package parser

import (
	"fmt"
	"strconv"
	"strings"
)

// ParseError represents a parsing error with location information
type ParseError struct {
	Message string
	Line    int
	Column  int
	Token   Token
}

func (pe ParseError) Error() string {
	return fmt.Sprintf("Parse error at line %d, column %d: %s (near '%s')",
		pe.Line, pe.Column, pe.Message, pe.Token.Literal)
}

// Parser implements a recursive descent Pratt parser
type Parser struct {
	lexer *Lexer

	curToken  Token
	peekToken Token

	prefixParseFns map[TokenType]func() Expression
	infixParseFns  map[TokenType]func(Expression) Expression

	errors []ParseError
}

// NewParser creates a new parser instance
func NewParser(lexer *Lexer) *Parser {
	p := &Parser{
		lexer:  lexer,
		errors: []ParseError{},
	}

	p.prefixParseFns = make(map[TokenType]func() Expression)
	p.registerPrefix(IDENT, p.parseIdentifier)
	p.registerPrefix(NUMBER, p.parseNumberLiteral)
	p.registerPrefix(STRING, p.parseStringLiteral)
	p.registerPrefix(TRUE, p.parseBooleanLiteral)
	p.registerPrefix(FALSE, p.parseBooleanLiteral)
	p.registerPrefix(NIL, p.parseNilLiteral)
	p.registerPrefix(LPAREN, p.parseGroupedExpression)
	p.registerPrefix(LBRACE, p.parseTableLiteral)
	p.registerPrefix(MINUS, p.parsePrefixExpression)

	p.infixParseFns = make(map[TokenType]func(Expression) Expression)
	p.registerInfix(PLUS, p.parseInfixExpression)
	p.registerInfix(MINUS, p.parseInfixExpression)
	p.registerInfix(SLASH, p.parseInfixExpression)
	p.registerInfix(STAR, p.parseInfixExpression)
	p.registerInfix(EQ, p.parseInfixExpression)
	p.registerInfix(NOT_EQ, p.parseInfixExpression)
	p.registerInfix(LT, p.parseInfixExpression)
	p.registerInfix(GT, p.parseInfixExpression)
	p.registerInfix(LT_EQ, p.parseInfixExpression)
	p.registerInfix(GT_EQ, p.parseInfixExpression)
	p.registerInfix(DOT, p.parseDotExpression)
	p.registerInfix(LBRACKET, p.parseIndexExpression)

	// Read two tokens, so curToken and peekToken are both set
	p.nextToken()
	p.nextToken()

	return p
}

// registerPrefix registers a prefix parse function
func (p *Parser) registerPrefix(tokenType TokenType, fn func() Expression) {
	p.prefixParseFns[tokenType] = fn
}

// registerInfix registers an infix parse function
func (p *Parser) registerInfix(tokenType TokenType, fn func(Expression) Expression) {
	p.infixParseFns[tokenType] = fn
}

// nextToken advances to the next token
func (p *Parser) nextToken() {
	p.curToken = p.peekToken
	p.peekToken = p.lexer.NextToken()
}

// ParseProgram parses the entire program
func (p *Parser) ParseProgram() *Program {
	program := &Program{}
	program.Statements = []Statement{}

	for !p.curTokenIs(EOF) {
		stmt := p.parseStatement()
		if stmt != nil {
			program.Statements = append(program.Statements, stmt)
		}
		p.nextToken()
	}

	return program
}

// parseStatement parses a statement
func (p *Parser) parseStatement() Statement {
	switch p.curToken.Type {
	case IDENT:
		// Try to parse as assignment (handles both simple and member access)
		return p.parseAssignStatement()
	case IF:
		return p.parseIfStatement()
	case FOR:
		return p.parseForStatement()
	case WHILE:
		return p.parseWhileStatement()
	case ECHO:
		return p.parseEchoStatement()
	case BREAK:
		return p.parseBreakStatement()
	case EXIT:
		return p.parseExitStatement()
	case ASSIGN:
		p.addError("assignment operator '=' without left-hand side identifier")
		return nil
	case ILLEGAL:
		p.addError(fmt.Sprintf("unexpected token '%s'", p.curToken.Literal))
		return nil
	case EOF:
		return nil
	default:
		p.addError(fmt.Sprintf("unexpected token '%s', expected statement", p.curToken.Literal))
		return nil
	}
}

