jni 0.4.0

use std::str;

use std::marker::PhantomData;

use std::iter::IntoIterator;

use std::sync::Mutex;
use std::sync::MutexGuard;

use errors::*;

use sys::{self, jvalue, jint, jsize, jbyte, jboolean, jbyteArray};
use std::os::raw::c_char;

use strings::JNIString;
use strings::JavaStr;

use objects::JMap;
use objects::JValue;
use objects::JClass;
use objects::JObject;
use objects::JString;
use objects::JThrowable;
use objects::JMethodID;
use objects::JStaticMethodID;
use objects::JFieldID;
use objects::GlobalRef;

use descriptors::Desc;

use signature::TypeSignature;
use signature::JavaType;
use signature::Primitive;

/// FFI-compatible JNIEnv struct. You can safely use this as the JNIEnv argument
/// to exported methods that will be called by java. This is where most of the
/// magic happens. All methods on this object are wrappers around JNI functions,
/// so the documentation on their behavior is still pretty applicable.
///
/// Since we're calling into the JVM with this, many methods also have the
/// potential to cause an exception to get thrown. If this is the case, an `Err`
/// result will be returned with the error kind `JavaException`. Note that this
/// will _not_ clear the exception - it's up to the caller to decide whether to
/// do so or to let it continue being thrown.
///
/// Because null pointers are a thing in Java, this also converts them to an
/// `Err` result with the kind `NullPtr`. This may occur when either a null
/// argument is passed to a method or when a null would be returned. Where
/// applicable, the null error is changed to a more applicable error type, such
/// as `MethodNotFound`.
#[repr(C)]
pub struct JNIEnv<'a> {
    internal: *mut sys::JNIEnv,
    lifetime: PhantomData<&'a ()>,
}

impl<'a> From<*mut sys::JNIEnv> for JNIEnv<'a> {
    fn from(other: *mut sys::JNIEnv) -> Self {
        JNIEnv {
            internal: other,
            lifetime: PhantomData,
        }
    }
}

impl<'a> JNIEnv<'a> {
    /// Get the java version that we're being executed from. This is encoded and
    /// will need to be checked against constants from the sys module.
    ///
    /// TODO: convert this to something more usable.
    pub fn get_version(&self) -> Result<jint> {
        Ok(unsafe { jni_unchecked!(self.internal, GetVersion) })
    }

    /// Define a new java class. See the JNI docs for more details - I've never
    /// had occasion to use this and haven't researched it fully.
    pub fn define_class<S>(&self, name: S, loader: JObject, buf: &[u8]) -> Result<JClass>
        where S: Into<JNIString>
    {
        non_null!(loader, "define_class loader argument");
        let name = name.into();
        let class = jni_call!(self.internal,
                              DefineClass,
                              name.as_ptr(),
                              loader.into_inner(),
                              buf.as_ptr() as *const jbyte,
                              buf.len() as jsize);
        Ok(class)
    }

    /// Look up a class by name.
    ///
    /// # Example
    /// ```rust,ignore
    /// let class: JClass<'a> = env.find_class("java/lang/String");
    /// ```
    pub fn find_class<S>(&self, name: S) -> Result<JClass<'a>>
        where S: Into<JNIString>
    {
        let name = name.into();
        let class = jni_call!(self.internal, FindClass, name.as_ptr());
        Ok(class)
    }

    /// Get the superclass for a particular class. As with `find_class`, takes
    /// a descriptor.
    pub fn get_superclass<T>(&self, class: T) -> Result<JClass>
        where T: Desc<'a, JClass<'a>>
    {
        let class = class.lookup(self)?;
        Ok(jni_call!(self.internal, GetSuperclass, class.into_inner()))
    }

    /// Tests whether class1 is assignable from class2.
    pub fn is_assignable_from<T, U>(&self, class1: T, class2: U) -> Result<bool>
        where T: Desc<'a, JClass<'a>>,
              U: Desc<'a, JClass<'a>>
    {
        let class1 = class1.lookup(self)?;
        let class2 = class2.lookup(self)?;
        Ok(unsafe {
               jni_unchecked!(self.internal,
                              IsAssignableFrom,
                              class1.into_inner(),
                              class2.into_inner())
           } == sys::JNI_TRUE)
    }

