fix: fish prompt display looks wrong in tide (prefix-dev#1424)

Fixes: prefix-dev#1407
Adapted the prompt logic from conda and made some small changes for
pixi fish shell.

The environment name is displayed on the right side per default, but can
be moved to the left like this: `set -gx CONDA_LEFT_PROMPT 1`
---------

Co-authored-by: Tim de Jager <[email protected]>

src/prompt.rs

@@ -19,10 +19,44 @@ pub fn get_zsh_hook(env_name: &str) -> String {
 /// Set default pixi prompt for the fish shell
 pub fn get_fish_prompt(env_name: &str) -> String {
     format!(
-        "functions -c fish_prompt old_fish_prompt; \
-         function fish_prompt; \
-             echo \"({})\" (old_fish_prompt); \
-         end;",
+        r#"
+        function __pixi_add_prompt
+            set_color -o green
+            echo -n "({}) "
+            set_color normal
+        end
+
+        if not functions -q __fish_prompt_orig
+            functions -c fish_prompt __fish_prompt_orig
+        end
+
+        if functions -q fish_right_prompt
+            if not functions -q __fish_right_prompt_orig
+                functions -c fish_right_prompt __fish_right_prompt_orig
+            end
+        else
+            function __fish_right_prompt_orig
+                # Placeholder function for when fish_right_prompt does not exist
+                echo ""
+            end
+        end
+
+        function fish_prompt
+            set -l last_status $status
+            if set -q PIXI_LEFT_PROMPT
+                __pixi_add_prompt
+            end
+            __fish_prompt_orig
+            return $last_status
+        end
+
+        function fish_right_prompt
+            if not set -q PIXI_LEFT_PROMPT
+                __pixi_add_prompt
+            end
+            __fish_right_prompt_orig
+        end
+        "#,
         env_name
     )
 }