"""
NexaWeb Native Parser
=====================

High-performance template parsing.
This is a Python stub that can be replaced with a native implementation.

The native implementation would use:
- Zero-copy string handling
- SIMD-accelerated scanning
- Efficient token pooling
"""

from __future__ import annotations

from dataclasses import dataclass
from enum import Enum, auto
from typing import Generator, Iterator, List, Optional, Tuple


class TokenType(Enum):
    """Token types for template parsing."""
    
    # Basic types
    TEXT = auto()
    NEWLINE = auto()
    WHITESPACE = auto()
    
    # Delimiters
    OPEN_EXPR = auto()      # {{
    CLOSE_EXPR = auto()     # }}
    OPEN_STMT = auto()      # {%
    CLOSE_STMT = auto()     # %}
    OPEN_COMMENT = auto()   # {#
    CLOSE_COMMENT = auto()  # #}
    OPEN_RAW = auto()       # {!
    CLOSE_RAW = auto()      # !}
    
    # Python tokens (within expressions)
    IDENTIFIER = auto()
    NUMBER = auto()
    STRING = auto()
    OPERATOR = auto()
    KEYWORD = auto()
    DOT = auto()
    COMMA = auto()
    COLON = auto()
    PIPE = auto()
    LPAREN = auto()
    RPAREN = auto()
    LBRACKET = auto()
    RBRACKET = auto()
    LBRACE = auto()
    RBRACE = auto()
    
    # Special
    EOF = auto()
    ERROR = auto()


@dataclass(slots=True)
class Token:
    """
    Parsed token.
    
    Using __slots__ for memory efficiency.
    Native implementation would use struct.
    
    Attributes:
        type: Token type
        value: Token string value
        line: Line number (1-indexed)
        column: Column number (1-indexed)
        start: Start position in source
        end: End position in source
    """
    
    type: TokenType
    value: str
    line: int
    column: int
    start: int
    end: int
    
    def __repr__(self) -> str:
        return f"Token({self.type.name}, {self.value!r}, {self.line}:{self.column})"


class NativeParser:
    """
    High-performance template lexer/parser.
    
    This Python implementation provides the same API as the
    native C++ version but with pure Python performance.
    
    Example:
        parser = NativeParser()
        
        tokens = list(parser.tokenize('''
            <h1>{{ title }}</h1>
            {% for item in items %}
                <li>{{ item }}</li>
            {% endfor %}
        '''))
        
        for token in tokens:
            print(token)
    
    Native implementation would provide:
        - 10-50x faster tokenization
        - Zero-copy where possible
        - SIMD string scanning
    """
    
    # Delimiter pairs
    DELIMITERS = {
        "{{": TokenType.OPEN_EXPR,
        "}}": TokenType.CLOSE_EXPR,
        "{%": TokenType.OPEN_STMT,
        "%}": TokenType.CLOSE_STMT,
        "{#": TokenType.OPEN_COMMENT,
        "#}": TokenType.CLOSE_COMMENT,
        "{!": TokenType.OPEN_RAW,
        "!}": TokenType.CLOSE_RAW,
    }
    
    # Python keywords
    KEYWORDS = frozenset([
        "if", "elif", "else", "for", "in", "while",
        "def", "class", "return", "yield", "break",
        "continue", "pass", "import", "from", "as",
        "try", "except", "finally", "raise", "with",
        "lambda", "and", "or", "not", "is", "True",
        "False", "None", "await", "async",
    ])
    
    # Operators
    OPERATORS = frozenset([
        "+", "-", "*", "/", "//", "%", "**",
        "==", "!=", "<", ">", "<=", ">=",
        "=", "+=", "-=", "*=", "/=",
        "&", "|", "^", "~", "<<", ">>",
    ])
    
    def __init__(self):
        """Initialize parser."""
        self._source = ""
        self._pos = 0
        self._line = 1
        self._column = 1
        self._tokens: List[Token] = []
    
    def tokenize(
        self,
        source: str,
        include_whitespace: bool = False,
    ) -> Generator[Token, None, None]:
        """
        Tokenize template source.
        