    /// Raise an exception from an existing object. This will continue being
    /// thrown in java unless `exception_clear` is called.
    pub fn throw<E>(&self, obj: E) -> Result<()>
        where E: Desc<'a, JThrowable<'a>>
    {
        let throwable: JThrowable<'a> = obj.lookup(self)?;
        let res: i32 = unsafe { jni_unchecked!(self.internal, Throw, throwable.into_inner()) };
        if res < 0 {
            Err(format!("throw failed with code {}", res).into())
        } else {
            Ok(())
        }
    }

    /// Create and throw a new exception from a class descriptor and an error
    /// message.
    pub fn throw_new<S, T>(&self, class: T, msg: S) -> Result<()>
        where S: Into<JNIString>,
              T: Desc<'a, JClass<'a>>
    {
        let class = class.lookup(self)?;
        let msg = msg.into();
        let res: i32 =
            unsafe { jni_unchecked!(self.internal, ThrowNew, class.into_inner(), msg.as_ptr()) };
        if res < 0 {
            Err(format!("throw failed with code {}", res).into())
        } else {
            Ok(())
        }
    }

    /// Check whether or not an exception is currently in the process of being
    /// thrown. An exception is in this state from the time it gets thrown and
    /// not caught in a java function until `exception_clear` is called.
    pub fn exception_occurred(&self) -> Result<JThrowable> {
        let throwable = jni_call!(self.internal, ExceptionOccurred);
        Ok(throwable)
    }

    /// Print exception information to the console.
    pub fn exception_describe(&self) -> Result<()> {
        unsafe { jni_unchecked!(self.internal, ExceptionDescribe) };
        Ok(())
    }

    /// Clear an exception in the process of being thrown. If this is never
    /// called, the exception will continue being thrown when control is
    /// returned to java.
    pub fn exception_clear(&self) -> Result<()> {
        unsafe { jni_unchecked!(self.internal, ExceptionClear) };
        Ok(())
    }

    /// Abort the JVM with an error message.
    #[allow(unused_variables, unreachable_code)]
    pub fn fatal_error<S: Into<JNIString>>(&self, msg: S) -> ! {
        let msg = msg.into();
        let res: Result<()> =
            catch!({
                       unsafe { jni_unchecked!(self.internal, FatalError, msg.as_ptr()) }
                       unreachable!()
                   });

        panic!(res.unwrap_err());
    }

    /// Check to see if an exception is being thrown. This only differs from
    /// `exception_occurred` in that it doesn't return the actual thrown
    /// exception.
    pub fn exception_check(&self) -> Result<bool> {
        let check = unsafe { jni_unchecked!(self.internal, ExceptionCheck) } == sys::JNI_TRUE;
        Ok(check)
    }

    /// Turns an object into a global ref. This has the benefit of removing the
    /// lifetime bounds since it's guaranteed to not get GC'd by java. It
    /// releases the GC pin upon being dropped.
    pub fn new_global_ref(&self, obj: JObject) -> Result<GlobalRef> {
        non_null!(obj, "new_global_ref obj argument");
        let new_ref: JObject = jni_call!(self.internal, NewGlobalRef, obj.into_inner());
        let global = unsafe { GlobalRef::new(self.internal, new_ref.into_inner()) };
        Ok(global)
    }

    // Not public yet - not sure what the GC behavior is. Needs more research
    #[allow(dead_code)]
    fn new_local_ref(&self, obj: JObject) -> Result<JObject> {
        non_null!(obj, "new_local_ref obj argument");
        Ok(jni_call!(self.internal, NewLocalRef, obj.into_inner()))
    }

    #[allow(dead_code)]
    fn delete_local_ref(&self, obj: JObject) -> Result<()> {
        non_null!(obj, "delete_local_ref obj argument");
        Ok(unsafe {
               jni_unchecked!(self.internal, DeleteLocalRef, obj.into_inner());
               check_exception!(self.internal);
           })
    }

    /// Allocates a new object from a class descriptor without running a
    /// constructor.
    pub fn alloc_object<T>(&self, class: T) -> Result<JObject>
        where T: Desc<'a, JClass<'a>>
    {
        let class = class.lookup(self)?;
        Ok(jni_call!(self.internal, AllocObject, class.into_inner()))
    }