// parseAssignStatement parses variable assignment
func (p *Parser) parseAssignStatement() *AssignStatement {
	stmt := &AssignStatement{}

	// Parse left-hand side expression (can be identifier or member access)
	stmt.Name = p.ParseExpression(LOWEST)
	if stmt.Name == nil {
		p.addError("expected expression for assignment left-hand side")
		return nil
	}

	// Check if next token is assignment operator
	if !p.peekTokenIs(ASSIGN) {
		p.addError("unexpected identifier, expected assignment or declaration")
		return nil
	}

	// Validate assignment target
	switch stmt.Name.(type) {
	case *Identifier, *DotExpression, *IndexExpression:
		// Valid assignment targets
	default:
		p.addError("invalid assignment target")
		return nil
	}

	if !p.expectPeek(ASSIGN) {
		return nil
	}

	p.nextToken()

	stmt.Value = p.ParseExpression(LOWEST)
	if stmt.Value == nil {
		p.addError("expected expression after assignment operator")
		return nil
	}

	return stmt
}

// parseEchoStatement parses echo statements
func (p *Parser) parseEchoStatement() *EchoStatement {
	stmt := &EchoStatement{}

	p.nextToken() // move past 'echo'

	stmt.Value = p.ParseExpression(LOWEST)
	if stmt.Value == nil {
		p.addError("expected expression after 'echo'")
		return nil
	}

	return stmt
}

// parseBreakStatement parses break statements
func (p *Parser) parseBreakStatement() *BreakStatement {
	return &BreakStatement{}
}

// parseExitStatement parses exit statements
func (p *Parser) parseExitStatement() *ExitStatement {
	stmt := &ExitStatement{}

	// Check if there's an optional expression after 'exit'
	// Only parse expression if next token can start an expression
	if p.canStartExpression(p.peekToken.Type) {
		p.nextToken() // move past 'exit'
		stmt.Value = p.ParseExpression(LOWEST)
		if stmt.Value == nil {
			p.addError("expected expression after 'exit'")
			return nil
		}
	}

	return stmt
}

// canStartExpression checks if a token type can start an expression
func (p *Parser) canStartExpression(tokenType TokenType) bool {
	switch tokenType {
	case IDENT, NUMBER, STRING, TRUE, FALSE, NIL, LPAREN, LBRACE, MINUS:
		return true
	default:
		return false
	}
}

// parseWhileStatement parses while loops: while condition do ... end
func (p *Parser) parseWhileStatement() *WhileStatement {
	stmt := &WhileStatement{}

	p.nextToken() // move past 'while'

	stmt.Condition = p.ParseExpression(LOWEST)
	if stmt.Condition == nil {
		p.addError("expected condition after 'while'")
		return nil
	}

	if !p.expectPeek(DO) {
		p.addError("expected 'do' after while condition")
		return nil
	}

	p.nextToken() // move past 'do'

	// Parse loop body
	stmt.Body = p.parseBlockStatements(END)

	if !p.curTokenIs(END) {
		p.addError("expected 'end' to close while loop")
		return nil
	}

	return stmt
}

// parseForStatement parses for loops (both numeric and for-in)
func (p *Parser) parseForStatement() Statement {
	p.nextToken() // move past 'for'

	if !p.curTokenIs(IDENT) {
		p.addError("expected identifier after 'for'")
		return nil
	}

	firstVar := &Identifier{Value: p.curToken.Literal}

	// Look ahead to determine which type of for loop
	if p.peekTokenIs(ASSIGN) {
		// Numeric for loop: for i = start, end, step do
		return p.parseNumericForStatement(firstVar)
	} else if p.peekTokenIs(COMMA) || p.peekTokenIs(IN) {
		// For-in loop: for k, v in expr do or for v in expr do
		return p.parseForInStatement(firstVar)
	} else {
		p.addError("expected '=', ',' or 'in' after for loop variable")
		return nil
	}
}

