"""Unit: the phase-109 never-frozen-turn frontend contract (tasks 01-02).

No new Python app logic exists for this task — the behavior lives in
``frontend/assets/app.js`` and is E2E-gated by the story suite (task 03).
Like the other frontend-adjacent unit files (the house
read-the-assets-as-text pattern, cf. ``test_frontend_tool_states.py``),
this module pins the JS markers the phase depends on: the thinking block
becomes a TOGGLE (D15) — ``thinking`` frames open it (idempotent),
``delta`` frames close it — while the phase-14 restore path and the
phase-17 follow-the-tail pin logic stay byte-for-byte untouched. Task 02
pins the persistent in-turn loader (D16): the static ``#turn-loader``
markup, ``setUiState`` as its SOLE visibility owner (the structural
never-stale guarantee), and the CSS contract (reused typing-dot
animation + reduced-motion + provenance).
"""
from __future__ import annotations

import re
from pathlib import Path

FRONTEND = Path(__file__).resolve().parents[2] / "frontend"
APP_JS = FRONTEND / "assets" / "app.js"
INDEX_HTML = FRONTEND / "index.html"
STYLES_CSS = FRONTEND / "assets" / "styles.css"


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


def _html() -> str:
    return INDEX_HTML.read_text(encoding="utf-8")


def _css() -> str:
    return STYLES_CSS.read_text(encoding="utf-8")


def _thinking_branch() -> str:
    """The `thinking` handler branch (between the thinking and tool
    branches of the turn dispatch)."""
    js = _js()
    thinking_idx = js.find('ev.type === "thinking"')
    tool_idx = js.find('ev.type === "tool"')
    assert -1 < thinking_idx < tool_idx, (
        "the turn handler must branch on thinking frames"
    )
    return js[thinking_idx:tool_idx]


def test_thinking_handler_reopens_the_collapsed_block() -> None:
    """Phase 109 (D15): the `thinking` handler re-opens the block —
    ``block.open = true`` sits in the handler, positioned AFTER the
    ``ensureThinkingBlock(wrap)`` line (the block must exist before it
    can be opened). Idempotent: a no-op while already open (the
    pre-delta live flow), a re-open after a `delta` closed it (the next
    agent round — the reported freeze, TODO.md L3)."""
    branch = _thinking_branch()
    ensure_idx = branch.find("ensureThinkingBlock(wrap)")
    assert ensure_idx != -1, "the handler must ensure the block first"
    reopen_idx = branch.find("block.open = true")
    assert reopen_idx != -1, (
        "the `thinking` handler must open the block (D15: "
        "open-while-thinking)"
    )
    assert ensure_idx < reopen_idx, (
        "`block.open = true` must sit AFTER `ensureThinkingBlock(wrap)` "
        "— the block must exist before it is opened"
    )


def test_delta_handler_still_closes_the_block() -> None:
    """Phase 109 (D15): the close side of the toggle survives — the
    `delta` handler still calls ``closeThinkingBlock(wrap)`` (closed
    while answering); nothing else about the block's lifecycle changes."""
    js = _js()
    delta_idx = js.find('ev.type === "delta"')
    done_idx = js.find('ev.type === "done"')
    assert -1 < delta_idx < done_idx, "the turn handler must branch on delta"
    branch = js[delta_idx:done_idx]
    assert "closeThinkingBlock(wrap)" in branch, (
        "the `delta` handler must keep closing the block (D15: "
        "closed-while-answering)"
    )


def test_close_thinking_block_docstring_says_toggle_not_one_way() -> None:
    """Phase 109 (D15): the narrative flips. The section comment
    documenting ``closeThinkingBlock`` no longer claims "never reopens"
    — nowhere in app.js does — and documents the toggle contract instead:
    open-while-thinking / closed-while-answering, naming the `thinking`
    handler's re-open and the `delta` handler's close. The function
    body itself is unchanged (idempotent close, no-op without a
    block)."""
    js = _js()
    fn = js.find("function closeThinkingBlock")
    assert fn != -1, "closeThinkingBlock must exist"
    body = js[fn : js.find("\n}\n", fn)]
    assert "block.open = false" in body, "the close side is unchanged"
    # The block comment that documents the helpers: walk back from the
    # function to its section comment start.
    comment_start = js.rfind("/*", 0, fn)
    assert comment_start != -1
    section = js[comment_start:fn]
    assert "never reopens" not in section, (
        "the one-way-door claim is gone (phase 109, D15)"
    )
    assert "never reopens" not in js, (
        "the 'never reopens' narrative must not survive anywhere in app.js"
    )
    # The toggle contract is documented — and it names both sides:
    # the `thinking` handler's re-open and the `delta` handler's close.
    assert "TOGGLE" in section, "the contract is named: a toggle"
    assert "open-while-thinking" in section
    assert "closed-while-answering" in section
    assert "`thinking`" in section, "the contract names the thinking handler"
    assert "re-opens" in section, "the contract names the thinking handler's re-open"
    assert "`delta`" in section, "the contract names the delta handler's close"


