+//! Safe wrapper around the LLVM C API.
+//!
+//! References returned from the LLVM API are tied to the `'llvm` lifetime which is bound to the
+//! context where the objects are created in.
+//! We do not offer wrappers to remove or delete any objects in the context and therefore all the
+//! references will be valid for the liftime of the context.
+
+use llvm_sys::analysis::{LLVMVerifierFailureAction, LLVMVerifyFunction};
+use llvm_sys::core::{
+    LLVMAddFunction, LLVMAppendBasicBlockInContext, LLVMBuildFAdd, LLVMBuildFCmp, LLVMBuildFMul,
+    LLVMBuildFSub, LLVMBuildRet, LLVMBuildUIToFP, LLVMConstReal, LLVMContextCreate,
+    LLVMContextDispose, LLVMCountBasicBlocks, LLVMCountParams, LLVMCreateBuilderInContext,
+    LLVMDisposeBuilder, LLVMDisposeModule, LLVMDoubleTypeInContext, LLVMDumpModule, LLVMDumpType,
+    LLVMDumpValue, LLVMGetNamedFunction, LLVMGetParam, LLVMGetReturnType, LLVMGetTypeKind,
+    LLVMGetValueKind, LLVMGetValueName2, LLVMModuleCreateWithNameInContext,
+    LLVMPositionBuilderAtEnd, LLVMSetValueName2, LLVMTypeOf,
+};
+use llvm_sys::prelude::{
+    LLVMBasicBlockRef, LLVMBool, LLVMBuilderRef, LLVMContextRef, LLVMModuleRef, LLVMTypeRef,
+    LLVMValueRef,
+};
+use llvm_sys::{LLVMRealPredicate, LLVMTypeKind, LLVMValueKind};
+
+use std::convert::TryFrom;
+use std::ffi::CStr;
+use std::marker::PhantomData;
+use std::ops::Deref;
+
+use crate::SmallCStr;
+
+// Definition of LLVM C API functions using our `repr(transparent)` types.
+extern "C" {
+    fn LLVMFunctionType(
+        ReturnType: Type<'_>,
+        ParamTypes: *mut Type<'_>,
+        ParamCount: ::libc::c_uint,
+        IsVarArg: LLVMBool,
+    ) -> LLVMTypeRef;
+    fn LLVMBuildCall2(
+        arg1: LLVMBuilderRef,
+        arg2: Type<'_>,
+        Fn: FnValue<'_>,
+        Args: *mut Value<'_>,
+        NumArgs: ::libc::c_uint,
+        Name: *const ::libc::c_char,
+    ) -> LLVMValueRef;
+}
+
+// ====================
+//   Module / Context
+// ====================
+
+/// Wrapper for a LLVM Module with its own LLVM Context.
+pub struct Module {
+    ctx: LLVMContextRef,
+    module: LLVMModuleRef,
+}
+
+impl<'llvm> Module {
+    /// Create a new Module instance.
+    ///
+    /// # Panics
+    ///
+    /// Panics if creating the context or the module fails.
+    pub fn new() -> Self {
+        let (ctx, module) = unsafe {
+            let c = LLVMContextCreate();
+            let m = LLVMModuleCreateWithNameInContext(b"module\0".as_ptr().cast(), c);
+            assert!(!c.is_null() && !m.is_null());
+            (c, m)
+        };
+
+        Module { ctx, module }
+    }
+
+    /// Dump LLVM IR emitted into the Module to stdout.
+    pub fn dump(&self) {
+        unsafe { LLVMDumpModule(self.module) };
+    }
+
+    /// Get a type reference representing a `f64` float.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn type_f64(&self) -> Type<'llvm> {
+        let type_ref = unsafe { LLVMDoubleTypeInContext(self.ctx) };
+        Type::new(type_ref)
+    }
+
+    /// Get a type reference representing a `fn(args) -> ret` function.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn type_fn(&'llvm self, args: &mut [Type<'llvm>], ret: Type<'llvm>) -> Type<'llvm> {
+        let type_ref = unsafe {
+            LLVMFunctionType(
+                ret,
+                args.as_mut_ptr(),
+                args.len() as libc::c_uint,
+                0, /* IsVarArg */
+            )
+        };
+        Type::new(type_ref)
+    }
+
+    /// Add a function with the given `name` and `fn_type` to the module and return a value
+    /// reference representing the function.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer or `name` could not be converted to a
+    /// [`SmallCStr`].
