# SPDX-FileCopyrightText: © 2026 Jeffrey C. Ollie <jeff@ocjtech.us>
# SPDX-License-Identifier: MIT

{
  description = "zig-maildir";

  inputs = {
    nixpkgs = {
      url = "https://channels.nixos.org/nixos-unstable/nixexprs.tar.xz";
    };
    # Mine, not the one in nixpkgs, which is Jari Vetoniemi's original and
    # takes different options.
    zon2nix = {
      url = "github:jcollie/zon2nix";
      inputs = {
        nixpkgs.follows = "nixpkgs";
      };
    };
  };

  outputs =
    {
      nixpkgs,
      zon2nix,
      ...
    }:
    let
      inherit (nixpkgs) lib;
      makePackages =
        system:
        import nixpkgs {
          inherit system;
        };
      forAllSystems = lib.genAttrs lib.systems.flakeExposed;
      # The virtual machine tests are NixOS ones, so they exist only where
      # NixOS does. Without this `nix flake check` tries to evaluate them for
      # Darwin and fails before it has run anything.
      forLinuxSystems = lib.genAttrs (
        lib.filter (system: lib.hasSuffix "-linux" system) lib.systems.flakeExposed
      );

      # The devshell's Zig, with one line of its own standard library put
      # right, because without it `zig build fuzz --fuzz` cannot compile.
      #
      # Zig 0.16.0's `compiler/test_runner.zig` reports a failing fuzz input by
      # asking `std.debug.writeStackTrace` to print what `@errorReturnTrace()`
      # gave it. Those are two different types: an error return trace is a
      # `builtin.StackTrace`, a ring buffer with a write index, and that
      # function takes a `debug.StackTrace`, which is a plain slice and a count
      # of what was skipped. It is a type error, it is on the path taken only
      # under `-ffuzz`, and it stops *any* project with a fuzz test in it from
      # building one. The fix is the function next door: `writeErrorReturnTrace`
      # takes exactly the type in hand and is what the other three places in
      # the same file use.
      #
      # `--replace-fail` is the whole safety of this: the day Zig ships the fix
      # the pattern will not be found, the build will fail here rather than
      # patch something else, and this can go.
      #
      # It buys the fuzzer and not its coverage. Nothing in this release
      # populates the table of program counters, so a bounded run ends with
      # "corrupted coverage file: pcs_len was zero" and an unbounded one
      # panics in the build runner's coverage thread; neither is a finding,
      # and a finding says "input saved to" above the report. The properties
      # in `tests/fuzz.zig` run as ordinary tests either way, and
      # `zig build fuzz-run` drives them with a loop of our own.
      fuzzableZig =
        pkgs:
        let
          # A farm of symlinks rather than a copy: the library is 217 MB, and
          # exactly one file of it is being changed.
          library = pkgs.runCommand "zig-0.16.0-lib-fuzz-fix" { } ''
            cp -rs --no-preserve=mode ${pkgs.zig_0_16}/lib/zig $out
            chmod -R u+w $out
            rm $out/compiler/test_runner.zig
            cp --no-preserve=mode \
              ${pkgs.zig_0_16}/lib/zig/compiler/test_runner.zig \
              $out/compiler/test_runner.zig
            substituteInPlace $out/compiler/test_runner.zig \
              --replace-fail \
                'std.debug.writeStackTrace(trace, stderr)' \
                'std.debug.writeErrorReturnTrace(trace, stderr)'
          '';
        in
        pkgs.symlinkJoin {
          name = "zig-0.16.0-fuzzable";
          paths = [ pkgs.zig_0_16 ];
          nativeBuildInputs = [ pkgs.makeWrapper ];
          postBuild = ''
            wrapProgram $out/bin/zig --set ZIG_LIB_DIR ${library}
          '';
        };
    in
    {
      packages = forAllSystems (
        system:
        let
          pkgs = makePackages system;
        in
        rec {
          zig-maildir = pkgs.callPackage ./package.nix { };
          default = zig-maildir;
          # The dependency farm on its own, so that a workflow job which runs
          # `zig build` for something other than the package -- the
          # documentation -- can be handed it without building the package to
          # get at it.
          zig-deps = pkgs.callPackage ./build.zig.zon.nix { };
        }
      );

      # The virtual machine test, which is here rather than in `zig build
      # test` because what it tests cannot be reached from a test binary: a
      # real Dovecot opening the same maildir this library wrote, with its own
      # idea of what a valid name and a valid flag are.
      checks = forLinuxSystems (
        system:
        let
          pkgs = makePackages system;
          zig-maildir = pkgs.callPackage ./package.nix { };
          test = file: pkgs.testers.runNixOSTest (import file { inherit zig-maildir; });
        in
        {
          inherit zig-maildir;
          dovecot = test ./tests/nixos/dovecot.nix;
        }
      );

      devShells = forAllSystems (
        system:
        let
          pkgs = makePackages system;
        in
        {
          default = pkgs.mkShell {
            name = "zig-maildir";
            nativeBuildInputs = [
              (fuzzableZig pkgs)
              pkgs.git-pages-cli
              pkgs.pinact
              pkgs.reuse

              # Wrapped so that the Zig it shells out to for `zig env` is the
              # one this project builds with, rather than whatever happens to
              # be on the caller's PATH. Without a Zig at all it prints
              # "unable to execute zig" and writes nothing, leaving the
              # previous build.zig.zon.nix in place looking untouched.
              (pkgs.symlinkJoin {
                name = "zon2nix";
                paths = [ zon2nix.packages.${system}.zon2nix ];
                nativeBuildInputs = [ pkgs.makeWrapper ];
                postBuild = ''
                  wrapProgram $out/bin/zon2nix \
                    --prefix PATH : ${lib.makeBinPath [ pkgs.zig_0_16 ]}
                '';
              })
            ]
            ++ lib.optionals pkgs.stdenv.hostPlatform.isLinux [
              # The other implementations to read what this one writes.
              # Dovecot is the one whose interpretation of a maildir is the de
              # facto standard; isync/mbsync and offlineimap each keep state of
              # their own alongside it and are unforgiving about names.
              pkgs.dovecot
              pkgs.isync

              pkgs.kcov
            ];
          };
        }
      );
    };
}