"""AST-level resource leak injection for Python."""

import ast
from typing import Optional

from app.dataset.rules.base import Mutation, MutationRule


class ResourceLeakRule(MutationRule):
    """Convert a `with open(...)` block into an unclosed `open(...).read()`.

    Uses `ast` to locate a with-statement managing a file resource and replaces
    it with a direct call chain that leaks the file handle.
    """

    name = "resource_leak"
    language = "python"
    defect_type = "resource_not_closed"

    def detect_and_mutate(self, source: str, filename: str = "") -> Optional[Mutation]:
        try:
            tree = ast.parse(source)
        except SyntaxError:
            return None

        for node in ast.walk(tree):
            if not isinstance(node, ast.With):
                continue
            first_item = node.items[0]
            ctx = first_item.context_expr
            if isinstance(ctx, ast.Call) and isinstance(ctx.func, ast.Name) and ctx.func.id == "open":
                start = node.lineno
                end = getattr(node, "end_lineno", node.lineno) or node.lineno
                lines = source.splitlines(keepends=True)
                # Keep the with header expression but replace 'with open(...)' by 'f = open(...)'
                header = lines[start - 1]
                header_expr = header.split("with ", 1)[1].split(" as ", 1)[0].strip().rstrip(":\n")
                var = header.split(" as ", 1)[1].strip().rstrip(":\n") if " as " in header else "f"
                body = lines[start:end]
                dedented = []
                for line in body[1:]:
                    if line.startswith("    "):
                        dedented.append(line[4:])
                    else:
                        dedented.append(line)
                replacement = [f"{var} = {header_expr}\n"] + dedented
                mutated = "".join(lines[: start - 1] + replacement + lines[end:])
                return Mutation(
                    defect_type=self.defect_type,
                    language=self.language,
                    line_start=start,
                    line_end=end,
                    mutated_source=mutated,
                    reference_fix="Use `with open(...) as f:` to ensure the file is closed.",
                    description="Replaced context-managed open() with an unclosed file handle.",
                )
        return None