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randomizeBreak

// TeamAssignment.cdc // Smart contract for randomly assigning NBA Top Shot usernames to NBA teams // Uses Flow's commit-reveal pattern with RandomConsumer VRF for provably fair randomness // Based on Flow team's recommended approach using RandomConsumer contract import RandomConsumer from 0x45caec600164c9e6 import Burner from 0xf233dcee88fe0abe access(all) contract randomizeBreak { // ============ Events (Matching Flow's Pattern) ============ // Event emitted when a commitment is made (lock phase) // Note: RandomnessSourced event is automatically emitted by RandomConsumer.requestRandomness() access(all) event CommitmentMade(commitmentId: UInt64, lockBlock: UInt64, usernames: [String], teams: [String], combos: [String]) // Event emitted when an assignment is made (matches Flow's ParticipantAssigned pattern) access(all) event ParticipantAssigned(username: String, team: String, assignmentIndex: UInt64, receiptID: String) // Event emitted when all assignments are complete (matches Flow's completion pattern) // Note: RandomnessFulfilled event is automatically emitted by RandomConsumer.fulfillRandomRequest() access(all) event TeamAssignmentComplete( commitmentId: UInt64, lockBlock: UInt64, revealBlock: UInt64, receiptID: String, verificationNote: String, assignments: {UInt64: Assignment} ) // ============ Data Structures ============ // Assignment structure access(all) struct Assignment { access(all) let username: String access(all) let team: String access(all) let assignmentIndex: UInt64 access(all) let timestamp: UFix64 init(username: String, team: String, assignmentIndex: UInt64, timestamp: UFix64) { self.username = username self.team = team self.assignmentIndex = assignmentIndex self.timestamp = timestamp } } // Receipt resource - returned from commit, submitted to reveal // Conforms to RandomConsumer.RequestWrapper for VRF integration access(all) resource Receipt { access(all) let usernames: [String] access(all) let teams: [String] access(all) let combos: [String] access(all) let lockBlock: UInt64 // Store block height when request is created access(all) var request: @RandomConsumer.Request? init( usernames: [String], teams: [String], combos: [String], request: @RandomConsumer.Request ) { self.usernames = usernames self.teams = teams self.combos = combos self.lockBlock = request.block // Store block height before moving request self.request <- request } // Required by RequestWrapper interface access(all) fun popRequest(): @RandomConsumer.Request? { let req <- self.request <- nil return <-req } // Get the block height from the request access(all) fun getRequestBlock(): UInt64? { return self.lockBlock } } // ============ Contract State ============ // Storage for all completed assignments access(all) var assignments: {UInt64: Assignment} // Consumer resource for VRF randomness access(self) let consumer: @RandomConsumer.Consumer // Counter for commitment IDs (for receiptID generation) access(all) var nextCommitmentId: UInt64 // ============ Contract Initialization ============ init() { self.assignments = {} self.consumer <- RandomConsumer.createConsumer() self.nextCommitmentId = 0 } // ============ Commit Phase ============ // Lock in the assignment - returns a Receipt for later reveal // The randomness is requested but NOT revealed yet // RandomConsumer.requestRandomness() automatically emits RandomnessSourced event access(all) fun commitAssignment( usernames: [String], teams: [String], combos: [String] ): @Receipt { pre { usernames.length > 0: "Must provide at least one username" (teams.length + combos.length) == usernames.length: "Number of single teams plus combos must equal number of usernames" } // Request randomness from the VRF // This automatically emits RandomnessSourced event with block, randomSource, and requestUUID let request <- self.consumer.requestRandomness() let lockBlock = request.block // Generate commitment ID for tracking let commitmentId = self.nextCommitmentId self.nextCommitmentId = commitmentId + 1 // Create the receipt let receipt <- create Receipt( usernames: usernames, teams: teams, combos: combos, request: <-request ) // Emit our commitment event emit CommitmentMade( commitmentId: commitmentId, lockBlock: lockBlock, usernames: usernames, teams: teams, combos: combos ) return <- receipt } // ============ Reveal Phase ============ // Reveal the assignments using the committed randomness // This consumes the receipt and returns the final assignments // RandomConsumer.fulfillRandomRequest() automatically emits RandomnessFulfilled event access(all) fun revealAndAssign(receipt: @Receipt): {UInt64: Assignment} { // Get values from receipt before we move/destroy it let lockBlock = receipt.getRequestBlock()! let revealBlock = getCurrentBlock().height let currentTime = getCurrentBlock().timestamp let receiptUUID = receipt.uuid // Generate receipt ID for events (using receipt's UUID) let receiptID = receiptUUID.toString() // Get the usernames and team options from receipt var remainingUsernames = receipt.usernames // Combine single teams and combos var allAssignments: [String] = [] var i = 0 while i < receipt.teams.length { allAssignments.append(receipt.teams[i]) i = i + 1 } i = 0 while i < receipt.combos.length { allAssignments.append(receipt.combos[i]) i = i + 1 } var result: {UInt64: Assignment} = {} var index: UInt64 = 0 // Pop the randomness request from the receipt and get the committed random seed let request <- receipt.popRequest() // Ensure we have a request if request == nil { panic("Receipt does not contain a valid request") } // Fulfill the committed randomness to get the seed value // This automatically emits RandomnessFulfilled event with randomResult and requestUUID // This uses the randomness from the LOCK block, not the reveal block var seedValue = self.consumer.fulfillRandomRequest(<-request!) // Perform the random assignments using the committed seed // Use XOR shift algorithm to derive multiple random values (PRG) while remainingUsernames.length > 0 { // XOR shift algorithm (no multiplication, no overflow) seedValue = seedValue ^ (seedValue << 13) seedValue = seedValue ^ (seedValue >> 7) seedValue = seedValue ^ (seedValue << 17) let usernameIndex = seedValue % UInt64(remainingUsernames.length) // Another round for assignment index seedValue = seedValue ^ (seedValue << 13) seedValue = seedValue ^ (seedValue >> 7) seedValue = seedValue ^ (seedValue << 17) let assignmentIndex = seedValue % UInt64(allAssignments.length) // Get selected username and team let selectedUsername = remainingUsernames[Int(usernameIndex)] let selectedAssignment = allAssignments[Int(assignmentIndex)] // Create assignment record let assignment = Assignment( username: selectedUsername, team: selectedAssignment, assignmentIndex: index, timestamp: currentTime ) // Store assignment result[index] = assignment self.assignments[index] = assignment // Emit individual assignment event (for real-time UI updates) emit ParticipantAssigned( username: selectedUsername, team: selectedAssignment, assignmentIndex: index, receiptID: receiptID ) // Remove assigned username and team from pools remainingUsernames = self.removeElement(arr: remainingUsernames, index: Int(usernameIndex)) allAssignments = self.removeElement(arr: allAssignments, index: Int(assignmentIndex)) index = index + 1 } // Generate commitment ID for the completion event (we'll use receipt UUID as base) let commitmentId = receiptUUID % 1000000 // Destroy the receipt (it's been used) Burner.burn(<-receipt) // Create verification note let verificationNote = "This assignment used Flow's Verifiable Random Function (VRF). The participants and teams were locked at block ".concat(lockBlock.toString()).concat(" and revealed at block ").concat(revealBlock.toString()).concat(". The random seed was determined by the blockchain AFTER the lock, making it impossible for anyone to predict or manipulate the results.") // Emit the main completion event (shareable proof of fairness) emit TeamAssignmentComplete( commitmentId: commitmentId, lockBlock: lockBlock, revealBlock: revealBlock, receiptID: receiptID, verificationNote: verificationNote, assignments: result ) return result } // ============ Helper Functions ============ // Remove element from array at index access(all) fun removeElement(arr: [String], index: Int): [String] { var result: [String] = [] var i = 0 while i < arr.length { if i != index { result.append(arr[i]) } i = i + 1 } return result } // ============ View Functions ============ // Get all completed assignments access(all) fun getAllAssignments(): {UInt64: Assignment} { return self.assignments } // Get assignment by index access(all) fun getAssignment(index: UInt64): Assignment? { return self.assignments[index] } }