{ lib }:

let
  inherit (lib)
    any
    filterAttrs
    foldl
    hasInfix
    isAttrs
    isFunction
    isList
    mapAttrs
    optional
    optionalAttrs
    optionalString
    removeSuffix
    replaceStrings
    toUpper
    ;

  inherit (lib.strings) toJSON;

  doubles = import ./doubles.nix { inherit lib; };
  parse = import ./parse.nix { inherit lib; };
  inspect = import ./inspect.nix { inherit lib; };
  platforms = import ./platforms.nix { inherit lib; };
  examples = import ./examples.nix { inherit lib; };
  architectures = import ./architectures.nix { inherit lib; };

  /**
    Elaborated systems contain functions, which means that they don't satisfy
    `==` for a lack of reflexivity.

    They might *appear* to satisfy `==` reflexivity when the same exact value is
    compared to itself, because object identity is used as an "optimization";
    compare the value with a reconstruction of itself, e.g. with `f == a: f a`,
    or perhaps calling `elaborate` twice, and one will see reflexivity fail as described.

    Hence a custom equality test.

    Note that this does not canonicalize the systems, so you'll want to make sure
    both arguments have been `elaborate`-d.
  */
  equals =
    let
      removeFunctions = a: filterAttrs (_: v: !isFunction v) a;
    in
    a: b: removeFunctions a == removeFunctions b;

  /**
    List of all Nix system doubles the nixpkgs flake will expose the package set
    for. All systems listed here must be supported by nixpkgs as `localSystem`.

    :::{.warning}
    This attribute is considered experimental and is subject to change.
    :::
  */
  flakeExposed = import ./flake-systems.nix { };

  # Turn localSystem or crossSystem, which could be system-string or attrset, into
  # attrset.
  systemToAttrs =
    systemOrArgs: if isAttrs systemOrArgs then systemOrArgs else { system = systemOrArgs; };

  # Elaborate a `localSystem` or `crossSystem` so that it contains everything
  # necessary.
  #
  # `parsed` is inferred from args, both because there are two options with one
  # clearly preferred, and to prevent cycles. A simpler fixed point where the RHS
  # always just used `final.*` would fail on both counts.
  elaborate =
    systemOrArgs:
    let
      allArgs = systemToAttrs systemOrArgs;

      # Those two will always be derived from "config", if given, so they should NOT
      # be overridden further down with "// args".
      args = builtins.removeAttrs allArgs [
        "parsed"
        "system"
      ];

      # TODO: deprecate args.rustc in favour of args.rust after 23.05 is EOL.
      rust = args.rust or args.rustc or { };

      final =
        {
          # Prefer to parse `config` as it is strictly more informative.
          parsed = parse.mkSystemFromString (args.config or allArgs.system);
          # This can be losslessly-extracted from `parsed` iff parsing succeeds.
          system = parse.doubleFromSystem final.parsed;
          # TODO: This currently can't be losslessly-extracted from `parsed`, for example
          # because of -mingw32.
          config = parse.tripleFromSystem final.parsed;
          # Determine whether we can execute binaries built for the provided platform.
          canExecute =
            platform:
            final.isAndroid == platform.isAndroid
            && parse.isCompatible final.parsed.cpu platform.parsed.cpu
            && final.parsed.kernel == platform.parsed.kernel;
          isCompatible =
            _:
            throw "2022-05-23: isCompatible has been removed in favor of canExecute, refer to the 22.11 changelog for details";
          # Derived meta-data
          useLLVM = final.isFreeBSD || final.isOpenBSD;

