using System.Text;
using PkmnLib.Plugin.Gen7.SourceGen.Parsing;

namespace PkmnLib.Plugin.Gen7.SourceGen.Emit;

/// <summary>
/// Emits a constants class of <c>public static readonly StringKey</c> fields for a
/// <see cref="ClassSpec"/>.
/// </summary>
public static class ConstantClassEmitter
{
    public static string Emit(ClassSpec spec, List<ExtractionDiagnostic> diagnostics)
    {
        var sb = new StringBuilder();
        sb.AppendLine($"// <auto-generated from Data/{spec.SourceFile} by PkmnLib.Plugin.Gen7.SourceGen />");
        sb.AppendLine("#nullable enable");
        sb.AppendLine("using PkmnLib.Static.Utils;");
        sb.AppendLine();
        sb.AppendLine("namespace PkmnLib.Plugin.Gen7.Common;");
        sb.AppendLine();
        sb.AppendLine($"public static class {spec.ClassName}");
        sb.AppendLine("{");
        var seen = new Dictionary<string, string>(StringComparer.Ordinal);
        foreach (var name in spec.Names)
        {
            var identifier = Sanitize(name);
            if (identifier.Length == 0)
            {
                diagnostics.Add(new ExtractionDiagnostic("PKMN7G002",
                    $"Name '{name}' in {spec.ClassName} does not produce a usable identifier and was skipped."));
                continue;
            }
            if (seen.TryGetValue(identifier, out var existing))
            {
                diagnostics.Add(new ExtractionDiagnostic("PKMN7G001",
                    $"Names '{existing}' and '{name}' in {spec.ClassName} both map to identifier '{identifier}'; '{name}' was skipped."));
                continue;
            }
            seen.Add(identifier, name);
            sb.AppendLine($"    public static readonly StringKey {identifier} = \"{name}\";");
        }
        sb.AppendLine("}");
        return sb.ToString();
    }

    /// <summary>
    /// Converts a raw data name to a PascalCase identifier: segments split on <c>_</c>/<c>-</c>
    /// runs, non-alphanumeric characters stripped, and a leading <c>_</c> added when the result
    /// would start with a digit.
    /// </summary>
    public static string Sanitize(string raw)
    {
        var sb = new StringBuilder(raw.Length);
        var newSegment = true;
        foreach (var c in raw)
        {
            if (c is '_' or '-')
            {
                newSegment = true;
                continue;
            }
            if (!char.IsLetterOrDigit(c))
                continue;
            sb.Append(newSegment ? char.ToUpperInvariant(c) : c);
            newSegment = false;
        }
        if (sb.Length == 0)
            return string.Empty;
        if (char.IsDigit(sb[0]))
            sb.Insert(0, '_');
        return sb.ToString();
    }
}