package parser

import (
	"fmt"
	"strconv"
)

// 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.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)

	// 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:
		if p.peekTokenIs(ASSIGN) {
			return p.parseAssignStatement()
		}
		p.addError("unexpected identifier, expected assignment or declaration")
		return nil
	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{}

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

	stmt.Name = &Identifier{Value: p.curToken.Literal}

	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
}

// 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{}

	value, err := strconv.ParseFloat(p.curToken.Literal, 64)
	if err != nil {
		p.addError(fmt.Sprintf("could not parse '%s' as number", p.curToken.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) 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
		if p.curTokenIs(IDENT) && p.peekTokenIs(ASSIGN) {
			pair.Key = &Identifier{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
}

// 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
}

// 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 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 LPAREN:
		return "("
	case RPAREN:
		return ")"
	case LBRACE:
		return "{"
	case RBRACE:
		return "}"
	case COMMA:
		return ","
	case VAR:
		return "var"
	case EOF:
		return "end of file"
	case ILLEGAL:
		return "illegal token"
	default:
		return "unknown"
	}
}