✨ Allow to compose songs with vocals only if band has vocalist

src/Duets.Cli/Components/Commands/RehearsalRoom/ComposeSong.Command.fs

@@ -38,11 +38,25 @@ module ComposeSongCommand =
             (showLengthError >> fun _ -> promptForLength name)
 
     and private promptForVocalStyle name length =
+        let hasVocalist =
+            Queries.Bands.currentBandHasAnyMemberWithRole (State.get ()) Vocals
+
+        if not hasVocalist then
+            "To compose songs with vocals, you need to have a vocalist in your band. You can hire a new member from the rehearsal room."
+            |> Styles.hint
+            |> showMessage
+
+        let vocalStyles =
+            if hasVocalist then
+                Data.VocalStyles.allNames
+            else
+                [ (Instrumental, Instrumental.ToString()) ]
+
         let vocalStyle =
             showChoicePrompt
                 Rehearsal.composeSongVocalStylePrompt
                 snd
-                Data.VocalStyles.allNames
+                vocalStyles
             |> fst
 
         Song.from name length vocalStyle |> composeWithProgressbar

src/Duets.Simulation/Queries/Bands.fs

@@ -104,3 +104,12 @@ module Bands =
             Lenses.State.bands_ >-> Lenses.Bands.simulatedBands_
 
         Optic.get simulatedLens_ state
+
+    /// Returns whether the given band has any member with the given role.
+    let hasAnyMemberWithRole (band: Band) (role: InstrumentType) =
+        band.Members |> List.exists (fun bandMember -> bandMember.Role = role)
+
+    /// Returns whether the current band has any member with the given role.
+    let currentBandHasAnyMemberWithRole state role =
+        let band = currentBand state
+        hasAnyMemberWithRole band role