// Copyright (c) 2026 Charles KWON OhJun (charleskwonohjun@gmail.com)
// All rights reserved.

// AST node definitions for the Five language.
//
// Design references:
//   - Harbour: HB_EXPR (hbcompdf.h:349) — expression union with ExprType discriminant
//   - Harbour: HB_HFUNC (hbcompdf.h:497) — function with separated pLocals/pStatics/pFields/pMemvars
//   - tsgo: Node with Kind discriminant + nodeData interface (internal/ast/ast.go)
//
// Key Harbour rules applied:
//   - LOCAL/STATIC/FIELD declarations must appear at function top, before executable code
//   - FuncDecl separates Decls (declarations) from Body (executable statements)
//   - (expr)->field for dynamic alias access (HB_ET_ALIASEXPR)
//   - &variable for macro (6 subtypes from Harbour: VAR, SYMBOL, ALIASED, EXPR, LIST, PARE)
package ast

import "five/compiler/token"

// --- Interfaces ---

// Node is the base interface for all AST nodes.
type Node interface {
	Pos() token.Position
	End() token.Position
}

// Expr represents an expression node (produces a value).
type Expr interface {
	Node
	exprNode()
}

// Stmt represents a statement node (performs an action).
type Stmt interface {
	Node
	stmtNode()
}

// Decl represents a declaration node (LOCAL, STATIC, FIELD, etc.).
type Decl interface {
	Node
	declNode()
}

// --- Program (top-level) ---

// File represents a single .prg source file.
type File struct {
	Name    string     // filename
	Imports []*ImportDecl
	Decls   []Decl     // top-level: FUNCTION, PROCEDURE, CLASS, etc.
}

func (f *File) Pos() token.Position {
	if len(f.Decls) > 0 {
		return f.Decls[0].Pos()
	}
	return token.Position{}
}
func (f *File) End() token.Position {
	if len(f.Decls) > 0 {
		return f.Decls[len(f.Decls)-1].End()
	}
	return token.Position{}
}

// --- Declarations ---

// ImportDecl: IMPORT "package/path" or IMPORT _ "package/path"
type ImportDecl struct {
	ImportPos token.Position
	Alias     string // "" = normal, "_" = blank import, "name" = alias
	Path      string // package path
}

func (d *ImportDecl) Pos() token.Position { return d.ImportPos }
func (d *ImportDecl) End() token.Position { return d.ImportPos }
func (d *ImportDecl) declNode()           {}

// FuncDecl represents FUNCTION or PROCEDURE.
// Harbour: HB_HFUNC — pLocals, pStatics, pFields separated from pcode.
// LOCAL/STATIC/FIELD must appear before executable code.
type FuncDecl struct {
	FuncPos    token.Position
	Name       string
	IsProc     bool          // PROCEDURE (no return value)
	IsStatic   bool          // STATIC FUNCTION/PROCEDURE — file-local visibility
	Params     []*ParamDecl  // declared parameters
	Decls      []Decl        // LOCAL, STATIC, FIELD — must come first
	Body       []Stmt        // executable statements — after declarations
	EndPos     token.Position
}

func (d *FuncDecl) Pos() token.Position { return d.FuncPos }
func (d *FuncDecl) End() token.Position { return d.EndPos }
func (d *FuncDecl) declNode()           {}

// ParamDecl represents a function parameter.
type ParamDecl struct {
	NamePos token.Position
	Name    string
	ByRef   bool   // @param or passed by reference
	AsType  string // optional type hint: AS NUMERIC, AS STRING, etc.
}

func (d *ParamDecl) Pos() token.Position { return d.NamePos }
func (d *ParamDecl) End() token.Position { return d.NamePos }
func (d *ParamDecl) declNode()           {}

// VarDecl represents LOCAL, STATIC, PRIVATE, PUBLIC, FIELD declarations.
// Harbour: LOCAL must be at function top (before executable code).
// PRIVATE/PUBLIC can appear anywhere (runtime memvar).
type VarDecl struct {
	DeclPos token.Position
	Scope   VarScope
	Vars    []*VarInit // one or more: LOCAL a := 1, b := 2, c
}

func (d *VarDecl) Pos() token.Position { return d.DeclPos }
func (d *VarDecl) End() token.Position {
	if len(d.Vars) > 0 {
		return d.Vars[len(d.Vars)-1].NamePos
	}
	return d.DeclPos
}
func (d *VarDecl) declNode()           {}
func (d *VarDecl) stmtNode()           {} // PRIVATE/PUBLIC can appear as statements

