Two Phase Commit Cross Shard Mock in Python

"""Mock cross-shard two-phase commit with caution handling."""

class Shard:
    def __init__(self, name):
        self.name = name
        self.prepared = False
        self.committed = False
        self.aborted = False

    def prepare(self):
        # Simulate potential failure (1 in 3 chance on third shard)
        if self.name == "shard3" and not self.prepared:
            print(f"  {self.name}: prepare FAILED")
            self.aborted = True
            return False
        self.prepared = True
        print(f"  {self.name}: prepared")
        return True

    def commit(self):
        self.committed = True
        print(f"  {self.name}: committed")

    def abort(self):
        self.aborted = True
        print(f"  {self.name}: aborted")


class TransactionCoordinator:
    def __init__(self, shards):
        self.shards = shards

    def run(self):
        print("Phase 1: Prepare")
        all_prepared = True
        for shard in self.shards:
            # Simulate independent preparation attempt
            if shard.prepare():
                continue
            all_prepared = False
            # Caution: abort already-prepared shards
            print("Caution: abort initiated - shard failed to prepare")
            break

        if all_prepared:
            print("Phase 2: Commit")
            for shard in self.shards:
                shard.commit()
        else:
            print("Phase 2: Abort (rollback)")
            for shard in self.shards:
                if shard.prepared and not shard.aborted:
                    shard.abort()
                elif shard.aborted:
                    print(f"  {shard.name}: already aborted")


if __name__ == "__main__":
    shards = [Shard("shard1"), Shard("shard2"), Shard("shard3")]
    coordinator = TransactionCoordinator(shards)
    coordinator.run()