using Editor.Prism.Core;

namespace Editor.Prism.Compiler.Ir;

/// <summary>
/// A statement.
/// <para>
/// <see cref="Origin"/> — the node that produced this statement — is on every single one, and it is
/// the whole source map. The backend records <c>emitted line -&gt; Origin</c> as it writes; inverting
/// that is what turns a raw compiler line number into a highlighted node.
/// </para>
/// </summary>
public abstract record IrStmt( NodeId Origin );

/// <summary>An ordered list of statements with its own scope.</summary>
public sealed class IrBlock
{
	/// <summary>Statements in emission order.</summary>
	public List<IrStmt> Statements { get; } = new();

	/// <summary>True when the block emits nothing.</summary>
	public bool IsEmpty => Statements.Count == 0;

	/// <summary>Append a statement. Null is ignored.</summary>
	public IrBlock Add( IrStmt statement )
	{
		if ( statement is not null ) Statements.Add( statement );
		return this;
	}

	/// <summary>Append a range of statements.</summary>
	public IrBlock AddRange( IEnumerable<IrStmt> statements )
	{
		if ( statements is null ) return this;

		foreach ( var statement in statements ) Add( statement );
		return this;
	}

	/// <inheritdoc/>
	public override string ToString() => $"{{ {Statements.Count} statements }}";
}

/// <summary>Declare a local and initialise it. The workhorse: every non-trivial expression binds to one.</summary>
public sealed record IrDecl( NodeId Origin, string Name, ShaderType Type, IrExpr Init ) : IrStmt( Origin );

/// <summary>Assign to an existing location.</summary>
public sealed record IrAssign( NodeId Origin, IrExpr Target, IrExpr Value ) : IrStmt( Origin );

/// <summary>Real branching. Only the taken side executes, unlike a ternary.</summary>
public sealed record IrIf( NodeId Origin, IrExpr Cond, IrBlock Then, IrBlock Else ) : IrStmt( Origin );

/// <summary>A counted loop over <c>[0, Count)</c>.</summary>
public sealed record IrFor( NodeId Origin, string Var, IrExpr Count, IrBlock Body ) : IrStmt( Origin );

/// <summary>A conditional loop.</summary>
public sealed record IrWhile( NodeId Origin, IrExpr Cond, IrBlock Body ) : IrStmt( Origin );

/// <summary>Leave the innermost loop.</summary>
public sealed record IrBreak( NodeId Origin ) : IrStmt( Origin );

/// <summary>Skip to the next iteration of the innermost loop.</summary>
public sealed record IrContinue( NodeId Origin ) : IrStmt( Origin );

/// <summary>Return a value from the enclosing function.</summary>
public sealed record IrReturn( NodeId Origin, IrExpr Value ) : IrStmt( Origin );

/// <summary>Kill the fragment. Pixel stage only.</summary>
public sealed record IrDiscard( NodeId Origin ) : IrStmt( Origin );

/// <summary>
/// Evaluate an expression for its side effects, e.g. <c>clip(...)</c> or an interlocked operation.
/// </summary>
public sealed record IrExprStmt( NodeId Origin, IrExpr Value ) : IrStmt( Origin );

/// <summary>A comment. Emitted only when the graph has comments or debug symbols enabled.</summary>
public sealed record IrComment( NodeId Origin, string Text ) : IrStmt( Origin );

/// <summary>A nested scope, used to keep temp names from colliding across inlined subgraphs.</summary>
public sealed record IrScope( NodeId Origin, IrBlock Body ) : IrStmt( Origin );