MongoDB aggregation. Trying to use switch in map

Question

Hi im trying to use a switch statement inside of map to increment a value depending on the case but im getting

MongoServerError: $switch found an unknown argument: $$favcast

is this viable?

 db.movies.aggregate([
 {$match: {cast: { $elemMatch: { $exists: true } }}},
 {$match:{ "tomatoes.viewer.rating": {$gte: 3}}},
 {$match:{ countries: {$in: ["USA"]}}},
 {$addFields: {num_favs: 0}},
 {$project: {
 _id: 0,
 cast: {
 $map: {
 input: "$cast",
 as: "favcast",
 in: { $switch: { 
 $$favcast:[
 { case: "Sandra Bullock", then: { $add: [ "$num_favs", 1] } },
 { case: "Tom Hanks", then: { $add: [ "$num_favs", 1] } },
 { case: "Julia Roberts", then: { $add: [ "$num_favs", 1] } },
 { case: "Kevin Spacey", then: { $add: [ "$num_favs", 1] } },
 { case: "George Clooney", then: { $add: [ "$num_favs", 1] } },
 ],
 default: { $add: [ "$num_favs", 0 ]}
 }
 }
 }
 }
 }
},
{$match:{ "num_favs": {$gt: 0}}},
{$project: { num_favs: 1, title: 1 }} 
])

Answer 1

I didn't end up making the switch work but this did the job for my query. $filter and $reduce

 db.movies.aggregate([
 {$match: {cast: { $elemMatch: { $exists: true } }}},
 {$match:{ countries: {$in: ["USA"]}}},
 {$match:{ "tomatoes.viewer.rating": {$gte: 3}}},
 {$addFields: {favcast: {$filter:{
 input: "$cast",
 as: "fave",
 cond: {$or: [
 {$eq: ["$$fave", "Sandra Bullock"] },
 {$eq: ["$$fave", "Tom Hanks"] },
 {$eq: ["$$fave", "Julia Roberts"] },
 {$eq: ["$$fave", "Kevin Spacey"] },
 {$eq: ["$$fave", "George Clooney"] },
 ]}
 } } } },
 {$addFields: { num_favs: 
 {$reduce: { 
 input: "$favcast",
 initialValue: {sum: 0},
 in: {
 sum: { $add : ["$$value.sum", 1] }
 }
 }}
 }},
 {$project: {title: 1, favcast: 1, num_favs: 1, _id: 0 }},
 {$sort: { num_favs: -1, "tomatoes.viewer.rating": -1 , title: -1}},
 {$skip : 20}
])