{ lib, stdenv
, fetch
, cmake
, python3
, libffi
, libbfd
, libxml2
, ncurses
, version
, release_version
, zlib
, buildPackages
, fetchpatch
, debugVersion ? false
, enableManpages ? false
, enableSharedLibraries ? true
}:

let
  inherit (lib) optional optionals optionalString;

  # Used when creating a versioned symlinks of libLLVM.dylib
  versionSuffixes = with lib;
    let parts = splitVersion release_version; in
    imap (i: _: concatStringsSep "." (take i parts)) parts;
in

stdenv.mkDerivation ({
  pname = "llvm";
  inherit version;

  src = fetch "llvm" "1qpls3vk85lydi5b4axl0809fv932qgsqgdgrk098567z4jc7mmn";

  unpackPhase = ''
    unpackFile $src
    mv llvm-${version}* llvm
    sourceRoot=$PWD/llvm
  '';

  outputs = [ "out" "python" ]
    ++ optional enableSharedLibraries "lib";

  nativeBuildInputs = [ cmake python3 ]
    ++ optional enableManpages python3.pkgs.sphinx;

  buildInputs = [ libxml2 libffi ];

  propagatedBuildInputs = [ ncurses zlib ];

  patches = [
    # Patches to fix tests, included in llvm_7
    (fetchpatch {
      url = "https://github.com/llvm-mirror/llvm/commit/737553be0c9c25c497b45a241689994f177d5a5d.patch";
      sha256 = "0hnaxnkx7zy5yg98f1ggv8a9l0r6g19n6ygqsv26masrnlcbccli";
    })
    (fetchpatch {
      url = "https://github.com/llvm-mirror/llvm/commit/1c0dd31a7837c3e2f1c4ac14e4d5ac640688bd1f.patch";
      includes = [ "test/tools/gold/X86/common.ll" ];
      sha256 = "0fxgrxmfnjx17w3lcq19rk68b2xksh1bynz3ina784kma7hp4wdb";
    })
  ];

  postPatch = optionalString stdenv.isDarwin ''
    substituteInPlace cmake/modules/AddLLVM.cmake \
      --replace 'set(_install_name_dir INSTALL_NAME_DIR "@rpath")' "set(_install_name_dir)" \
      --replace 'set(_install_rpath "@loader_path/../lib" ''${extra_libdir})' ""
  ''
  # Patch llvm-config to return correct library path based on --link-{shared,static}.
  + optionalString (enableSharedLibraries) ''
    substitute '${./llvm-outputs.patch}' ./llvm-outputs.patch --subst-var lib
    patch -p1 < ./llvm-outputs.patch
  '' + ''
    # FileSystem permissions tests fail with various special bits
    substituteInPlace unittests/Support/CMakeLists.txt \
      --replace "Path.cpp" ""
    rm unittests/Support/Path.cpp
  '' + optionalString stdenv.hostPlatform.isMusl ''
    patch -p1 -i ${../TLI-musl.patch}
    substituteInPlace unittests/Support/CMakeLists.txt \
      --replace "add_subdirectory(DynamicLibrary)" ""
    rm unittests/Support/DynamicLibrary/DynamicLibraryTest.cpp
  '';

  # hacky fix: created binaries need to be run before installation
  preBuild = ''
    mkdir -p $out/
    ln -sv $PWD/lib $out
  '';

  cmakeFlags = with stdenv; [
    "-DCMAKE_BUILD_TYPE=${if debugVersion then "Debug" else "Release"}"
    "-DLLVM_INSTALL_UTILS=ON"  # Needed by rustc
    "-DLLVM_BUILD_TESTS=ON"
    "-DLLVM_ENABLE_FFI=ON"
    "-DLLVM_ENABLE_RTTI=ON"
    "-DLLVM_HOST_TRIPLE=${stdenv.hostPlatform.config}"
    "-DLLVM_DEFAULT_TARGET_TRIPLE=${stdenv.hostPlatform.config}"
    "-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=WebAssembly"
    "-DLLVM_ENABLE_DUMP=ON"
  ] ++ optionals enableSharedLibraries [
    "-DLLVM_LINK_LLVM_DYLIB=ON"
  ] ++ optionals enableManpages [
    "-DLLVM_BUILD_DOCS=ON"
    "-DLLVM_ENABLE_SPHINX=ON"
    "-DSPHINX_OUTPUT_MAN=ON"
    "-DSPHINX_OUTPUT_HTML=OFF"
    "-DSPHINX_WARNINGS_AS_ERRORS=OFF"
  ] ++ optionals (!isDarwin) [
    "-DLLVM_BINUTILS_INCDIR=${libbfd.dev}/include"
  ] ++ optionals (isDarwin) [
    "-DLLVM_ENABLE_LIBCXX=ON"
    "-DCAN_TARGET_i386=false"
  ] ++ optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
    "-DCMAKE_CROSSCOMPILING=True"
    "-DLLVM_TABLEGEN=${buildPackages.llvm_6}/bin/llvm-tblgen"
  ];

  postBuild = ''
    rm -fR $out
  '';

  preCheck = ''
    export LD_LIBRARY_PATH=$LD_LIBRARY_PATH''${LD_LIBRARY_PATH:+:}$PWD/lib
  '';

  postInstall = ''
    mkdir -p $python/share
    mv $out/share/opt-viewer $python/share/opt-viewer
  ''
  + optionalString enableSharedLibraries ''
    moveToOutput "lib/libLLVM-*" "$lib"
    moveToOutput "lib/libLLVM${stdenv.hostPlatform.extensions.sharedLibrary}" "$lib"
    substituteInPlace "$out/lib/cmake/llvm/LLVMExports-${if debugVersion then "debug" else "release"}.cmake" \
      --replace "\''${_IMPORT_PREFIX}/lib/libLLVM-" "$lib/lib/libLLVM-"
  ''
  + optionalString (stdenv.isDarwin && enableSharedLibraries) ''
    substituteInPlace "$out/lib/cmake/llvm/LLVMExports-${if debugVersion then "debug" else "release"}.cmake" \
      --replace "\''${_IMPORT_PREFIX}/lib/libLLVM.dylib" "$lib/lib/libLLVM.dylib"
    ${lib.concatMapStringsSep "\n" (v: ''
      ln -s $lib/lib/libLLVM.dylib $lib/lib/libLLVM-${v}.dylib
    '') versionSuffixes}
  '';

  doCheck = stdenv.isLinux && (!stdenv.isi686);

  checkTarget = "check-all";

  requiredSystemFeatures = [ "big-parallel" ];
  meta = {
    description = "Collection of modular and reusable compiler and toolchain technologies";
    homepage    = "https://llvm.org/";
    license     = lib.licenses.ncsa;
    maintainers = with lib.maintainers; [ lovek323 raskin dtzWill ];
    platforms   = lib.platforms.all;
  };
} // lib.optionalAttrs enableManpages {
  pname = "llvm-manpages";

  buildPhase = ''
    make docs-llvm-man
  '';

  propagatedBuildInputs = [];

  installPhase = ''
    make -C docs install
  '';

  outputs = [ "out" ];

  doCheck = false;

  meta.description = "man pages for LLVM ${version}";
})