Add configurable no-prefer penalty to solver

main.go

@@ -240,13 +240,13 @@ func handleListTrips(db *sql.DB) http.HandlerFunc {
 			return
 		}
 		rows, err := db.Query(`
-			SELECT t.id, t.name, t.room_size, t.prefer_not_multiple, COALESCE(
+			SELECT t.id, t.name, t.room_size, t.prefer_not_multiple, t.no_prefer_cost, COALESCE(
 				json_agg(json_build_object('id', ta.id, 'email', ta.email)) FILTER (WHERE ta.id IS NOT NULL),
 				'[]'
 			)
 			FROM trips t
 			LEFT JOIN trip_admins ta ON ta.trip_id = t.id
-			GROUP BY t.id, t.name, t.room_size, t.prefer_not_multiple
+			GROUP BY t.id, t.name, t.room_size, t.prefer_not_multiple, t.no_prefer_cost
 			ORDER BY t.id`)
 		if err != nil {
 			http.Error(w, err.Error(), http.StatusInternalServerError)
@@ -263,6 +263,7 @@ func handleListTrips(db *sql.DB) http.HandlerFunc {
 			Name               string      `json:"name"`
 			RoomSize           int         `json:"room_size"`
 			PreferNotMultiple  int         `json:"prefer_not_multiple"`
+			NoPreferCost       int         `json:"no_prefer_cost"`
 			Admins             []tripAdmin `json:"admins"`
 		}
 
@@ -270,7 +271,7 @@ func handleListTrips(db *sql.DB) http.HandlerFunc {
 		for rows.Next() {
 			var t trip
 			var adminsJSON string
-			if err := rows.Scan(&t.ID, &t.Name, &t.RoomSize, &t.PreferNotMultiple, &adminsJSON); err != nil {
+			if err := rows.Scan(&t.ID, &t.Name, &t.RoomSize, &t.PreferNotMultiple, &t.NoPreferCost, &adminsJSON); err != nil {
 				http.Error(w, err.Error(), http.StatusInternalServerError)
 				return
 			}
@@ -389,14 +390,14 @@ func handleGetTrip(db *sql.DB) http.HandlerFunc {
 			return
 		}
 		var name string
-		var roomSize, preferNotMultiple int
+		var roomSize, preferNotMultiple, noPreferCost int
-		err := db.QueryRow("SELECT name, room_size, prefer_not_multiple FROM trips WHERE id = $1", tripID).Scan(&name, &roomSize, &preferNotMultiple)
+		err := db.QueryRow("SELECT name, room_size, prefer_not_multiple, no_prefer_cost FROM trips WHERE id = $1", tripID).Scan(&name, &roomSize, &preferNotMultiple, &noPreferCost)
 		if err != nil {
 			http.Error(w, "trip not found", http.StatusNotFound)
 			return
 		}
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]any{"id": tripID, "name": name, "room_size": roomSize, "prefer_not_multiple": preferNotMultiple})
+		json.NewEncoder(w).Encode(map[string]any{"id": tripID, "name": name, "room_size": roomSize, "prefer_not_multiple": preferNotMultiple, "no_prefer_cost": noPreferCost})
 	}
 }
 
@@ -564,6 +565,7 @@ func handleUpdateTrip(db *sql.DB) http.HandlerFunc {
 		var body struct {
 			RoomSize          *int `json:"room_size"`
 			PreferNotMultiple *int `json:"prefer_not_multiple"`
+			NoPreferCost      *int `json:"no_prefer_cost"`
 		}
 		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 			http.Error(w, "invalid request body", http.StatusBadRequest)
@@ -581,6 +583,12 @@ func handleUpdateTrip(db *sql.DB) http.HandlerFunc {
 				return
 			}
 		}
+		if body.NoPreferCost != nil {
+			if *body.NoPreferCost < 0 {
+				http.Error(w, "no_prefer_cost must be at least 0", http.StatusBadRequest)
+				return
+			}
+		}
 		if body.RoomSize != nil {
 			if _, err := db.Exec("UPDATE trips SET room_size = $1 WHERE id = $2", *body.RoomSize, tripID); err != nil {
 				http.Error(w, err.Error(), http.StatusInternalServerError)
@@ -593,6 +601,12 @@ func handleUpdateTrip(db *sql.DB) http.HandlerFunc {
 				return
 			}
 		}
+		if body.NoPreferCost != nil {
+			if _, err := db.Exec("UPDATE trips SET no_prefer_cost = $1 WHERE id = $2", *body.NoPreferCost, tripID); err != nil {
+				http.Error(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+		}
 		w.WriteHeader(http.StatusNoContent)
 	}
 }
@@ -729,8 +743,8 @@ func handleSolve(db *sql.DB) http.HandlerFunc {
 			return
 		}
 