// VarScope indicates where a variable lives.
type VarScope int

const (
	ScopeLocal   VarScope = iota // LOCAL — stack, function-top only
	ScopeStatic                  // STATIC — module-level, function-top only
	ScopePrivate                 // PRIVATE — runtime memvar, anywhere
	ScopePublic                  // PUBLIC — runtime memvar, anywhere
	ScopeField                   // FIELD — database field declaration, function-top only
)

// VarInit represents a single variable with optional initializer.
type VarInit struct {
	NamePos token.Position
	Name    string
	Init    Expr   // nil if no initializer
	AsType  string // optional type hint
}

// ClassDecl represents CLASS ... ENDCLASS.
type ClassDecl struct {
	ClassPos   token.Position
	Name       string
	ParentName string        // INHERIT FROM parent
	Members    []Decl        // DATA, METHOD, ACCESS, ASSIGN declarations
	EndPos     token.Position
}

func (d *ClassDecl) Pos() token.Position { return d.ClassPos }
func (d *ClassDecl) End() token.Position { return d.EndPos }
func (d *ClassDecl) declNode()           {}

// DataDecl represents DATA member in a class.
type DataDecl struct {
	DataPos token.Position
	Name    string
	Init    Expr   // INIT expression (nil if none)
	AsType  string // AS type hint
}

func (d *DataDecl) Pos() token.Position { return d.DataPos }
func (d *DataDecl) End() token.Position { return d.DataPos }
func (d *DataDecl) declNode()           {}

// MethodDecl represents METHOD declaration in a class or standalone.
type MethodDecl struct {
	MethodPos  token.Position
	Name       string
	ClassName  string         // METHOD name CLASS classname (standalone)
	Params     []*ParamDecl
	IsInline   bool           // INLINE method
	InlineBody Expr           // inline expression body — `RETURN <expr>` equivalent
	IsOperator bool           // OPERATOR overload — OperatorOp carries the slot
	OperatorOp int            // operator slot (hbrt.Op* constant); valid only when IsOperator
	IsSetGet   bool           // METHOD name(x) SETGET — getter if no arg, setter if arg
	IsAccess   bool           // ACCESS name METHOD getterName
	IsAssign   bool           // ASSIGN name METHOD setterName
	AccessName string         // property name for ACCESS/ASSIGN
	Decls      []Decl
	Body       []Stmt
	EndPos     token.Position
}

func (d *MethodDecl) Pos() token.Position { return d.MethodPos }
func (d *MethodDecl) End() token.Position { return d.EndPos }
func (d *MethodDecl) declNode()           {}

// GoDumpDecl represents inline Go code from #pragma BEGINDUMP ... #pragma ENDDUMP.
// Five extension: allows embedding raw Go code directly in PRG files.
type GoDumpDecl struct {
	DumpPos token.Position
	Code    string // raw Go source code
}

func (d *GoDumpDecl) Pos() token.Position { return d.DumpPos }
func (d *GoDumpDecl) End() token.Position { return d.DumpPos }
func (d *GoDumpDecl) declNode()           {}

// --- Expressions ---

// LiteralExpr represents a literal value.
// Harbour: HB_ET_NIL, HB_ET_NUMERIC, HB_ET_STRING, HB_ET_LOGICAL, HB_ET_DATE, HB_ET_TIMESTAMP
type LiteralExpr struct {
	ValuePos token.Position
	Kind     token.Kind // INT, LONG, DOUBLE, STRING, TRUE, FALSE, NIL_LIT, DATE_LIT
	Value    string     // raw literal text
}

func (e *LiteralExpr) Pos() token.Position { return e.ValuePos }
func (e *LiteralExpr) End() token.Position { return e.ValuePos }
func (e *LiteralExpr) exprNode()           {}

// IdentExpr represents a variable or function name.
// Harbour: HB_ET_VARIABLE, HB_ET_FUNNAME
type IdentExpr struct {
	NamePos token.Position
	Name    string
}

func (e *IdentExpr) Pos() token.Position { return e.NamePos }
func (e *IdentExpr) End() token.Position { return e.NamePos }
func (e *IdentExpr) exprNode()           {}