    /// Common functionality for finding methods.
    fn get_method_id_base<T, U, V, C, R>(&self,
                                         class: T,
                                         name: U,
                                         sig: V,
                                         get_method: C)
                                         -> Result<R>
        where T: Desc<'a, JClass<'a>>,
              U: Into<JNIString>,
              V: Into<JNIString>,
              C: Fn(&JClass<'a>, &JNIString, &JNIString) -> Result<R>
    {
        let class = class.lookup(self)?;
        let ffi_name = name.into();
        let sig = sig.into();

        let res: Result<R> = catch!({
                                        get_method(&class, &ffi_name, &sig)
                                    });

        match res {
            Ok(m) => Ok(m),
            Err(e) => {
                match e.kind() {
                    &ErrorKind::NullPtr(_) => {
                        let name: String = ffi_name.into();
                        let sig: String = sig.into();
                        return Err(ErrorKind::MethodNotFound(name, sig).into());
                    }
                    _ => return Err(e),
                }
            }
        }
    }

    /// Look up a method by class descriptor, name, and
    /// signature.
    ///
    /// # Example
    /// ```rust,ignore
    /// let method_id: JMethodID = env.get_method_id(
    ///     "java/lang/String", "substring", "(II)Ljava/lang/String;",
    /// );
    /// ```
    pub fn get_method_id<T, U, V>(&self, class: T, name: U, sig: V) -> Result<JMethodID<'a>>
        where T: Desc<'a, JClass<'a>>,
              U: Into<JNIString>,
              V: Into<JNIString>
    {
        self.get_method_id_base(class, name, sig, |class, name, sig| {
            Ok(jni_call!(self.internal,
                         GetMethodID,
                         class.into_inner(),
                         name.as_ptr(),
                         sig.as_ptr()))
        })
    }
    /// Look up a static method by class descriptor, name, and
    /// signature.
    ///
    /// # Example
    /// ```rust,ignore
    /// let method_id: JMethodID = env.get_static_method_id(
    ///     "java/lang/String", "valueOf", "(I)Ljava/lang/String;",
    /// );
    /// ```
    pub fn get_static_method_id<T, U, V>(&self,
                                         class: T,
                                         name: U,
                                         sig: V)
                                         -> Result<JStaticMethodID<'a>>
        where T: Desc<'a, JClass<'a>>,
              U: Into<JNIString>,
              V: Into<JNIString>
    {
        self.get_method_id_base(class, name, sig, |class, name, sig| {
            Ok(jni_call!(self.internal,
                         GetStaticMethodID,
                         class.into_inner(),
                         name.as_ptr(),
                         sig.as_ptr()))
        })
    }
    /// Look up the field ID for a class/name/type combination.
    ///
    /// # Example
    /// ```rust,ignore
    /// let field_id = env.get_field_id("com/my/Class", "intField", "I");
    /// ```
    pub fn get_field_id<T, U, V>(&self, class: T, name: U, sig: V) -> Result<JFieldID<'a>>
        where T: Desc<'a, JClass<'a>>,
              U: Into<JNIString>,
              V: Into<JNIString>
    {
        let class = class.lookup(self)?;
        let ffi_name = name.into();
        let ffi_sig = sig.into();

        let res: Result<JFieldID> = catch!({
                                               Ok(jni_call!(self.internal,
                                                            GetFieldID,
                                                            class.into_inner(),
                                                            ffi_name.as_ptr(),
                                                            ffi_sig.as_ptr()))
                                           });

        match res {
            Ok(m) => Ok(m),
            Err(e) => {
                match e.kind() {
                    &ErrorKind::NullPtr(_) => {
                        let name: String = ffi_name.into();
                        let sig: String = ffi_sig.into();
                        return Err(ErrorKind::FieldNotFound(name, sig).into());
                    }
                    _ => return Err(e),
                }
            }
        }
    }

    /// Get the class for an object.
    pub fn get_object_class(&self, obj: JObject) -> Result<JClass> {
        Ok(jni_call!(self.internal, GetObjectClass, obj.into_inner()))
    }

    /// Call a static method in an unsafe manner. This does nothing to check
    /// whether the method is valid to call on the class, whether the return
    /// type is correct, or whether the number of args is valid for the method.
    ///
    /// Under the hood, this simply calls the `CallStatic<Type>MethodA` method
    /// with the provided arguments.
    #[allow(unused_unsafe)]
    pub unsafe fn call_static_method_unsafe<T, U>(&self,
                                                  class: T,
                                                  method_id: U,
                                                  ret: JavaType,
                                                  args: &[JValue])
                                                  -> Result<JValue>
        where T: Desc<'a, JClass<'a>>,
              U: Desc<'a, JStaticMethodID<'a>>
    {
        let class = class.lookup(self)?;

        let method_id = method_id.lookup(self)?.into_inner();

        let class = class.into_inner();
        let args: Vec<jvalue> = args.into_iter().map(|v| v.to_jni()).collect();
        let jni_args = args.as_ptr();