-		var roomSize, pnMultiple int
+		var roomSize, pnMultiple, npCost int
-		err := db.QueryRow("SELECT room_size, prefer_not_multiple FROM trips WHERE id = $1", tripID).Scan(&roomSize, &pnMultiple)
+		err := db.QueryRow("SELECT room_size, prefer_not_multiple, no_prefer_cost FROM trips WHERE id = $1", tripID).Scan(&roomSize, &pnMultiple, &npCost)
 		if err != nil {
 			http.Error(w, "trip not found", http.StatusNotFound)
 			return
@@ -863,18 +877,34 @@ func handleSolve(db *sql.DB) http.HandlerFunc {
 			groups[root] = append(groups[root], i)
 		}
 
+		hasPrefer := make([]bool, n)
+		for pk, kind := range overalls {
+			if kind == "prefer" {
+				hasPrefer[idx[pk.a]] = true
+			}
+		}
+
 		score := func(assignment []int) int {
 			s := 0
+			gotPrefer := make([]bool, n)
 			for pk, kind := range overalls {
 				ai, bi := idx[pk.a], idx[pk.b]
 				sameRoom := assignment[ai] == assignment[bi]
 				switch kind {
 				case "prefer":
-					if sameRoom { s++ }
+					if sameRoom {
+						s++
+						gotPrefer[ai] = true
+					}
 				case "prefer_not":
 					if sameRoom { s -= pnMultiple }
 				}
 			}
+			for i := 0; i < n; i++ {
+				if hasPrefer[i] && !gotPrefer[i] {
+					s -= npCost
+				}
+			}
 			return s
 		}
 

schema.sql

@@ -12,7 +12,8 @@ CREATE TABLE IF NOT EXISTS trips (
     id BIGSERIAL PRIMARY KEY,
     name TEXT NOT NULL,
     room_size INTEGER NOT NULL DEFAULT 2,
-    prefer_not_multiple INTEGER NOT NULL DEFAULT 5
+    prefer_not_multiple INTEGER NOT NULL DEFAULT 5,
+    no_prefer_cost INTEGER NOT NULL DEFAULT 10
 );
 
 CREATE TABLE IF NOT EXISTS trip_admins (

static/trip.html

@@ -87,6 +87,7 @@
         <div id="trip-settings">
             <label>Students per room: <input id="room-size" type="number" min="1"></label>
             <label>Prefer Not cost: <input id="pn-multiple" type="number" min="1"></label>
+            <label>No Prefer cost: <input id="np-cost" type="number" min="0"></label>
         </div>
         <div id="conflicts"></div>
         <div id="mismatches"></div>

static/trip.js

@@ -17,6 +17,7 @@ try {
 document.getElementById('trip-name').textContent = trip.name;
 document.getElementById('room-size').value = trip.room_size;
 document.getElementById('pn-multiple').value = trip.prefer_not_multiple;
+document.getElementById('np-cost').value = trip.no_prefer_cost;
 document.getElementById('main').style.display = 'block';
 document.getElementById('logout-btn').addEventListener('click', logout);
 document.getElementById('room-size').addEventListener('change', async () => {
@@ -27,6 +28,10 @@ document.getElementById('pn-multiple').addEventListener('change', async () => {
     const val = parseInt(document.getElementById('pn-multiple').value);
     if (val >= 1) await api('PATCH', '/api/trips/' + tripID, { prefer_not_multiple: val });
 });
+document.getElementById('np-cost').addEventListener('change', async () => {
+    const val = parseInt(document.getElementById('np-cost').value);
+    if (val >= 0) await api('PATCH', '/api/trips/' + tripID, { no_prefer_cost: val });
+});
 
 let lastOveralls = {};