feat context: Add types and loading functions

context/context.go

@@ -0,0 +1,51 @@
+package context
+
+import (
+	"encoding/json"
+	"github.com/polydawn/meep"
+	"io/ioutil"
+	"path"
+)
+
+type ResourceSet struct {
+	Name   string                 `json:"name"`
+	Values map[string]interface{} `json:"values"`
+}
+
+type Context struct {
+	Name         string                 `json:"context"`
+	Global       map[string]interface{} `json:"global"`
+	ResourceSets []ResourceSet          `json:"include"`
+	BaseDir      string
+}
+
+type ContextLoadingError struct {
+	meep.AllTraits
+	Filename string
+}
+
+// Attempt to load and deserialise a Context from the specified file.
+func LoadContextFromFile(filename string) (*Context, error) {
+	file, err := ioutil.ReadFile(filename)
+
+	if err != nil {
+		return nil, meep.New(
+			&ContextLoadingError{Filename: filename},
+			meep.Cause(err),
+		)
+	}
+
+	var c Context
+
+	err = json.Unmarshal(file, &c)
+	if err != nil {
+		return nil, meep.New(
+			&ContextLoadingError{Filename: filename},
+			meep.Cause(err),
+		)
+	}
+
+	c.BaseDir = path.Dir(filename)
+
+	return &c, nil
+}