using System;
using System.Text;

namespace Vellum.Generator
{
    /// <summary>
    /// Writes generated code a line at a time, tracking the indentation.
    /// </summary>
    public sealed class CodeWriter
    {
        private const string IndentUnit = "    ";

        // Generated files use CRLF, matching what the rest of the tree checks in.
        private const string LineEnding = "\r\n";

        private readonly StringBuilder text = new StringBuilder();
        private int depth;

        public void Indent()
        {
            ++depth;
        }

        public void Dedent()
        {
            if (depth == 0)
            {
                throw new InvalidOperationException("Dedent without a matching Indent.");
            }

            --depth;
        }

        public void NewLine()
        {
            text.Append(LineEnding);
        }

        /// <summary>
        /// Writes <paramref name="content"/> on its own line at the current indentation.  Empty content writes a
        /// blank line.
        /// </summary>
        public void AddLine(string content)
        {
            if (content.Length == 0)
            {
                NewLine();
                return;
            }

            for (int i = 0; i < depth; ++i)
            {
                text.Append(IndentUnit);
            }

            text.Append(content);
            text.Append(LineEnding);
        }

        public void OpenNewBlock()
        {
            AddLine("{");
            Indent();
        }

        public void OpenNewBlock(string header)
        {
            AddLine(header);
            OpenNewBlock();
        }

        public void CloseBlock()
        {
            Dedent();
            AddLine("}");
        }

        /// <summary>
        /// Returns everything written so far.
        /// </summary>
        public override string ToString()
        {
            return text.ToString();
        }
    }
}