/// <summary>
/// Gets the value associated with the specified <paramref name="key"/>,
/// recursively resolving placeholders.
/// </summary>
/// <param name="key">
/// The key whose value to resolve.
/// </param>
public string GetValue(string key)
{
if (key is null)
{
throw new ArgumentNullException(nameof(key));
}
string resolveExpression(string input, ImmutableHashSet <string> path)
{
if (path.Contains(input))
{
throw new ValueUnresolvableException(
$"Encountered loop while trying to resolve expression: '{input}'."
+ $"Path: ['{String.Join("' -> '", path)}']"
);
}
var nextPath = path.Add(input);
return(options
.ToRegexPatterns()
.Aggregate(input, (input, pattern) =>
Regex.Replace(
input: input,
pattern: pattern,
evaluator: m => resolveOrMap(m, nextPath),
options: RegexOptions.IgnoreCase
)
));
}
string resolveOrMap(Match match, ImmutableHashSet <string> path) =>
provider.TryGetValue(match.Groups[1].Value) switch
{
(true, string val) => resolveExpression(val, path),
_ => mapUnresolvable(match.Value) ?? "",
};
