Adds support to pass file path in mapping (#58)

Co-authored-by: Poonam Jadhav <poonam@circleci.com>

src/examples/example.yml

@@ -15,3 +15,7 @@ usage:
             mapping: |
               src/.* build-code true
               doc/.* build-docs true
+        - path-filtering/filter:
+            base-revision: main
+            config-path: .circleci/continue-config.yml
+            mapping: .circleci/mapping.conf

src/jobs/filter.yml

@@ -20,7 +20,8 @@ parameters:
     default: ""
     description: >
       Mapping of path regular expressions to pipeline parameters and
-      values. One mapping per line, whitespace-delimited.
+      values. If the value is a file, then it will be loaded from the disk. 
+      One mapping per line, whitespace-delimited.
   config-path:
     type: string
     default: ".circleci/continue_config.yml"

src/scripts/create-parameters.py

@@ -54,10 +54,17 @@ def checkout(revision):
   capture_output=True
 ).stdout.decode('utf-8').splitlines()
 
-mappings = [
-  m.split() for m in
-  os.environ.get('MAPPING').splitlines()
-]
+mappingConfig = os.environ.get('MAPPING')
+if os.path.exists(mappingConfig):
+  with open(mappingConfig) as f:
+    mappings = [
+      m.split() for m in f.read().splitlines()
+    ]
+else:
+  mappings = [
+    m.split() for m in
+    mappingConfig.splitlines()
+  ]
 
 def check_mapping(m):
   if 3 != len(m):
@@ -78,4 +85,3 @@ def convert_mapping(m):
 
 with open(output_path, 'w') as fp:
   fp.write(json.dumps(mappings))
-