// parseNumericForStatement parses numeric for loops: for i = start, end, step do
func (p *Parser) parseNumericForStatement(variable *Identifier) *ForStatement {
	stmt := &ForStatement{Variable: variable}

	if !p.expectPeek(ASSIGN) {
		return nil
	}

	p.nextToken() // move past '='

	// Parse start expression
	stmt.Start = p.ParseExpression(LOWEST)
	if stmt.Start == nil {
		p.addError("expected start expression in for loop")
		return nil
	}

	if !p.expectPeek(COMMA) {
		p.addError("expected ',' after start expression in for loop")
		return nil
	}

	p.nextToken() // move past ','

	// Parse end expression
	stmt.End = p.ParseExpression(LOWEST)
	if stmt.End == nil {
		p.addError("expected end expression in for loop")
		return nil
	}

	// Optional step expression
	if p.peekTokenIs(COMMA) {
		p.nextToken() // move to ','
		p.nextToken() // move past ','

		stmt.Step = p.ParseExpression(LOWEST)
		if stmt.Step == nil {
			p.addError("expected step expression in for loop")
			return nil
		}
	}

	if !p.expectPeek(DO) {
		p.addError("expected 'do' after for loop header")
		return nil
	}

	p.nextToken() // move past 'do'

	// Parse loop body
	stmt.Body = p.parseBlockStatements(END)

	if !p.curTokenIs(END) {
		p.addError("expected 'end' to close for loop")
		return nil
	}

	return stmt
}

// parseForInStatement parses for-in loops: for k, v in expr do or for v in expr do
func (p *Parser) parseForInStatement(firstVar *Identifier) *ForInStatement {
	stmt := &ForInStatement{}

	if p.peekTokenIs(COMMA) {
		// Two variables: for k, v in expr do
		stmt.Key = firstVar
		p.nextToken() // move to ','
		p.nextToken() // move past ','

		if !p.curTokenIs(IDENT) {
			p.addError("expected identifier after ',' in for loop")
			return nil
		}

		stmt.Value = &Identifier{Value: p.curToken.Literal}
	} else {
		// Single variable: for v in expr do
		stmt.Value = firstVar
	}

	if !p.expectPeek(IN) {
		p.addError("expected 'in' in for loop")
		return nil
	}

	p.nextToken() // move past 'in'

	// Parse iterable expression
	stmt.Iterable = p.ParseExpression(LOWEST)
	if stmt.Iterable == nil {
		p.addError("expected expression after 'in' in for loop")
		return nil
	}

	if !p.expectPeek(DO) {
		p.addError("expected 'do' after for loop header")
		return nil
	}

	p.nextToken() // move past 'do'

	// Parse loop body
	stmt.Body = p.parseBlockStatements(END)

	if !p.curTokenIs(END) {
		p.addError("expected 'end' to close for loop")
		return nil
	}

	return stmt
}

// parseIfStatement parses if/elseif/else/end statements
func (p *Parser) parseIfStatement() *IfStatement {
	stmt := &IfStatement{}

	p.nextToken() // move past 'if'

	stmt.Condition = p.ParseExpression(LOWEST)
	if stmt.Condition == nil {
		p.addError("expected condition after 'if'")
		return nil
	}

	// Optional 'then' keyword
	if p.peekTokenIs(THEN) {
		p.nextToken()
	}

	p.nextToken() // move past condition (and optional 'then')

	// Check if we immediately hit END (missing body)
	if p.curTokenIs(END) {
		p.addError("expected 'end' to close if statement")
		return nil
	}

	// Parse if body
	stmt.Body = p.parseBlockStatements(ELSEIF, ELSE, END)

	// Parse elseif clauses
	for p.curTokenIs(ELSEIF) {
		elseif := ElseIfClause{}

		p.nextToken() // move past 'elseif'

		elseif.Condition = p.ParseExpression(LOWEST)
		if elseif.Condition == nil {
			p.addError("expected condition after 'elseif'")
			return nil
		}

		// Optional 'then' keyword
		if p.peekTokenIs(THEN) {
			p.nextToken()
		}

		p.nextToken() // move past condition (and optional 'then')

		elseif.Body = p.parseBlockStatements(ELSEIF, ELSE, END)
		stmt.ElseIfs = append(stmt.ElseIfs, elseif)
	}

