use crate::{backend::runtime::RuntimeFunctionError, eval::PrimitiveType, ir::Type};
use codespan_reporting::diagnostic::Diagnostic;
use cranelift_codegen::{isa::LookupError, settings::SetError, CodegenError};
use cranelift_module::ModuleError;
use internment::ArcIntern;
use thiserror::Error;

/// An error in the translation to a backend (either the JIT or the static compiler).
///
/// In general, this is just a nice summary error type for a bunch of downstream
/// errors; the exception are internal errors from builtin functions or variable
/// lookups.
///
/// Unlike some other errors in the system, the translation to a `Diagnostic` does
/// not necessarily provide a whole lot of value, because we have lost most of the
/// source information by the time we're generating these errors. That being said,
/// people who want to provide nicer error messages might consider using the
/// translation through `Diagnostic` anyways, just in case we add more information
/// in the future.
///
/// Finally, the `PartialEq` for this function is a bit fuzzy. In some cases, it
/// ensures that the errors match exactly. In other cases, though, it just checks to
/// see if the two errors are of the same class; e.g., it will return true if both
/// errors are `BackendError::CodegenError`, regardless of what the specific
/// `CodegenError` is.
#[derive(Debug, Error)]
pub enum BackendError {
    #[error("Cranelift module error: {0}")]
    Cranelift(#[from] ModuleError),
    #[error("Builtin function error: {0}")]
    BuiltinError(#[from] RuntimeFunctionError),
    #[error("Internal variable lookup error")]
    VariableLookupFailure(ArcIntern<String>),
    #[error(transparent)]
    CodegenError(#[from] CodegenError),
    #[error(transparent)]
    SetError(#[from] SetError),
    #[error(transparent)]
    LookupError(#[from] LookupError),
    #[error(transparent)]
    Write(#[from] cranelift_object::object::write::Error),
    #[error("Invalid type cast from {from} to {to}")]
    InvalidTypeCast { from: PrimitiveType, to: Type },
    #[error("Unknown string constant '{0}")]
    UnknownString(ArcIntern<String>),
    #[error("Compiler doesn't currently support function arguments")]
    NoFunctionArguments {
        function_name: String,
        argument_name: String,
    },
}

impl From<BackendError> for Diagnostic<usize> {
    fn from(value: BackendError) -> Self {
        match value {
            BackendError::Cranelift(me) => {
                Diagnostic::error().with_message(format!("Internal cranelift error: {}", me))
                    .with_notes(vec![format!("{:?}", me)])
            }
            BackendError::BuiltinError(me) => {
                Diagnostic::error().with_message(format!("Internal runtime function error: {}", me))
            }
            BackendError::VariableLookupFailure(x) => Diagnostic::error()
                .with_message(format!("Internal variable lookup error for {}", x)),
            BackendError::CodegenError(me) => {
                Diagnostic::error().with_message(format!("Internal codegen error: {}", me))
            }
            BackendError::SetError(me) => {
                Diagnostic::error().with_message(format!("Internal backend setup error: {}", me))
            }
            BackendError::LookupError(me) => {
                Diagnostic::error().with_message(format!("Internal error: {}", me))
            }
            BackendError::Write(me) => {
                Diagnostic::error().with_message(format!("Cranelift object write error: {}", me))
            }
            BackendError::InvalidTypeCast { from, to } => Diagnostic::error().with_message(
                format!("Internal error trying to cast from {} to {}", from, to),
            ),
            BackendError::UnknownString(str) => Diagnostic::error()
                .with_message(format!("Unknown string found trying to compile: '{}'", str)),
            BackendError::NoFunctionArguments {
                function_name,
                argument_name,
            } => Diagnostic::error().with_message(format!(
                "Function {} takes a function argument ({}), which is not supported",
                function_name, argument_name
            )),
        }
    }
}

impl PartialEq for BackendError {
    fn eq(&self, other: &Self) -> bool {
        match self {
            BackendError::BuiltinError(a) => match other {
                BackendError::BuiltinError(b) => a == b,
                _ => false,
            },

            // because the underlying `CodegenError` doesn't implement `PartialEq',
            // we just check that they're both `CodegenError`s.
            BackendError::CodegenError(_) => matches!(other, BackendError::CodegenError(_)),

            // because the underlying `ModuleError` doesn't implement `PartialEq',
            // we just check that they're both `Cranelift`s.
            BackendError::Cranelift(_) => matches!(other, BackendError::Cranelift(_)),

            BackendError::LookupError(a) => match other {
                BackendError::LookupError(b) => a == b,
                _ => false,
            },

            BackendError::SetError(a) => match other {
                BackendError::SetError(b) => a == b,
                _ => false,
            },

            BackendError::VariableLookupFailure(a) => match other {
                BackendError::VariableLookupFailure(b) => a == b,
                _ => false,
            },

            BackendError::Write(a) => match other {
                BackendError::Write(b) => a == b,
                _ => false,
            },

            BackendError::InvalidTypeCast {
                from: from1,
                to: to1,
            } => match other {
                BackendError::InvalidTypeCast {
                    from: from2,
                    to: to2,
                } => from1 == from2 && to1 == to2,
                _ => false,
            },

            BackendError::UnknownString(a) => match other {
                BackendError::UnknownString(b) => a == b,
                _ => false,
            },

            BackendError::NoFunctionArguments {
                function_name: f1,
                argument_name: a1,
            } => match other {
                BackendError::NoFunctionArguments {
                    function_name: f2,
                    argument_name: a2,
                } => f1 == f2 && a1 == a2,
                _ => false,
            },
        }
    }
}