Adding cache to conda install

.github/workflows/book.yml

@@ -25,14 +25,41 @@ jobs:
 
     # Install dependencies
     # Install Mambaforge
-
-    - name: Setup Jupyterbook
+    - name: Setup Mambaforge 
       uses: conda-incubator/setup-miniconda@v3
       with:
-        environment-file: binder/conda/environment.yml
-        mamba-version: "*"
-
-    # Build the book
+        miniforge-variant: Mambaforge
+        miniforge-version: latest
+        use-mamba: true
+        activate-environment: jupyterbook-atlas
+
+    - name: Get Date
+      id: get-date
+      run: echo "today=$(/bin/date -u '+%Y%m%d')" >> $GITHUB_OUTPUT
+      shell: bash
+
+    - name: Cache Conda env
+      uses: actions/cache@v3
+      with:
+        path: ${{ env.CONDA }}/envs
+        key:
+          conda-${{ runner.os }}-
+          ${{ runner.arch }}-
+          ${{ steps.get-date.outputs.today }}-
+          ${{ hashFiles('binder/conda/environment.yml') }}-
+          ${{ env.CACHE_NUMBER }}
+      env:
+         # Increase this value to reset cache if etc/example-environment.yml has not changed
+         CACHE_NUMBER: 0
+      id: cache
+
+    - name: Update environment
+      run:
+        mamba env update -n jupyterbook-atlas -f
+        binder/conda/environment.yml
+      if: steps.cache.outputs.cache-hit != 'true'
+
+      # Build the book
     - name: Build the book
       run: |
         jupyter-book build .