// SelfExpr represents :: (Self access in class method).
// Harbour: HB_ET_SELF
type SelfExpr struct {
	ColonPos token.Position
}

func (e *SelfExpr) Pos() token.Position { return e.ColonPos }
func (e *SelfExpr) End() token.Position { return e.ColonPos }
func (e *SelfExpr) exprNode()           {}

// BinaryExpr represents a binary operation.
// Harbour: HB_EO_PLUS, HB_EO_MINUS, HB_EO_EQUAL, etc.
type BinaryExpr struct {
	Left  Expr
	OpPos token.Position
	Op    token.Kind
	Right Expr
}

func (e *BinaryExpr) Pos() token.Position { return e.Left.Pos() }
func (e *BinaryExpr) End() token.Position { return e.Right.End() }
func (e *BinaryExpr) exprNode()           {}

// UnaryExpr represents a prefix unary operation.
// Harbour: HB_EO_NEGATE, HB_EO_NOT, HB_EO_PREINC, HB_EO_PREDEC
type UnaryExpr struct {
	OpPos token.Position
	Op    token.Kind // MINUS, NOT, INC, DEC
	X     Expr
}

func (e *UnaryExpr) Pos() token.Position { return e.OpPos }
func (e *UnaryExpr) End() token.Position { return e.X.End() }
func (e *UnaryExpr) exprNode()           {}

// PostfixExpr represents postfix ++ or --.
// Harbour: HB_EO_POSTINC, HB_EO_POSTDEC
type PostfixExpr struct {
	X     Expr
	OpPos token.Position
	Op    token.Kind // INC, DEC
}

func (e *PostfixExpr) Pos() token.Position { return e.X.Pos() }
func (e *PostfixExpr) End() token.Position { return e.OpPos }
func (e *PostfixExpr) exprNode()           {}

// AssignExpr represents assignment: x := value, x += value, etc.
// Harbour: HB_EO_ASSIGN, HB_EO_PLUSEQ, etc.
type AssignExpr struct {
	Left  Expr
	OpPos token.Position
	Op    token.Kind // ASSIGN, PLUSEQ, MINUSEQ, etc.
	Right Expr
}

func (e *AssignExpr) Pos() token.Position { return e.Left.Pos() }
func (e *AssignExpr) End() token.Position { return e.Right.End() }
func (e *AssignExpr) exprNode()           {}

// CallExpr represents a function call: func(args...)
// Harbour: HB_ET_FUNCALL — pFunName + pParms
type CallExpr struct {
	Func   Expr   // function expression (IdentExpr, or macro)
	LParen token.Position
	Args   []Expr
	RParen token.Position
}

func (e *CallExpr) Pos() token.Position { return e.Func.Pos() }
func (e *CallExpr) End() token.Position { return e.RParen }
func (e *CallExpr) exprNode()           {}

// DotExpr represents package member access: pkg.Member
// Used for Go package function calls: sql.Open(), fmt.Println()
type DotExpr struct {
	X       Expr   // package (IdentExpr)
	DotPos  token.Position
	Member  string // function/field name
}

func (e *DotExpr) Pos() token.Position { return e.X.Pos() }
func (e *DotExpr) End() token.Position { return e.DotPos }
func (e *DotExpr) exprNode()           {}

// SendExpr represents method call: obj:method(args...)
// Harbour: HB_ET_SEND — pObject + szMessage/pMessage + pParms
type SendExpr struct {
	Object  Expr
	ColonPos token.Position
	Method  string // static message name
	MacroMethod Expr // if &macro message (nil for static)
	HasParens bool   // true if () present (method call vs field access)
	LParen  token.Position
	Args    []Expr
	RParen  token.Position
	IsAssign bool // obj:prop := value (setter)
}

func (e *SendExpr) Pos() token.Position { return e.Object.Pos() }
func (e *SendExpr) End() token.Position { return e.RParen }
func (e *SendExpr) exprNode()           {}

// IndexExpr represents array index: arr[index]
// Harbour: HB_ET_ARRAYAT
type IndexExpr struct {
	X        Expr
	LBracket token.Position
	Index    Expr
	RBracket token.Position
}

func (e *IndexExpr) Pos() token.Position { return e.X.Pos() }
func (e *IndexExpr) End() token.Position { return e.RBracket }
func (e *IndexExpr) exprNode()           {}

