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

// exprreg.go — Expression parser registries for Pratt parser.
//
// Three registries:
//   prefixParsers  — unary prefix: -, !, ++, --, <-, ASYNC, AWAIT
//   postfixParsers — postfix: (), [], :, ., ?:, ++, --, ->
//   primaryParsers — atoms: INT, STRING, IDENT, (, {, ::
//
// Adding a new operator = one line in init().

package parser

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

// PrefixParser parses a prefix unary expression.
type PrefixParser func(p *Parser) ast.Expr

// PostfixParser parses a postfix expression given the left-hand side.
type PostfixParser func(p *Parser, x ast.Expr) ast.Expr

// PrimaryParser parses an atomic/primary expression.
type PrimaryParser func(p *Parser) ast.Expr

var (
	prefixParsers  map[token.Kind]PrefixParser
	postfixParsers map[token.Kind]PostfixParser
	primaryParsers map[token.Kind]PrimaryParser
)

func init() {
	prefixParsers = map[token.Kind]PrefixParser{
		token.MINUS:      prefixUnary(token.MINUS),
		token.PLUS:       prefixPlus,
		token.NOT:        prefixUnary(token.NOT),
		token.INC:        prefixUnary(token.INC),
		token.DEC:        prefixUnary(token.DEC),
		token.ARROW_LEFT: prefixChanRecv,
		token.ASYNC_KW:   prefixAsync,
		token.AWAIT_KW:   prefixAwait,
		token.AT:         prefixRef,
	}

	postfixParsers = map[token.Kind]PostfixParser{
		token.LPAREN:     postfixCall,
		token.LBRACKET:   postfixIndex,
		token.COLON:      postfixSend,
		token.QMARK:      postfixNilSafe,
		token.DOT:        postfixDot,
		token.ARROW:      postfixAlias,
		token.INC:        postfixIncDec(token.INC),
		token.DEC:        postfixIncDec(token.DEC),
		token.COLONCOLON: postfixSelfStop,
	}

	primaryParsers = map[token.Kind]PrimaryParser{
		token.INT:      primaryLiteral,
		token.LONG:     primaryLiteral,
		token.DOUBLE:   primaryLiteral,
		token.STRING:   primaryLiteral,
		token.DATE_LIT: primaryLiteral,
		token.TRUE:     primaryLiteral,
		token.FALSE:    primaryLiteral,
		token.NIL_LIT:  primaryLiteral,

		token.COLONCOLON: primarySelf,
		token.LPAREN:     primaryParen,
		token.IF:         primaryIf,
		token.IDENT:      primaryIdent,
		token.AMPERSAND:  primaryMacro,
		token.COLON:      primaryWithSend,
		token.LBRACE:     primaryArrayOrBlock,
	}
}

// --- Prefix parsers ---

func prefixUnary(op token.Kind) PrefixParser {
	return func(p *Parser) ast.Expr {
		tok := p.advance()
		x := p.parseUnaryExpr()
		return &ast.UnaryExpr{OpPos: tok.Pos, Op: op, X: x}
	}
}

func prefixPlus(p *Parser) ast.Expr {
	p.advance() // unary plus — no-op
	return p.parseUnaryExpr()
}

func prefixChanRecv(p *Parser) ast.Expr {
	pos := p.advance().Pos
	ch := p.parsePostfixExpr()
	return &ast.ChanRecvExpr{ArrowPos: pos, Chan: ch}
}

func prefixAsync(p *Parser) ast.Expr {
	pos := p.advance().Pos
	call := p.parsePostfixExpr()
	return &ast.AsyncExpr{AsyncPos: pos, Call: call}
}

func prefixAwait(p *Parser) ast.Expr {
	pos := p.advance().Pos
	future := p.parsePostfixExpr()
	return &ast.AwaitExpr{AwaitPos: pos, Future: future}
}

func prefixRef(p *Parser) ast.Expr {
	op := p.advance()
	x := p.parseUnaryExpr()
	return &ast.RefExpr{AtPos: op.Pos, X: x}
}

