"""Unit: a hidden tab never stops a turn (phase 73, task 02).

The JS behavior itself is E2E-covered (tests/e2e/test_hidden_tab_stream.py,
task 03); here we pin the app.js mechanisms the story depends on — the
pagehide-partial ↔ settle correlation (C1 hardening, unconditional) and the
visibility-aware pre-token guard (task 01, C2 confirmed) — so a silent
regression in app.js is caught without a browser (house pattern:
tests/unit/test_frontend_feedback.py).
"""
from __future__ import annotations

import re
from pathlib import Path

FRONTEND = Path(__file__).resolve().parents[2] / "frontend"
APP_JS = FRONTEND / "assets" / "app.js"


def _js() -> str:
    return APP_JS.read_text(encoding="utf-8")


# ---------- C1: the pagehide partial is replaced, never duplicated ----------


def test_leave_partial_index_is_a_module_turn_local() -> None:
    """`leavePartialIndex` is a module-scope turn local (like
    persistedOnLeave): declared -1, reset at the top of runTurn, and
    written ONLY by the pagehide handler (the one `= conversation.length
    - 1` assignment). No other code may move the correlation."""
    js = _js()
    assert "let leavePartialIndex = -1" in js, "module-scope declaration"
    # The two -1 writes are the declaration and the runTurn reset.
    assert js.count("leavePartialIndex = -1;") == 2, (
        "only the declaration and the runTurn reset write -1"
    )
    # The one and only index write is the pagehide handler's.
    assert js.count("leavePartialIndex = conversation.length - 1") == 1, (
        "only the pagehide handler records the partial's index"
    )
    # The reset sits at the top of runTurn, with the other turn locals
    # (the acc / thinkingAcc / persistedOnLeave group, just before the
    # fresh AbortController).
    turn = js.find("async function runTurn")
    abort_idx = js.find("turnAbort = new AbortController()", turn)
    assert -1 < turn < abort_idx, "runTurn must exist"
    turn_top = js[turn:abort_idx]
    assert "leavePartialIndex = -1;" in turn_top, "reset per turn at the top"
    assert turn_top.index("persistedOnLeave = false;") < turn_top.index(
        "leavePartialIndex = -1;"
    ), "reset alongside the other turn locals (phase-20 group)"


def test_pagehide_records_the_partial_index_after_the_push() -> None:
    """The pagehide handler keeps its phase-20 guards (idempotency,
    in-flight only, nothing brain-side yet) and, AFTER the partial is
    pushed through rememberBrainTurn, records the pushed record's index
    so the turn's settle can find it."""
    js = _js()
    fn = js.find('window.addEventListener("pagehide"')
    assert fn != -1, "the pagehide listener must exist"
    body = js[fn: js.find("\n});", fn)]
    assert "if (persistedOnLeave) return;" in body, "phase-20 idempotency guard"
    assert "if (!acc) return;" in body, "nothing brain-side yet → no save"
    i_guard = body.index("persistedOnLeave = true;")
    i_push = body.index("rememberBrainTurn(acc, { thinking: thinkingAcc || undefined });")
    i_index = body.index("leavePartialIndex = conversation.length - 1")
    assert i_guard < i_push < i_index, (
        "flag → push the partial → record its index (the record it just pushed)"
    )


def test_remember_brain_turn_replaces_in_place_with_identity_guard() -> None:
    """rememberBrainTurn's optional in-place mode: `replaceIndex >= 0`
    REPLACES the record at that index instead of appending — and only
    when the index STILL points at a brain record (the identity guard:
    a New-Chat click or restore between pagehide and settle falls back
    to the append). Either way the record is written once, and the
    save points (localStorage + the headless auto-save) run once on the
    written record."""
    js = _js()
    fn = js.find("function rememberBrainTurn")
    assert fn != -1, "rememberBrainTurn must exist"
    body = js[fn: js.find("\n}\n", fn)]
    assert "function rememberBrainTurn(rawText, meta, replaceIndex = -1)" in body, (
        "the optional in-place mode defaults to the plain append"
    )
    assert 'const rec = { who: "brain", text: rawText || "…", ...meta }' in body, (
        "one record object, written once"
    )
    assert (
        'if (replaceIndex >= 0 && conversation[replaceIndex]?.who === "brain")' in body
    ), "identity guard: the index must still point at a brain record"
    assert "conversation[replaceIndex] = rec" in body, "the in-place replace"
    assert "conversation.push(rec)" in body, "the append (no partial / guard miss)"
    i_replace = body.index("conversation[replaceIndex] = rec")
    i_push = body.index("conversation.push(rec)")
    assert i_replace < i_push, "replace branch precedes the append fallback"
    i_save = body.index("saveConversation()")
    i_persist = body.index("persistConversation()")
    assert i_push < i_save < i_persist, (
        "both save points run ONCE, after the single write — the auto-save "
        "refreshes the row exactly once for the replaced record"
    )