// AliasExpr represents field access: alias->field or (expr)->field
// Harbour: HB_ET_ALIASVAR, HB_ET_ALIASEXPR
type AliasExpr struct {
	Alias    Expr // IdentExpr for static alias, any Expr for (dynamic)->field
	ArrowPos token.Position
	Field    Expr // IdentExpr or MacroExpr
}

func (e *AliasExpr) Pos() token.Position { return e.Alias.Pos() }
func (e *AliasExpr) End() token.Position { return e.Field.End() }
func (e *AliasExpr) exprNode()           {}

// MacroExpr represents macro expansion: &variable or &(expression)
// Harbour: HB_ET_MACRO with 6 subtypes
type MacroExpr struct {
	AmpPos token.Position
	Expr   Expr // variable or parenthesized expression
}

func (e *MacroExpr) Pos() token.Position { return e.AmpPos }
func (e *MacroExpr) End() token.Position { return e.Expr.End() }
func (e *MacroExpr) exprNode()           {}

// BlockExpr represents a code block: {|params| body}
// Harbour: HB_ET_CODEBLOCK — pLocals + pExprList
type BlockExpr struct {
	LBrace token.Position
	Params []string // parameter names (between | |)
	Body   Expr     // single expression (or comma-separated list)
	RBrace token.Position
}

func (e *BlockExpr) Pos() token.Position { return e.LBrace }
func (e *BlockExpr) End() token.Position { return e.RBrace }
func (e *BlockExpr) exprNode()           {}

// ArrayLitExpr represents a literal array: {1, 2, 3}
// Harbour: HB_ET_ARRAY
type ArrayLitExpr struct {
	LBrace token.Position
	Items  []Expr
	RBrace token.Position
}

func (e *ArrayLitExpr) Pos() token.Position { return e.LBrace }
func (e *ArrayLitExpr) End() token.Position { return e.RBrace }
func (e *ArrayLitExpr) exprNode()           {}

// SeqExpr is a comma-separated expression list used inside code
// blocks: `{|p| e1, e2, e3 }`. All sub-expressions are evaluated in
// order, the last value is the block's return. Without this node the
// parser kept only the last expr and silently dropped the side
// effects of every preceding one — a real miscompile that bit
// `SUM x, y, z TO sx, sy, sz` (only sz accumulated).
type SeqExpr struct {
	Items   []Expr
	StartAt token.Position
	EndAt   token.Position
}

func (e *SeqExpr) Pos() token.Position { return e.StartAt }
func (e *SeqExpr) End() token.Position { return e.EndAt }
func (e *SeqExpr) exprNode()           {}

// HashLitExpr represents a literal hash: {"a" => 1, "b" => 2}
// Harbour: HB_ET_HASH
type HashLitExpr struct {
	LBrace token.Position
	Keys   []Expr
	Values []Expr
	RBrace token.Position
}

func (e *HashLitExpr) Pos() token.Position { return e.LBrace }
func (e *HashLitExpr) End() token.Position { return e.RBrace }
func (e *HashLitExpr) exprNode()           {}

// IIfExpr represents inline if: IIF(cond, trueVal, falseVal)
// Harbour: HB_ET_IIF
type IIfExpr struct {
	IfPos token.Position
	Cond  Expr
	True  Expr
	False Expr
}

func (e *IIfExpr) Pos() token.Position { return e.IfPos }
func (e *IIfExpr) End() token.Position { return e.False.End() }
func (e *IIfExpr) exprNode()           {}

// RefExpr represents pass-by-reference: @variable
// Harbour: HB_ET_REFERENCE, HB_ET_VARREF, HB_ET_FUNREF
type RefExpr struct {
	AtPos token.Position
	X     Expr
}

func (e *RefExpr) Pos() token.Position { return e.AtPos }
func (e *RefExpr) End() token.Position { return e.X.End() }
func (e *RefExpr) exprNode()           {}

// --- Statements ---

// ExprStmt wraps an expression as a statement (function calls, assignments).
type ExprStmt struct {
	X Expr
}

func (s *ExprStmt) Pos() token.Position { return s.X.Pos() }
func (s *ExprStmt) End() token.Position { return s.X.End() }
func (s *ExprStmt) stmtNode()           {}