// --- Postfix parsers ---

func postfixCall(p *Parser, x ast.Expr) ast.Expr {
	lp := p.advance().Pos
	var args []ast.Expr
	if !p.at(token.RPAREN) {
		args = p.parseExprList()
	}
	rp := p.expect(token.RPAREN).Pos
	return &ast.CallExpr{Func: x, LParen: lp, Args: args, RParen: rp}
}

func postfixIndex(p *Parser, x ast.Expr) ast.Expr {
	lb := p.advance().Pos

	// Slice syntax detection
	if p.isSliceSyntax() {
		var low, high ast.Expr
		if !p.at(token.COLON) {
			low = p.parseSliceIndex()
		}
		p.expect(token.COLON)
		if !p.at(token.RBRACKET) {
			high = p.parseSliceIndex()
		}
		rb := p.expect(token.RBRACKET).Pos
		return &ast.SliceExpr{X: x, LBracket: lb, Low: low, High: high, RBracket: rb}
	}

	// Normal array index
	index := p.parseExpr()
	rb := token.Position{}
	for p.match(token.COMMA) {
		rb = p.current.Pos
		x = &ast.IndexExpr{X: x, LBracket: lb, Index: index, RBracket: rb}
		index = p.parseExpr()
		lb = rb
	}
	rb = p.expect(token.RBRACKET).Pos
	return &ast.IndexExpr{X: x, LBracket: lb, Index: index, RBracket: rb}
}

func postfixDot(p *Parser, x ast.Expr) ast.Expr {
	if p.peekLitAt(1) != "" {
		dotPos := p.advance().Pos
		member := p.advance()
		return &ast.DotExpr{X: x, DotPos: dotPos, Member: member.Literal}
	}
	return nil // signal: stop postfix loop
}

func postfixIncDec(op token.Kind) PostfixParser {
	return func(p *Parser, x ast.Expr) ast.Expr {
		opPos := p.advance().Pos
		return &ast.PostfixExpr{X: x, OpPos: opPos, Op: op}
	}
}

func postfixSelfStop(p *Parser, x ast.Expr) ast.Expr {
	return nil // :: after expression — stop
}

// postfixNilSafe and postfixSend/postfixAlias are complex — kept in expr.go
// They call back into the main parser methods.

func postfixNilSafe(p *Parser, x ast.Expr) ast.Expr {
	if p.peekAt(1) != token.COLON {
		return nil // bare ? = QOut, not postfix
	}
	p.advance() // consume ?
	qpos := p.advance().Pos // consume :
	methodName := p.expectMethodName().Literal
	var args []ast.Expr
	hasParens := false
	if p.at(token.LPAREN) {
		hasParens = true
		p.advance()
		if !p.at(token.RPAREN) {
			args = p.parseExprList()
		}
		p.expect(token.RPAREN)
	}
	return &ast.NilSafeExpr{X: x, QPos: qpos, Method: methodName, Args: args, HasParens: hasParens}
}

func postfixAlias(p *Parser, x ast.Expr) ast.Expr {
	arrowPos := p.advance().Pos
	field := p.parsePrimaryExpr()
	return &ast.AliasExpr{Alias: x, ArrowPos: arrowPos, Field: field}
}

func postfixSend(p *Parser, x ast.Expr) ast.Expr {
	return p.parsePostfixSend(x)
}

// --- Primary parsers ---

func primaryLiteral(p *Parser) ast.Expr {
	tok := p.advance()
	return &ast.LiteralExpr{ValuePos: tok.Pos, Kind: tok.Kind, Value: tok.Literal}
}

func primaryParen(p *Parser) ast.Expr {
	p.advance()
	expr := p.parseExpr()
	for p.match(token.COMMA) {
		expr = p.parseExpr()
	}
	p.expect(token.RPAREN)
	return expr
}

func primaryIf(p *Parser) ast.Expr {
	if p.peekAt(1) == token.LPAREN {
		return p.parseIIF()
	}
	p.error("expected expression, got IF")
	tok := p.advance()
	return &ast.LiteralExpr{ValuePos: tok.Pos, Kind: token.NIL_LIT, Value: "NIL"}
}

func primaryIdent(p *Parser) ast.Expr {
	return p.parsePrimaryIdent()
}

func primaryMacro(p *Parser) ast.Expr {
	return p.parseMacro()
}

func primaryWithSend(p *Parser) ast.Expr {
	return p.parsePrimaryWithSend()
}

func primaryArrayOrBlock(p *Parser) ast.Expr {
	return p.parseArrayOrBlock()
}

func primarySelf(p *Parser) ast.Expr {
	return p.parsePrimarySelf()
}