You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: integrity.rs
    path of file: ./repos/holochain/crates/test_utils/wasm/wasm_workspace/countersigning/src
    
    the code of the file until where you have to start completion: use hdi::prelude::*;

#[hdk_entry_helper]
pub enum Thing {
    Valid,
    Invalid,
}

impl From<Thing> for ValidateCallbackResult {
    fn from(thing: Thing) -> Self {
        match thing {
            Thing::Valid => ValidateCallbackResult::Valid,
            Thing::Invalid => ValidateCallbackResult::Invalid("never valid".to_string()),
        }
    }
}

#[hdk_entry_types]
#[unit_enum(EntryTypesUnit)]
pub enum EntryTypes {
    Thing(Thing),
}

#[hdk_extern]
fn validate(op: Op) -> ExternResult<ValidateCallbackResult> {
    match op {
        Op::StoreRecord(StoreRecord {
            record:
                Record {
                    signed_action,
                    entry: RecordEntry::Present(entry),
                },
        }) => {
            match signed_action.action().entry_type().and_then(|entry_type| match entry_type {
                EntryType::App(AppEntryDef { entry_index, zome_index, .. }) => Some((zome_index, entry_index)),
                _ =>
    
fn validate(op: Op) -> ExternResult<ValidateCallbackResult> {
    match op {
        Op::StoreRecord(StoreRecord {
            record:
                Record {
                    signed_action,
                    entry: RecordEntry::Present(entry),
                },
        }) => {
            match signed_action.action().entry_type().and_then(|entry_type| match entry_type {
                EntryType::App(AppEntryDef { entry_index, zome_index, .. }) => Some((zome_index, entry_index)),
                _ => None,
            }) {
                Some((zome_index, entry_index)) => {
                    match EntryTypes::deserialize_from_type(*zome_index, *entry_index, &entry) {
                        Ok(Some(EntryTypes::Thing(thing))) => Ok(thing.into()),
                        Ok(None) => Ok(ValidateCallbackResult::Valid),
                        Err(WasmError {
                            error: WasmErrorInner::Deserialize(_),
                            ..
                        }) => Ok(ValidateCallbackResult::Invalid(
                            "Failed to deserialize entry".to_string(),
                        )),
                        Err(e) => Err(e),
                    }
                }
                None => Ok(ValidateCallbackResult::Valid),
            }
        }
        _ => Ok(ValidateCallbackResult::Valid),
    }
}