feat: validation, postgress connection,

projects/greenlight/internal/data/runtime.go

@@ -1,14 +1,59 @@
 package data
 
 import (
+	"errors"
 	"fmt"
 	"strconv"
+	"strings"
 )
 
+// Define an error that our UnmarshalJSON() method can return if we're unable to parse
+// or convert the JSON string successfully.
+var ErrInvalidRuntimeFormat = errors.New("invalid runtime format")
+
 // Declare a custom Runtime type, which has the underlying type int32 (the same as our
 // Movie struct field).
 type Runtime int32
 
+// Implement a UnmarshalJSON() method on the Runtime type so that it satisfies the
+// json.Unmarshaler interface. IMPORTANT: Because UnmarshalJSON() needs to modify the
+// receiver (our Runtime type), we must use a pointer receiver for this to work
+// correctly. Otherwise, we will only be modifying a copy (which is then discarded when
+// this method returns).
+func (r *Runtime) UnmarshalJSON(jsonValue []byte) error {
+	// We expect that the incoming JSON value will be a string in the format
+	// "<runtime> mins", and the first thing we need to do is remove the surrounding
+	// double-quotes from this string. If we can't unquote it, then we return the
+	// ErrInvalidRuntimeFormat error.
+	unquotedJSONValue, err := strconv.Unquote(string(jsonValue))
+	if err != nil {
+		return ErrInvalidRuntimeFormat
+	}
+
+	// Split the string to isolate the part containing the number.
+	parts := strings.Split(unquotedJSONValue, " ")
+
+	// Sanity check the parts of the string to make sure it was in the expected format.
+	// If it isn't, we return the ErrInvalidRuntimeFormat error again.
+	if len(parts) != 2 || parts[1] != "mins" {
+		return ErrInvalidRuntimeFormat
+	}
+
+	// Otherwise, parse the string containing the number into an int32. Again, if this
+	// fails return the ErrInvalidRuntimeFormat error.
+	i, err := strconv.ParseInt(parts[0], 10, 32)
+	if err != nil {
+		return ErrInvalidRuntimeFormat
+	}
+
+	// Convert the int32 to a Runtime type and assign this to the receiver. Note that we use
+	// use the * operator to deference the receiver (which is a pointer to a Runtime
+	// type) in order to set the underlying value of the pointer.
+	*r = Runtime(i)
+
+	return nil
+}
+
 // Implement a MarshalJSON() method on the Runtime type so that it satisfies the
 // json.Marshaler interface. This should return the JSON-encoded value for the movie
 // runtime (in our case, it will return a string in the format "<runtime> mins").