	// Parse else clause
	if p.curTokenIs(ELSE) {
		p.nextToken() // move past 'else'
		stmt.Else = p.parseBlockStatements(END)
	}

	if !p.curTokenIs(END) {
		p.addError("expected 'end' to close if statement")
		return nil
	}

	return stmt
}

// parseBlockStatements parses statements until one of the terminator tokens
func (p *Parser) parseBlockStatements(terminators ...TokenType) []Statement {
	statements := []Statement{}

	for !p.curTokenIs(EOF) && !p.isTerminator(terminators...) {
		stmt := p.parseStatement()
		if stmt != nil {
			statements = append(statements, stmt)
		}
		p.nextToken()
	}

	return statements
}

// isTerminator checks if current token is one of the terminators
func (p *Parser) isTerminator(terminators ...TokenType) bool {
	for _, terminator := range terminators {
		if p.curTokenIs(terminator) {
			return true
		}
	}
	return false
}

// ParseExpression parses expressions using Pratt parsing
func (p *Parser) ParseExpression(precedence Precedence) Expression {
	prefix := p.prefixParseFns[p.curToken.Type]
	if prefix == nil {
		p.noPrefixParseFnError(p.curToken.Type)
		return nil
	}

	leftExp := prefix()
	if leftExp == nil {
		return nil
	}

	for !p.peekTokenIs(EOF) && precedence < p.peekPrecedence() {
		infix := p.infixParseFns[p.peekToken.Type]
		if infix == nil {
			return leftExp
		}

		p.nextToken()
		leftExp = infix(leftExp)
		if leftExp == nil {
			return nil
		}
	}

	return leftExp
}

// Expression parsing functions
func (p *Parser) parseIdentifier() Expression {
	return &Identifier{Value: p.curToken.Literal}
}

func (p *Parser) parseNumberLiteral() Expression {
	lit := &NumberLiteral{}
	literal := p.curToken.Literal

	var value float64
	var err error

	// Check for hexadecimal (0x/0X prefix)
	if strings.HasPrefix(literal, "0x") || strings.HasPrefix(literal, "0X") {
		// Validate hex format
		if len(literal) <= 2 {
			p.addError(fmt.Sprintf("could not parse '%s' as hexadecimal number", literal))
			return nil
		}
		hexPart := literal[2:]
		for _, ch := range hexPart {
			if !((ch >= '0' && ch <= '9') || (ch >= 'a' && ch <= 'f') || (ch >= 'A' && ch <= 'F')) {
				p.addError(fmt.Sprintf("could not parse '%s' as hexadecimal number", literal))
				return nil
			}
		}
		// Parse as hex and convert to float64
		intVal, parseErr := strconv.ParseInt(literal, 0, 64)
		if parseErr != nil {
			p.addError(fmt.Sprintf("could not parse '%s' as hexadecimal number", literal))
			return nil
		}
		value = float64(intVal)
	} else if strings.HasPrefix(literal, "0b") || strings.HasPrefix(literal, "0B") {
		// Validate binary format
		if len(literal) <= 2 {
			p.addError(fmt.Sprintf("could not parse '%s' as binary number", literal))
			return nil
		}
		binaryPart := literal[2:]
		for _, ch := range binaryPart {
			if ch != '0' && ch != '1' {
				p.addError(fmt.Sprintf("could not parse '%s' as binary number", literal))
				return nil
			}
		}
		// Parse binary manually since Go doesn't support 0b in ParseInt with base 0
		binaryStr := literal[2:] // remove "0b" prefix
		intVal, parseErr := strconv.ParseInt(binaryStr, 2, 64)
		if parseErr != nil {
			p.addError(fmt.Sprintf("could not parse '%s' as binary number", literal))
			return nil
		}
		value = float64(intVal)
	} else {
		// Parse as regular decimal (handles scientific notation automatically)
		value, err = strconv.ParseFloat(literal, 64)
		if err != nil {
			p.addError(fmt.Sprintf("could not parse '%s' as number", literal))
			return nil
		}
	}

	lit.Value = value
	return lit
}

func (p *Parser) parseStringLiteral() Expression {
	return &StringLiteral{Value: p.curToken.Literal}
}