+    pub fn add_fn(&'llvm self, name: &str, fn_type: Type<'llvm>) -> FnValue<'llvm> {
+        debug_assert_eq!(
+            fn_type.kind(),
+            LLVMTypeKind::LLVMFunctionTypeKind,
+            "Expected a function type when adding a function!"
+        );
+
+        let name = SmallCStr::try_from(name)
+            .expect("Failed to convert 'name' argument to small C string!");
+
+        let value_ref = unsafe { LLVMAddFunction(self.module, name.as_ptr(), fn_type.0) };
+        FnValue::new(value_ref)
+    }
+
+    /// Get a function value reference to the function with the given `name` if it was previously
+    /// added to the module with [`add_fn`][Module::add_fn].
+    ///
+    /// # Panics
+    ///
+    /// Panics if `name` could not be converted to a [`SmallCStr`].
+    pub fn get_fn(&'llvm self, name: &str) -> Option<FnValue<'llvm>> {
+        let name = SmallCStr::try_from(name)
+            .expect("Failed to convert 'name' argument to small C string!");
+
+        let value_ref = unsafe { LLVMGetNamedFunction(self.module, name.as_ptr()) };
+
+        (!value_ref.is_null()).then(|| FnValue::new(value_ref))
+    }
+
+    /// Append a Basic Block to the end of the function referenced by the value reference
+    /// `fn_value`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn append_basic_block(&'llvm self, fn_value: FnValue<'llvm>) -> BasicBlock<'llvm> {
+        let block = unsafe {
+            LLVMAppendBasicBlockInContext(
+                self.ctx,
+                fn_value.value_ref(),
+                b"block\0".as_ptr().cast(),
+            )
+        };
+        assert!(!block.is_null());
+
+        BasicBlock(block, PhantomData)
+    }
+}
+
+impl Drop for Module {
+    fn drop(&mut self) {
+        unsafe {
+            LLVMDisposeModule(self.module);
+            LLVMContextDispose(self.ctx);
+        }
+    }
+}
+
+// ===========
+//   Builder
+// ===========
+
+/// Wrapper for a LLVM IR Builder.
+pub struct Builder<'llvm> {
+    builder: LLVMBuilderRef,
+    _ctx: PhantomData<&'llvm ()>,
+}
+
+impl<'llvm> Builder<'llvm> {
+    /// Create a new LLVM IR Builder with the `module`s context.
+    ///
+    /// # Panics
+    ///
+    /// Panics if creating the IR Builder fails.
+    pub fn with_ctx(module: &'llvm Module) -> Builder<'llvm> {
+        let builder = unsafe { LLVMCreateBuilderInContext(module.ctx) };
+        assert!(!builder.is_null());
+
+        Builder {
+            builder,
+            _ctx: PhantomData,
+        }
+    }
+
+    /// Position the IR Builder at the end of the given Basic Block.
+    pub fn pos_at_end(&self, bb: BasicBlock<'llvm>) {
+        unsafe {
+            LLVMPositionBuilderAtEnd(self.builder, bb.0);
+        }
+    }
+
+    /// Emit a [fadd](https://llvm.org/docs/LangRef.html#fadd-instruction) instruction.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn fadd(&self, lhs: Value<'llvm>, rhs: Value<'llvm>) -> Value<'llvm> {
+        debug_assert!(lhs.is_f64(), "fadd: Expected f64 as lhs operand!");
+        debug_assert!(rhs.is_f64(), "fadd: Expected f64 as rhs operand!");
+
+        let value_ref = unsafe {
+            LLVMBuildFAdd(
+                self.builder,
+                lhs.value_ref(),
+                rhs.value_ref(),
+                b"fadd\0".as_ptr().cast(),
+            )
+        };
+        Value::new(value_ref)
+    }
+
+    /// Emit a [fsub](https://llvm.org/docs/LangRef.html#fsub-instruction) instruction.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn fsub(&self, lhs: Value<'llvm>, rhs: Value<'llvm>) -> Value<'llvm> {
+        debug_assert!(lhs.is_f64(), "fsub: Expected f64 as lhs operand!");
+        debug_assert!(rhs.is_f64(), "fsub: Expected f64 as rhs operand!");
+
+        let value_ref = unsafe {
+            LLVMBuildFSub(
+                self.builder,
+                lhs.value_ref(),
+                rhs.value_ref(),
+                b"fsub\0".as_ptr().cast(),
+            )
+        };
+        Value::new(value_ref)
