modrun 1.1.0

//! Public error type for modrun.

use std::any::type_name;
use std::error;
use std::fmt;
use std::io;
use std::result;
use std::time::Duration;

/// Owned user error retained as [`std::error::Error::source`].
pub type BoxError = Box<dyn error::Error + Send + Sync>;

/// Result alias used throughout the crate and by hooks / fallible constructors.
pub type Result<T> = result::Result<T, Error>;

/// Errors produced while wiring, starting, or stopping an application.
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum Error {
    /// A required group has no members.
    #[error("required group is empty: {type_name}")]
    EmptyGroup {
        /// Group type name shown in diagnostics (`Group<T>`).
        type_name: &'static str,
    },

    /// A group member provider's result type does not match the declared element type.
    #[error("provide_group_dyn type mismatch: expected {expected}, got {actual}")]
    GroupMemberTypeMismatch {
        /// Element type the caller declared.
        expected: &'static str,
        /// Result type reported by the erased provider.
        actual: &'static str,
    },

    /// A public type was registered more than once.
    #[error("type already provided: {0}")]
    AlreadyProvided(&'static str),

    /// A private type was registered more than once in the same module.
    #[error("type already provided privately in module '{module}': {type_name}")]
    AlreadyProvidedPrivate {
        /// Module name shown in diagnostics.
        module: &'static str,
        /// Type name that collided.
        type_name: &'static str,
    },

    /// The dependency graph contains a cycle.
    #[error("dependency cycle detected involving: {0}")]
    Cycle(String),

    /// A value was requested before it had been constructed.
    #[error("dependency not constructed yet: {0}")]
    NotConstructed(&'static str),

    /// No provider exists for a requested type.
    #[error("missing provider for type: {type_name} (from module '{module}')")]
    MissingProvider {
        /// Missing type.
        type_name: &'static str,
        /// Scope that requested it.
        module: &'static str,
    },

    /// A provider depends on something nothing registers.
    #[error(
        "provider for {provider} in module '{module}' needs a dependency nothing provides: {dependency}{}",
        group_registration_hint(.dependency)
    )]
    ProviderMissingDep {
        /// Provider result type.
        provider: &'static str,
        /// Module that owns the provider.
        module: &'static str,
        /// Missing dependency type.
        dependency: &'static str,
    },

    /// An invoker depends on something nothing registers.
    #[error(
        "invoker in module '{module}' needs a dependency nothing provides: {dependency}{}",
        group_registration_hint(.dependency)
    )]
    InvokerMissingDep {
        /// Module that owns the invoker.
        module: &'static str,
        /// Missing dependency type.
        dependency: &'static str,
    },

    /// Internal downcast of a cached value failed.
    #[error("failed to downcast value to {0}")]
    Downcast(&'static str),

    /// A fallible constructor returned an error.
    #[error("constructor for {type_name} failed: {source}")]
    ConstructorFailed {
        /// Type being constructed.
        type_name: &'static str,
        /// The user error from the constructor.
        #[source]
        source: BoxError,
    },

    /// A fallible invoker returned an error.
    #[error("invoker {name} failed: {source}")]
    InvokerFailed {
        /// Rust type name of the invoker function.
        name: &'static str,
        /// The user error from the invoker.
        #[source]
        source: BoxError,
    },

    /// Hook registration after start completed.
    #[error("cannot append lifecycle hook after start has finished")]
    AppendAfterStart,

    /// Hook registration while stopping.
    #[error("cannot append lifecycle hook while stopping")]
    AppendWhileStopping,

    /// Graph construction exceeded its budget.
    #[error("application build timed out after {0:?}")]
    BuildTimeout(Duration),

    /// Start phase exceeded its budget.
    #[error("application start timed out after {0:?}")]
    StartTimeout(Duration),

    /// Stop phase exceeded its budget.
    #[error("application stop timed out after {0:?}")]
    StopTimeout(Duration),

    /// Unwind after a failed/cancelled start exceeded its budget.
    #[error("application stop timed out after {0:?} while unwinding")]
    UnwindTimeout(Duration),

    /// A background [`crate::task`] failed while start was still running, and
    /// unwind did not surface a more specific join error.
    #[error("background task failed during start")]
    TaskFailedDuringStart,

    /// Failed to install a SIGINT listener.
    #[error("failed to listen for SIGINT: {0}")]
    SigintListen(#[source] io::Error),

    /// Failed to install a SIGTERM listener.
    #[error("failed to listen for SIGTERM: {0}")]
    SigtermListen(#[source] io::Error),

    /// Failed to install a process-signal listener (non-Unix platforms).
    #[error("failed to listen for process signal: {0}")]
    SignalListen(#[source] io::Error),

    /// Several OnStop hooks failed; see [`MultipleStopError::errors`].
    #[error(transparent)]
    MultipleStop(MultipleStopError),

    /// Cleanup failed after an earlier phase error; both are retained.
    #[error("cleanup failed after an earlier phase error: {cleanup}; earlier: {earlier}")]
    CleanupAfterFailure {
        /// Error from stop/unwind.
        #[source]
        cleanup: Box<Error>,
        /// Error from the earlier phase.
        earlier: Box<Error>,
    },

