"""AST-level resource leak injection for JavaScript using esprima."""

from typing import Optional

import esprima

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


class JSResourceLeakRule(MutationRule):
    """Remove a fetch Response body close/usage, leaking the reader.

    Uses `esprima` to locate a `try/finally` that closes a reader and removes
    the finally block.
    """

    name = "js_resource_leak"
    language = "javascript"
    defect_type = "resource_not_closed"

    def detect_and_mutate(self, source: str, filename: str = "") -> Optional[Mutation]:
        # Modern JS is usually ESM: try module grammar first, then script.
        try:
            tree = esprima.parseModule(source, loc=True)
        except Exception:
            try:
                tree = esprima.parseScript(source, loc=True)
            except Exception:
                return None

        def walk(node):
            yield node
            for key in node.__dict__:
                child = getattr(node, key)
                if isinstance(child, list):
                    for item in child:
                        if hasattr(item, "type"):
                            yield from walk(item)
                elif hasattr(child, "type"):
                    yield from walk(child)

        for node in walk(tree):
            if node.type != "TryStatement" or not node.finalizer:
                continue
            start = node.loc.start.line
            end = node.finalizer.loc.end.line
            lines = source.splitlines(keepends=True)
            # Drop the finally block entirely, close the try block
            finally_start = node.finalizer.loc.start.line - 1
            mutated = "".join(lines[:finally_start] + ["    }\n"] + lines[end:])
            return Mutation(
                defect_type=self.defect_type,
                language=self.language,
                line_start=start,
                line_end=end,
                mutated_source=mutated,
                reference_fix="Restore finally block to close/release resources.",
                description="Removed finally block, leaving resource unreleased.",
            )
        return None