"""Unit: the document modal's history-entry lifecycle (phase 144, task 02).

Back while the ``#doc-modal`` document viewer is open must CLOSE the modal
— not navigate the view behind it (TODO.md L6). The mechanics live in
``frontend/assets/document-modal.js``: the open owns ONE state-only
history entry (``{ modal: "doc", source, path }`` — the second arg
``""`` keeps the URL where it is, so the router's pathname-only
popstate is a no-op and the Sources drill re-adopts the state it was
already showing); Back closes the modal (remembering the landed state
as ``lastPrev``); a button/Escape/backdrop close removes the entry IN
PLACE (``replaceState(entry.prev)`` — the next Back behaves as if the
modal never opened); Forward onto the entry re-opens the same document
(the browser owns its entries — the phase-99 D2 convention).

The browser behavior itself is E2E-gated by the phase-144 story suite
(``tests/e2e/test_modal_back_button.py`` — task 03 drives the real
history via ``page.goBack()``/``page.goForward()``); like
``test_remove_confirm_modal.py`` (the house pattern for a frontend
module whose real behavior is E2E-gated), this module pins the
source-level contract a silent regression would break:

* a second push on the forward re-open (the adopt branch must assign
  ``entry`` WITHOUT a ``pushState``);
* a ``replaceState`` on a non-modal current entry (the close's
  in-place removal is guarded by ``!closingViaBack`` AND
  ``history.state.modal === "doc"`` — the fail-safe);
* a double-registered popstate listener;
* a ``history.back()``/``history.go()`` introduction (the browser owns
  its entries — the closed set of ``history.*`` sites is the one push,
  the two replaces, and the read-only ``history.state`` accesses);
* a lost ``lastPrev`` write (it must land BEFORE the
  ``closingViaBack``-wrapped close in the back branch);
* a fallback-path push (the ``window.open`` no-skeleton fallback's
  early ``return`` precedes the first ``history.`` use in the open).
"""
from __future__ import annotations

import re
from pathlib import Path

FRONTEND = Path(__file__).resolve().parents[2] / "frontend"
MODAL_JS = FRONTEND / "assets" / "document-modal.js"


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


def _fn(js: str, name: str) -> str:
    """The source of a top-level function via balanced-brace counting
    (the test_remove_confirm_modal.py helper — ``export function``
    matches the plain ``function name(`` search)."""
    start = js.find(f"function {name}(")
    assert start != -1, f"{name}() must exist in document-modal.js"
    depth = 0
    for i in range(js.find("{", start), len(js)):
        if js[i] == "{":
            depth += 1
        elif js[i] == "}":
            depth -= 1
            if depth == 0:
                return js[start : i + 1]
    raise AssertionError(f"unbalanced braces in {name}()")


def _block(source: str, from_i: int) -> str:
    """The ``{ … }`` block opening at the first ``{`` at/after
    ``from_i`` — balanced-brace walk, braces included."""
    brace = source.find("{", from_i)
    assert brace != -1, "no block opener found"
    depth = 0
    for i in range(brace, len(source)):
        if source[i] == "{":
            depth += 1
        elif source[i] == "}":
            depth -= 1
            if depth == 0:
                return source[brace : i + 1]
    raise AssertionError("unbalanced braces in the entry/popstate block")


def _popstate_handler(js: str) -> str:
    """The module-top-level popstate handler's ``{ … }`` body."""
    i = js.find('window.addEventListener("popstate"')
    assert i != -1, "the popstate listener must be registered at module top level"
    arrow = js.find("=> {", i)
    assert arrow != -1, "the popstate listener must be an arrow function"
    return _block(js, arrow)


# ---------- the module state: one declaration, no second writer site ----------


def test_history_state_is_declared_exactly_once() -> None:
    """REGRESSION: a duplicated module-level declaration / second
    writer site for the entry state. ``entry`` / ``lastPrev`` /
    ``closingViaBack`` are each declared by EXACTLY ONE ``let`` (the
    single writer sites — open/close, the popstate handler, the
    popstate handler — are pinned by the per-branch tests below)."""
    js = _js()
    assert js.count("let entry = null;") == 1
    assert len(re.findall(r"let\s+entry\s*=", js)) == 1
    assert js.count("let lastPrev = null;") == 1
    assert len(re.findall(r"let\s+lastPrev\s*=", js)) == 1
    assert js.count("let closingViaBack = false;") == 1
    assert len(re.findall(r"let\s+closingViaBack\s*=", js)) == 1


