workshop-library/library.go

package main

import (
	"fmt"
	"sync"
	"time"
	"log/slog"
)

// Participant struct
type Participant struct {
	ID           int
	Preferences  []int
	AssignedTo   int
	RejectedFrom map[int]bool
	mu           sync.Mutex
}

// Workshop struct
type Workshop struct {
	ID           int
	Capacity     int
	Participants []int
	mu           sync.Mutex
}

// Concurrent Stable Matching Algorithm
func StableMatch(participants []Participant, workshops []Workshop) {
	var wg sync.WaitGroup
	numWorkers := 10
	tasks := make(chan *Participant, len(participants))

	worker := func() {
		defer wg.Done()
		for p := range tasks {
			assignParticipant(p, &workshops, participants)
		}
	}

	for i := 0; i < numWorkers; i++ {
		wg.Add(1)
		go worker()
	}

	for i := range participants {
		tasks <- &participants[i]
	}
	close(tasks)

	wg.Wait()
}

// Assign a participant to a workshop
func assignParticipant(p *Participant, workshops *[]Workshop, participants []Participant) {
	p.mu.Lock()
	defer p.mu.Unlock()

	assigned := false

	for _, workshopID := range p.Preferences {
		if p.RejectedFrom[workshopID] {
			continue
		}

		if workshopID-1 < 0 || workshopID-1 >= len(*workshops) {
			continue // Prevent index out of range
		}

		w := &(*workshops)[workshopID-1]
		w.mu.Lock()

		if len(w.Participants) < w.Capacity {
			p.AssignedTo = workshopID
			w.Participants = append(w.Participants, p.ID)
			w.mu.Unlock()
			assigned = true
			break
		} else {
			weakestID, weakestIndex := findWeakestParticipant(w.Participants, participants, workshopID)
			if weakestIndex != -1 && isPreferred(p.ID, weakestID, workshopID, participants) {
				replaceParticipant(weakestID, p, w, weakestIndex, participants)
				w.mu.Unlock()
				assigned = true
				break
			} else {
				p.RejectedFrom[workshopID] = true
			}
		}
		w.mu.Unlock()
	}

	if !assigned {
		for i := range *workshops {
			w := &(*workshops)[i]
			w.mu.Lock()
			if len(w.Participants) < w.Capacity {
				p.AssignedTo = w.ID
				w.Participants = append(w.Participants, p.ID)
				w.mu.Unlock()
				slog.Info("Participant is assigned to Workshop as fallback\n", slog.Int("ParticipantId", p.ID), slog.Int("WorkshopId", w.ID))
				assigned = true
				break
			}
			w.mu.Unlock()
		}
	}

	if !assigned {
		slog.Info("❌ Participant could not be assigned\n", slog.Int("ParticipantId", p.ID))
		p.AssignedTo = -1
	}
}

// Replace weakest participant in a workshop
func replaceParticipant(weakestID int, newP *Participant, w *Workshop, weakestIndex int, participants []Participant) {
	for i, id := range w.Participants {
		if id == weakestID {
			w.Participants = append(w.Participants[:i], w.Participants[i+1:]...)
			break
		}
	}
	w.Participants[weakestIndex] = newP.ID
	newP.AssignedTo = w.ID
	participants[weakestID-1].AssignedTo = -1
	participants[weakestID-1].RejectedFrom[w.ID] = true
}

// Find the weakest participant in a workshop
func findWeakestParticipant(participantIDs []int, participants []Participant, workshopID int) (int, int) {
	weakestID := -1
	weakestIndex := -1
	lowestRank := 4 

	for i, id := range participantIDs {
		if id-1 < 0 || id-1 >= len(participants) {
			continue
		}
		for rank, pref := range participants[id-1].Preferences {
			if pref == workshopID && rank < lowestRank {
				lowestRank = rank
				weakestID = id
				weakestIndex = i
			}
		}
	}

	return weakestID, weakestIndex
}

// Check if participant A is preferred over B for a workshop
func isPreferred(aID, bID, workshopID int, participants []Participant) bool {
	if aID-1 < 0 || aID-1 >= len(participants) || bID-1 < 0 || bID-1 >= len(participants) {
		return false
	}

	aRank, bRank := 4, 4

	for rank, pref := range participants[aID-1].Preferences {
		if pref == workshopID {
			aRank = rank
		}
	}
	for rank, pref := range participants[bID-1].Preferences {
		if pref == workshopID {
			bRank = rank
		}
	}

	return aRank < bRank
}

// Print final assignments
func PrintAssignments(participants []Participant, workshops []Workshop) {
	fmt.Println("\nFinal Assignments:")
	for _, p := range participants {
		fmt.Printf("Participant %d → Workshop %d\n", p.ID, p.AssignedTo)
	}

	fmt.Println("\nWorkshops and their Participants:")
	for _, w := range workshops {
		fmt.Printf("Workshop %d: %v\n", w.ID, w.Participants)
	}
}

// Print statistics
func PrintStatistics(participants []Participant, workshops []Workshop, duration time.Duration) {
	totalParticipants := len(participants)
	totalWorkshops := len(workshops)
	assignedCount := 0
	unassignedCount := 0
	firstChoiceCount := 0
	secondChoiceCount := 0
	thirdChoiceCount := 0
	fallbackCount := 0

	// Count participant assignment stats
	for _, p := range participants {
		if p.AssignedTo != -1 {
			assignedCount++

			// Check which preference was assigned
			if p.AssignedTo == p.Preferences[0] {
				firstChoiceCount++
			} else if p.AssignedTo == p.Preferences[1] {
				secondChoiceCount++
			} else if p.AssignedTo == p.Preferences[2] {
				thirdChoiceCount++
			} else {
				fallbackCount++
			}
		} else {
			unassignedCount++
		}
	}

	// Calculate workshop utilization
	fmt.Println("\nWorkshop Utilization:")
	for _, w := range workshops {
		usage := float64(len(w.Participants)) / float64(w.Capacity) * 100
		fmt.Printf("Workshop %d: %d/%d participants (%.2f%% full)\n", w.ID, len(w.Participants), w.Capacity, usage)
	}

	// Print summary statistics
	fmt.Println("\n🔹 Matching Statistics:")
	fmt.Printf("⏳ Runtime: %d ms\n", duration.Milliseconds())
	fmt.Printf("📌 Total Participants: %d\n", totalParticipants)
	fmt.Printf("🏫 Total Workshops: %d\n", totalWorkshops)
	fmt.Printf("✅ Assigned Participants: %d (%.2f%%)\n", assignedCount, float64(assignedCount)/float64(totalParticipants)*100)
	fmt.Printf("❌ Unassigned Participants: %d (%.2f%%)\n", unassignedCount, float64(unassignedCount)/float64(totalParticipants)*100)
	fmt.Printf("🥇 First Choice Assigned: %d (%.2f%%)\n", firstChoiceCount, float64(firstChoiceCount)/float64(totalParticipants)*100)
	fmt.Printf("🥈 Second Choice Assigned: %d (%.2f%%)\n", secondChoiceCount, float64(secondChoiceCount)/float64(totalParticipants)*100)
	fmt.Printf("🥉 Third Choice Assigned: %d (%.2f%%)\n", thirdChoiceCount, float64(thirdChoiceCount)/float64(totalParticipants)*100)
	fmt.Printf("⚠️ Assigned via Fallback: %d (%.2f%%)\n", fallbackCount, float64(fallbackCount)/float64(totalParticipants)*100)
}