        Args:
            source: Template source code
            include_whitespace: Include whitespace tokens
            
        Yields:
            Token objects
        """
        self._source = source
        self._pos = 0
        self._line = 1
        self._column = 1
        
        in_expression = False
        
        while self._pos < len(source):
            # Check for delimiters
            delimiter_token = self._scan_delimiter()
            
            if delimiter_token:
                yield delimiter_token
                
                if delimiter_token.type in (
                    TokenType.OPEN_EXPR,
                    TokenType.OPEN_STMT,
                ):
                    in_expression = True
                elif delimiter_token.type in (
                    TokenType.CLOSE_EXPR,
                    TokenType.CLOSE_STMT,
                ):
                    in_expression = False
                    
                continue
            
            if in_expression:
                # Scan Python token
                token = self._scan_python_token()
                if token:
                    if token.type == TokenType.WHITESPACE and not include_whitespace:
                        continue
                    yield token
            else:
                # Scan text
                token = self._scan_text()
                if token:
                    yield token
        
        # EOF token
        yield Token(
            type=TokenType.EOF,
            value="",
            line=self._line,
            column=self._column,
            start=self._pos,
            end=self._pos,
        )
    
    def _scan_delimiter(self) -> Optional[Token]:
        """Scan for delimiter tokens."""
        for delim, token_type in self.DELIMITERS.items():
            if self._source[self._pos:].startswith(delim):
                start = self._pos
                start_line = self._line
                start_column = self._column
                
                self._advance(len(delim))
                
                return Token(
                    type=token_type,
                    value=delim,
                    line=start_line,
                    column=start_column,
                    start=start,
                    end=self._pos,
                )
        
        return None
    
    def _scan_text(self) -> Optional[Token]:
        """Scan text until next delimiter."""
        start = self._pos
        start_line = self._line
        start_column = self._column
        
        while self._pos < len(self._source):
            # Check for delimiter start
            remaining = self._source[self._pos:]
            if any(remaining.startswith(d) for d in self.DELIMITERS):
                break
            
            self._advance(1)
        
        if self._pos > start:
            return Token(
                type=TokenType.TEXT,
                value=self._source[start:self._pos],
                line=start_line,
                column=start_column,
                start=start,
                end=self._pos,
            )
        
        return None
    
    def _scan_python_token(self) -> Optional[Token]:
        """Scan Python expression token."""
        # Skip whitespace
        if self._current().isspace():
            return self._scan_whitespace()
        
        # String
        if self._current() in ('"', "'"):
            return self._scan_string()
        
        # Number
        if self._current().isdigit():
            return self._scan_number()
        
        # Identifier or keyword
        if self._current().isalpha() or self._current() == "_":
            return self._scan_identifier()
        
        # Operators and punctuation
        return self._scan_operator_or_punctuation()
    
    def _scan_whitespace(self) -> Token:
        """Scan whitespace."""
        start = self._pos
        start_line = self._line
        start_column = self._column
        
        while self._pos < len(self._source) and self._current().isspace():
            if self._current() == "\n":
                self._line += 1
                self._column = 1
                self._pos += 1
            else:
                self._advance(1)
        
        return Token(
            type=TokenType.WHITESPACE,
            value=self._source[start:self._pos],
            line=start_line,
            column=start_column,
            start=start,
            end=self._pos,
        )
    
    def _scan_string(self) -> Token:
        """Scan string literal."""
        start = self._pos
        start_line = self._line
        start_column = self._column
        quote = self._current()
        
        self._advance(1)  # Opening quote
        
        # Check for triple quote
        triple = False
        if self._pos + 1 < len(self._source):
            if self._source[self._pos:self._pos+2] == quote * 2:
                triple = True
                self._advance(2)
        
        # Scan until closing quote
        while self._pos < len(self._source):
            if self._current() == "\\":
                self._advance(2)  # Skip escape sequence
                continue
            
            if triple:
                if self._source[self._pos:self._pos+3] == quote * 3:
                    self._advance(3)
                    break
            else:
                if self._current() == quote:
                    self._advance(1)
                    break
            
            if self._current() == "\n":
                self._line += 1
                self._column = 1
                self._pos += 1
            else:
                self._advance(1)
        
        return Token(
            type=TokenType.STRING,
            value=self._source[start:self._pos],
            line=start_line,
            column=start_column,
            start=start,
            end=self._pos,
        )
    
    def _scan_number(self) -> Token:
        """Scan number literal."""
        start = self._pos
        start_line = self._line
        start_column = self._column
        