func (p *Parser) parseBooleanLiteral() Expression {
	return &BooleanLiteral{Value: p.curTokenIs(TRUE)}
}

func (p *Parser) parseNilLiteral() Expression {
	return &NilLiteral{}
}

func (p *Parser) parsePrefixExpression() Expression {
	expression := &PrefixExpression{
		Operator: p.curToken.Literal,
	}

	p.nextToken()

	expression.Right = p.ParseExpression(PREFIX)
	if expression.Right == nil {
		p.addError(fmt.Sprintf("expected expression after prefix operator '%s'", expression.Operator))
		return nil
	}

	return expression
}

func (p *Parser) parseGroupedExpression() Expression {
	p.nextToken()

	exp := p.ParseExpression(LOWEST)
	if exp == nil {
		return nil
	}

	if !p.expectPeek(RPAREN) {
		return nil
	}

	return exp
}

func (p *Parser) parseTableLiteral() Expression {
	table := &TableLiteral{}
	table.Pairs = []TablePair{}

	if p.peekTokenIs(RBRACE) {
		p.nextToken()
		return table
	}

	p.nextToken()

	for {
		// Check for EOF
		if p.curTokenIs(EOF) {
			p.addError("unexpected end of input, expected }")
			return nil
		}

		pair := TablePair{}

		// Check if this is a key=value pair (identifier or string key)
		if (p.curTokenIs(IDENT) || p.curTokenIs(STRING)) && p.peekTokenIs(ASSIGN) {
			if p.curTokenIs(IDENT) {
				pair.Key = &Identifier{Value: p.curToken.Literal}
			} else {
				pair.Key = &StringLiteral{Value: p.curToken.Literal}
			}
			p.nextToken() // move to =
			p.nextToken() // move past =

			// Check for EOF after =
			if p.curTokenIs(EOF) {
				p.addError("expected expression after assignment operator")
				return nil
			}

			pair.Value = p.ParseExpression(LOWEST)
		} else {
			// Array-style element
			pair.Value = p.ParseExpression(LOWEST)
		}

		if pair.Value == nil {
			return nil
		}

		table.Pairs = append(table.Pairs, pair)

		if !p.peekTokenIs(COMMA) {
			break
		}

		p.nextToken() // consume comma
		p.nextToken() // move to next element

		// Allow trailing comma
		if p.curTokenIs(RBRACE) {
			break
		}

		// Check for EOF after comma
		if p.curTokenIs(EOF) {
			p.addError("expected next token to be }")
			return nil
		}
	}

	if !p.expectPeek(RBRACE) {
		return nil
	}

	return table
}

func (p *Parser) parseInfixExpression(left Expression) Expression {
	expression := &InfixExpression{
		Left:     left,
		Operator: p.curToken.Literal,
	}

	precedence := p.curPrecedence()
	p.nextToken()
	expression.Right = p.ParseExpression(precedence)

	if expression.Right == nil {
		p.addError(fmt.Sprintf("expected expression after operator '%s'", expression.Operator))
		return nil
	}

	return expression
}

func (p *Parser) parseDotExpression(left Expression) Expression {
	if !p.expectPeekIdent() {
		p.addError("expected identifier after '.'")
		return nil
	}

	return &DotExpression{
		Left: left,
		Key:  p.curToken.Literal,
	}
}

func (p *Parser) parseIndexExpression(left Expression) Expression {
	p.nextToken() // move past '['

	index := p.ParseExpression(LOWEST)
	if index == nil {
		p.addError("expected expression inside brackets")
		return nil
	}

	if !p.expectPeek(RBRACKET) {
		p.addError("expected ']' after index expression")
		return nil
	}

	return &IndexExpression{
		Left:  left,
		Index: index,
	}
}

// Helper methods
func (p *Parser) curTokenIs(t TokenType) bool {
	return p.curToken.Type == t
}

func (p *Parser) peekTokenIs(t TokenType) bool {
	return p.peekToken.Type == t
}

func (p *Parser) expectPeek(t TokenType) bool {
	if p.peekTokenIs(t) {
		p.nextToken()
		return true
	}
	p.peekError(t)
	return false
}