// ReturnStmt represents RETURN [expr].
type ReturnStmt struct {
	ReturnPos token.Position
	Value     Expr   // first/only return value (nil for bare RETURN)
	Values    []Expr // multi-return: RETURN a, b, c (nil if single)
}

func (s *ReturnStmt) Pos() token.Position { return s.ReturnPos }
func (s *ReturnStmt) End() token.Position {
	if s.Value != nil {
		return s.Value.End()
	}
	return s.ReturnPos
}
func (s *ReturnStmt) stmtNode() {}

// QOutStmt represents ? expr, expr, ... (shorthand for QOut).
type QOutStmt struct {
	QPos  token.Position
	IsQQ  bool   // true for ?? (QQOut)
	Exprs []Expr
}

func (s *QOutStmt) Pos() token.Position { return s.QPos }
func (s *QOutStmt) End() token.Position {
	if len(s.Exprs) > 0 {
		return s.Exprs[len(s.Exprs)-1].End()
	}
	return s.QPos
}
func (s *QOutStmt) stmtNode() {}

// IfStmt represents IF / ELSEIF / ELSE / ENDIF.
// Harbour: uses PHB_ELSEIF chain for fixups.
type IfStmt struct {
	IfPos    token.Position
	Cond     Expr
	Body     []Stmt
	ElseIfs  []*ElseIfClause
	ElseBody []Stmt // nil if no ELSE
	EndPos   token.Position
}

type ElseIfClause struct {
	ElseIfPos token.Position
	Cond      Expr
	Body      []Stmt
}

func (s *IfStmt) Pos() token.Position { return s.IfPos }
func (s *IfStmt) End() token.Position { return s.EndPos }
func (s *IfStmt) stmtNode()           {}

// DoWhileStmt represents DO WHILE cond ... ENDDO.
type DoWhileStmt struct {
	DoPos  token.Position
	Cond   Expr
	Body   []Stmt
	EndPos token.Position
}

func (s *DoWhileStmt) Pos() token.Position { return s.DoPos }
func (s *DoWhileStmt) End() token.Position { return s.EndPos }
func (s *DoWhileStmt) stmtNode()           {}

// ForStmt represents FOR var := start TO end [STEP step] ... NEXT.
type ForStmt struct {
	ForPos  token.Position
	Var     string
	Start   Expr
	To      Expr
	Step    Expr // nil for default step 1
	Body    []Stmt
	NextPos token.Position
}

func (s *ForStmt) Pos() token.Position { return s.ForPos }
func (s *ForStmt) End() token.Position { return s.NextPos }
func (s *ForStmt) stmtNode()           {}

// ForEachStmt represents FOR EACH var IN collection ... NEXT.
// Harbour: HB_ENUMERATOR structure.
type ForEachStmt struct {
	ForPos     token.Position
	Var        string
	Collection Expr
	Descend    bool // FOR EACH DESCEND
	Body       []Stmt
	NextPos    token.Position
}

func (s *ForEachStmt) Pos() token.Position { return s.ForPos }
func (s *ForEachStmt) End() token.Position { return s.NextPos }
func (s *ForEachStmt) stmtNode()           {}

// SwitchStmt represents SWITCH expr ... CASE ... OTHERWISE ... END.
// Harbour: HB_SWITCHCMD structure.
type SwitchStmt struct {
	SwitchPos token.Position
	Expr      Expr
	Cases     []*CaseClause
	Otherwise []Stmt // nil if no OTHERWISE
	EndPos    token.Position
}

type CaseClause struct {
	CasePos token.Position
	Value   Expr   // case value
	Body    []Stmt
}

func (s *SwitchStmt) Pos() token.Position { return s.SwitchPos }
func (s *SwitchStmt) End() token.Position { return s.EndPos }
func (s *SwitchStmt) stmtNode()           {}

// SeqStmt represents BEGIN SEQUENCE ... RECOVER [USING var] ... END.
type SeqStmt struct {
	BeginPos   token.Position
	Body       []Stmt
	RecoverVar string // variable name after USING (empty if none)
	RecoverBody []Stmt // nil if no RECOVER
	EndPos     token.Position
}

func (s *SeqStmt) Pos() token.Position { return s.BeginPos }
func (s *SeqStmt) End() token.Position { return s.EndPos }
func (s *SeqStmt) stmtNode()           {}