          libc =
            if final.isDarwin then
              "libSystem"
            else if final.isMinGW then
              "msvcrt"
            else if final.isWasi then
              "wasilibc"
            else if final.isWasm && !final.isWasi then
              null
            else if final.isRedox then
              "relibc"
            else if final.isMusl then
              "musl"
            else if final.isUClibc then
              "uclibc"
            else if final.isAndroid then
              "bionic"
            else if final.isLLVMLibc then
              "llvm"
            else if
              final.isLinux # default
            then
              "glibc"
            else if final.isFreeBSD then
              "fblibc"
            else if final.isOpenBSD then
              "oblibc"
            else if final.isNetBSD then
              "nblibc"
            else if final.isAvr then
              "avrlibc"
            else if final.isGhcjs then
              null
            else if final.isNone then
              "newlib"
            # TODO(@Ericson2314) think more about other operating systems
            else
              "native/impure";
          # Choose what linker we wish to use by default. Someday we might also
          # choose the C compiler, runtime library, C++ standard library, etc. in
          # this way, nice and orthogonally, and deprecate `useLLVM`. But due to
          # the monolithic GCC build we cannot actually make those choices
          # independently, so we are just doing `linker` and keeping `useLLVM` for
          # now.
          linker =
            if final.useLLVM or false then
              "lld"
            else if final.isDarwin then
              "cctools"
            # "bfd" and "gold" both come from GNU binutils. The existence of Gold
            # is why we use the more obscure "bfd" and not "binutils" for this
            # choice.
            else
              "bfd";
          # The standard lib directory name that non-nixpkgs binaries distributed
          # for this platform normally assume.
          libDir =
            if final.isLinux then
              if final.isx86_64 || final.isMips64 || final.isPower64 then "lib64" else "lib"
            else
              null;
          extensions =
            optionalAttrs final.hasSharedLibraries {
              sharedLibrary =
                if final.isDarwin then
                  ".dylib"
                else if final.isWindows then
                  ".dll"
                else
                  ".so";
            }
            // {
              staticLibrary = if final.isWindows then ".lib" else ".a";
              library = if final.isStatic then final.extensions.staticLibrary else final.extensions.sharedLibrary;
              executable = if final.isWindows then ".exe" else "";
            };
          # Misc boolean options
          useAndroidPrebuilt = false;
          useiOSPrebuilt = false;

          # Output from uname
          uname = {
            # uname -s
            system =
              {
                linux = "Linux";
                windows = "Windows";
                darwin = "Darwin";
                netbsd = "NetBSD";
                freebsd = "FreeBSD";
                openbsd = "OpenBSD";
                wasi = "Wasi";
                redox = "Redox";
                genode = "Genode";
              }
              .${final.parsed.kernel.name} or null;

            # uname -m
            processor =
              if final.isPower64 then
                "ppc64${optionalString final.isLittleEndian "le"}"
              else if final.isPower then
                "ppc${optionalString final.isLittleEndian "le"}"
              else if final.isMips64 then
                "mips64" # endianness is *not* included on mips64
              else
                final.parsed.cpu.name;

            # uname -r
            release = null;
          };

          # It is important that hasSharedLibraries==false when the platform has no
          # dynamic library loader.  Various tools (including the gcc build system)
          # have knowledge of which platforms are incapable of dynamic linking, and
          # will still build on/for those platforms with --enable-shared, but simply
          # omit any `.so` build products such as libgcc_s.so.  When that happens,
          # it causes hard-to-troubleshoot build failures.
          hasSharedLibraries =
            with final;
            (
              isAndroid
              || isGnu
              || isMusl # Linux (allows multiple libcs)
              || isDarwin
              || isSunOS
              || isOpenBSD
              || isFreeBSD
              || isNetBSD # BSDs
              || isCygwin
              || isMinGW
              || isWindows # Windows
              || isWasm # WASM
            )
            && !isStatic;

          # The difference between `isStatic` and `hasSharedLibraries` is mainly the
          # addition of the `staticMarker` (see make-derivation.nix).  Some
          # platforms, like embedded machines without a libc (e.g. arm-none-eabi)
          # don't support dynamic linking, but don't get the `staticMarker`.
          # `pkgsStatic` sets `isStatic=true`, so `pkgsStatic.hostPlatform` always
          # has the `staticMarker`.
          isStatic = final.isWasi || final.isRedox;

          # Just a guess, based on `system`
          inherit
            (
              {
                linux-kernel = args.linux-kernel or { };
                gcc = args.gcc or { };
              }
              // platforms.select final
            )
            linux-kernel
            gcc
            ;

          # TODO: remove after 23.05 is EOL, with an error pointing to the rust.* attrs.
          rustc = args.rustc or { };

          linuxArch =
            if final.isAarch32 then
              "arm"
            else if final.isAarch64 then
              "arm64"
            else if final.isx86_32 then
              "i386"
            else if final.isx86_64 then
              "x86_64"
            # linux kernel does not distinguish microblaze/microblazeel
            else if final.isMicroBlaze then
              "microblaze"
            else if final.isMips32 then
              "mips"
            else if final.isMips64 then
              "mips" # linux kernel does not distinguish mips32/mips64
            else if final.isPower then
              "powerpc"
            else if final.isRiscV then
              "riscv"
            else if final.isS390 then
              "s390"
            else if final.isLoongArch64 then
              "loongarch"
            else
              final.parsed.cpu.name;