        // TODO clean this up
        Ok(match ret {
               JavaType::Object(_) |
               JavaType::Array(_) => {
            let obj: JObject = jni_call!(self.internal,
                                         CallStaticObjectMethodA,
                                         class,
                                         method_id,
                                         jni_args);
            obj.into()
        } // JavaType::Object
               JavaType::Method(_) => unimplemented!(),
               JavaType::Primitive(p) => {
            let v: JValue = match p {
                Primitive::Boolean => {
                    (jni_unchecked!(self.internal,
                                    CallStaticBooleanMethodA,
                                    class,
                                    method_id,
                                    jni_args) == sys::JNI_TRUE)
                            .into()
                }
                Primitive::Char => {
                    jni_unchecked!(self.internal,
                                   CallStaticCharMethodA,
                                   class,
                                   method_id,
                                   jni_args)
                            .into()
                }
                Primitive::Short => {
                    jni_unchecked!(self.internal,
                                   CallStaticShortMethodA,
                                   class,
                                   method_id,
                                   jni_args)
                            .into()
                }
                Primitive::Int => {
                    jni_unchecked!(self.internal,
                                   CallStaticIntMethodA,
                                   class,
                                   method_id,
                                   jni_args)
                            .into()
                }
                Primitive::Long => {
                    jni_unchecked!(self.internal,
                                   CallStaticLongMethodA,
                                   class,
                                   method_id,
                                   jni_args)
                            .into()
                }
                Primitive::Float => {
                    jni_unchecked!(self.internal,
                                   CallStaticFloatMethodA,
                                   class,
                                   method_id,
                                   jni_args)
                            .into()
                }
                Primitive::Double => {
                    jni_unchecked!(self.internal,
                                   CallStaticDoubleMethodA,
                                   class,
                                   method_id,
                                   jni_args)
                            .into()
                }
                Primitive::Byte => {
                    jni_unchecked!(self.internal,
                                   CallStaticByteMethodA,
                                   class,
                                   method_id,
                                   jni_args)
                            .into()
                }
                Primitive::Void => {
                    jni_unchecked!(self.internal,
                                   CallStaticVoidMethodA,
                                   class,
                                   method_id,
                                   jni_args)
                            .into()
                }
            };
            v.into()
        } // JavaType::Primitive
           }) // match parsed.ret
    }

    /// Call an object method in an unsafe manner. This does nothing to check
    /// whether the method is valid to call on the object, whether the return
    /// type is correct, or whether the number of args is valid for the method.
    ///
    /// Under the hood, this simply calls the `Call<Type>MethodA` method with
    /// the provided arguments.
    #[allow(unused_unsafe)]
    pub unsafe fn call_method_unsafe<T>(&self,
                                        obj: JObject,
                                        method_id: T,
                                        ret: JavaType,
                                        args: &[JValue])
                                        -> Result<JValue>
        where T: Desc<'a, JMethodID<'a>>
    {
        let method_id = method_id.lookup(self)?.into_inner();

        let obj = obj.into_inner();

        let args: Vec<jvalue> = args.into_iter().map(|v| v.to_jni()).collect();
        let jni_args = args.as_ptr();