# ---------- the open: one state-only entry, adopt vs push vs replace ----------


def test_open_pushes_exactly_one_state_only_entry() -> None:
    """REGRESSION: a double push (two entries per open) or a
    URL-MOVING push. The push is exactly ONE
    ``history.pushState({ modal: "doc", source, path }, "")`` — the
    ``""`` second arg is what keeps the URL where it is (state-only;
    the router's pathname-only popstate stays a no-op)."""
    open_body = _fn(_js(), "openDocumentModal")
    assert open_body.count("history.pushState(") == 1, (
        "exactly one pushState in the open — a second push stacks a dead history step"
    )
    assert 'history.pushState({ modal: "doc", source, path }, "")' in open_body, (
        "the push must be state-only: the state key modal: \"doc\" + the "
        "doc name, and the \"\" second arg (the URL must not move)"
    )


def test_open_entry_chain_adopts_on_forward_and_replaces_on_defensive_reopen() -> None:
    """REGRESSION: a second push on the forward re-open. The chain is
    ``if (entry) → replaceState IN PLACE (keep entry, update
    source/path — the defensive re-open-while-open never stacks)
    → else if the current entry is already a modal entry → ADOPT
    (assign ``entry = { prev: lastPrev, source, path }`` WITHOUT any
    pushState — the browser already sits on the entry) → else push.
    The push lives ONLY in the final else."""
    open_body = _fn(_js(), "openDocumentModal")
    st_i = open_body.find("const st = history.state;")
    def_i = open_body.find("if (entry) {", st_i)
    adopt_i = open_body.find('else if (st && st.modal === "doc") {', def_i)
    else_i = open_body.find("} else {", adopt_i)
    push_i = open_body.find('history.pushState({ modal: "doc", source, path }, "");', else_i)
    assert -1 < st_i < def_i < adopt_i < else_i < push_i, (
        "chain order: const st → if (entry) → else if (adopt) → else → push"
    )
    # Defensive re-open: replaceState in place, entry KEPT (updated).
    defensive = open_body[def_i:adopt_i]
    assert "entry.source = source;" in defensive
    assert "entry.path = path;" in defensive
    assert 'history.replaceState({ modal: "doc", source, path }, "")' in defensive
    assert "pushState" not in defensive, "a defensive re-open must never push"
    # Forward re-open: ADOPT — assign entry from lastPrev, no push.
    adopt = open_body[adopt_i:else_i]
    assert "entry = { prev: lastPrev, source, path };" in adopt, (
        "the adopt must take lastPrev (the below-entry remembered at the back-close)"
    )
    assert "pushState" not in adopt, (
        "a second push on the forward re-open stacks a dead history step"
    )
    # Normal open: push with prev = the entry we sat on, in the final else.
    assert "entry = { prev: st, source, path };" in open_body[else_i:push_i]
    assert open_body.count("history.pushState(") == 1


def test_window_open_fallback_precedes_the_entry_logic() -> None:
    """REGRESSION: a fallback-path push. A page WITHOUT the modal
    skeleton falls back to ``window.open(fullPageUrl…)`` in a new tab —
    that path must not touch the history AT ALL: the fallback's early
    ``return`` precedes the first ``history.`` use in the open."""
    open_body = _fn(_js(), "openDocumentModal")
    guard_i = open_body.find("if (!modalEl || !titleEl || !metaEl || !contentEl) {")
    open_i = open_body.find('window.open(fullPageUrl(source, path), "_blank", "noopener");')
    ret_i = open_body.find("return;", open_i)
    first_hist_i = open_body.find("history.")
    assert -1 < guard_i < open_i < ret_i < first_hist_i, (
        "the window.open fallback must early-return before any history use"
    )


