"""Where to look, and what to look for there (contributor-scan, Req 2).

Pair scoring could rely on a labelled function: the corpus declares which function carries the bug and which
family it belongs to. A contributor has neither — *which code is risky* is the question they are asking. So a
repository scan derives its regions from the code itself: entry points where the mapper found them, whole
files where it did not, and each region carries only the families its shape and language actually admit.

Two restraints are deliberate:

* **The rank comes from what ``EntryPointRecord`` already carries**, not from a new signal invented here. The
  mapper has already decided whether a handler is public or local-only and whether it sits at a trust
  boundary; a second opinion computed from the same evidence would be a way of disagreeing with ourselves.
* **A family is offered only where its arbiter could answer.** An obligation needs a reachable operation, so
  ``access_control`` is offered where there is a handler and withheld from a library file that has none.
  Asking every family of every region is the unbounded version of this, and at repository scale the budget is
  the thing being spent.
"""

from __future__ import annotations

from collections.abc import Sequence
from dataclasses import dataclass, replace

from .specs import config_specs, dominance_specs, taint_specs

# From `mapping.AccessLevel`. A publicly reachable handler at a trust boundary is where a missing check costs
# most, so it is looked at first when the budget is finite.
_ACCESS_RANK: dict[str, float] = {
    "public": 1.0,
    "authenticated": 0.8,
    "role-restricted": 0.6,
    "contract-only/callback": 0.4,
    "review-required": 0.3,
    "local-only": 0.2,
}

# Languages whose facts the model layer carries. Anything else yields no region rather than an empty scan
# that looks like a clean bill of health.
_LANGUAGES = {"python", "javascript", "typescript", "java", "c", "c_cpp", "php"}
_NORMALISE = {"typescript": "javascript", "c_cpp": "c"}

# What a CPG calls a file's top-level code. A module body is a method like any other to the engine, and
# naming it here is what lets a region ask about the code that is not inside any function.
MODULE_SCOPE = "<module>"

# What the mapper emits for `if __name__ == '__main__':` -- a marker for a module-level entry point, not
# the name of a function. Sent to the engine as a function name it matched nothing, so a repository's
# module-level settings were unaskable: VAmPI's `host='0.0.0.0'` went unreported.
_MODULE_MARKERS = frozenset({"__main__"})


@dataclass(frozen=True)
class ScanRegion:
    """A place to arbitrate, and the families worth arbitrating there."""

    path: str
    function: str | None  # None for a file-level fallback: there is no labelled function on a scan path
    language: str
    families: tuple[str, ...]
    rank: float
    source: str  # "entry_point" | "module_scope" | "file_fallback"
    # Does the project's own build declaration name this file? True when it declares nothing at all --
    # silence is not exclusion, and no repository is penalised for a build system we cannot read.
    shipped: bool = True


def regions_for(entries: Sequence[object], targets: Sequence[object], *, shipped: frozenset[str] | None = None) -> tuple[ScanRegion, ...]:
    """Regions for a repository, strongest first.

    A file with an entry point yields regions for its handlers only — a fallback region beside them would
    scan the same code twice and spend the budget on duplicates.
    """
    by_path: dict[str, str] = {}
    for target in targets:
        language = _language_of(target)
        if language:
            by_path[str(getattr(target, "path", ""))] = language

    # One region per (path, function). The mapper can emit several entry points for a single file -- on a
    # ten-line Flask file it produced three, one named and two nameless -- and turning each into a region
    # scanned the same code repeatedly, multiplying Joern invocations for no new coverage. Where several
    # entries agree on a region, the highest access rank wins, because that is the one worth looking at first.
    best: dict[tuple[str, str | None], ScanRegion] = {}
    for entry in entries:
        path = str(getattr(entry, "path", ""))
        language = by_path.get(path)
        if language is None:
            continue
        # A handler its own contract declares OPEN carries no authorization obligation: there is nothing
        # for a guard to be missing from. The declaration is what makes this sound -- an OpenAPI operation
        # with no `security` block, a `wp_ajax_nopriv_` hook, a REST `permission_callback => __return_true`.
        # An INFERRED "public" is the opposite case and must keep the family, because for a decorator
        # framework it means only that no `@login_required` was found, which is the bug itself.
        declared_open = bool(getattr(entry, "access_declared", False)) and str(getattr(entry, "access_level", "")) == "public"
        families = _families(language, has_handler=not declared_open)
        if not families:
            continue
        function = getattr(entry, "function_name", None) or None
        module_body = function in _MODULE_MARKERS
        if module_body:
            # A module body is not a handler, whatever the mapper called it, so it is offered the families a
            # file gets rather than the families a handler gets. Carrying `access_control` here entailed a
            # missing authorization check on `if __name__ == '__main__':`.
            function, families = MODULE_SCOPE, _families(language, has_handler=False)
            if not families:
                continue
        rank = _ACCESS_RANK.get(str(getattr(entry, "access_level", "")), 0.5)
        key = (path, function)
        current = best.get(key)
        if current is None or rank > current.rank:
            best[key] = ScanRegion(
                path=path,
                function=function,
                language=language,
                families=families,
                rank=rank,
                source="module_scope" if module_body else "entry_point",
            )

    # A nameless entry point IS the file. Where a named region already covers that file it adds nothing but
    # a second full-file pass, so it is dropped -- unless the file has no named region at all.
    named_paths = {path for path, function in best if function is not None}
    regions = [region for (path, function), region in best.items() if function is not None or path not in named_paths]

    # Every file whose regions are all function-scoped still has code that is in no function: the settings, the
    # route registrations, the globals. Those regions cannot see it -- their queries filter by function name --
    # and there is no file-level region beside them, because one would duplicate every function's findings.
    # So the module body gets its own region, which partitions the file rather than overlapping it.
    #
    # This was cheap to add only after batching: before it, a region was a JVM.
    scoped = {region.path for region in regions if region.function is not None}
    have_module = {region.path for region in regions if region.function == MODULE_SCOPE}
    for path in sorted(scoped - have_module):
        language = by_path.get(path)
        if language is None:
            continue
        families = _families(language, has_handler=False)
        if families:
            regions.append(
                ScanRegion(path=path, function=MODULE_SCOPE, language=language, families=families, rank=0.15, source="module_scope")
            )

    covered = {region.path for region in regions}

    for path, language in by_path.items():
        if path in covered:
            continue
        families = _families(language, has_handler=False)
        if not families:
            continue
        regions.append(ScanRegion(path=path, function=None, language=language, families=families, rank=0.1, source="file_fallback"))

    # A total order: rank descending, then path and function, so two runs of one repository agree.
    if shipped is not None:
        regions = [replace(region, shipped=region.path in shipped) for region in regions]

    # Shipped first, then rank. A project's own build declaration outranks any score computed here: libpng's
    # twenty-five entry points were all `main()` in example programs and test tools, and they took the
    # interprocedural analysis with them.
    return tuple(sorted(regions, key=lambda r: (not r.shipped, -r.rank, r.path, r.function or "")))


def _language_of(target: object) -> str | None:
    language = str(getattr(target, "language", "") or "")
    if language not in _LANGUAGES:
        return None
    return _NORMALISE.get(language, language)


def _families(language: str, *, has_handler: bool) -> tuple[str, ...]:
    """The families this language has facts for, minus those whose arbiter needs a handler and has none."""
    families = set(taint_specs(language=language))
    families |= set(config_specs(language=language))
    if has_handler:
        families |= set(dominance_specs(language=language))
    return tuple(sorted(families))