MessageFormatter.cs

namespace ServiceStack.FluentValidation.Internal
{
    using System.Collections.Generic;

    /// <summary>
    /// Assists in the construction of validation messages.
    /// </summary>
    public class MessageFormatter {
        readonly Dictionary<string, object> placeholderValues = new Dictionary<string, object>();
        object[] additionalArgs;

        /// <summary>
        /// Default Property Name placeholder.
        /// </summary>
        public const string PropertyName = "PropertyName";

        /// <summary>
        /// Adds a value for a validation message placeholder.
        /// </summary>
        /// <param name="name"></param>
        /// <param name="value"></param>
        /// <returns></returns>
        public MessageFormatter AppendArgument(string name, object value) {
            placeholderValues[name] = value;
            return this;
        }

        /// <summary>
        /// Appends a property name to the message.
        /// </summary>
        /// <param name="name">The name of the property</param>
        /// <returns></returns>
        public MessageFormatter AppendPropertyName(string name) {
            return AppendArgument(PropertyName, name);
        }

        /// <summary>
        /// Adds additional arguments to the message for use with standard string placeholders.
        /// </summary>
        /// <param name="additionalArgs">Additional arguments</param>
        /// <returns></returns>
        public MessageFormatter AppendAdditionalArguments(params object[] additionalArgs) {
            this.additionalArgs = additionalArgs;
            return this;
        }

        /// <summary>
        /// Constructs the final message from the specified template. 
        /// </summary>
        /// <param name="messageTemplate">Message template</param>
        /// <returns>The message with placeholders replaced with their appropriate values</returns>
        public string BuildMessage(string messageTemplate) {

            string result = messageTemplate;

            foreach(var pair in placeholderValues) {
                result = ReplacePlaceholderWithValue(result, pair.Key, pair.Value);
            }

            if(ShouldUseAdditionalArgs) {
                return string.Format(result, additionalArgs);
            }
            return result;
        }

        private bool ShouldUseAdditionalArgs {
            get { return additionalArgs != null && additionalArgs.Length > 0; }
        }

        string ReplacePlaceholderWithValue(string template, string key, object value) {
            string placeholder = "{" + key + "}";
            return template.Replace(placeholder, value == null ? null : value.ToString());
        }
    }
}