    /// An application hook returned this failure.
    ///
    /// Prefer [`Error::hook`] rather than constructing this variant directly.
    /// [`crate::Lifecycle`] overwrites [`Self::Hook::name`] with the registering
    /// hook's [`Hook::name`](crate::Hook::name) when start/stop returns this
    /// variant. [`Error::Io`] and other variants are left unchanged.
    #[error("{}", hook_failed_message(.name, .source))]
    Hook {
        /// [`crate::Hook::name`]; defaults to `"unnamed"` from [`Error::hook`]
        /// until [`crate::Lifecycle`] attaches the registering hook's name.
        name: &'static str,
        /// The user error from the hook.
        #[source]
        source: BoxError,
    },

    /// I/O failure with a short context label (e.g. bind / serve).
    ///
    /// Prefer [`Error::io`] rather than constructing this variant directly.
    #[error("{context}: {source}")]
    Io {
        /// What was being done when I/O failed.
        context: String,
        /// Underlying I/O error.
        #[source]
        source: io::Error,
    },
}

/// Several OnStop hook failures aggregated into one error.
#[derive(Debug)]
#[non_exhaustive]
pub struct MultipleStopError {
    count: usize,
    summary: String,
    errors: Vec<Error>,
}

impl MultipleStopError {
    /// Number of failed hooks.
    #[must_use]
    pub fn count(&self) -> usize {
        self.count
    }

    /// Semicolon-joined displays for easy logging.
    #[must_use]
    pub fn summary(&self) -> &str {
        &self.summary
    }

    /// Individual failures in stop order.
    #[must_use]
    pub fn errors(&self) -> &[Error] {
        &self.errors
    }
}

impl fmt::Display for MultipleStopError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{} OnStop hooks failed: {}", self.count, self.summary)
    }
}

impl error::Error for MultipleStopError {
    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
        self.errors
            .first()
            .map(|e| e as &(dyn error::Error + 'static))
    }
}

impl Error {
    /// Wrap a hook failure, keeping the original error as [`std::error::Error::source`].
    ///
    /// Accepts anything convertible to [`BoxError`], including `&str`, `String`,
    /// [`std::io::Error`], and types that implement [`std::error::Error`].
    /// [`crate::Lifecycle`] overwrites [`Self::Hook::name`] with the registering
    /// hook's [`Hook::name`](crate::Hook::name) when start/stop returns this variant.
    pub fn hook(err: impl Into<BoxError>) -> Self {
        Self::Hook {
            name: "unnamed",
            source: err.into(),
        }
    }

    /// Attach a hook name when the failure is already [`Error::Hook`].
    /// Other variants (for example [`Error::Io`]) are left unchanged so
    /// callers can still match on them.
    pub(crate) fn with_hook_name(self, hook_name: &'static str) -> Self {
        match self {
            Self::Hook { source, .. } => Self::Hook {
                name: hook_name,
                source,
            },
            other => other,
        }
    }

    /// Wrap an I/O failure with a short context label (e.g. `"bind 127.0.0.1:3000"`).
    ///
    /// There is no `From<std::io::Error>` impl, so `listener.bind().await?` does
    /// not compile in a `modrun::Result` function — map with this helper instead.
    pub fn io(context: impl Into<String>, source: io::Error) -> Self {
        Self::Io {
            context: context.into(),
            source,
        }
    }

    pub(crate) fn constructor_failed<T: ?Sized>(err: impl Into<BoxError>) -> Self {
        Self::ConstructorFailed {
            type_name: type_name::<T>(),
            source: err.into(),
        }
    }

    pub(crate) fn invoker_failed(name: &'static str, err: impl Into<BoxError>) -> Self {
        Self::InvokerFailed {
            name,
            source: err.into(),
        }
    }

    pub(crate) fn multiple_stop(errors: Vec<Error>) -> Self {
        let count = errors.len();
        let summary = errors
            .iter()
            .map(ToString::to_string)
            .collect::<Vec<_>>()
            .join("; ");
        Self::MultipleStop(MultipleStopError {
            count,
            summary,
            errors,
        })
    }
}

/// Wrap a user-facing fallible value with constructor/invoker context.
pub(crate) fn user_ctor_err<T: ?Sized>(err: impl Into<BoxError>) -> Error {
    Error::constructor_failed::<T>(err)
}

pub(crate) fn user_invoke_err(name: &'static str, err: impl Into<BoxError>) -> Error {
    Error::invoker_failed(name, err)
}

fn hook_failed_message(name: &'static str, source: &BoxError) -> String {
    format!("hook '{name}' failed: {source}")
}

fn group_registration_hint(dependency: &str) -> &'static str {
    if dependency.contains("Group<") {
        "; register the group with init_group, provide_group, or require_group"
    } else {
        ""
    }
}