        # Integer part
        while self._pos < len(self._source) and self._current().isdigit():
            self._advance(1)
        
        # Decimal part
        if self._pos < len(self._source) and self._current() == ".":
            self._advance(1)
            while self._pos < len(self._source) and self._current().isdigit():
                self._advance(1)
        
        # Exponent
        if self._pos < len(self._source) and self._current() in ("e", "E"):
            self._advance(1)
            if self._pos < len(self._source) and self._current() in ("+", "-"):
                self._advance(1)
            while self._pos < len(self._source) and self._current().isdigit():
                self._advance(1)
        
        return Token(
            type=TokenType.NUMBER,
            value=self._source[start:self._pos],
            line=start_line,
            column=start_column,
            start=start,
            end=self._pos,
        )
    
    def _scan_identifier(self) -> Token:
        """Scan identifier or keyword."""
        start = self._pos
        start_line = self._line
        start_column = self._column
        
        while self._pos < len(self._source):
            char = self._current()
            if not (char.isalnum() or char == "_"):
                break
            self._advance(1)
        
        value = self._source[start:self._pos]
        token_type = TokenType.KEYWORD if value in self.KEYWORDS else TokenType.IDENTIFIER
        
        return Token(
            type=token_type,
            value=value,
            line=start_line,
            column=start_column,
            start=start,
            end=self._pos,
        )
    
    def _scan_operator_or_punctuation(self) -> Token:
        """Scan operator or punctuation."""
        start = self._pos
        start_line = self._line
        start_column = self._column
        char = self._current()
        
        # Single character punctuation
        punctuation = {
            ".": TokenType.DOT,
            ",": TokenType.COMMA,
            ":": TokenType.COLON,
            "|": TokenType.PIPE,
            "(": TokenType.LPAREN,
            ")": TokenType.RPAREN,
            "[": TokenType.LBRACKET,
            "]": TokenType.RBRACKET,
            "{": TokenType.LBRACE,
            "}": TokenType.RBRACE,
        }
        
        if char in punctuation:
            self._advance(1)
            return Token(
                type=punctuation[char],
                value=char,
                line=start_line,
                column=start_column,
                start=start,
                end=self._pos,
            )
        
        # Operators (try longest match first)
        for length in (2, 1):
            if self._pos + length <= len(self._source):
                op = self._source[self._pos:self._pos+length]
                if op in self.OPERATORS:
                    self._advance(length)
                    return Token(
                        type=TokenType.OPERATOR,
                        value=op,
                        line=start_line,
                        column=start_column,
                        start=start,
                        end=self._pos,
                    )
        
        # Unknown character
        self._advance(1)
        return Token(
            type=TokenType.ERROR,
            value=char,
            line=start_line,
            column=start_column,
            start=start,
            end=self._pos,
        )
    
    def _current(self) -> str:
        """Get current character."""
        if self._pos < len(self._source):
            return self._source[self._pos]
        return ""
    
    def _advance(self, count: int = 1) -> None:
        """Advance position."""
        for _ in range(count):
            if self._pos < len(self._source):
                if self._source[self._pos] == "\n":
                    self._line += 1
                    self._column = 1
                else:
                    self._column += 1
                self._pos += 1


# Native implementation placeholder
"""
// C++ Native Implementation (parser.cpp)

#include <string_view>
#include <vector>
#include <span>

namespace nexaweb {

enum class TokenType : uint8_t {
    TEXT, NEWLINE, WHITESPACE,
    OPEN_EXPR, CLOSE_EXPR,
    OPEN_STMT, CLOSE_STMT,
    OPEN_COMMENT, CLOSE_COMMENT,
    IDENTIFIER, NUMBER, STRING,
    OPERATOR, KEYWORD,
    // ... etc
};

struct Token {
    TokenType type;
    std::string_view value;  // Zero-copy reference
    uint32_t line;
    uint32_t column;
    uint32_t start;
    uint32_t end;
};

class NativeParser {
public:
    // Returns span to avoid copying
    std::span<Token> tokenize(std::string_view source);
    
private:
    std::vector<Token> tokens_;
    std::string_view source_;
    size_t pos_ = 0;
    uint32_t line_ = 1;
    uint32_t column_ = 1;
    
    // SIMD-accelerated delimiter search
    size_t find_delimiter() const;
    
    // Token scanning
    Token scan_text();
    Token scan_string();
    Token scan_number();
    Token scan_identifier();
};

}  // namespace nexaweb
"""
