// ============================================================================
// Turn tracker — round/phase state machine with player rotation
// ============================================================================
//
// Models a multi-player turn order: the active player index cycles 0..n-1,
// incrementing the round each time play wraps back to player 0. A `phase`
// state machine guards the upkeep → main → end → upkeep cycle, with a *->over
// catch-all so the game always terminates.
//
// Run:  soma run turn_tracker.cell --signal demo
// Test: soma test turn_tracker.cell
// Verify: soma verify turn_tracker.cell   (needs soma.toml)

cell TurnTracker {
    face {
        signal next_turn(active: Int, round: Int, players: Int) -> Map
        signal play_rounds(players: Int, turns: Int) -> Map
        signal demo() -> Map
    }

    state phase {
        initial: upkeep
        upkeep -> main
        main   -> end
        end    -> upkeep
        *      -> over
    }

    // Advance to the next player; wrapping past the last player bumps round.
    on next_turn(active: Int, round: Int, players: Int) {
        let nxt = (active + 1) % players
        let r = round
        if nxt == 0 { r = round + 1 }
        return map("active", nxt, "round", r)
    }

    // Simulate `turns` total turns over `players` seats.
    on play_rounds(players: Int, turns: Int) {
        let active = 0
        let round = 1
        for t in range(0, turns) {
            let s = next_turn(active, round, players)
            active = s.active
            round = s.round
        }
        return map("active", active, "round", round)
    }

    on demo() {
        // 3 players, 7 turns: turns wrap at 3 and 6 → round 3, active 1
        return play_rounds(3, 7)
    }
}

cell test TurnTrackerTests {
    rules {
        // player 1 → 2 of 3, same round
        assert next_turn(1, 5, 3).active == 2
        assert next_turn(1, 5, 3).round == 5
        // wrapping past player 2 → player 0, round increments
        assert next_turn(2, 5, 3).active == 0
        assert next_turn(2, 5, 3).round == 6
        // 3 players, 7 turns
        assert play_rounds(3, 7).round == 3
        assert play_rounds(3, 7).active == 1
        // 2 players, 4 turns → back to start of round 3
        assert play_rounds(2, 4).round == 3
        assert play_rounds(2, 4).active == 0
    }
}