          # https://source.denx.de/u-boot/u-boot/-/blob/9bfb567e5f1bfe7de8eb41f8c6d00f49d2b9a426/common/image.c#L81-106
          ubootArch =
            if final.isx86_32 then
              "x86" # not i386
            else if final.isMips64 then
              "mips64" # uboot *does* distinguish between mips32/mips64
            else
              final.linuxArch; # other cases appear to agree with linuxArch

          qemuArch =
            if final.isAarch32 then
              "arm"
            else if final.isS390 && !final.isS390x then
              null
            else if final.isx86_64 then
              "x86_64"
            else if final.isx86 then
              "i386"
            else if final.isMips64n32 then
              "mipsn32${optionalString final.isLittleEndian "el"}"
            else if final.isMips64 then
              "mips64${optionalString final.isLittleEndian "el"}"
            else
              final.uname.processor;

          # Name used by UEFI for architectures.
          efiArch =
            if final.isx86_32 then
              "ia32"
            else if final.isx86_64 then
              "x64"
            else if final.isAarch32 then
              "arm"
            else if final.isAarch64 then
              "aa64"
            else
              final.parsed.cpu.name;

          darwinArch =
            {
              armv7a = "armv7";
              aarch64 = "arm64";
            }
            .${final.parsed.cpu.name} or final.parsed.cpu.name;

          darwinPlatform =
            if final.isMacOS then
              "macos"
            else if final.isiOS then
              "ios"
            else
              null;
          # The canonical name for this attribute is darwinSdkVersion, but some
          # platforms define the old name "sdkVer".
          darwinSdkVersion = final.sdkVer or "11.3";
          darwinMinVersion = final.darwinSdkVersion;
          darwinMinVersionVariable =
            if final.isMacOS then
              "MACOSX_DEPLOYMENT_TARGET"
            else if final.isiOS then
              "IPHONEOS_DEPLOYMENT_TARGET"
            else
              null;

          # Remove before 25.05
          androidSdkVersion =
            if (args ? sdkVer && !args ? androidSdkVersion) then
              throw "For android `sdkVer` has been renamed to `androidSdkVersion`"
            else if (args ? androidSdkVersion) then
              args.androidSdkVersion
            else
              null;
          androidNdkVersion =
            if (args ? ndkVer && !args ? androidNdkVersion) then
              throw "For android `ndkVer` has been renamed to `androidNdkVersion`"
            else if (args ? androidSdkVersion) then
              args.androidNdkVersion
            else
              null;
        }
        // (
          let
            selectEmulator =
              pkgs:
              let
                wine = (pkgs.winePackagesFor "wine${toString final.parsed.cpu.bits}").minimal;
              in
              # Note: we guarantee that the return value is either `null` or a path
              # to an emulator program. That is, if an emulator requires additional
              # arguments, a wrapper should be used.
              if pkgs.stdenv.hostPlatform.canExecute final then
                lib.getExe (pkgs.writeShellScriptBin "exec" ''exec "$@"'')
              else if final.isWindows then
                "${wine}/bin/wine${optionalString (final.parsed.cpu.bits == 64) "64"}"
              else if final.isLinux && pkgs.stdenv.hostPlatform.isLinux && final.qemuArch != null then
                "${pkgs.qemu-user}/bin/qemu-${final.qemuArch}"
              else if final.isWasi then
                "${pkgs.wasmtime}/bin/wasmtime"
              else if final.isMmix then
                "${pkgs.mmixware}/bin/mmix"
              else
                null;
          in
          {
            emulatorAvailable = pkgs: (selectEmulator pkgs) != null;

            # whether final.emulator pkgs.pkgsStatic works
            staticEmulatorAvailable =
              pkgs: final.emulatorAvailable pkgs && (final.isLinux || final.isWasi || final.isMmix);

            emulator =
              pkgs:
              if (final.emulatorAvailable pkgs) then
                selectEmulator pkgs
              else
                throw "Don't know how to run ${final.config} executables.";

          }
        )
        // mapAttrs (n: v: v final.parsed) inspect.predicates
        // mapAttrs (n: v: v final.gcc.arch or "default") architectures.predicates
        // args
        // {
          rust = rust // {
            # Once args.rustc.platform.target-family is deprecated and
            # removed, there will no longer be any need to modify any
            # values from args.rust.platform, so we can drop all the
            # "args ? rust" etc. checks, and merge args.rust.platform in
            # /after/.
            platform = rust.platform or { } // {
              # https://doc.rust-lang.org/reference/conditional-compilation.html#target_arch
              arch =
                if rust ? platform then
                  rust.platform.arch
                else if final.isAarch32 then
                  "arm"
                else if final.isMips64 then
                  "mips64" # never add "el" suffix
                else if final.isPower64 then
                  "powerpc64" # never add "le" suffix
                else
                  final.parsed.cpu.name;