// === Five Go Extensions ===

// MultiAssignStmt: a, b, c := expr  or  a, b := Func()
// Also handles: a, b := b, a (parallel swap)
// Blank identifier _ discards the value.
type MultiAssignStmt struct {
	AssignPos token.Position
	Targets   []string // variable names ("_" = discard)
	Values    []Expr   // right-hand side expressions
}

func (s *MultiAssignStmt) Pos() token.Position { return s.AssignPos }
func (s *MultiAssignStmt) End() token.Position { return s.AssignPos }
func (s *MultiAssignStmt) stmtNode()           {}

// DeferStmt: DEFER expr (execute when function returns)
type DeferStmt struct {
	DeferPos token.Position
	Call     Expr // expression to defer (usually a method/function call)
}

func (s *DeferStmt) Pos() token.Position { return s.DeferPos }
func (s *DeferStmt) End() token.Position { return s.DeferPos }
func (s *DeferStmt) stmtNode()           {}

// ConstDecl: CONST block with optional auto-increment
type ConstDecl struct {
	ConstPos token.Position
	Items    []ConstItem
}

type ConstItem struct {
	Name  string
	Value Expr // nil = auto-increment from previous
}

func (d *ConstDecl) Pos() token.Position { return d.ConstPos }
func (d *ConstDecl) End() token.Position { return d.ConstPos }
func (d *ConstDecl) declNode()           {}

// SliceExpr: a[low:high] — sub-array or sub-string
type SliceExpr struct {
	X         Expr
	LBracket  token.Position
	Low       Expr // nil = from start
	High      Expr // nil = to end
	RBracket  token.Position
}

func (e *SliceExpr) Pos() token.Position { return e.X.Pos() }
func (e *SliceExpr) End() token.Position { return e.RBracket }
func (e *SliceExpr) exprNode()           {}

// NilSafeExpr: obj?:Method() — returns NIL if obj is NIL
type NilSafeExpr struct {
	X        Expr
	QPos     token.Position
	Method   string
	Args     []Expr
	HasParens bool
}

func (e *NilSafeExpr) Pos() token.Position { return e.X.Pos() }
func (e *NilSafeExpr) End() token.Position { return e.QPos }
func (e *NilSafeExpr) exprNode()           {}

// InterpolatedString: f"Hello {name}, age {age}"
type InterpolatedString struct {
	FPos  token.Position
	Parts []Expr // alternating: LiteralExpr (text), other Expr (interpolated)
}

func (e *InterpolatedString) Pos() token.Position { return e.FPos }
func (e *InterpolatedString) End() token.Position { return e.FPos }
func (e *InterpolatedString) exprNode()           {}

// === Five Concurrency Extensions ===

// ChanSendStmt: ch <- value
type ChanSendStmt struct {
	ChanPos token.Position
	Chan    Expr // channel expression
	Value   Expr // value to send
}

func (s *ChanSendStmt) Pos() token.Position { return s.ChanPos }
func (s *ChanSendStmt) End() token.Position { return s.ChanPos }
func (s *ChanSendStmt) stmtNode()           {}

// ChanRecvExpr: <- ch (receive from channel, used as expression)
type ChanRecvExpr struct {
	ArrowPos token.Position
	Chan     Expr
}

func (e *ChanRecvExpr) Pos() token.Position { return e.ArrowPos }
func (e *ChanRecvExpr) End() token.Position { return e.ArrowPos }
func (e *ChanRecvExpr) exprNode()           {}

// WatchStmt: WATCH / CASE <- ch / CASE ch <- val / OTHERWISE / ENDWATCH
type WatchStmt struct {
	WatchPos  token.Position
	Cases     []*WatchCase
	Otherwise []Stmt
	EndPos    token.Position
}

type WatchCase struct {
	CasePos  token.Position
	RecvChan Expr   // CASE val := <- ch  (receive)
	RecvVar  string // variable name for received value ("" if none)
	SendChan Expr   // CASE ch <- val (send)
	SendVal  Expr   // value to send
	Body     []Stmt
}

func (s *WatchStmt) Pos() token.Position { return s.WatchPos }
func (s *WatchStmt) End() token.Position { return s.EndPos }
func (s *WatchStmt) stmtNode()           {}

// GoBlockStmt: GO { ... } — inline goroutine
type GoBlockStmt struct {
	GoPos token.Position
	Block *BlockExpr // code block to execute
}

func (s *GoBlockStmt) Pos() token.Position { return s.GoPos }
func (s *GoBlockStmt) End() token.Position { return s.GoPos }
func (s *GoBlockStmt) stmtNode()           {}

