{ lib }:

let
  inherit (lib)
    any
    filterAttrs
    foldl
    hasInfix
    isFunction
    isList
    isString
    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 { };

  # 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 = args': let
    args = if isString args' then { system = args'; }
           else args';

    # 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 (if args ? config then args.config else args.system);
      # Either of these can be losslessly-extracted from `parsed` iff parsing succeeds.
      system = parse.doubleFromSystem final.parsed;
      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.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 (if final.isAarch64 then "11.0" else "10.12");
      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${toString final.parsed.cpu.bits}").minimal;
          in
          # Note: we guarantee that the return value is either `null` or a path
          # to an emulator program. That is, if an emulator requires additional
          # arguments, a wrapper should be used.
          if pkgs.stdenv.hostPlatform.canExecute final
          then "${pkgs.execline}/bin/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
    ;
}
