# Copyright 2019 PrivateStorage.io, LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

version: 2.1

jobs:
  build:
    docker:
      # Run in a highly Nix-capable environment.  This lets us use Stack's nix
      # integration and other useful Nix features to specify and run the
      # build.
      - image: "nixorg/nix:circleci"

    environment:
      # Specify a revision of NixOS/nixpkgs to run against.  This essentially
      # pins the majority of the software involved in the build.  This
      # revision is selected arbitrarily.  It's somewhat current as of the
      # time of this comment.  We can bump it to a newer version when that
      # makes sense.  Meanwhile, the platform won't shift around beneath us
      # unexpectedly.
      NIXPKGS_REV: "3c83ad6ac13b67101cc3e2e07781963a010c1624"

    steps:
      - run:
          # Get NIX_PATH set for the rest of the job so that the revision of
          # nixpkgs we selected will be used everywhere Nix pulls in software.
          # There is no way to set an environment variable containing the
          # value of another environment variable on CircleCI except to use
          # the `BASE_ENV` feature as we do here.
          name: "Setup NIX_PATH Environment Variable"
          command: |
            echo "export NIX_PATH=nixpkgs=https://github.com/NixOS/nixpkgs/archive/$NIXPKGS_REV.tar.gz" >> $BASH_ENV

      # Get *our* source code.
      - "checkout"

      - "run":
          # CircleCI won't let us interpolate NIXPKGS_REV into a cache key.
          # Only CircleCI's own environment variables or variables set via the
          # web interface in a "context" can be interpolated into cache keys.
          # However, we can interpolate the checksum of a file...  Since we
          # don't care about the exact revision, we just care that a new
          # revision gives us a new string, we can write the revision to a
          # file and then put the checksum of that file into the cache key.
          # This way, we don't have to maintain the nixpkgs revision in two
          # places and risk having them desynchronize.
          name: "Prepare For Cache Key"
          command: |
            echo "${NIXPKGS_REV}" > nixpkgs.rev

      - restore_cache:
          # Get all of Nix's state relating to the particular revision of
          # nixpkgs we're using.  It will always be the same.  CircleCI
          # artifacts and nixpkgs store objects are probably mostly hosted in
          # the same place (S3) so there's not a lot of difference for
          # anything that's pre-built.  For anything we end up building
          # ourselves, though, this saves us all of the build time (less the
          # download time).
          #
          # Read about caching dependencies: https://circleci.com/docs/2.0/caching/
          name: "Restore Nix Store Paths"
          keys:
            # Construct cache keys that allow sharing as long as nixpkgs and
            # the Ristretto library are the same.
            #
            # If the Ristretto library changes, we have to rebuild it so we
            # may as well throw away the part of the cache with the old build
            # and make a new one with the new build so we don't have to
            # rebuild it *again* next time.
            #
            # If nixpkgs changes then potentially a lot of cached packages for
            # the base system will be invalidated so we may as well drop them
            # and make a new cache with the new packages.
            - paymentserver-nix-store-v1-{{ checksum "nixpkgs.rev" }}-{{ checksum "ristretto.nix" }}
            - paymentserver-nix-store-v1-{{ checksum "nixpkgs.rev" }}-
            - paymentserver-nix-store-v1-

      - restore_cache:
          # Restore the cache of Stack's state.  This will have all of the
          # compiled Haskell libraries we depend on and even the compiled
          # output of our own libraries, if the source hasn't changed since
          # the cache was written (but usually it will have).
          name: "Restore Cached Dependencies"
          keys:
            - paymentserver-v1-{{ checksum "stack.yaml" }}-{{ checksum "PaymentServer.cabal" }}
            - paymentserver-v1-{{ checksum "stack.yaml" }}

      - run:
          # Build just our dependencies.  It's nice to have this as a separate
          # step so failures here are more easily identified as being
          # unrelated to our code.
          #
          # See below for explanation of the various flags passed in.  If the
          # flags here differ from those below in a way that makes ghc think a
          # library needs to be rebuilt then we'll build everything twice and
          # our cache will be useless!  Try not to make that happen.
          name: "Build Dependencies"
          command: |
            BUILD="stack build \
            --no-terminal \
            --only-dependencies \
            --fast \
            --jobs 1 \
            --interleaved-output"
            nix-shell shell.nix --run "$BUILD"

          # Give it a good long while.  stripe-core, in particular, can take a
          # while to build.
          no_output_timeout: "20m"

      - save_cache:
          # We can save the stack cache right here.  It will have everything
          # we want in it now that the dependencies have been built.  And this
          # way we get to save the cache whether or not the test suite goes on
          # to succeed.
          name: "Cache Dependencies"
          key: paymentserver-v1-{{ checksum "stack.yaml" }}-{{ checksum "PaymentServer.cabal" }}
          paths:
            - "/root/.stack"
            - ".stack-work"

      - run:
          name: "Building"
          command: |
            # shell.nix gives us the stack we want.  Then stack.yaml specifies
            # some more of the Nix-based environment to be able to build and
            # run the tests.
            #
            # --no-terminal avoids having fancy progress reports written to
            # stdout.
            #
            # --fast turns off compiler optimizations which probably doesn't
            # make a lot of difference in our code but it can speed up build
            # times for our dependencies (as well as reduce compiler memory
            # usage which may be important at least for stripe-core).
            #
            # --haddock builds the Haskell API documentation.
            # --haddock-internal builds docs even for unexposed modules.
            # --no-haddock-deps skips building docs for all our dependencies.
            BUILD="stack build \
              --no-terminal \
              --fast \
              --haddock \
              --haddock-internal \
              --no-haddock-deps"
            nix-shell shell.nix --run "$BUILD"

      - save_cache:
          name: "Cache Nix Store Paths"
          key: paymentserver-nix-store-v1-{{ checksum "nixpkgs.rev" }}-{{ checksum "ristretto.nix" }}
          paths:
            - "/nix"

      - store_artifacts:
          # There may be useful build logs here.
          path: ".stack-work/logs"

      - run:
          name: "Prepare Artifacts for Upload"
          command: |
            mv $(nix-shell shell.nix --run "stack path --local-doc-root")/PaymentServer-* /tmp/PaymentServer-docs

      - store_artifacts:
          # This contains the html haddock output for the project.
          path: "/tmp/PaymentServer-docs"
          destination: "docs"

workflows:
  version: 2
  everything:
    jobs:
      - "build"
