name: Nix CI
on:
  push:
    # don't run on tags, run on commits
    # https://github.com/orgs/community/discussions/25615
    tags-ignore:
      - "**"
    branches:
      - main
  merge_group:
  schedule:
    - cron: 0 0 * * *
  workflow_dispatch:

jobs:
  # Merge similar `individual` caches
  # Purge `individual` caches and old `common` caches
  # Save new `common` caches
  merge-similar-caches:
    name: Merge similar caches
    strategy:
      matrix:
        os: [ubuntu-latest]
    runs-on: ${{ matrix.os }}
    steps:
      - name: Checkout this repo
        uses: actions/checkout@v4

      - name: Install nix
        uses: https://github.com/DeterminateSystems/nix-installer-action@main

      - uses: nix-community/cache-nix-action@v6
        name: create and purge common cache
        with:
          primary-key: similar-cache-${{ matrix.os }}-common-${{ hashFiles('flake.lock') }}
          # if no hit on the primary key, restore individual caches that match `ci.yaml`
          restore-prefixes-all-matches: |
            similar-cache-${{ matrix.os }}-individual-${{ hashFiles('flake.lock', '*.nix') }}
          # do purge caches
          purge: true
          # purge old versions of the `common` cache and any versions of individual caches
          purge-prefixes: |
            similar-cache-${{ matrix.os }}-common-
          # created more than 0 seconds ago relative to the start of the `Post Restore` phase
          purge-created: 0
          # except the version with the `primary-key`, if it exists
          purge-primary-key: never

      - uses: nix-community/cache-nix-action@v6
        name: purge some individual caches
        with:
          primary-key: similar-cache-${{ matrix.os }}-common-${{ hashFiles('flake.lock') }}
          # if no hit on the primary key, restore individual caches that match `ci.yaml`
          restore-prefixes-all-matches: |
            similar-cache-${{ matrix.os }}-individual-${{ hashFiles('flake.lock', '*.nix') }}
          # do purge caches
          purge: true
          # purge old versions of the `common` cache and any versions of individual caches
          purge-prefixes: |
            similar-cache-${{ matrix.os }}-individual-
          # created more than 0 seconds ago relative to the start of the `Post Restore` phase
          purge-created: 259200
          # except the version with the `primary-key`, if it exists
          purge-primary-key: never
          token: ${{ secrets.GH_TOKEN_FOR_UPDATES  }}

  # Check that the `common` cache is restored correctly
  merge-similar-caches-check:
    name: Check a `common` cache is restored correctly
    needs: merge-similar-caches
    strategy:
      matrix:
        os: [ubuntu-latest]
    runs-on: ${{ matrix.os }}
    steps:
      - name: Checkout this repo
        uses: actions/checkout@v4

      - name: Install nix
        uses: https://github.com/DeterminateSystems/nix-installer-action@main

      - name: Restore Nix store
      - uses: nix-community/cache-nix-action@v6
        with:
          primary-key: similar-cache-${{ matrix.os }}-common-${{ hashFiles('flake.lock') }}