"""Foreground-app parsing from `dumpsys activity activities` (RESEARCH_SHIELD R4).

Primary pattern: ``mResumedActivity: ActivityRecord{... u0 <pkg>/<activity> ...}``
(Shield Android 11). ``topResumedActivity`` (newer firmware) is the fallback,
checked only after the primary — per R4 finding 1. ``dumpsys window`` focus is
NOT parsed (R4 finding 2: the first ``mCurrentFocus`` can be literally null).

Multi-line ActivityRecord wraps are handled by joining the block until the
record closes or a state line arrives (R4 finding 3: match on the joined
block, not per-line). ``ResumedActivity``/``Resumed`` duplicates are tolerated.
"""

import re

_RESUMED_MARKERS = (
    ("mResumedActivity", "mResumedActivity:"),
    ("topResumedActivity", "topResumedActivity:"),
    ("ResumedActivity", "ResumedActivity:"),
    ("Resumed", "Resumed:"),
)

# `u0 <pkg>/<activity>` — the userId prefix tolerates u0..uN; the package is
# anything up to the first `/` (or closing brace when the activity is bare).
_PACKAGE_RE = re.compile(r"u\d+\s+(\S+?)\s*/|u\d+\s+(\S+?)\s*}")


def _marker_kind(stripped: str) -> str | None:
    for kind, marker in _RESUMED_MARKERS:
        if stripped.startswith(marker):
            return kind
    return None


def _resumed_blocks(dump: str) -> list[tuple[str, str]]:
    """(kind, joined-text) blocks for each resumed-activity line, in order."""
    blocks: list[tuple[str, str]] = []
    kind: str | None = None
    buf = ""
    for raw in dump.split("\n"):
        stripped = raw.strip()
        marker = _marker_kind(stripped)
        if marker is not None:
            if buf:
                blocks.append((kind, buf))
            kind, buf = marker, stripped
            continue
        if kind is None:
            continue
        # Continuation of a wrapped ActivityRecord: join until the record
        # closes (brace) or the state line completes the block (R4 finding 3).
        buf += " " + stripped
        if "}" in stripped or "state=" in stripped:
            blocks.append((kind, buf))
            kind, buf = None, ""
    if buf:
        blocks.append((kind, buf))
    return blocks


def _extract_package(text: str) -> str | None:
    match = _PACKAGE_RE.search(text)
    if match is None:
        return None
    package = match.group(1) or match.group(2)
    if not package or package in ("null", "Window{"):
        return None
    return package


def parse_foreground(dump: str) -> str | None:
    """Foreground package: mResumedActivity primary, topResumed fallback.

    Returns None when neither pattern matches (e.g. pre-parse wrappers) —
    callers must not fall back to window-focus parsing (R4 finding 2).
    """
    if not dump:
        return None
    blocks = _resumed_blocks(dump)
    for kind, text in blocks:
        if kind == "topResumedActivity":
            continue
        package = _extract_package(text)
        if package:
            return package
    for kind, text in blocks:
        if kind != "topResumedActivity":
            continue
        package = _extract_package(text)
        if package:
            return package
    return None