        // TODO clean this up
        Ok(match ret {
               JavaType::Object(_) |
               JavaType::Array(_) => {
            let obj: JObject =
                jni_call!(self.internal, CallObjectMethodA, obj, method_id, jni_args);
            obj.into()
        } // JavaType::Object
               JavaType::Method(_) => unimplemented!(),
               JavaType::Primitive(p) => {
            let v: JValue = match p {
                Primitive::Boolean => {
                    (jni_unchecked!(self.internal,
                                    CallBooleanMethodA,
                                    obj,
                                    method_id,
                                    jni_args) == sys::JNI_TRUE)
                            .into()
                }
                Primitive::Char => {
                    jni_unchecked!(self.internal, CallCharMethodA, obj, method_id, jni_args).into()
                }
                Primitive::Short => {
                    jni_unchecked!(self.internal, CallShortMethodA, obj, method_id, jni_args).into()
                }
                Primitive::Int => {
                    jni_unchecked!(self.internal, CallIntMethodA, obj, method_id, jni_args).into()
                }
                Primitive::Long => {
                    jni_unchecked!(self.internal, CallLongMethodA, obj, method_id, jni_args).into()
                }
                Primitive::Float => {
                    jni_unchecked!(self.internal, CallFloatMethodA, obj, method_id, jni_args).into()
                }
                Primitive::Double => {
                    jni_unchecked!(self.internal, CallDoubleMethodA, obj, method_id, jni_args)
                        .into()
                }
                Primitive::Byte => {
                    jni_unchecked!(self.internal, CallByteMethodA, obj, method_id, jni_args).into()
                }
                Primitive::Void => {
                    jni_unchecked!(self.internal, CallVoidMethodA, obj, method_id, jni_args);
                    return Ok(JValue::Void);
                }
            };
            v.into()
        } // JavaType::Primitive
           }) // match parsed.ret
    }

    /// Calls an object method safely. This comes with a number of
    /// lookups/checks. It
    ///
    /// * Parses the type signature to find the number of arguments and return
    ///   type
    /// * Looks up the JClass for the given object.
    /// * Looks up the JMethodID for the class/name/signature combination
    /// * Ensures that the number of args matches the signature
    /// * Calls `call_method_unsafe` with the verified safe arguments.
    ///
    /// Note: this may cause a java exception if the arguments are the wrong
    /// type, in addition to if the method itself throws.
    pub fn call_method<S, T>(&'a self,
                             obj: JObject,
                             name: S,
                             sig: T,
                             args: &[JValue])
                             -> Result<JValue>
        where S: Into<JNIString>,
              T: Into<JNIString> + AsRef<str>
    {
        non_null!(obj, "call_method obj argument");

        // parse the signature
        let parsed = TypeSignature::from_str(sig.as_ref())?;
        if parsed.args.len() != args.len() {
            return Err(ErrorKind::InvalidArgList.into());
        }

        let class = self.get_object_class(obj)?;

        unsafe { self.call_method_unsafe(obj, (class, name, sig), parsed.ret, args) }
    }

    /// Calls a static method safely. This comes with a number of
    /// lookups/checks. It
    ///
    /// * Parses the type signature to find the number of arguments and return
    ///   type
    /// * Looks up the JMethodID for the class/name/signature combination
    /// * Ensures that the number of args matches the signature
    /// * Calls `call_method_unsafe` with the verified safe arguments.
    ///
    /// Note: this may cause a java exception if the arguments are the wrong
    /// type, in addition to if the method itself throws.
    pub fn call_static_method<T, U, V>(&self,
                                       class: T,
                                       name: U,
                                       sig: V,
                                       args: &[JValue])
                                       -> Result<JValue>
        where T: Desc<'a, JClass<'a>>,
              U: Into<JNIString>,
              V: Into<JNIString> + AsRef<str>
    {
        let parsed = TypeSignature::from_str(&sig)?;
        if parsed.args.len() != args.len() {
            return Err(ErrorKind::InvalidArgList.into());
        }

        // go ahead and look up the class since it's already Copy,
        // and we'll need that for the next call.
        let class = class.lookup(self)?;

        unsafe { self.call_static_method_unsafe(class, (class, name, sig), parsed.ret, args) }
    }

    /// Create a new object using a constructor. This is done safely using
    /// checks similar to those in `call_static_method`.
    pub fn new_object<T, U>(&self,
                            class: T,
                            ctor_sig: U,
                            ctor_args: &[JValue])
                            -> Result<JObject<'a>>
        where T: Desc<'a, JClass<'a>>,
              U: Into<JNIString> + AsRef<str>
    {
        // parse the signature
        let parsed = TypeSignature::from_str(&ctor_sig)?;

        if parsed.args.len() != ctor_args.len() {
            return Err(ErrorKind::InvalidArgList.into());
        }

        if parsed.ret != JavaType::Primitive(Primitive::Void) {
            return Err(ErrorKind::InvalidCtorReturn.into());
        }

        let jni_args: Vec<jvalue> = ctor_args.into_iter().map(|v| v.to_jni()).collect();