def test_restore_path_still_collapses_stored_blocks() -> None:
    """Phase-14 contract regression: ``renderStoredMessage`` restores
    stored thinking blocks COLLAPSED (``block.open = false``) — the
    phase-109 toggle only changes the LIVE `thinking` handler, the
    restore path is untouched."""
    js = _js()
    fn = js.find("function renderStoredMessage")
    assert fn != -1, "renderStoredMessage must exist"
    body = js[fn : js.find("\n}\n", fn)]
    assert "if (m.thinking)" in body
    assert "ensureThinkingBlock(wrap)" in body
    assert "block.open = false" in body, "stored blocks restore collapsed"
    # The live re-open must NOT have leaked into the restore path:
    # only the collapse assignment may appear in the function body.
    assert "block.open = true" not in body, (
        "the restore path must never open a stored block (phase-14)"
    )


def test_follow_the_tail_pin_logic_is_untouched() -> None:
    """Cross-file regression (phase 17): the follow-the-tail pin is
    unchanged — ``THINKING_NEAR_BOTTOM_PX`` (32px band) +
    ``isThinkingNearBottom`` and the pre-render capture
    ``const pinned = block.open && isThinkingNearBottom(textEl);``
    (measured BEFORE the re-render) still sit in the `thinking` handler.
    The capture already keys off ``block.open``, so a re-opened block
    resumes pinned tail-following exactly like the live pre-delta
    block — no pin logic change needed for D15."""
    js = _js()
    assert "export const THINKING_NEAR_BOTTOM_PX = 32;" in js, (
        "the 32px window band is unchanged"
    )
    fn = re.search(
        r"function isThinkingNearBottom\(textEl\) \{([\s\S]*?)\n\}", js
    )
    assert fn, "isThinkingNearBottom must still exist"
    assert "THINKING_NEAR_BOTTOM_PX" in fn.group(1)
    branch = _thinking_branch()
    capture = "const pinned = block.open && isThinkingNearBottom(textEl);"
    assert capture in branch, (
        "the pre-render `block.open &&` guard line is unchanged — D15 "
        "keeps the pin logic untouched (it already reads block.open "
        "before the re-render)"
    )
    capture_idx = branch.find(capture)
    render_idx = branch.find("textEl.innerHTML = renderMarkdown(thinkingAcc)")
    assert -1 < capture_idx < render_idx, (
        "pin state is still measured BEFORE the re-render (phase-17 "
        "regression — the 2-newline-gap fix)"
    )
    assert "textEl.scrollTop = textEl.scrollHeight" in branch, (
        "pinned tail-following is intact"
    )


# ---------- task 02: the persistent in-turn loader (D16) ----------


def test_index_html_carries_exactly_one_turn_loader() -> None:
    """Phase 109 (D16): ``index.html`` carries exactly ONE static
    ``#turn-loader`` — an empty ``<div>`` (never constructed in JS: the
    createElement/textContent house rule), ``aria-hidden="true"``
    (decorative — ``#send-status`` carries the meaning), ``hidden`` by
    default (idle on load), and it sits INSIDE the composer form — the
    composer's status row, the visible companion of the ``#send-status``
    line."""
    html = _html()
    assert html.count('id="turn-loader"') == 1, (
        "exactly one #turn-loader — static markup, never JS-built"
    )
    match = re.search(r'<div\s+id="turn-loader"[^>]*>', html)
    assert match, "the loader must be a static <div>"
    tag = match.group(0)
    assert 'class="turn-loader"' in tag
    assert 'aria-hidden="true"' in tag, "decorative — aria-hidden"
    # the hidden attribute (a standalone word in the tag, not the
    # substring of some other attribute value): ships hidden (idle).
    assert re.search(r"\shidden\s*/?>$", tag), (
        "the loader ships hidden (idle on load)"
    )
    # empty element: the closing tag follows immediately — no children,
    # no JS-built HTML anywhere near it.
    assert html[match.end() : match.end() + 6] == "</div>", (
        "the loader element is empty (static shell)"
    )
    # inside the composer form (the status row), not elsewhere in the
    # shell.
    composer_idx = html.find('<form class="composer" id="composer"')
    assert composer_idx != -1
    form_end = html.find("</form>", composer_idx)
    assert composer_idx < match.start() < form_end, (
        "the loader sits in the composer's status row"
    )