// ParallelForStmt: PARALLEL FOR i := 1 TO n / body / NEXT
type ParallelForStmt struct {
	ForPos token.Position
	Var    string
	Start  Expr
	To     Expr
	Step   Expr // nil = default 1
	Body   []Stmt
	EndPos token.Position
}

func (s *ParallelForStmt) Pos() token.Position { return s.ForPos }
func (s *ParallelForStmt) End() token.Position { return s.EndPos }
func (s *ParallelForStmt) stmtNode()           {}

// AsyncExpr: ASYNC expr — returns a future/channel
type AsyncExpr struct {
	AsyncPos token.Position
	Call     Expr
}

func (e *AsyncExpr) Pos() token.Position { return e.AsyncPos }
func (e *AsyncExpr) End() token.Position { return e.AsyncPos }
func (e *AsyncExpr) exprNode()           {}

// AwaitExpr: AWAIT future — blocks until result ready
type AwaitExpr struct {
	AwaitPos token.Position
	Future   Expr
}

func (e *AwaitExpr) Pos() token.Position { return e.AwaitPos }
func (e *AwaitExpr) End() token.Position { return e.AwaitPos }
func (e *AwaitExpr) exprNode()           {}

// TimeoutStmt: WITH TIMEOUT n / body / ENDWITH
type TimeoutStmt struct {
	WithPos  token.Position
	Duration Expr   // timeout in seconds
	Body     []Stmt
	EndPos   token.Position
}

func (s *TimeoutStmt) Pos() token.Position { return s.WithPos }
func (s *TimeoutStmt) End() token.Position { return s.EndPos }
func (s *TimeoutStmt) stmtNode()           {}

// === End Five Go Extensions ===

// ExitStmt represents EXIT (break out of loop).
type ExitStmt struct {
	ExitPos token.Position
}

func (s *ExitStmt) Pos() token.Position { return s.ExitPos }
func (s *ExitStmt) End() token.Position { return s.ExitPos }
func (s *ExitStmt) stmtNode()           {}

// LoopStmt represents LOOP (continue to next iteration).
type LoopStmt struct {
	LoopPos token.Position
}

func (s *LoopStmt) Pos() token.Position { return s.LoopPos }
func (s *LoopStmt) End() token.Position { return s.LoopPos }
func (s *LoopStmt) stmtNode()           {}

// --- xBase command statements ---

// UseCmd represents USE [file] [VIA driver] [ALIAS name] [EXCLUSIVE|SHARED]
type UseCmd struct {
	UsePos    token.Position
	File      Expr   // filename expression (nil = close current)
	Via       string // RDD driver name
	Alias     string // alias name (static)
	AliasExpr Expr   // alias expression for ALIAS (expr) — dynamic alias
	Shared    bool   // SHARED flag
	ReadOnly  bool   // READONLY flag
}

func (s *UseCmd) Pos() token.Position { return s.UsePos }
func (s *UseCmd) End() token.Position { return s.UsePos }
func (s *UseCmd) stmtNode()           {}

// SelectCmd represents SELECT area
type SelectCmd struct {
	SelectPos token.Position
	Area      Expr // area number or alias name
}

func (s *SelectCmd) Pos() token.Position { return s.SelectPos }
func (s *SelectCmd) End() token.Position { return s.SelectPos }
func (s *SelectCmd) stmtNode()           {}

// GoCmd represents GO TOP / GO BOTTOM / GO recno / GOTO recno
type GoCmd struct {
	GoPos     token.Position
	Direction string // "TOP", "BOTTOM", or ""
	RecNo     Expr   // record number expression (nil for TOP/BOTTOM)
}

func (s *GoCmd) Pos() token.Position { return s.GoPos }
func (s *GoCmd) End() token.Position { return s.GoPos }
func (s *GoCmd) stmtNode()           {}

// SkipCmd represents SKIP [n]
type SkipCmd struct {
	SkipPos token.Position
	Count   Expr // nil for SKIP 1
}

func (s *SkipCmd) Pos() token.Position { return s.SkipPos }
func (s *SkipCmd) End() token.Position { return s.SkipPos }
func (s *SkipCmd) stmtNode()           {}

// SeekCmd represents SEEK expr [SOFTSEEK]
type SeekCmd struct {
	SeekPos  token.Position
	Key      Expr
	SoftSeek bool
}

func (s *SeekCmd) Pos() token.Position { return s.SeekPos }
func (s *SeekCmd) End() token.Position { return s.SeekPos }
func (s *SeekCmd) stmtNode()           {}