/// Aggregate multiple hook failures into a single error.
pub(crate) fn aggregate_errors(errors: Vec<Error>) -> Result<()> {
    match errors.len() {
        0 => Ok(()),
        1 => Err(errors.into_iter().next().expect("len checked")),
        _ => Err(Error::multiple_stop(errors)),
    }
}

/// Prefer a cleanup failure as the primary error, while retaining the earlier
/// phase error when both fail.
pub(crate) fn combine_results(earlier: Result<()>, later: Result<()>) -> Result<()> {
    match earlier {
        Ok(()) => later,
        Err(e) => Err(with_cleanup(e, later)),
    }
}

/// Keep a phase error; if cleanup also failed, wrap both.
pub(crate) fn with_cleanup(earlier: Error, cleanup: Result<()>) -> Error {
    match cleanup {
        Ok(()) => earlier,
        Err(cleanup) => Error::CleanupAfterFailure {
            cleanup: Box::new(cleanup),
            earlier: Box::new(earlier),
        },
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::error::Error as StdError;
    use std::io;

    #[test]
    fn hook_preserves_io_source() {
        let err = Error::hook(io::Error::other("disk full"));
        let src = StdError::source(&err).expect("source");
        assert!(src.to_string().contains("disk full"), "source was {src}");
    }

    #[test]
    fn constructor_failed_preserves_source() {
        let err = Error::constructor_failed::<u32>("nope");
        let src = StdError::source(&err).expect("source");
        assert!(src.to_string().contains("nope"), "source was {src}");
        assert!(
            err.to_string().contains("constructor for"),
            "display was {err}"
        );
    }

    #[test]
    fn io_helper_sets_context_and_source() {
        let err = Error::io("bind", io::Error::other("addr in use"));
        match &err {
            Error::Io { context, source } => {
                assert_eq!(context, "bind");
                assert!(source.to_string().contains("addr in use"));
            }
            other => panic!("expected Io, got {other}"),
        }
        assert!(StdError::source(&err).is_some());
    }

    #[test]
    fn cleanup_after_failure_source_is_cleanup() {
        let err = Error::CleanupAfterFailure {
            cleanup: Box::new(Error::hook("cleanup")),
            earlier: Box::new(Error::hook("earlier")),
        };
        let src = StdError::source(&err).expect("source");
        assert!(src.to_string().contains("cleanup"), "source was {src}");
    }

    #[test]
    fn with_cleanup_ok_is_the_phase_error() {
        let err = with_cleanup(Error::hook("earlier"), Ok(()));
        assert!(err.to_string().contains("earlier"), "display was {err}");
        assert!(!err.to_string().contains("cleanup failed"));
    }

    #[test]
    fn with_cleanup_err_wraps_both() {
        let err = with_cleanup(Error::hook("earlier"), Err(Error::hook("cleanup")));
        match err {
            Error::CleanupAfterFailure { cleanup, earlier } => {
                assert!(cleanup.to_string().contains("cleanup"));
                assert!(earlier.to_string().contains("earlier"));
            }
            other => panic!("expected CleanupAfterFailure, got {other}"),
        }
    }

    #[test]
    fn multiple_stop_source_is_first_error() {
        let err = Error::multiple_stop(vec![Error::hook("stop-a"), Error::hook("stop-b")]);
        let src = StdError::source(&err).expect("source");
        assert!(src.to_string().contains("stop-a"), "source was {src}");
        match &err {
            Error::MultipleStop(inner) => {
                assert_eq!(inner.count(), 2);
                assert!(inner.summary().contains("stop-a"));
                assert!(inner.errors()[1].to_string().contains("stop-b"));
            }
            other => panic!("expected MultipleStop, got {other}"),
        }
    }

    #[test]
    fn hook_display_includes_context() {
        let err = Error::hook("boom");
        let msg = err.to_string();
        assert!(msg.contains("boom"), "unexpected: {msg}");
        assert!(msg.contains("hook 'unnamed' failed"), "unexpected: {msg}");
    }

    #[test]
    fn with_hook_name_labels_unnamed_hook() {
        let err = Error::hook("boom").with_hook_name("http");
        match &err {
            Error::Hook { name, .. } => assert_eq!(*name, "http"),
            other => panic!("expected Hook, got {other}"),
        }
        let msg = err.to_string();
        assert!(msg.contains("http"), "unexpected: {msg}");
        assert!(msg.contains("boom"), "unexpected: {msg}");
    }

    #[test]
    fn with_hook_name_leaves_io_unchanged() {
        let err = Error::io("bind", io::Error::other("addr in use")).with_hook_name("http.serve");
        match err {
            Error::Io { context, .. } => assert_eq!(context, "bind"),
            other => panic!("expected Io, got {other}"),
        }
    }

    #[test]
    fn invoker_failed_includes_function_name() {
        let err = Error::invoker_failed("boot", "nope");
        let msg = err.to_string();
        assert!(msg.contains("boot"), "unexpected: {msg}");
        assert!(msg.contains("nope"), "unexpected: {msg}");
        let src = StdError::source(&err).expect("source");
        assert!(src.to_string().contains("nope"), "source was {src}");
    }
}