// expectPeekIdent accepts IDENT or keyword tokens as identifiers
func (p *Parser) expectPeekIdent() bool {
	if p.peekTokenIs(IDENT) || p.isKeyword(p.peekToken.Type) {
		p.nextToken()
		return true
	}
	p.peekError(IDENT)
	return false
}

// isKeyword checks if a token type is a keyword that can be used as identifier
func (p *Parser) isKeyword(t TokenType) bool {
	switch t {
	case TRUE, FALSE, NIL, IF, THEN, ELSEIF, ELSE, END, ECHO, FOR, WHILE, IN, DO, BREAK, EXIT:
		return true
	default:
		return false
	}
}

// Error handling methods
func (p *Parser) addError(message string) {
	p.errors = append(p.errors, ParseError{
		Message: message,
		Line:    p.curToken.Line,
		Column:  p.curToken.Column,
		Token:   p.curToken,
	})
}

func (p *Parser) peekError(t TokenType) {
	message := fmt.Sprintf("expected next token to be %s, got %s instead",
		tokenTypeString(t), tokenTypeString(p.peekToken.Type))
	p.errors = append(p.errors, ParseError{
		Message: message,
		Line:    p.peekToken.Line,
		Column:  p.peekToken.Column,
		Token:   p.peekToken,
	})
}

func (p *Parser) noPrefixParseFnError(t TokenType) {
	var message string
	switch t {
	case ASSIGN:
		message = "unexpected assignment operator, missing left-hand side identifier"
	case PLUS, MINUS, STAR, SLASH:
		message = fmt.Sprintf("unexpected operator '%s', missing left operand", tokenTypeString(t))
	case RPAREN:
		message = "unexpected closing parenthesis"
	case RBRACE:
		message = "unexpected closing brace"
	case RBRACKET:
		message = "unexpected closing bracket"
	case EOF:
		message = "unexpected end of input"
	default:
		message = fmt.Sprintf("unexpected token '%s'", tokenTypeString(t))
	}

	p.addError(message)
}

func (p *Parser) peekPrecedence() Precedence {
	if p, ok := precedences[p.peekToken.Type]; ok {
		return p
	}
	return LOWEST
}

func (p *Parser) curPrecedence() Precedence {
	if p, ok := precedences[p.curToken.Type]; ok {
		return p
	}
	return LOWEST
}

// Errors returns all parsing errors
func (p *Parser) Errors() []ParseError {
	return p.errors
}

// HasErrors returns true if there are any parsing errors
func (p *Parser) HasErrors() bool {
	return len(p.errors) > 0
}

// ErrorStrings returns error messages as strings for backward compatibility
func (p *Parser) ErrorStrings() []string {
	result := make([]string, len(p.errors))
	for i, err := range p.errors {
		result[i] = err.Error()
	}
	return result
}

// tokenTypeString returns a human-readable string for token types
func tokenTypeString(t TokenType) string {
	switch t {
	case IDENT:
		return "identifier"
	case NUMBER:
		return "number"
	case STRING:
		return "string"
	case TRUE, FALSE:
		return "boolean"
	case NIL:
		return "nil"
	case ASSIGN:
		return "="
	case PLUS:
		return "+"
	case MINUS:
		return "-"
	case STAR:
		return "*"
	case SLASH:
		return "/"
	case DOT:
		return "."
	case EQ:
		return "=="
	case NOT_EQ:
		return "!="
	case LT:
		return "<"
	case GT:
		return ">"
	case LT_EQ:
		return "<="
	case GT_EQ:
		return ">="
	case LPAREN:
		return "("
	case RPAREN:
		return ")"
	case LBRACE:
		return "{"
	case RBRACE:
		return "}"
	case LBRACKET:
		return "["
	case RBRACKET:
		return "]"
	case COMMA:
		return ","
	case IF:
		return "if"
	case THEN:
		return "then"
	case ELSEIF:
		return "elseif"
	case ELSE:
		return "else"
	case END:
		return "end"
	case ECHO:
		return "echo"
	case FOR:
		return "for"
	case WHILE:
		return "while"
	case IN:
		return "in"
	case DO:
		return "do"
	case BREAK:
		return "break"
	case EXIT:
		return "exit"
	case EOF:
		return "end of file"
	case ILLEGAL:
		return "illegal token"
	default:
		return "unknown"
	}
}