        // build strings
        let name = "<init>";

        let class = class.lookup(self)?;

        let method_id: JMethodID = (class, name, ctor_sig).lookup(self)?;

        let jni_args = jni_args.as_ptr();

        Ok(jni_call!(self.internal,
                     NewObjectA,
                     class.into_inner(),
                     method_id.into_inner(),
                     jni_args))
    }

    /// Cast a JObject to a JMap. This won't throw exceptions or return errors
    /// in the event that the object isn't actually a map, but the methods on
    /// the resulting map object will.
    pub fn get_map(&self, obj: JObject<'a>) -> Result<JMap> {
        non_null!(obj, "get_map obj argument");
        JMap::from_env(self, obj)
    }

    /// Get a JavaStr from a JString. This allows conversions from java string
    /// objects to rust strings.
    ///
    /// This entails a call to `GetStringUTFChars` and only decodes java's
    /// modified UTF-8 format on conversion to a rust-compatible string.
    pub fn get_string(&self, obj: JString<'a>) -> Result<JavaStr> {
        non_null!(obj, "get_string obj argument");
        JavaStr::from_env(self, obj)
    }

    /// Get a pointer to the character array beneath a JString. This is in
    /// Java's modified UTF-8 and will leak memory if `release_string_utf_chars`
    /// is never called.
    #[allow(unused_unsafe)]
    pub unsafe fn get_string_utf_chars(&self, obj: JString) -> Result<*const c_char> {
        non_null!(obj, "get_string_utf_chars obj argument");
        let ptr: *const c_char = jni_call!(self.internal,
                                           GetStringUTFChars,
                                           obj.into_inner(),
                                           ::std::ptr::null::<jboolean>() as *mut jboolean);
        Ok(ptr)
    }

    /// Unpin the array returned by `get_string_utf_chars`.
    #[allow(unused_unsafe)]
    pub unsafe fn release_string_utf_chars(&self, obj: JString, arr: *const c_char) -> Result<()> {
        non_null!(obj, "release_string_utf_chars obj argument");
        jni_unchecked!(self.internal, ReleaseStringUTFChars, obj.into_inner(), arr);
        check_exception!(self.internal);
        Ok(())
    }

    /// Create a new java string object from a rust string. This requires a
    /// re-encoding of rusts *real* UTF-8 strings to java's modified UTF-8
    /// format.
    pub fn new_string<S: Into<JNIString>>(&self, from: S) -> Result<JString<'a>> {
        let ffi_str = from.into();
        Ok(jni_call!(self.internal, NewStringUTF, ffi_str.as_ptr()))
    }

    /// Create a new java byte array from a rust byte slice.
    pub fn new_byte_array(&self, buf: &[i8]) -> Result<jbyteArray> {
        let length = buf.len() as i32;
        let bytes: jbyteArray = jni_call!(self.internal, NewByteArray, length);
        unsafe {
            jni_unchecked!(self.internal, SetByteArrayRegion, bytes, 0, length, buf.as_ptr());
        }
        Ok(bytes)
    }

    /// Get a field without checking the provided type against the actual field.
    #[allow(unused_unsafe)]
    pub unsafe fn get_field_unsafe<T>(&self, obj: JObject, field: T, ty: JavaType) -> Result<JValue>
        where T: Desc<'a, JFieldID<'a>>
    {
        non_null!(obj, "get_field_typed obj argument");

        let field = field.lookup(self)?.into_inner();
        let obj = obj.into_inner();

        // TODO clean this up
        Ok(match ty {
               JavaType::Object(_) |
               JavaType::Array(_) => {
            let obj: JObject = jni_call!(self.internal, GetObjectField, obj, field);
            obj.into()
        } // JavaType::Object
               JavaType::Method(_) => unimplemented!(),
               JavaType::Primitive(p) => {
            let v: JValue = match p {
                Primitive::Boolean => {
                    (jni_unchecked!(self.internal, GetBooleanField, obj, field) == sys::JNI_TRUE)
                        .into()
                }
                Primitive::Char => jni_unchecked!(self.internal, GetCharField, obj, field).into(),
                Primitive::Short => jni_unchecked!(self.internal, GetShortField, obj, field).into(),
                Primitive::Int => jni_unchecked!(self.internal, GetIntField, obj, field).into(),
                Primitive::Long => jni_unchecked!(self.internal, GetLongField, obj, field).into(),
                Primitive::Float => jni_unchecked!(self.internal, GetFloatField, obj, field).into(),
                Primitive::Double => {
                    jni_unchecked!(self.internal, GetDoubleField, obj, field).into()
                }
                Primitive::Byte => jni_unchecked!(self.internal, GetByteField, obj, field).into(),
                Primitive::Void => {
                    return Err(ErrorKind::WrongJValueType("void", "see java field").into());
                }
            };
            v.into()
        } // JavaType::Primitive
           }) // match parsed.ret
    }

