "gredit"
+              "renmark"
+              "preview"
             ]
           )
           ++ [

home-manager/packages.nix

@@ -61,6 +61,7 @@ with pkgs;
   edge-pkgs.jnv # interactive jq - Use unstable because it is a fresh tool
   ripgrep # `rg`
   bat # alt cat
+  mdcat # pipe friendly markdown viewer rather than glow
   hexyl # hex viewer
   dysk # alt df
   fd # alt find
@@ -129,6 +130,7 @@ with pkgs;
   archive-home-files
   prs
   gredit
+  preview
 ])
 ++ (lib.optionals stdenv.isLinux [
   # Fix missing locales as `locale: Cannot set LC_CTYPE to default locale`
@@ -146,6 +148,8 @@ with pkgs;
   # Do not install in dawin yet: https://github.com/NixOS/nixpkgs/blob/b4b293ec6c61e846d69224ea0637411283e2ad39/pkgs/by-name/ch/chawan/package.nix#L82
   # Keybindigs: https://git.sr.ht/~bptato/chawan/tree/master/item/res/config.toml
   chawan # `cha`
+
+  homemade-pkgs.renmark # Depend on chawan
 ])
 ++ (lib.optionals stdenv.isDarwin [
   # https://github.com/NixOS/nixpkgs/issues/240819

pkgs/default.nix

@@ -70,4 +70,6 @@
 
   gredit = pkgs.callPackage ./gredit { };
   git-resolve-conflict = pkgs.callPackage ./git-resolve-conflict { };
+  renmark = pkgs.callPackage ./renmark { };
+  preview = pkgs.callPackage ./preview { };
 }

pkgs/preview/default.nix

@@ -0,0 +1,25 @@
+{ pkgs, ... }:
+pkgs.writeShellApplication rec {
+  name = "preview";
+  text = builtins.readFile ./${name}.bash;
+  # TODO: Support KDL highlight
+  # - bat does not support KDL, however TUI editors with pipe is not to be easy handled
+  # - Helix does not have readonly mode and the KDL highlighting is not correct
+  #   https://github.com/helix-editor/helix/discussions/9245
+  # - micro https://github.com/kachick/micro-kdl
+  # - vim https://github.com/imsnif/kdl.vim
+  runtimeInputs =
+    (with pkgs; [
+      file # Detect file/mime type
+      coreutils # For `basename`
+      bat # code
+      hexyl # binary
+      # libsixel
+      mdcat # markdown - Avoid renmark to keep compatibility in darwin
+    ])
+    ++ [
+      (import ../la { inherit pkgs; }) # directory
+    ];
+  # Especially provided for fzf: https://github.com/junegunn/fzf/issues/2855#issuecomment-1164015794
+  meta.description = "Run preview commands that are suitable for the file type";
+}

pkgs/preview/preview.bash

@@ -0,0 +1,33 @@
+path="$1"
+filename=$(basename -- "$path")
+extension="${filename##*.}"
+
+case "$(file --dereference --brief --mime-type "$path")" in
+text/html)
+	cha "$path"
+	;;
+text/*)
+	case "$extension" in
+	md | markdown)
+		mdcat "$path"
+		;;
+	*)
+		bat --color=always "$path"
+		;;
+	esac
+	;;
+inode/directory)
+	la "$path"
+	;;
+application/x-executable)
+	hexyl "$path"
+	;;
+# image/*)
+# # TODO: Support images/PDF after using sixel supported terminals for main. Alacritty isn't
+# # https://github.com/alacritty/alacritty/issues/910
+# 	img2sixel "$path"
+# 	;;
+*)
+	bat --color=always "$path"
+	;;
+esac

pkgs/renmark/default.nix

@@ -0,0 +1,14 @@
+{ pkgs, ... }:
+pkgs.writeShellApplication rec {
+  name = "renmark";
+  text = builtins.readFile ./${name}.bash;
+  # Old candidates
+  # - glow, pandoc, inlyne, chawan built-in markdown renderer, mdcat, gh-markdown-preview, Lynx, w3m
+  #
+  # After several candidates, I think this combination is the best for now.
+  runtimeInputs = with pkgs; [
+    chawan
+    comrak
+  ];
+  meta.description = "RENder MARkdown in terminal. See GH-740";
+}

pkgs/renmark/renmark.bash

@@ -0,0 +1 @@
+comrak "$@" | cha --type 'text/html'

pkgs/walk/default.nix

@@ -2,9 +2,10 @@
 pkgs.writeShellApplication rec {
   name = "walk";
   text = builtins.readFile ./${name}.bash;
-  runtimeInputs = with pkgs; [
-    fzf
-    fd
-    bat
-  ];
+  runtimeInputs =
+    (with pkgs; [
+      fzf
+      fd
+    ])
+    ++ [ (import ../preview { inherit pkgs; }) ];
 }

pkgs/walk/walk.bash

@@ -10,4 +10,4 @@ fi
 
 # shellcheck disable=SC2016
 fd --type f --hidden --follow --exclude .git . "$@" |
-	fzf --query "$query" --preview 'bat --color=always {}' --preview-window '~3' --bind 'enter:become(command "$EDITOR" {})'
+	fzf --query "$query" --preview 'preview {}' --preview-window '~3' --bind 'enter:become(command "$EDITOR" {})'