def test_every_settle_writes_through_the_correlation() -> None:
    """The three brain-record write sites in runTurn's settle paths —
    the `done` save point, the zero-frame empty-answer fallback, and the
    stop-path partial — all pass `leavePartialIndex`, so the replace is
    the only write after a pagehide partial (the invariant). The
    pagehide handler itself pushes with the plain two-arg form (it IS
    the partial)."""
    js = _js()
    # done save point.
    done = js.find('ev.type === "done"')
    done_branch = js[done: js.find('ev.type === "error"', done)]
    assert "leavePartialIndex" in done_branch, "the done settle is correlated"
    # zero-frame empty-answer fallback.
    fallback = js.find("!aborted && !wrap")
    fallback_block = js[fallback: js.find(") catch (err) {", fallback)]
    assert "leavePartialIndex" in fallback_block, "the fallback settle is correlated"
    # stop-path partial (the `stopped` marker persist).
    catch = js.find("} catch (err) {")
    stop_idx = js.find('stoppedByUser || err?.name === "AbortError"', catch)
    stop_branch = js[stop_idx: js.find("} else {", stop_idx)]
    assert "leavePartialIndex" in stop_branch, "the stop settle is correlated"
    # The pagehide handler pushes the plain two-arg partial (the record
    # that the settles replace).
    fn = js.find('window.addEventListener("pagehide"')
    body = js[fn: js.find("\n});", fn)]
    assert "rememberBrainTurn(acc, { thinking: thinkingAcc || undefined });" in body
    assert "leavePartialIndex" not in body.replace(
        "leavePartialIndex = conversation.length - 1", ""
    ), "the pagehide handler only records the index — it never settles"


def test_real_navigation_behavior_is_unchanged() -> None:
    """The leave-save invariant: a REAL navigation never runs a settle
    (the page unloads), so the pagehide partial stays persisted exactly
    as phase 20 left it — the handler's guards and the rememberBrainTurn
    ride-through (localStorage + auto-save) are untouched."""
    js = _js()
    fn = js.find('window.addEventListener("pagehide"')
    body = js[fn: js.find("\n});", fn)]
    for guard in (
        "if (persistedOnLeave) return;",
        "if (uiState !== UI_STATE.thinking && uiState !== UI_STATE.streaming)",
        "if (!acc) return;",
    ):
        assert guard in body, f"phase-20 guard intact: {guard}"
    # The phase-48 teardown contract (real close / navigation / Stop still
    # aborts the fetch) is untouched.
    assert "turnAbort?.abort()" in js, "the abort owner still aborts the fetch"
    assert re.search(r"export\s+const\s+TURN_TIMEOUT_MS\s*=\s*300_?000\s*;", js), (
        "the guard constant is still 300s (raised from the phase-17/48 value)"
    )


# ---------- C2: hidden time does not count toward the pre-token guard ----------


def test_guard_arms_with_a_rearmable_callback() -> None:
    """armTurnTimeout remembers the guard's callback (turnTimeoutCb) so
    the visibility listener can re-arm it; clearTurnTimeout clears BOTH
    the timer and the callback — armed ⇔ callback set."""
    js = _js()
    fn = js.find("function armTurnTimeout")
    assert fn != -1, "armTurnTimeout must exist"
    body = js[fn: js.find("\n}\n", fn)]
    assert "turnTimeoutCb = onTimeout" in body, "the callback is remembered"
    assert body.index("turnTimeoutCb = onTimeout") < body.index(
        "turnTimeout = setTimeout(onTimeout, TURN_TIMEOUT_MS)"
    ), "the callback is stored with the arm"
    cfn = js.find("function clearTurnTimeout")
    cbody = js[cfn: js.find("\n}\n", cfn)]
    assert "clearTimeout(turnTimeout)" in cbody
    assert "turnTimeout = 0" in cbody
    assert "turnTimeoutCb = null" in cbody, "clearing the timer drops the callback"


def test_visibility_rearm_counts_only_visible_pre_token_time() -> None:
    """On visibilitychange, when the tab returns to VISIBLE with the
    guard still armed (the pre-token window — the timer id is non-zero
    and the callback set), it re-arms with a FRESH TURN_TIMEOUT_MS via
    armTurnTimeout (the same arm path — one timer, one owner). Hidden
    transitions never re-arm. Exactly one such listener exists."""
    js = _js()
    assert js.count('document.addEventListener("visibilitychange"') == 1, (
        "one visibility listener (the guard re-arm)"
    )
    fn = js.find('document.addEventListener("visibilitychange"')
    body = js[fn: js.find("});", fn)]
    assert 'document.visibilityState === "visible"' in body, (
        "only a return to visible re-arms — hidden transitions do not extend it"
    )
    assert "turnTimeout && turnTimeoutCb" in body, (
        "only an ARMED guard (pre-token window) is re-armed — the timer clears "
        "on the first thinking/delta/retry frame and every terminal transition"
    )
    assert "armTurnTimeout(turnTimeoutCb)" in body, (
        "the re-arm goes through the same arm path (a fresh TURN_TIMEOUT_MS)"
    )
    assert "TURN_TIMEOUT_MS" in body or "armTurnTimeout" in body, (
        "the fresh deadline is the owner-locked TURN_TIMEOUT_MS"
    )


def test_header_documents_the_phase_73_contract() -> None:
    """House convention: the file-header doc inventories each phase's
    contract — phase 73 documents the hidden-tab rule (only close /
    navigation / Stop aborts) and both hardenings."""
    js = _js()
    header = js[: js.find("import {")]
    assert "phase 73" in header.lower(), "the header must carry the phase-73 section"
    assert "leavePartialIndex" in header, "the correlation local is documented"
    assert "visibilitychange" in header, "the visibility re-arm is documented"