type BlockIndex = nat64;
type Memo = nat64;
type AccountIdentifier = blob;
type Tokens = record { e8s : nat64 };
type Timestamp = record { timestamp_nanos : nat64 };

type Operation = variant {
    Mint : record {
        to : AccountIdentifier;
        amount : Tokens;
    };
    Burn : record {
        from : AccountIdentifier;
        amount : Tokens;
    };
    Transfer : record {
        from : AccountIdentifier;
        to : AccountIdentifier;
        amount : Tokens;
        fee : Tokens;
    };
    Approve : record {
        from : AccountIdentifier;
        spender : AccountIdentifier;
        allowance_e8s : int;
        fee : Tokens;
        expires_at : opt Timestamp;
    };
    TransferFrom : record {
        from : AccountIdentifier;
        to : AccountIdentifier;
        spender : AccountIdentifier;
        amount : Tokens;
        fee : Tokens;
    };
};

type Transaction = record {
    memo : Memo;
    icrc1_memo : opt blob;
    // Optional to support potential future variant extensions.
    operation : opt Operation;
    created_at_time : Timestamp;
};

type Block = record {
    parent_hash : opt blob;
    transaction : Transaction;
    timestamp : Timestamp;
};

type GetBlocksArgs = record {
    start : BlockIndex;
    length : nat64;
};

type BlockRange = record {
    blocks : vec Block;
};

type GetBlocksError = variant {

    /// The [GetBlocksArgs.start] is below the first block that
    /// archive node stores.
    BadFirstBlockIndex : record {
        requested_index : BlockIndex;
        first_valid_index : BlockIndex;
    };

    /// Reserved for future use.
    Other : record {
        error_code : nat64;
        error_message : text;
    };
};

type GetBlocksResult = variant {
    Ok : BlockRange;
    Err : GetBlocksError;
};

service : {
    get_blocks : (GetBlocksArgs) -> (GetBlocksResult) query;
}