    /// Set a field without any type checking.
    pub unsafe fn set_field_unsafe<T>(&self, obj: JObject, field: T, val: JValue) -> Result<()>
        where T: Desc<'a, JFieldID<'a>>
    {
        non_null!(obj, "set_field_typed obj argument");

        let field = field.lookup(self)?.into_inner();
        let obj = obj.into_inner();

        // TODO clean this up
        match val {
            JValue::Object(o) => {
                jni_unchecked!(self.internal, SetObjectField, obj, field, o.into_inner());
            } // JavaType::Object
            JValue::Bool(b) => {
                jni_unchecked!(self.internal, SetBooleanField, obj, field, b);
            }
            JValue::Char(c) => {
                jni_unchecked!(self.internal, SetCharField, obj, field, c);
            }
            JValue::Short(s) => {
                jni_unchecked!(self.internal, SetShortField, obj, field, s);
            }
            JValue::Int(i) => {
                jni_unchecked!(self.internal, SetIntField, obj, field, i);
            }
            JValue::Long(l) => {
                jni_unchecked!(self.internal, SetLongField, obj, field, l);
            }
            JValue::Float(f) => {
                jni_unchecked!(self.internal, SetFloatField, obj, field, f);
            }
            JValue::Double(d) => {
                jni_unchecked!(self.internal, SetDoubleField, obj, field, d);
            }
            JValue::Byte(b) => {
                jni_unchecked!(self.internal, SetByteField, obj, field, b);
            }
            JValue::Void => {
                return Err(ErrorKind::WrongJValueType("void", "see java field").into());
            }
        };

        Ok(())
    }

    /// Get a field. Requires an object class lookup and a field id lookup
    /// internally.
    pub fn get_field<S, T>(&self, obj: JObject, name: S, ty: T) -> Result<JValue>
        where S: Into<JNIString>,
              T: Into<JNIString> + AsRef<str>
    {
        let class: JClass = self.get_object_class(obj)?;

        let parsed = JavaType::from_str(ty.as_ref())?;

        let field_id: JFieldID = (class, name, ty).lookup(self)?;

        unsafe { self.get_field_unsafe(obj, field_id, parsed) }
    }

    /// Set a field. Does the same lookups as `get_field` and ensures that the
    /// type matches the given value.
    pub fn set_field<S, T>(&self, obj: JObject, name: S, ty: T, val: JValue) -> Result<()>
        where S: Into<JNIString>,
              T: Into<JNIString> + AsRef<str>
    {
        let parsed = JavaType::from_str(ty.as_ref())?;
        let in_type = val.primitive_type();

        match parsed {
            JavaType::Object(_) |
            JavaType::Array(_) => {
                if let None = in_type {
                    // we're good here
                } else {
                    return Err(ErrorKind::WrongJValueType(val.type_name(), "see java field")
                                   .into());
                }
            }
            JavaType::Primitive(p) => {
                if let Some(in_p) = in_type {
                    if in_p == p {
                        // good
                    } else {
                        return Err(ErrorKind::WrongJValueType(val.type_name(), "see java field")
                                       .into());
                    }
                } else {
                    return Err(ErrorKind::WrongJValueType(val.type_name(), "see java field")
                                   .into());
                }
            }
            JavaType::Method(_) => unimplemented!(),
        }

        let class = self.get_object_class(obj)?;

        unsafe { self.set_field_unsafe(obj, (class, name, ty), val) }
    }

    /// Surrenders ownership of a rust object to Java. Requires an object with a
    /// `long` field to store the pointer. The Rust value will be wrapped in a
    /// Mutex since Java will be controlling where it'll be used thread-wise.
    /// Unsafe because it leaks memory if `take_rust_field` is never called (so
    /// be sure to make a finalizer).
    ///
    /// **DO NOT** make a copy of the object containing one of these fields. If
    /// you've set up a finalizer to pass it back to Rust upon being GC'd, it
    /// will point to invalid memory and will likely attempt to be deallocated
    /// again.
    #[allow(unused_variables)]
    pub unsafe fn set_rust_field<S, T>(&self, obj: JObject, field: S, rust_object: T) -> Result<()>
        where S: AsRef<str>,
              T: Send + 'static
    {
        let class = self.get_object_class(obj)?;
        let field_id: JFieldID = (class, &field, "J").lookup(self)?;

        let guard = self.lock_obj(obj)?;