# ---------- the close: in-place removal, guarded; entry always nulled ----------


def test_close_removes_the_entry_in_place_and_only_on_a_modal_entry() -> None:
    """REGRESSION: a ``replaceState`` on the wrong entry. The in-place
    removal ``history.replaceState(entry.prev, "")`` is guarded by
    BOTH ``!closingViaBack`` (a back close already moved us off the
    entry — the browser owns that pop) AND the current entry still
    being a modal entry (the fail-safe: a non-modal current entry is
    NEVER overwritten). Exactly one replaceState in the close."""
    close_body = _fn(_js(), "closeDocumentModal")
    assert close_body.count("history.replaceState(") == 1
    guard = 'if (entry && !closingViaBack && history.state && history.state.modal === "doc") {'
    guard_i = close_body.find(guard)
    assert guard_i != -1, (
        "the close's in-place removal must be guarded by !closingViaBack AND "
        "history.state.modal === \"doc\""
    )
    # The single replace sits INSIDE the guard block.
    block = _block(close_body, guard_i)
    assert 'history.replaceState(entry.prev, "");' in block, (
        "the removal must restore entry.prev (byte-for-byte view state)"
    )


def test_close_nulls_the_entry_unconditionally() -> None:
    """REGRESSION: a lost ``entry = null`` — the adopt's memory
    surviving a close (a later popstate would then close/adopt against
    a stale entry). ``entry = null`` runs OUTSIDE the guarded if,
    between the removal and the hide, on EVERY close (back or not)."""
    close_body = _fn(_js(), "closeDocumentModal")
    guard_i = close_body.find('if (entry && !closingViaBack && history.state')
    brace_i = close_body.find("{", guard_i)
    block = _block(close_body, guard_i)
    assert "entry = null" not in block, "entry = null must not sit inside the guard"
    null_i = close_body.find("entry = null;", brace_i + len(block))
    hide_i = close_body.find("modalEl.hidden = true;", null_i)
    assert -1 < null_i < hide_i, "entry = null must run (before the hide) on every close"


# ---------- the popstate listener: once, mutually exclusive branches ----------


def test_popstate_listener_registered_exactly_once() -> None:
    """REGRESSION: a double-registered popstate listener (two closes /
    two re-opens per navigation). The module registers EXACTLY ONE
    ``window.addEventListener("popstate"`` at top level."""
    js = _js()
    assert js.count('window.addEventListener("popstate"') == 1


def test_popstate_forward_branch_reopens_and_returns() -> None:
    """REGRESSION: the forward branch falling THROUGH into the
    back-close branch. Forward = the modal is closed and we landed on
    a modal entry — re-open the doc the entry names (trigger null —
    focus goes to the content target) and RETURN before the back
    branch (the two branches are mutually exclusive)."""
    handler = _popstate_handler(_js())
    const_i = handler.find("const st = event.state;")
    flag_i = handler.find('const isModalEntry = st && st.modal === "doc";')
    fwd_i = handler.find("if (isModalEntry && modalEl && modalEl.hidden) {")
    reopen_i = handler.find("openDocumentModal(st.source, st.path, null);", fwd_i)
    ret_i = handler.find("return;", reopen_i)
    back_i = handler.find("if (!isModalEntry && modalEl && !modalEl.hidden && entry) {", ret_i)
    assert -1 < const_i < flag_i < fwd_i < reopen_i < ret_i < back_i, (
        "forward: land on a modal entry with the modal closed → re-open the "
        "named doc (null trigger) → RETURN before the back-close branch"
    )


def test_popstate_back_branch_remembers_lastprev_then_closes_guarded() -> None:
    """REGRESSION: a lost ``lastPrev`` write (the forward re-open's
    adopt would then restore ``prev: null`` and corrupt the entry
    below). Back = the modal is open and we landed on a NON-modal
    state: write ``lastPrev = st`` FIRST, then the close wrapped in
    ``closingViaBack = true`` … ``= false`` (keeps the close from also
    replaceState-ing the entry the browser already popped). The flag
    and the below-entry have their single writer sites here."""
    js = _js()
    handler = _popstate_handler(js)
    back_i = handler.find("if (!isModalEntry && modalEl && !modalEl.hidden && entry) {")
    assert back_i != -1, (
        "the back branch (non-modal land + modal open + entry) is gone"
    )
    lastprev_i = handler.find("lastPrev = st;", back_i)
    setflag_i = handler.find("closingViaBack = true;", lastprev_i)
    close_i = handler.find("closeDocumentModal();", setflag_i)
    resetflag_i = handler.find("closingViaBack = false;", close_i)
    assert -1 < lastprev_i < setflag_i < close_i < resetflag_i, (
        "back: lastPrev = st → closingViaBack = true → close → = false"
    )
    # The single writer sites (no second writer anywhere in the module).
    assert js.count("lastPrev = st;") == 1
    assert js.count("closingViaBack = true;") == 1
    assert handler.count("closingViaBack = false;") == 1