// ReplaceCmd represents REPLACE field WITH expr [, field WITH expr ...]
type ReplaceCmd struct {
	ReplacePos token.Position
	Fields     []ReplaceField
}

type ReplaceField struct {
	Field Expr // field expression (may include alias)
	Value Expr
}

func (s *ReplaceCmd) Pos() token.Position { return s.ReplacePos }
func (s *ReplaceCmd) End() token.Position { return s.ReplacePos }
func (s *ReplaceCmd) stmtNode()           {}

// AppendCmd represents APPEND BLANK
type AppendCmd struct {
	AppendPos token.Position
}

func (s *AppendCmd) Pos() token.Position { return s.AppendPos }
func (s *AppendCmd) End() token.Position { return s.AppendPos }
func (s *AppendCmd) stmtNode()           {}

// DeleteCmd represents DELETE (mark current record for deletion)
type DeleteCmd struct {
	DeletePos token.Position
}

func (s *DeleteCmd) Pos() token.Position { return s.DeletePos }
func (s *DeleteCmd) End() token.Position { return s.DeletePos }
func (s *DeleteCmd) stmtNode()           {}

// IndexCmd represents INDEX ON expr [TAG tagname] TO file [FOR cond] [UNIQUE] [DESCENDING]
type IndexCmd struct {
	IndexPos   token.Position
	KeyExpr    Expr
	File       Expr
	ForCond    Expr   // nil if no FOR
	TagName    string // TAG name for CDX compound index (empty = NTX)
	Unique     bool
	Descending bool
}

func (s *IndexCmd) Pos() token.Position { return s.IndexPos }
func (s *IndexCmd) End() token.Position { return s.IndexPos }
func (s *IndexCmd) stmtNode()           {}

// SetCmd represents SET commands: SET FILTER TO expr, SET RELATION TO expr INTO alias, etc.
type SetCmd struct {
	SetPos  token.Position
	Setting string // "FILTER", "RELATION", "ORDER", "INDEX", etc.
	Expr    Expr   // the value expression
	Extra   string // extra info (INTO alias, etc.)
}

func (s *SetCmd) Pos() token.Position { return s.SetPos }
func (s *SetCmd) End() token.Position { return s.SetPos }
func (s *SetCmd) stmtNode()           {}

// AtSayCmd represents @ row, col SAY expr [PICTURE pic]
type AtSayCmd struct {
	AtPos   token.Position
	Row     Expr
	Col     Expr
	SayExpr Expr
	Picture Expr // nil if no PICTURE
}

func (s *AtSayCmd) Pos() token.Position { return s.AtPos }
func (s *AtSayCmd) End() token.Position { return s.AtPos }
func (s *AtSayCmd) stmtNode()           {}

// AtGetCmd represents @ row, col GET var [PICTURE pic] [VALID valid] [WHEN when]
type AtGetCmd struct {
	AtPos   token.Position
	Row     Expr
	Col     Expr
	Var     Expr   // the variable expression
	VarName string // variable name as string
	Picture Expr   // nil if no PICTURE
	Valid   Expr   // nil if no VALID (code block)
	When    Expr   // nil if no WHEN (code block)
}

func (s *AtGetCmd) Pos() token.Position { return s.AtPos }
func (s *AtGetCmd) End() token.Position { return s.AtPos }
func (s *AtGetCmd) stmtNode()           {}

// AtSayGetCmd represents @ row, col SAY expr GET var [PICTURE pic] [VALID valid] [WHEN when]
type AtSayGetCmd struct {
	AtPos   token.Position
	Row     Expr
	Col     Expr
	SayExpr Expr
	Var     Expr
	VarName string
	Picture Expr
	Valid   Expr
	When    Expr
}

func (s *AtSayGetCmd) Pos() token.Position { return s.AtPos }
func (s *AtSayGetCmd) End() token.Position { return s.AtPos }
func (s *AtSayGetCmd) stmtNode()           {}

// ReadCmd represents READ [SAVE]
type ReadCmd struct {
	ReadPos token.Position
	Save    bool
}

func (s *ReadCmd) Pos() token.Position { return s.ReadPos }
func (s *ReadCmd) End() token.Position { return s.ReadPos }
func (s *ReadCmd) stmtNode()           {}