        // Check to see if we've already set this value. If it's not null, that
        // means that we're going to leak memory if it gets overwritten.
        let field_ptr =
            self.get_field_unsafe(obj, field_id, JavaType::Primitive(Primitive::Long))?
                .j()? as *mut Mutex<T>;
        if !field_ptr.is_null() {
            return Err(format!("field already set: {}", field.as_ref()).into());
        }

        let mbox = Box::new(::std::sync::Mutex::new(rust_object));
        let ptr: *mut Mutex<T> = Box::into_raw(mbox);

        self.set_field_unsafe(obj, field_id, (ptr as ::sys::jlong).into())
    }

    /// Gets a lock on a Rust value that's been given to a Java object. Java
    /// still retains ownership and `take_rust_field` will still need to be
    /// called at some point. Checks for a null pointer, but assumes that the
    /// data it ponts to is valid for T.
    #[allow(unused_variables)]
    pub unsafe fn get_rust_field<S, T>(&self, obj: JObject, field: S) -> Result<MutexGuard<T>>
        where S: Into<JNIString>,
              T: Send + 'static
    {
        let guard = self.lock_obj(obj)?;

        let ptr = self.get_field(obj, field, "J")?
            .j()? as *mut Mutex<T>;
        non_null!(ptr, "rust value from Java");
        Ok((*ptr).lock().unwrap())
    }

    /// Take a Rust field back from Java. Makes sure that the pointer is
    /// non-null, but still assumes that the data it points to is valid for T.
    /// Sets the field to a null pointer to signal that it's empty.
    ///
    /// This will return an error in the event that there's an outstanding lock
    /// on the object.
    #[allow(unused_variables)]
    pub unsafe fn take_rust_field<S, T>(&self, obj: JObject, field: S) -> Result<T>
        where S: AsRef<str>,
              T: Send + 'static
    {
        let class = self.get_object_class(obj)?;
        let field_id: JFieldID = (class, &field, "J").lookup(self)?;

        let mbox = {
            let guard = self.lock_obj(obj)?;

            let ptr =
                self.get_field_unsafe(obj, field_id, JavaType::Primitive(Primitive::Long))?
                    .j()? as *mut Mutex<T>;

            non_null!(ptr, "rust value from Java");

            let mbox = Box::from_raw(ptr);

            // attempt to acquire the lock. This prevents us from consuming the
            // mutex if there's an outstanding lock. No one else will be able to
            // get a new one as long as we're in the guarded scope.
            let _ = mbox.try_lock()?;

            self.set_field_unsafe(obj,
                                  field_id,
                                  (::std::ptr::null_mut::<()>() as sys::jlong).into())?;

            mbox
        };

        Ok(mbox.into_inner().unwrap())
    }

    /// Lock a Java object. The MonitorGuard that this returns is responsible
    /// for ensuring that it gets unlocked.
    pub fn lock_obj(&self, obj: JObject) -> Result<MonitorGuard<'a>> {
        unsafe {
            let _ = jni_unchecked!(self.internal, MonitorEnter, obj.into_inner());
        }

        Ok(MonitorGuard {
               obj: obj.into_inner(),
               env: self.internal,
               life: Default::default(),
           })
    }
}

/// Guard for a lock on a java object. This gets returned from the `lock_obj`
/// method.
pub struct MonitorGuard<'a> {
    obj: sys::jobject,
    env: *mut sys::JNIEnv,
    life: PhantomData<&'a ()>,
}

impl<'a> Drop for MonitorGuard<'a> {
    fn drop(&mut self) {
        let res: Result<()> = catch!({
                                         unsafe { jni_unchecked!(self.env, MonitorExit, self.obj) };
                                         Ok(())
                                     });

        match res {
            Err(e) => warn!("error releasing java monitor: {}", e),
            _ => {}
        }
    }
}