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

// stmtreg.go — Statement parser registry.
//
// Instead of a 800+ line switch in parseStmt(), each statement type
// registers its parser function. New statements can be added by
// simply adding one line to initStmtRegistry().
//
// Pattern: token.Kind → func(*Parser) ast.Stmt

package parser

import (
	"five/compiler/ast"
	"five/compiler/token"
)

// StmtParser is a function that parses a statement starting with the current token.
type StmtParser func(p *Parser) ast.Stmt

// stmtRegistry maps token kinds to their statement parsers.
var stmtRegistry map[token.Kind]StmtParser

func init() {
	stmtRegistry = map[token.Kind]StmtParser{
		// Control flow
		token.IF:     (*Parser).stmtIf,
		token.DO:     (*Parser).stmtDo,
		token.WHILE:  (*Parser).stmtWhile,
		token.FOR:    (*Parser).stmtFor,
		token.BEGIN:  (*Parser).stmtBegin,
		token.SWITCH: (*Parser).stmtSwitch,
		token.RETURN: (*Parser).stmtReturn,
		token.EXIT:   (*Parser).stmtExit,
		token.LOOP:   (*Parser).stmtLoop,

		// I/O
		token.QMARK:  (*Parser).stmtQOut,
		token.QQMARK: (*Parser).stmtQQOut,

		// Variables
		token.PRIVATE:    (*Parser).stmtPrivate,
		token.PUBLIC:     (*Parser).stmtPublic,
		token.LOCAL:      (*Parser).stmtVarDecl,
		token.STATIC:     (*Parser).stmtVarDecl,
		token.PARAMETERS: (*Parser).stmtParameters,
		token.DECLARE:    (*Parser).stmtDeclare,

		// xBase database
		token.USE:       (*Parser).stmtUse,
		token.SELECT:    (*Parser).stmtSelect,
		token.GO:        (*Parser).stmtGo,
		token.GOTO:      (*Parser).stmtGo,
		token.SKIP_KW:   (*Parser).stmtSkip,
		token.SEEK:      (*Parser).stmtSeek,
		token.REPLACE:   (*Parser).stmtReplace,
		token.APPEND:    (*Parser).stmtAppend,
		token.DELETE_KW: (*Parser).stmtDelete,
		token.RECALL:    (*Parser).stmtRecallPackZap,
		token.PACK:      (*Parser).stmtRecallPackZap,
		token.ZAP:       (*Parser).stmtRecallPackZap,
		token.INDEX:     (*Parser).stmtIndex,
		token.SET:       (*Parser).stmtSet,

		// Screen
		token.AT: (*Parser).stmtAt,

		// Five Go extensions
		token.DEFER_KW:    (*Parser).stmtDefer,
		token.CONST_KW:    (*Parser).stmtConst,
		token.WATCH_KW:    (*Parser).stmtWatch,
		token.WITH:        (*Parser).stmtWith,
		token.PARALLEL_KW: (*Parser).stmtParallel,
		token.SPAWN_KW:    (*Parser).stmtSpawn,
		token.ARROW_LEFT:  (*Parser).stmtArrowLeft,
	}
}

// lookupStmtParser finds a registered parser for the current token.
func (p *Parser) lookupStmtParser() StmtParser {
	if fn, ok := stmtRegistry[p.current.Kind]; ok {
		return fn
	}
	return nil
}

// --- Thin wrappers: each calls the existing parse method ---

// rewriteAsIdent treats the current keyword token as an identifier for expression parsing.
// Instead of mutating the token array (which breaks backtracking), it temporarily
// overwrites the current token and restores nothing — the token is consumed immediately.
func (p *Parser) rewriteAsIdent(name string) {
	p.current = token.Token{Kind: token.IDENT, Literal: name, Pos: p.current.Pos}
}

func (p *Parser) stmtIf() ast.Stmt {
	if p.peekAt(1) == token.LPAREN {
		if p.looksLikeIIF() {
			return p.parseExprStmt()
		}
	}
	return p.parseIf()
}

func (p *Parser) stmtDo() ast.Stmt {
	if p.peekAt(1) == token.LPAREN {
		p.rewriteAsIdent("Do")
		return p.parseExprStmt()
	}
	if p.peekAt(1) == token.CASE || token.LookupKeyword(p.peekLitAt(1)) == token.CASE {
		return p.parseDoCase()
	}
	if p.peekAt(1) == token.WHILE {
		return p.parseDoWhile()
	}
	if p.peekAt(1) == token.IDENT {
		return p.parseDoProc()
	}
	return p.parseDoWhile()
}

func (p *Parser) stmtWhile() ast.Stmt {
	if p.peekAt(1) == token.LPAREN {
		p.rewriteAsIdent("While")
		return p.parseExprStmt()
	}
	return p.parseDoWhile()
}

func (p *Parser) stmtFor() ast.Stmt {
	next := p.peekAt(1)
	if next == token.ASSIGN || next == token.LPAREN ||
		next == token.PLUSEQ || next == token.MINUSEQ {
		p.rewriteAsIdent("for")
		return p.parseExprStmt()
	}
	return p.parseFor()
}

func (p *Parser) stmtBegin() ast.Stmt {
	if p.peekAt(1) != token.SEQUENCE && p.peekAt(1) != token.NEWLINE && p.peekAt(1) != token.EOF {
		p.rewriteAsIdent("begin")
		return p.parseExprStmt()
	}
	return p.parseBeginSequence()
}

func (p *Parser) stmtSwitch() ast.Stmt { return p.parseSwitch() }

func (p *Parser) stmtReturn() ast.Stmt {
	next := p.peekAt(1)
	if next == token.ASSIGN || next == token.PLUSEQ || next == token.MINUSEQ {
		p.rewriteAsIdent("return")
		return p.parseExprStmt()
	}
	return p.parseReturn()
}