+    }
+
+    /// Emit a [fmul](https://llvm.org/docs/LangRef.html#fmul-instruction) instruction.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn fmul(&self, lhs: Value<'llvm>, rhs: Value<'llvm>) -> Value<'llvm> {
+        debug_assert!(lhs.is_f64(), "fmul: Expected f64 as lhs operand!");
+        debug_assert!(rhs.is_f64(), "fmul: Expected f64 as rhs operand!");
+
+        let value_ref = unsafe {
+            LLVMBuildFMul(
+                self.builder,
+                lhs.value_ref(),
+                rhs.value_ref(),
+                b"fmul\0".as_ptr().cast(),
+            )
+        };
+        Value::new(value_ref)
+    }
+
+    /// Emit a [fcmult](https://llvm.org/docs/LangRef.html#fcmp-instruction) instruction.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn fcmpult(&self, lhs: Value<'llvm>, rhs: Value<'llvm>) -> Value<'llvm> {
+        debug_assert!(lhs.is_f64(), "fcmplt: Expected f64 as lhs operand!");
+        debug_assert!(rhs.is_f64(), "fcmplt: Expected f64 as rhs operand!");
+
+        let value_ref = unsafe {
+            LLVMBuildFCmp(
+                self.builder,
+                LLVMRealPredicate::LLVMRealULT,
+                lhs.value_ref(),
+                rhs.value_ref(),
+                b"fcmplt\0".as_ptr().cast(),
+            )
+        };
+        Value::new(value_ref)
+    }
+
+    /// Emit a [uitofp](https://llvm.org/docs/LangRef.html#uitofp-to-instruction) instruction.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn uitofp(&self, val: Value<'llvm>, dest_type: Type<'llvm>) -> Value<'llvm> {
+        debug_assert!(val.is_int(), "uitofp: Expected integer operand!");
+
+        let value_ref = unsafe {
+            LLVMBuildUIToFP(
+                self.builder,
+                val.value_ref(),
+                dest_type.0,
+                b"uitofp\0".as_ptr().cast(),
+            )
+        };
+        Value::new(value_ref)
+    }
+
+    /// Emit a [call](https://llvm.org/docs/LangRef.html#call-instruction) instruction.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn call(&self, fn_value: FnValue<'llvm>, args: &mut [Value<'llvm>]) -> Value<'llvm> {
+        let value_ref = unsafe {
+            LLVMBuildCall2(
+                self.builder,
+                fn_value.ret_type(),
+                fn_value,
+                args.as_mut_ptr(),
+                args.len() as libc::c_uint,
+                b"call\0".as_ptr().cast(),
+            )
+        };
+        Value::new(value_ref)
+    }
+
+    /// Emit a [ret](https://llvm.org/docs/LangRef.html#ret-instruction) instruction.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn ret(&self, ret: Value<'llvm>) {
+        let ret = unsafe { LLVMBuildRet(self.builder, ret.value_ref()) };
+        assert!(!ret.is_null());
+    }
+}
+
+impl Drop for Builder<'_> {
+    fn drop(&mut self) {
+        unsafe { LLVMDisposeBuilder(self.builder) }
+    }
+}
+
+// ==============
+//   BasicBlock
+// ==============
+
+/// Wrapper for a LLVM Basic Block.
+#[derive(Copy, Clone)]
+pub struct BasicBlock<'llvm>(LLVMBasicBlockRef, PhantomData<&'llvm ()>);
+
+// ========
+//   Type
+// ========
+
+/// Wrapper for a LLVM Type Reference.
+#[derive(Copy, Clone)]
+#[repr(transparent)]
+pub struct Type<'llvm>(LLVMTypeRef, PhantomData<&'llvm ()>);
+
+impl<'llvm> Type<'llvm> {
+    fn new(type_ref: LLVMTypeRef) -> Self {
+        assert!(!type_ref.is_null());
+        Type(type_ref, PhantomData)
+    }
+
+    fn kind(&self) -> LLVMTypeKind {
+        unsafe { LLVMGetTypeKind(self.0) }
+    }
+
+    /// Dump the LLVM Type to stdout.
+    pub fn dump(&self) {
+        unsafe { LLVMDumpType(self.0) };
+    }
+
+    /// Get a value reference representing the const `f64` value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn const_f64(self, n: f64) -> Value<'llvm> {
+        debug_assert_eq!(
+            self.kind(),
+            LLVMTypeKind::LLVMDoubleTypeKind,
+            "Expected a double type when creating const f64 value!"
