using System.Linq.Expressions;
using System.Text.RegularExpressions;

namespace GitVersion.Helpers;

internal static class StringFormatWithExtension
{
    // This regex matches an expression to replace.
    // - env:ENV name OR a member name
    // - optional fallback value after " ?? "
    // - the fallback value should be a quoted string, but simple unquoted text is allowed for back compat
    private static readonly Regex TokensRegex = new(@"{((env:(?<envvar>\w+))|(?<member>\w+))(\s+(\?\?)??\s+((?<fallback>\w+)|""(?<fallback>.*)""))??}", RegexOptions.Compiled);

    /// <summary>
    /// Formats the <paramref name="template"/>, replacing each expression wrapped in curly braces
    /// with the corresponding property from the <paramref name="source"/> or <paramref name="environment"/>.
    /// </summary>
    /// <param name="template" this="true">The source template, which may contain expressions to be replaced, e.g '{Foo.Bar.CurrencySymbol} foo {Foo.Bar.Price}'</param>
    /// <param name="source">The source object to apply to the <paramref name="template"/></param>
    /// <param name="environment"></param>
    /// <exception cref="ArgumentNullException">The <paramref name="template"/> is null.</exception>
    /// <exception cref="ArgumentException">An environment variable was null and no fallback was provided.</exception>
    /// <remarks>
    /// An expression containing "." is treated as a property or field access on the <paramref name="source"/>.
    /// An expression starting with "env:" is replaced with the value of the corresponding variable from the <paramref name="environment"/>.
    /// Each expression may specify a single hardcoded fallback value using the {Prop ?? "fallback"} syntax, which applies if the expression evaluates to null.
    /// </remarks>
    /// <example>
    /// // replace an expression with a property value
    /// "Hello {Name}".FormatWith(new { Name = "Fred" }, env);
    /// "Hello {Name ?? \"Fred\"}".FormatWith(new { Name = GetNameOrNull() }, env);
    /// // replace an expression with an environment variable
    /// "{env:BUILD_NUMBER}".FormatWith(new { }, env);
    /// "{env:BUILD_NUMBER ?? \"0\"}".FormatWith(new { }, env);
    /// </example>
    public static string FormatWith<T>(this string template, T? source, IEnvironment environment)
    {
        if (template == null)
        {
            throw new ArgumentNullException(nameof(template));
        }

        foreach (Match match in TokensRegex.Matches(template))
        {
            string propertyValue;
            string? fallback = match.Groups["fallback"].Success ? match.Groups["fallback"].Value : null;

            if (match.Groups["envvar"].Success)
            {
                string envVar = match.Groups["envvar"].Value;
                propertyValue = environment.GetEnvironmentVariable(envVar) ?? fallback
                    ?? throw new ArgumentException($"Environment variable {envVar} not found and no fallback string provided");
            }
            else
            {
                var objType = source?.GetType();
                string memberAccessExpression = match.Groups["member"].Value;
                var expression = CompileDataBinder(objType, memberAccessExpression);
                // It would be better to throw if the expression and fallback produce null, but provide an empty string for back compat.
                propertyValue = expression(source)?.ToString() ?? fallback ?? "";
            }

            template = template.Replace(match.Value, propertyValue);
        }

        return template;
    }

    private static Func<object?, object> CompileDataBinder(Type? type, string expr)
    {
        ParameterExpression param = Expression.Parameter(typeof(object));
        Expression body = Expression.Convert(param, type);
        body = expr.Split('.').Aggregate(body, Expression.PropertyOrField);
        body = Expression.Convert(body, typeof(object)); // Convert result in case the body produces a Nullable value type.
        return Expression.Lambda<Func<object?, object>>(body, param).Compile();
    }
}