let
  pkgs = import <nixpkgs> { };
  rootSrc = pkgs.nix-gitignore.gitignoreSource [] ./.;
  nixfmt = import (builtins.fetchTarball
  "https://github.com/serokell/nixfmt/archive/master.tar.gz") { };

  # Taken from:
  # http://www.cs.yale.edu/homes/lucas.paul/posts/2017-04-10-hakyll-on-nix.html
  websiteBuilder = pkgs.stdenv.mkDerivation {
    name = "website-builder";
    src = ./hakyll;
    phases = "unpackPhase buildPhase";
    buildInputs =
    [(pkgs.haskellPackages.ghcWithPackages (p: with p; [hakyll]))];
    buildPhase = ''
      mkdir -p $out/bin
      ghc -O2 -dynamic --make Main.hs -o $out/bin/build-site
    '';
  };
  baseTask = pkgs.stdenv.mkDerivation {
    name = "website-task";
    src = rootSrc;
    buildInputs = [pkgs.perl];
    phases = "unpackPhase buildPhase";
    buildPhase = ''
      echo "ERROR: base task buildPhase not overriden."
      exit 1
    '';
  };
in with pkgs;
with pkgs.stdenv; rec {
  subtasks = rec {
    fixme = baseTask.overrideAttrs (baseAttrs: {
      name = "${baseAttrs.name}-fixme";
      buildInputs = baseAttrs.buildInputs ++ [ag];
      buildPhase = ''
        ag FIXME --ignore default.nix --ignore pastebin/skeleton.org || {
          touch $out
        }
      '';
    });
    perlPodCheck = baseTask.overrideAttrs (baseAttrs: {
      name = "${baseAttrs.name}-perl-podcheck";
      buildPhase = ''
        podchecker website pastebin/website-pastebin slides/website-slides
        touch $out
      '';
    });
    batsTest = baseTask.overrideAttrs (baseAttrs: {
      name = "${baseAttrs.name}-bats-test";
      buildInputs = baseAttrs.buildInputs ++ [bats];
      buildPhase = ''
        patchShebangs .
        ./t/website.bats
        touch $out
      '';
    });
    perlInternalTest = baseTask.overrideAttrs (baseAttrs: {
      name = "${baseAttrs.name}-perl-test";
      buildPhase = ''
        patchShebangs .
        ./website test
        touch $out
      '';
    });
    formatNix = baseTask.overrideAttrs (baseAttrs: {
      name = "${baseAttrs.name}-nixfmt";
      buildInputs = baseAttrs.buildInputs ++ [nixfmt];
      buildPhase = ''
        diff <(nixfmt < default.nix) default.nix
        touch $out
      '';
    });
    docs = baseTask.overrideAttrs (baseAttrs: {
      name = "${baseAttrs.name}-docs";
      buildInputs = [ websiteBuilder pandoc ];
      buildPhase = ''
        export LOCALE_ARCHIVE="${pkgs.glibcLocales}/lib/locale/locale-archive";
        export LANG=en_US.UTF-8

        ls pastebin/*.org | awk -F. '{print $1}' | xargs -I{} pandoc -o {}.html {}.org --standalone

        build-site build

        mkdir $out
        cp -r _site/* $out
      '';
    });
  };
  test = baseTask.overrideAttrs (baseAttrs: rec {
    name = "${baseAttrs.name}-test";
    buildInputs = [
      subtasks.fixme
      subtasks.perlPodCheck
      subtasks.batsTest
      subtasks.perlInternalTest
      subtasks.formatNix
    ];
    buildPhase = ''
      echo "Ran tests for:"
      for d in ${builtins.toString buildInputs}; do
        echo "  $d"
      done
      echo "All tests passed!"
      touch $out
    '';
  });
  shell = mkShell rec {
    name = "website-shell";
    buildInputs = [
      websiteBuilder
      (pkgs.haskellPackages.ghcWithPackages (p: with p; [hakyll]))
      nixfmt
    ];
  };
  publishScript = pkgs.writeShellScriptBin "publish.sh" ''
    set -euo pipefail
    ${pkgs.rsync}/bin/rsync --verbose                               \
                            --copy-links                            \
                            --progress                              \
                            --stats                                 \
                            --update                                \
                            --recursive                             \
                            --rsh="ssh -o StrictHostKeyChecking=no" \
                            ${subtasks.docs}/                       \
                            "$SERVER_URL:$DOCS_SERVER_PATH"
  '';
}