+        );
+
+        let value_ref = unsafe { LLVMConstReal(self.0, n) };
+        Value::new(value_ref)
+    }
+}
+
+// =========
+//   Value
+// =========
+
+/// Wrapper for a LLVM Value Reference.
+#[derive(Copy, Clone)]
+#[repr(transparent)]
+pub struct Value<'llvm>(LLVMValueRef, PhantomData<&'llvm ()>);
+
+impl<'llvm> Value<'llvm> {
+    fn new(value_ref: LLVMValueRef) -> Self {
+        assert!(!value_ref.is_null());
+        Value(value_ref, PhantomData)
+    }
+
+    #[inline]
+    fn value_ref(&self) -> LLVMValueRef {
+        self.0
+    }
+
+    fn kind(&self) -> LLVMValueKind {
+        unsafe { LLVMGetValueKind(self.value_ref()) }
+    }
+
+    /// Dump the LLVM Value to stdout.
+    pub fn dump(&self) {
+        unsafe { LLVMDumpValue(self.value_ref()) };
+    }
+
+    /// Get a type reference representing for the given value reference.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn type_of(&self) -> Type<'llvm> {
+        let type_ref = unsafe { LLVMTypeOf(self.value_ref()) };
+        Type::new(type_ref)
+    }
+
+    /// Set the name for the given value reference.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn set_name(&self, name: &str) {
+        unsafe { LLVMSetValueName2(self.value_ref(), name.as_ptr().cast(), name.len()) };
+    }
+
+    /// Get the name for the given value reference.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn get_name(&self) -> &'llvm str {
+        let name = unsafe {
+            let mut len: libc::size_t = 0;
+            let name = LLVMGetValueName2(self.0, &mut len as _);
+            assert!(!name.is_null());
+
+            CStr::from_ptr(name)
+        };
+
+        // TODO: Does this string live for the time of the LLVM context?!
+        name.to_str()
+            .expect("Expected valid UTF8 string from LLVM API")
+    }
+
+    /// Check if value is of `f64` type.
+    pub fn is_f64(&self) -> bool {
+        self.type_of().kind() == LLVMTypeKind::LLVMDoubleTypeKind
+    }
+
+    /// Check if value is of integer type.
+    pub fn is_int(&self) -> bool {
+        self.type_of().kind() == LLVMTypeKind::LLVMIntegerTypeKind
+    }
+}
+
+/// Wrapper for a LLVM Value Reference specialized for contexts where function values are needed.
+#[derive(Copy, Clone)]
+#[repr(transparent)]
+pub struct FnValue<'llvm>(Value<'llvm>);
+
+impl<'llvm> Deref for FnValue<'llvm> {
+    type Target = Value<'llvm>;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<'llvm> FnValue<'llvm> {
+    fn new(value_ref: LLVMValueRef) -> Self {
+        let value = Value::new(value_ref);
+        debug_assert_eq!(
+            value.kind(),
+            LLVMValueKind::LLVMFunctionValueKind,
+            "Expected a fn value when constructing FnValue!"
+        );
+
+        FnValue(value)
+    }
+
+    /// Get a type reference representing the return value of the given function value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer.
+    pub fn ret_type(&self) -> Type<'llvm> {
+        let type_ref = unsafe { LLVMGetReturnType(LLVMTypeOf(self.value_ref())) };
+        Type::new(type_ref)
+    }
+
+    /// Get the number of function arguments for the given function value.
+    pub fn args(&self) -> usize {
+        unsafe { LLVMCountParams(self.value_ref()) as usize }
+    }
+
+    /// Get a value reference for the function argument at index `idx`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if LLVM API returns a `null` pointer or indexed out of bounds.
+    pub fn arg(&self, idx: usize) -> Value<'llvm> {
+        assert!(idx < self.args());
+
+        let value_ref = unsafe { LLVMGetParam(self.value_ref(), idx as libc::c_uint) };
+        Value::new(value_ref)
+    }
+
+    /// Get the number of Basic Blocks for the given function value.
+    pub fn basic_blocks(&self) -> usize {
+        unsafe { LLVMCountBasicBlocks(self.value_ref()) as usize }
+    }
+
+    /// Verify that the given function is valid.
+    pub fn verify(&self) -> bool {
+        unsafe {
+            LLVMVerifyFunction(
+                self.value_ref(),
+                LLVMVerifierFailureAction::LLVMPrintMessageAction,
+            ) == 0
+        }
+    }
+}
+

+