func (p *Parser) stmtExit() ast.Stmt {
	pos := p.advance().Pos
	return &ast.ExitStmt{ExitPos: pos}
}

func (p *Parser) stmtLoop() ast.Stmt {
	pos := p.advance().Pos
	return &ast.LoopStmt{LoopPos: pos}
}

func (p *Parser) stmtQOut() ast.Stmt  { return p.parseQOut(false) }
func (p *Parser) stmtQQOut() ast.Stmt { return p.parseQOut(true) }

func (p *Parser) stmtPrivate() ast.Stmt { return p.parsePrivatePublic(ast.ScopePrivate) }
func (p *Parser) stmtPublic() ast.Stmt  { return p.parsePrivatePublic(ast.ScopePublic) }
func (p *Parser) stmtVarDecl() ast.Stmt { return p.parseVarDecl() }

func (p *Parser) stmtParameters() ast.Stmt {
	p.current = token.Token{Kind: token.LOCAL, Literal: "LOCAL", Pos: p.current.Pos}
	return p.parseVarDecl()
}

func (p *Parser) stmtDeclare() ast.Stmt {
	p.skipToEndOfLine()
	p.expectEndOfStmt()
	return &ast.ExprStmt{X: &ast.LiteralExpr{Kind: token.NIL_LIT, Value: "NIL"}}
}

func (p *Parser) stmtUse() ast.Stmt     { return p.parseUse() }
func (p *Parser) stmtSelect() ast.Stmt  { return p.parseSelect() }
func (p *Parser) stmtSkip() ast.Stmt    { return p.parseSkip() }
func (p *Parser) stmtSeek() ast.Stmt    { return p.parseSeek() }
func (p *Parser) stmtReplace() ast.Stmt { return p.parseReplace() }
func (p *Parser) stmtAppend() ast.Stmt  { return p.parseAppend() }
func (p *Parser) stmtIndex() ast.Stmt   { return p.parseIndex() }
func (p *Parser) stmtAt() ast.Stmt      { return p.parseAtCmd() }

func (p *Parser) stmtGo() ast.Stmt {
	if p.current.Kind == token.GO && p.peekAt(1) == token.LPAREN {
		p.rewriteAsIdent("Go")
		return p.parseExprStmt()
	}
	return p.parseGo()
}

func (p *Parser) stmtDelete() ast.Stmt {
	pos := p.advance().Pos
	if p.current.Kind == token.IDENT {
		upper := p.currentUpper()
		if upper == "FILE" {
			p.skipToEndOfLine()
			p.expectEndOfStmt()
			return &ast.ExprStmt{X: &ast.LiteralExpr{Kind: token.NIL_LIT, Value: "NIL"}}
		}
		if upper == "ALL" || upper == "TAG" {
			p.skipToEndOfLine()
			p.expectEndOfStmt()
			return &ast.ExprStmt{X: &ast.LiteralExpr{Kind: token.NIL_LIT, Value: "NIL"}}
		}
	}
	p.expectEndOfStmt()
	return &ast.ExprStmt{X: &ast.CallExpr{
		Func: &ast.IdentExpr{NamePos: pos, Name: "DbDelete"},
	}}
}

func (p *Parser) stmtRecallPackZap() ast.Stmt {
	tok := p.advance()
	var fname string
	switch tok.Kind {
	case token.RECALL:
		fname = "DbRecall"
	case token.PACK:
		fname = "__DbPack"
	case token.ZAP:
		fname = "__DbZap"
	}
	p.expectEndOfStmt()
	return &ast.ExprStmt{X: &ast.CallExpr{
		Func: &ast.IdentExpr{NamePos: tok.Pos, Name: fname},
	}}
}

func (p *Parser) stmtSet() ast.Stmt {
	// `Set(...)` with parentheses is a function call (the Harbour Set()
	// runtime function for reading/writing SET slots), not a SET command.
	// Treat it as an expression statement so the args reach the call.
	if p.peekAt(1) == token.LPAREN {
		p.rewriteAsIdent("Set")
		return p.parseExprStmt()
	}
	return p.parseSet()
}

func (p *Parser) stmtDefer() ast.Stmt    { return p.parseDefer() }
func (p *Parser) stmtConst() ast.Stmt    { return p.parseConstBlock() }
func (p *Parser) stmtWatch() ast.Stmt    { return p.parseWatch() }
func (p *Parser) stmtParallel() ast.Stmt { return p.parseParallelFor() }

func (p *Parser) stmtWith() ast.Stmt {
	if p.peekAt(1) == token.TIMEOUT_KW {
		return p.parseWithTimeout()
	}
	p.skipToEndOfLine()
	p.expectEndOfStmt()
	return &ast.ExprStmt{X: &ast.LiteralExpr{Kind: token.NIL_LIT, Value: "NIL"}}
}

func (p *Parser) stmtSpawn() ast.Stmt {
	goPos := p.advance().Pos
	block := p.parseArrayOrBlock()
	if blk, ok := block.(*ast.BlockExpr); ok {
		p.expectEndOfStmt()
		return &ast.GoBlockStmt{GoPos: goPos, Block: blk}
	}
	p.expectEndOfStmt()
	return &ast.ExprStmt{X: block}
}

func (p *Parser) stmtArrowLeft() ast.Stmt {
	pos := p.advance().Pos
	ch := p.parseExpr()
	p.expectEndOfStmt()
	return &ast.ExprStmt{X: &ast.ChanRecvExpr{ArrowPos: pos, Chan: ch}}
}