using System;
using System.IO;
using Finn.AST;

namespace Finn;

class ASTPrinter : IVisitor<string>
{
	public string print(Expr expr)
	{
		return expr.accept(this);
	}

	private string parenthesize(string name, params Expr[] exprs)
	{
		var w = new StringWriter();
		w.Write($"({name}");
		foreach (Expr expr in exprs)
		{
			w.Write(" ");
			w.Write(expr.accept(this));
		}
		w.Write(")");
		return w.ToString();
	}

	public string visitBinaryExpr(Binary expr)
	{
		return parenthesize(expr.Op.lexeme, expr.Left, expr.Right);
	}

	public string visitGroupingExpr(Grouping expr)
	{
		return parenthesize("group", expr.Expression);
	}

	public string visitLiteralExpr(Literal expr)
	{
		return expr.Value.ToString() ?? "";
	}

	private string formatName(Name name)
	{
		if (name.Quoted) return $"@\"{name.Value}\"";
		return name.Value;
	}

	public string visitIdentifierExpr(Identifier expr)
	{
		return formatName(expr.Value);
	}

	public string visitUnaryExpr(Unary expr)
	{
		return parenthesize(expr.Op.lexeme, expr.Right);
	}

	public string visitIfExpr(If expr)
	{
		return parenthesize("if", expr.Condition, expr.Then, expr.Else);
	}

	public string visitSequenceExpr(Sequence expr)
	{
		return parenthesize("seq", expr.Left, expr.Right);
	}

	public string visitSelectorExpr(Selector expr)
	{
		return parenthesize(".", expr.Left, new Identifier { Value = expr.FieldName });
	}

	public string visitListExpr(List expr)
	{
		return parenthesize("list", expr.Elements);
	}

	public string visitVariantExpr(Variant expr)
	{
		if (expr.Argument == null)
		{
			return parenthesize("variant", new Identifier { Value = expr.Tag });
		}
		return parenthesize("variant", new Identifier { Value = expr.Tag }, expr.Argument);
	}

	public string visitRecordExpr(Record expr)
	{
		StringWriter w = new StringWriter();
		w.Write("(record");

		writeFields("extend", expr.Extensions);

		if (expr.Base != null)
		{
			w.Write(" (base ");
			w.Write(print(expr.Base.Value));
			writeFields("update", expr.Base.Updates);
			w.Write(')');
		}
		w.Write(')');

		return w.ToString();

		void writeFields(string header, Field[] fields)
		{
			if (fields.Length != 0)
			{
				w.Write($" ({header}");
				foreach (var field in fields)
				{
					w.Write(' ');
					var name = formatName(field.Name);
					if (field.Value == null)
					{
						w.Write(name);
					}
					else
					{
						w.Write(parenthesize(name, field.Value));
					}
				}
				w.Write(')');
			}

		}
	}
}