# Time-locked savings: lock TCN until a block height you choose.
# Nobody can withdraw early - not even the saver. Useful for self-discipline,
# long-term goals or proving that funds are committed.
contract Savings

const MAX_LOCK: int = 2_628_000        # about 5 years (1 block = 1 minute)

state balances: map[address, int]
state unlock_at: map[address, int]
state total_locked: int

event Locked(saver: address, amount: int, unlock_height: int)
event Withdrawn(saver: address, amount: int)

action deposit(unlock_height: int) payable:
    require value > 0, "attach TCN with --value"
    require unlock_height > height, "the unlock height must be in the future"
    require unlock_height <= height + MAX_LOCK, "locks are limited to about 5 years"
    require unlock_height >= unlock_at[caller], "you cannot shorten an existing lock"
    balances[caller] += value
    unlock_at[caller] = unlock_height
    total_locked += value
    emit Locked(caller, value, unlock_height)

action withdraw():
    let amount: int = balances[caller]
    require amount > 0, "you have no savings here"
    require height >= unlock_at[caller], "your savings are still locked"
    # Effects first ...
    balances.remove(caller)
    unlock_at.remove(caller)
    total_locked -= amount
    # ... interaction last.
    send(caller, amount)
    emit Withdrawn(caller, amount)

view balance_of(saver: address) -> int:
    return balances[saver]

view unlock_height_of(saver: address) -> int:
    return unlock_at[saver]

view blocks_left(saver: address) -> int:
    return max(0, unlock_at[saver] - height)

view total() -> int:
    return total_locked