"""
F-string expression transformer for Dana language parsing.

This module handles the f_string rule in the grammar:
    f_string: "f" REGULAR_STRING

It parses f-strings with embedded expressions, returning a LiteralExpression(FStringExpression(...)).
Follows the style and best practices of StatementTransformer and ExpressionTransformer.

Copyright © 2025 Aitomatic, Inc.
MIT License

Community Values:
    1. Attribution: Please maintain attribution to Aitomatic and Dana/Dana in derivative works.
    2. Contributions: If you find Dana/Dana valuable, consider contributing improvements back rather than creating separate, similar implementations.
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Learn more: https://aitomatic.com
GitHub: https://github.com/aitomatic/dana
Discord: https://discord.gg/6jGD4PYk
"""

import logging
from typing import Any

from dana.core.lang.ast import (
    FStringExpression,
    Identifier,
    LiteralExpression,
)
from dana.core.lang.parser.transformer.base_transformer import BaseTransformer
from dana.core.lang.parser.utils.identifier_utils import is_valid_identifier


class FStringTransformer(BaseTransformer):
    """
    Transforms f-string parse tree nodes into AST FStringExpression nodes.

    Handles the f_string rule in the Dana grammar, parsing embedded expressions and returning
    a LiteralExpression(FStringExpression(...)).
    """

    def debug(self, message):
        """Log debug messages."""
        logging.debug(f"FStringTransformer: {message}")

    # === Entry Point ===
    def fstring(self, items):
        """
        Transform an f-string rule into a LiteralExpression node with FStringExpression.
        Grammar: fstring: F_STRING
        Example: f"Hello {name}!" -> LiteralExpression(value=FStringExpression(parts=["Hello ", Identifier(name="local:name"), "!"]))
        """
        # Get the string value from F_STRING (items[0])
        s = items[0].value

        # Remove 'f' or 'F' prefix
        if s.startswith("f") or s.startswith("F"):
            s = s[1:]

        # Remove quotes (single or double)
        if s.startswith('"') and s.endswith('"'):
            s = s[1:-1]
        elif s.startswith("'") and s.endswith("'"):
            s = s[1:-1]

        parts = self._parse_fstring_parts(s)
        fstring_expr = FStringExpression(parts=parts)
        setattr(fstring_expr, "_is_fstring", True)
        setattr(fstring_expr, "_original_text", s)
        return LiteralExpression(value=fstring_expr)

    # === Parsing Helpers ===
    def _parse_fstring_parts(self, s: str) -> list:
        """
        Parse an f-string into its component parts (literals and expressions).
        Returns a list of strings and AST nodes.
        Example: 'Hello {name}!' -> ["Hello ", Identifier(name="local:name"), "!"]
        """
        parts = []
        current_text = ""
        i = 0
        while i < len(s):
            if s[i] == "{" and (i == 0 or s[i - 1] != "\\"):
                # Found start of expression
                if current_text:
                    parts.append(current_text)
                    current_text = ""
                # Find the matching closing brace
                brace_level = 1
                expr_text = ""
                i += 1
                while i < len(s) and brace_level > 0:
                    if s[i] == "{" and s[i - 1] != "\\":
                        brace_level += 1
                    elif s[i] == "}" and s[i - 1] != "\\":
                        brace_level -= 1
                    if brace_level > 0:
                        expr_text += s[i]
                    i += 1
                if brace_level != 0:
                    raise ValueError("Unbalanced braces in f-string expression.")
                if expr_text:
                    expr_text = expr_text.strip()
                    part = self._parse_expression_in_fstring(expr_text)
                    parts.append(part)
            else:
                current_text += s[i]
                i += 1
        if current_text:
            parts.append(current_text)
        return parts

    def _parse_expression_in_fstring(self, expr_text: str) -> Any:
        """
        Parse an expression found in an f-string placeholder.

        ARCHITECTURAL FIX: Delegate to the proven DanaParser.parse_expression()
        instead of reimplementing expression parsing with incomplete support.

        This ensures f-string expressions use the same comprehensive parsing
        infrastructure as the rest of Dana, supporting:
        - Subscript expressions: datasets[0], user['key']
        - Function calls: len(items), str(value)
        - Attribute access: obj.attr.method()
        - All binary/unary operators
        - Complex nested expressions

        F-string expressions now behave EXACTLY like regular Dana expressions.
        """
        try:
            # Use the same proven parser infrastructure as the rest of Dana
            from dana.core.lang.parser.utils.parsing_utils import ParserCache

            parser = ParserCache.get_parser("dana")
            ast_node = parser.parse_expression(expr_text)

            self.debug(f"Successfully parsed f-string expression '{expr_text}' -> {type(ast_node).__name__}")
            return ast_node

        except Exception as e:
            # Fallback: treat as simple identifier (no scope prefix - same as main parser)
            self.debug(f"F-string expression parsing failed for '{expr_text}': {e}")
            self.debug("Falling back to simple identifier")

            # Clean the expression text for use as identifier
            clean_text = expr_text.strip()
            if is_valid_identifier(clean_text):
                return Identifier(name=clean_text)  # No automatic local: prefix
            else:
                # Last resort: return as literal expression
                return LiteralExpression(value=expr_text)

    def _parse_expression_term(self, term: str) -> Any:
        """
        Parse a single term in an f-string expression.

        Delegates to the main parsing logic for consistency.
        F-string expressions behave exactly like regular Dana expressions.
        """
        return self._parse_expression_in_fstring(term)