def test_popstate_passes_through_everything_else() -> None:
    """REGRESSION: a handler branch firing on entries that are not the
    modal's (the router's view entries, the drill's ``kb`` entries) or
    on a modal entry with the modal still open. The forward branch
    requires ``isModalEntry`` (and the modal hidden) and the back
    branch requires ``entry`` (falsy when the modal is closed) — and
    AFTER the back branch closes the handler does NOTHING (the tail is
    empty): every other popstate falls through untouched."""
    handler = _popstate_handler(_js())
    back_i = handler.find("if (!isModalEntry && modalEl && !modalEl.hidden && entry) {")
    assert back_i != -1, "the back branch (non-modal land + modal open + entry) is gone"
    brace_i = handler.find("{", back_i)
    back_block = _block(handler, back_i)
    tail = handler[brace_i + len(back_block) :]
    # The only thing after the back branch is the handler's own closing
    # brace — no code runs on any other popstate (the pass-through).
    assert tail.strip() in ("", "}"), (
        "no code after the back branch — the pass-through must be a no-op"
    )


# ---------- the no-leak guarantee: the closed set of history.* sites ----------


def test_history_call_sites_are_the_closed_set() -> None:
    """REGRESSION: a ``history.back()``/``history.go()`` introduction,
    or ANY untracked ``history.*`` call site. The browser owns its
    entries (the phase-99 D2 convention): the module's ONLY
    ``history.`` sites are the one ``pushState`` (the open), the two
    ``replaceState`` (the defensive re-open, the non-back close), and
    the read-only ``history.state`` accesses."""
    js = _js()
    sites = re.findall(r"history\.\w+", js)
    assert sorted(set(sites)) == [
        "history.pushState",
        "history.replaceState",
        "history.state",
    ], f"an untracked history.* site slipped in: {sorted(set(sites))}"
    assert sites.count("history.pushState") == 1
    assert sites.count("history.replaceState") == 2
    assert "history.back(" not in js, "the browser owns its entries — no history.back()"
    assert "history.go(" not in js, "the browser owns its entries — no history.go()"


# ---------- the pre-phase contract a regression could plausibly break ----------


def test_pre_phase_contract_pins_still_hold() -> None:
    """The phase-26 contracts the entry logic sits beside (a regression
    in the rework must not break them): the Escape capture closes via
    ``closeDocumentModal()``; the per-open keydown capture is added on
    open and removed on close (document-level, capture phase); the
    ``fetchSeq`` stale-guard lines survive (both checkpoints in the
    fetch chain + the close bump); the trigger-focus restore in the
    close (best-effort, contained in the DOM)."""
    js = _js()
    keydown = _fn(js, "onModalKeydown")
    esc_i = keydown.find('if (e.key === "Escape") {')
    prevent_i = keydown.find("e.preventDefault();", esc_i)
    close_i = keydown.find("closeDocumentModal();", prevent_i)
    assert -1 < esc_i < prevent_i < close_i, "Escape: prevent + closeDocumentModal()"
    open_body = _fn(js, "openDocumentModal")
    close_body = _fn(js, "closeDocumentModal")
    assert (
        'document.addEventListener("keydown", onModalKeydown, true);' in open_body
    ), "the per-open capture is added on open (document-level, capture)"
    assert (
        'document.removeEventListener("keydown", onModalKeydown, true);' in close_body
    ), "the per-open capture is removed on close"
    # The fetchSeq stale guard: the sequence, both checkpoints, the
    # catch checkpoint, and the close bump (any in-flight fetch is
    # stale after a close).
    assert open_body.count("const seq = ++fetchSeq;") == 1
    assert open_body.count("if (seq !== fetchSeq) return;") == 2, (
        "both render checkpoints (pre- and post-json) must stay stale-guarded"
    )
    assert "if (seq === fetchSeq) renderNotFound(path);" in open_body
    assert "fetchSeq += 1;" in close_body
    # The trigger-focus restore (best-effort: contained in the DOM).
    assert (
        "triggerEl && typeof triggerEl.focus === \"function\" && document.contains(triggerEl)"
        in close_body
    )
    assert "triggerEl.focus({ preventScroll: true });" in close_body
    assert "triggerEl = null;" in close_body