feat: add party-size queueing and call modes

server/internal/domain/call_selection.go

@@ -0,0 +1,47 @@
+package domain
+
+import (
+	"errors"
+
+	"calllinesystem/server/internal/model"
+)
+
+var ErrFirstTicketExceedsPeopleTarget = errors.New("first ticket party size exceeds people target")
+
+// SelectTicketsForCall preserves the incoming FIFO order. Ticket mode selects
+// up to target tickets. People mode selects the longest leading sequence whose
+// total party size does not exceed target; tickets are never split or skipped.
+func SelectTicketsForCall(tickets []model.QueueTicket, mode string, target int) ([]model.QueueTicket, int, error) {
+	if target < 1 || len(tickets) == 0 {
+		return nil, 0, nil
+	}
+	if mode == model.CallModeTicket {
+		count := min(target, len(tickets))
+		selected := tickets[:count]
+		return selected, totalPartySize(selected), nil
+	}
+	if mode != model.CallModePeople {
+		return nil, 0, errors.New("unsupported call mode")
+	}
+	total := 0
+	count := 0
+	for _, ticket := range tickets {
+		if total+ticket.PartySize > target {
+			break
+		}
+		total += ticket.PartySize
+		count++
+	}
+	if count == 0 {
+		return nil, 0, ErrFirstTicketExceedsPeopleTarget
+	}
+	return tickets[:count], total, nil
+}
+
+func totalPartySize(tickets []model.QueueTicket) int {
+	total := 0
+	for _, ticket := range tickets {
+		total += ticket.PartySize
+	}
+	return total
+}