fish: Add fish prompt for customization

Signed-off-by: Nicholas Mello <nick@nmello.dev>

fish/functions/fish_prompt.fish

@@ -0,0 +1,64 @@
+function fish_prompt
+    set -l last_status $status
+    set -l cwd (prompt_pwd)
+    set -l jobs_count (count (jobs -p))
+
+    # --- Base path ---
+    set_color cyan
+    echo -n $cwd
+
+    # --- Git Info ---
+    if command -sq git
+        if git rev-parse --is-inside-work-tree >/dev/null 2>&1
+            set -l branch (git symbolic-ref --short HEAD 2>/dev/null; or git rev-parse --short HEAD)
+
+            # Ahead / behind vs upstream
+            set -l ahead 0
+            set -l behind 0
+            set -l counts (git rev-list --left-right --count @{upstream}...HEAD 2>/dev/null)
+
+            if test -n "$counts"
+                set behind (echo $counts | awk '{print $1}')
+                set ahead (echo $counts | awk '{print $2}')
+            end
+
+            # Dirty working tree?
+            git diff --quiet --ignore-submodules HEAD >/dev/null 2>&1
+            or set -l dirty "*"
+
+            set_color magenta
+            echo -n " ["$branch
+
+            if test $ahead -gt 0
+                echo -n " ↑$ahead"
+            end
+
+            if test $behind -gt 0
+                echo -n " ↓$behind"
+            end
+
+            if test -n "$dirty"
+                echo -n " $dirty"
+            end
+
+            echo -n "]"
+        end
+    end
+
+    if test $jobs_count -gt 0
+        set_color yellow
+        echo -n " [$jobs_count jobs]"
+        set_color normal
+    end
+
+    # --- Exit status ---
+    if test $last_status -ne 0
+        set_color red
+        echo -n " [$last_status]"
+    end
+
+    # --- Final prompt character ---
+    set_color green
+    echo -n "> "
+    set_color normal
+end