{ stdenv
, fetchFromGitHub
, fetchpatch
, fetchurl
}:

# This file is responsible for fetching the sage source and adding necessary patches.
# It does not actually build anything, it just copies the patched sources to $out.
# This is done because multiple derivations rely on these sources and they should
# all get the same sources with the same patches applied.

stdenv.mkDerivation rec {
  version = "10.2";
  pname = "sage-src";

  src = fetchFromGitHub {
    owner = "sagemath";
    repo = "sage";
    rev = version;
    sha256 = "sha256-VXnPdJhtw5Y/anecrVpevJDCyBVfnjksyuuZslNipm4=";
  };

  # contains essential files (e.g., setup.cfg) generated by the bootstrap script.
  # TODO: investigate https://github.com/sagemath/sage/pull/35950
  configure-src = fetchurl {
    # the hash below is the tagged commit's _parent_. it can also be found by looking for
    # the "configure" asset at https://github.com/sagemath/sage/releases/tag/${version}
    url = "mirror://sageupstream/configure/configure-b2813506039143e6f0abe859ab67a343abf72c2e.tar.gz";
    sha256 = "sha256-a1v0XyoKI+zO6Sjm8DzEwItRHbIgRDbpj4UfwVH+/hw=";
  };

  # Patches needed because of particularities of nix or the way this is packaged.
  # The goal is to upstream all of them and get rid of this list.
  nixPatches = [
    # Parallelize docubuild using subprocesses, fixing an isolation issue. See
    # https://groups.google.com/forum/#!topic/sage-packaging/YGOm8tkADrE
    ./patches/sphinx-docbuild-subprocesses.patch

    # After updating smypow to (https://github.com/sagemath/sage/issues/3360)
    # we can now set the cache dir to be within the .sage directory. This is
    # not strictly necessary, but keeps us from littering in the user's HOME.
    ./patches/sympow-cache.patch
  ];

  # Since sage unfortunately does not release bugfix releases, packagers must
  # fix those bugs themselves. This is for critical bugfixes, where "critical"
  # == "causes (transient) doctest failures / somebody complained".
  bugfixPatches = [
    # Sage uses mixed integer programs (MIPs) to find edge disjoint
    # spanning trees. For some reason, aarch64 glpk takes much longer
    # than x86_64 glpk to solve such MIPs. Since the MIP formulation
    # has "numerous problems" and will be replaced by a polynomial
    # algorithm soon, disable this test for now.
    # https://github.com/sagemath/sage/issues/34575
    ./patches/disable-slow-glpk-test.patch
  ];

  # Patches needed because of package updates. We could just pin the versions of
  # dependencies, but that would lead to rebuilds, confusion and the burdons of
  # maintaining multiple versions of dependencies. Instead we try to make sage
  # compatible with never dependency versions when possible. All these changes
  # should come from or be proposed to upstream. This list will probably never
  # be empty since dependencies update all the time.
  packageUpgradePatches = [
    # https://github.com/sagemath/sage/pull/37123, to land in 10.3.beta7
    (fetchpatch {
      name = "scipy-1.12-upgrade.patch";
      url = "https://github.com/sagemath/sage/commit/54eec464e9fdf18b411d9148aecb918178e95909.diff";
      sha256 = "sha256-9wyNrcSfF6mYFTIV4ev2OdD7igb0AeyZZYWSc/+JrIU=";
    })
  ];

  patches = nixPatches ++ bugfixPatches ++ packageUpgradePatches;

  # do not create .orig backup files if patch applies with fuzz
  patchFlags = [ "--no-backup-if-mismatch" "-p1" ];

  postPatch = ''
    # Make sure sage can at least be imported without setting any environment
    # variables. It won't be close to feature complete though.
    sed -i \
      "s|var(\"SAGE_ROOT\".*|var(\"SAGE_ROOT\", \"$out\")|" \
      src/sage/env.py

    # sage --docbuild unsets JUPYTER_PATH, which breaks our docbuilding
    # https://trac.sagemath.org/ticket/33650#comment:32
    sed -i "/export JUPYTER_PATH/d" src/bin/sage
  '';

  buildPhase = "# do nothing";

  installPhase = ''
    cp -r . "$out"
    tar xkzf ${configure-src} -C "$out"
    rm "$out/configure"
  '';
}