def test_set_ui_state_is_the_sole_owner_of_the_loader() -> None:
    """Phase 109 (D16) — the never-stale guarantee, structural: in
    ``app.js`` the string ``turnLoader.hidden`` appears EXACTLY ONCE,
    inside ``setUiState`` (the cross-file single-owner check — any
    second write site fails this test). The toggle is
    ``turnLoader.hidden = !inFlight`` next to the existing ``is-stop``
    toggle: shown iff ``uiState`` is thinking|streaming. Every terminal
    path funnels through ``setUiState`` (done → idle, error → error,
    stop/timeout → their landings), so the loader hides in every
    terminal state BY CONSTRUCTION — no per-handler cleanup."""
    js = _js()
    # The element lookup joins the other module-top lookups.
    assert 'const turnLoader = document.querySelector("#turn-loader");' in js
    # THE invariant: exactly one write site in the whole file.
    assert js.count("turnLoader.hidden") == 1, (
        "setUiState is the SOLE writer of the loader's hidden attribute — "
        "a second write site breaks the §7.4 never-stale guarantee"
    )
    # ...and it sits INSIDE setUiState, next to the is-stop toggle.
    fn = js.find("export function setUiState")
    assert fn != -1
    body_end = js.find("\n}\n", fn)
    owner_idx = js.find("turnLoader.hidden")
    assert fn < owner_idx < body_end, (
        "the toggle must live inside setUiState (the single entry point)"
    )
    stop_idx = js.find('sendBtn.classList.toggle("is-stop", inFlight);', fn)
    assert -1 < stop_idx < owner_idx, (
        "the loader toggle joins the existing is-stop toggle"
    )
    assert "turnLoader.hidden = !inFlight;" in js, (
        "shown iff inFlight (thinking|streaming)"
    )


def test_loader_css_reuses_the_typing_animation_and_reduced_motion() -> None:
    """Phase 109 (D16) — the CSS contract: the ``.turn-loader`` rule
    sits NEXT TO the typing-dots rules (after the ``@keyframes typing``
    block), reuses the SAME animation name (``typing`` — no new
    animation family), a ``prefers-reduced-motion`` block covers it
    (static dots, no pulse — §7.2 house law), and the provenance
    comment names phase 109 + ``TODO.md``."""
    css = _css()
    keyframes_idx = css.find("@keyframes typing")
    assert keyframes_idx != -1, "the typing-dot keyframes exist"
    # The MAIN rule (".turn-loader {" — the reduced-motion block's
    # selector list never starts that exact string) must sit next to
    # (after) the typing-dots rules.
    rule_idx = css.find(".turn-loader {")
    assert rule_idx != -1, "styles.css must carry a .turn-loader rule"
    assert keyframes_idx < rule_idx, (
        "the .turn-loader rule sits next to (after) the typing-dots rules"
    )
    # The provenance comment: the /* ... */ block immediately preceding
    # the rule names phase 109 and TODO.md.
    comment_start = css.rfind("/*", 0, rule_idx)
    assert comment_start != -1
    comment = css[comment_start:rule_idx]
    assert "Phase 109" in comment, "the provenance comment names phase 109"
    assert "TODO.md" in comment, "the provenance comment cites the source"
    # Reuses the EXISTING typing-dot animation: the same animation name
    # in the rule and its pseudo-element rules (no new @keyframes
    # family anywhere).
    rule_block = css[rule_idx : rule_idx + 1200]
    assert re.search(r"animation:\s*typing\b", rule_block), (
        "the loader reuses the typing dots' animation (same name — no "
        "new animation family)"
    )
    assert "@keyframes turn" not in css, "no new animation family for the loader"
    # The prefers-reduced-motion block covers it: static dots, no pulse.
    reduced_ok = False
    for m in re.finditer(r"@media \(prefers-reduced-motion: reduce\) \{([\s\S]*?)\n\}", css):
        if ".turn-loader" in m.group(1) and "animation: none" in m.group(1):
            reduced_ok = True
            break
    assert reduced_ok, (
        "a prefers-reduced-motion block must cover .turn-loader (static "
        "dots, no pulse — §7.2)"
    )


def test_loader_is_aria_hidden_and_status_untouched() -> None:
    """Phase 109 (D16) — the a11y split is untouched: the loader is
    ``aria-hidden`` (decoration), and ``#send-status`` keeps its exact
    attributes in ``index.html`` — still the sole ``aria-live``
    announcer (the house a11y split: visual cues are aria-hidden, the
    live region carries the state text)."""
    html = _html()
    match = re.search(r'<div\s+id="turn-loader"[^>]*>', html)
    assert match and 'aria-hidden="true"' in match.group(0)
    # #send-status is unchanged: one element, the exact same tag —
    # the visually-hidden polite live region inside the send button,
    # still the chat view's state announcer.
    assert html.count('id="send-status"') == 1
    status = re.search(r'<span[^>]*id="send-status"[^>]*></span>', html)
    assert status, "the #send-status live region is intact"
    tag = status.group(0)
    assert tag == (
        '<span class="visually-hidden" aria-live="polite" '
        'id="send-status"></span>'
    ), "the #send-status attributes are byte-unchanged"
    # the loader added no a11y surface: it is aria-hidden and carries
    # no live region of its own.
    assert 'aria-live' not in match.group(0)