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use std::marker::PhantomData;

use crate::{
    aggregates::Aggregate,
    errors::AggregateError,
};

/// A framework for rigorously testing the aggregate logic, one of the
/// ***most important*** parts of any CQRS system.
///
/// ```
/// # use cqrs_es2::test::TestFramework;
/// # use cqrs_es2::doc::{Customer, CustomerEvent, AddCustomerName, NameAdded, CustomerCommand};
/// type CustomerTestFramework = TestFramework<Customer>;
///
/// CustomerTestFramework::default()
///         .given_no_previous_events()
///         .when(CustomerCommand::AddCustomerName(AddCustomerName{
///                 changed_name: "John Doe".to_string()
///             }))
///         .then_expect_events(vec![
///             CustomerEvent::NameAdded(NameAdded{
///                 changed_name: "John Doe".to_string()
///             })
///         ]);
///
/// CustomerTestFramework::default()
///         .given(vec![
///             CustomerEvent::NameAdded(NameAdded {
///                 changed_name: "John Doe".to_string()
///             })
///         ])
///         .when(CustomerCommand::AddCustomerName(AddCustomerName{ changed_name: "John Doe".to_string() }))
///         .then_expect_error("a name has already been added for this customer")
/// ```
pub struct TestFramework<A> {
    _phantom: PhantomData<A>,
}

impl<A> TestFramework<A>
where
    A: Aggregate,
{
    /// Initiates an aggregate test with no previous events.
    #[must_use]
    pub fn given_no_previous_events(
        &self
    ) -> AggregateTestExecutor<A> {
        AggregateTestExecutor { events: Vec::new() }
    }
    /// Initiates an aggregate test with a collection of previous
    /// events.
    #[must_use]
    pub fn given(
        &self,
        events: Vec<A::Event>,
    ) -> AggregateTestExecutor<A> {
        AggregateTestExecutor { events }
    }
}

impl<A> Default for TestFramework<A>
where
    A: Aggregate,
{
    fn default() -> Self {
        TestFramework {
            _phantom: PhantomData,
        }
    }
}

/// Holds the initial event state of an aggregate and accepts a
/// command.
pub struct AggregateTestExecutor<A>
where
    A: Aggregate, {
    events: Vec<A::Event>,
}

impl<A> AggregateTestExecutor<A>
where
    A: Aggregate,
{
    /// Consumes a command and using the state details previously
    /// passed provides a validator object to test against.
    pub fn when(
        self,
        command: A::Command,
    ) -> AggregateResultValidator<A> {
        let mut aggregate = A::default();
        for event in self.events {
            aggregate.apply(&event);
        }
        let result = aggregate.handle(command);
        AggregateResultValidator { result }
    }
}

/// Validation object for the `TestFramework` package.
pub struct AggregateResultValidator<A>
where
    A: Aggregate, {
    result: Result<Vec<A::Event>, AggregateError>,
}

impl<A: Aggregate> AggregateResultValidator<A> {
    /// Verifies that the expected events have been produced by the
    /// command.
    pub fn then_expect_events(
        self,
        expected_events: Vec<A::Event>,
    ) {
        let events = match self.result {
            Ok(expected_events) => expected_events,
            Err(err) => {
                panic!(
                    "expected success, received aggregate error: \
                     '{}'",
                    err
                );
            },
        };
        assert_eq!(&events[..], &expected_events[..]);
    }
    /// Verifies that an `AggregateError` with the expected message is
    /// produced with the command.
    pub fn then_expect_error(
        self,
        error_message: &str,
    ) {
        match self.result {
            Ok(events) => {
                panic!(
                    "expected error, received events: '{:?}'",
                    events
                );
            },
            Err(err) => {
                match err {
                    AggregateError::TechnicalError(err) => {
                        panic!(
                            "expected user error but found \
                             technical error: {}",
                            err
                        )
                    },
                    AggregateError::UserError(err) => {
                        assert_eq!(
                            err.message,
                            Some(error_message.to_string())
                        );
                    },
                }
            },
        };
    }
}

#[cfg(test)]
mod test_framework_tests {}