              # https://doc.rust-lang.org/reference/conditional-compilation.html#target_os
              os =
                if rust ? platform then
                  rust.platform.os or "none"
                else if final.isDarwin then
                  "macos"
                else if final.isWasm && !final.isWasi then
                  "unknown" # Needed for {wasm32,wasm64}-unknown-unknown.
                else
                  final.parsed.kernel.name;

              # https://doc.rust-lang.org/reference/conditional-compilation.html#target_family
              target-family =
                if args ? rust.platform.target-family then
                  args.rust.platform.target-family
                else if args ? rustc.platform.target-family then
                  (
                    # Since https://github.com/rust-lang/rust/pull/84072
                    # `target-family` is a list instead of single value.
                    let
                      f = args.rustc.platform.target-family;
                    in
                    if isList f then f else [ f ]
                  )
                else
                  optional final.isUnix "unix" ++ optional final.isWindows "windows" ++ optional final.isWasm "wasm";

              # https://doc.rust-lang.org/reference/conditional-compilation.html#target_vendor
              vendor =
                let
                  inherit (final.parsed) vendor;
                in
                rust.platform.vendor or {
                  "w64" = "pc";
                }
                .${vendor.name} or vendor.name;
            };

            # The name of the rust target, even if it is custom. Adjustments are
            # because rust has slightly different naming conventions than we do.
            rustcTarget =
              let
                inherit (final.parsed) cpu kernel abi;
                cpu_ =
                  rust.platform.arch or {
                    "armv7a" = "armv7";
                    "armv7l" = "armv7";
                    "armv6l" = "arm";
                    "armv5tel" = "armv5te";
                    "riscv32" = "riscv32gc";
                    "riscv64" = "riscv64gc";
                  }
                  .${cpu.name} or cpu.name;
                vendor_ = final.rust.platform.vendor;
                # TODO: deprecate args.rustc in favour of args.rust after 23.05 is EOL.
              in
              args.rust.rustcTarget or args.rustc.config or (
                # Rust uses `wasm32-wasip?` rather than `wasm32-unknown-wasi`.
                # We cannot know which subversion does the user want, and
                # currently use WASI 0.1 as default for compatibility. Custom
                # users can set `rust.rustcTarget` to override it.
                if final.isWasi then
                  "${cpu_}-wasip1"
                else
                  "${cpu_}-${vendor_}-${kernel.name}${optionalString (abi.name != "unknown") "-${abi.name}"}"
              );

            # The name of the rust target if it is standard, or the json file
            # containing the custom target spec.
            rustcTargetSpec =
              rust.rustcTargetSpec or (
                if rust ? platform then
                  builtins.toFile (final.rust.rustcTarget + ".json") (toJSON rust.platform)
                else
                  final.rust.rustcTarget
              );

            # The name of the rust target if it is standard, or the
            # basename of the file containing the custom target spec,
            # without the .json extension.
            #
            # This is the name used by Cargo for target subdirectories.
            cargoShortTarget = removeSuffix ".json" (baseNameOf "${final.rust.rustcTargetSpec}");

            # When used as part of an environment variable name, triples are
            # uppercased and have all hyphens replaced by underscores:
            #
            # https://github.com/rust-lang/cargo/pull/9169
            # https://github.com/rust-lang/cargo/issues/8285#issuecomment-634202431
            cargoEnvVarTarget = replaceStrings [ "-" ] [ "_" ] (toUpper final.rust.cargoShortTarget);

            # True if the target is no_std
            # https://github.com/rust-lang/rust/blob/2e44c17c12cec45b6a682b1e53a04ac5b5fcc9d2/src/bootstrap/config.rs#L415-L421
            isNoStdTarget = any (t: hasInfix t final.rust.rustcTarget) [
              "-none"
              "nvptx"
              "switch"
              "-uefi"
            ];
          };
        };
    in
    assert final.useAndroidPrebuilt -> final.isAndroid;
    assert foldl (pass: { assertion, message }: if assertion final then pass else throw message) true (
      final.parsed.abi.assertions or [ ]
    );
    final;

in

# Everything in this attrset is the public interface of the file.
{
  inherit
    architectures
    doubles
    elaborate
    equals
    examples
    flakeExposed
    inspect
    parse
    platforms
    systemToAttrs
    ;
}
