"""Session-mutation operations for slash commands (/retry, /undo) and
read-only aggregators (/status, /usage). Operates on the webui's own
JSON Session store (api/models.py), not on hermes-agent's SQLite.

Behavior parity reference: gateway/run.py:_handle_*_command in
the hermes-agent repo.
"""
from __future__ import annotations
import json
import logging
from typing import Any

from api.config import LOCK, _get_session_agent_lock
from api.models import get_session, SESSIONS

logger = logging.getLogger(__name__)

AUTO_TITLE_LABELS = {'untitled', 'new chat'}


def _live_active_stream_id(session) -> str | None:
    """Return session.active_stream_id ONLY if that stream is live in THIS
    process; else None.

    After a restart/crash the persisted active_stream_id survives in the
    session JSON but the in-memory STREAMS / ACTIVE_RUNS that actually drive a
    live turn were wiped. Exposing that dead id (e.g. via /api/session/status to
    the hidden-tab poller) would make a client attach its renderer to a stream
    that never emits — a permanent fake "thinking" state. Liveness test mirrors
    routes._clear_stale_stream_state: live iff present in STREAMS (open SSE
    channel) or ACTIVE_RUNS (worker bookkeeping).
    """
    stream_id = getattr(session, 'active_stream_id', None)
    if not stream_id:
        return None
    try:
        from api import config as _cfg
        with _cfg.STREAMS_LOCK:
            if stream_id in _cfg.STREAMS:
                return stream_id
        with _cfg.ACTIVE_RUNS_LOCK:
            if stream_id in (_cfg.ACTIVE_RUNS or {}):
                return stream_id
    except Exception:
        # On any introspection failure, fail SAFE (report no live stream) rather
        # than surfacing a possibly-stale id.
        return None
    return None


def session_has_manual_title(session) -> bool:
    """Return whether adaptive title refresh should leave this title alone."""
    return getattr(session, 'manual_title', False) is True


def apply_session_title_rename(session, raw_title) -> str:
    """Apply user-driven rename semantics to a Session object.

    Non-empty custom titles are protected from adaptive refresh. Clearing the
    title, or resetting it to an automatic label, removes that protection so the
    normal auto-title path can run again.
    """
    title = str(raw_title or '').strip()[:80]
    if not title:
        title = 'Untitled'
    manual_title = title.strip().casefold() not in AUTO_TITLE_LABELS
    session.title = title
    session.manual_title = manual_title
    session.llm_title_generated = False
    return title


def mark_session_title_generated(session) -> None:
    """Mark a session title as generated by the title model."""
    session.llm_title_generated = True
    session.manual_title = False


def _truncate_at_last_user(messages):
    history = messages or []
    last_user_idx = None
    for i in range(len(history) - 1, -1, -1):
        if isinstance(history[i], dict) and history[i].get('role') == 'user':
            last_user_idx = i
            break
    if last_user_idx is None:
        return None
    return history[:last_user_idx]


def _truncation_watermark_for(messages):
    history = list(messages or [])
    if not history:
        return 0.0
    try:
        return float(history[-1].get('timestamp') or 0)
    except (AttributeError, TypeError, ValueError):
        return 0.0


def truncate_context_for_display_keep(
    context_messages: list | None,
    full_messages: list | None,
    keep: int,
) -> list:
    """Align model context with display prefix ``full_messages[:keep]``."""
    if keep <= 0:
        return []
    ctx = context_messages if isinstance(context_messages, list) else []
    msgs = full_messages if isinstance(full_messages, list) else []
    if not ctx:
        return []
    if len(ctx) <= len(msgs):
        return ctx[:keep]
    if len(msgs) == 0:
        return []

    def _row_signature(row: Any) -> tuple[str, ...] | None:
        if not isinstance(row, dict):
            return None
        tool_calls = row.get('tool_calls')
        tool_calls_sig = json.dumps(tool_calls, sort_keys=True, default=str) if tool_calls else ''
        return (
            str(row.get('role') or ''),
            str(row.get('content') or ''),
            str(row.get('tool_call_id') or ''),
            str(row.get('tool_use_id') or ''),
            str(row.get('tool_name') or row.get('name') or ''),
            tool_calls_sig,
        )

    def _first_match_from(message: Any, start_idx: int) -> tuple[int | None, int | None]:
        msg_sig = _row_signature(message)
        if msg_sig is None:
            return None, None
        msg_id = message.get('id')
        msg_ts = message.get('timestamp')
        weak_matches: list[int] = []
        for idx in range(start_idx, len(ctx)):
            context_row = ctx[idx]
            context_sig = _row_signature(context_row)
            if context_sig is None:
                continue

            context_id = context_row.get('id')
            if context_id is not None and msg_id is not None:
                if context_id == msg_id:
                    return idx, None
                continue

            if context_sig != msg_sig:
                continue

            context_ts = context_row.get('timestamp')
            if context_ts is not None and msg_ts is not None:
                if context_ts == msg_ts:
                    return idx, None
                continue

            weak_matches.append(idx)
            if len(weak_matches) > 1:
                return None, weak_matches[0]
        return (weak_matches[0], None) if len(weak_matches) == 1 else (None, None)

    matches = [None] * len(msgs)
    ambiguous_matches = [None] * len(msgs)
    next_ctx_idx = 0
    for msg_idx, message in enumerate(msgs):
        match_idx, ambiguous_idx = _first_match_from(message, next_ctx_idx)
        matches[msg_idx] = match_idx
        ambiguous_matches[msg_idx] = ambiguous_idx
        if match_idx is not None:
            next_ctx_idx = match_idx + 1

    # Cut at the first unkept display turn, or fallback to the last kept turn
    # if the boundary is not directly alignable.
    if keep < len(msgs):
        last_kept = None
        if keep > 0:
            last_kept = matches[keep - 1]
        first_unkept = matches[keep]
        if first_unkept is not None:
            if (
                last_kept is not None
                and isinstance(msgs[keep - 1], dict)
                and msgs[keep - 1].get('role') == 'user'
            ):
                return ctx[:last_kept + 1]
            return ctx[:first_unkept]
        if last_kept is not None:
            ambiguous_first_unkept = ambiguous_matches[keep]
            if (
                ambiguous_first_unkept is not None
                and isinstance(msgs[keep - 1], dict)
                and msgs[keep - 1].get('role') != 'user'
            ):
                return ctx[:ambiguous_first_unkept]
            return ctx[:last_kept + 1]

    # Final fallback preserves #5096 behavior when alignment is unreliable.
    prefix_len = max(0, len(ctx) - len(msgs))
    prefix = ctx[:prefix_len]
    suffix = ctx[prefix_len:]
    return prefix + suffix[:keep]


def truncate_session_at_keep(session, keep: int) -> tuple[int, int]:
    """Truncate display + context; set watermark/boundary. Returns old counts."""
    full_messages = list(session.messages or [])
    old_msg_count = len(full_messages)
    old_ctx_count = len(getattr(session, 'context_messages', None) or [])
    session.messages = full_messages[:keep]
    if isinstance(getattr(session, 'context_messages', None), list):
        session.context_messages = truncate_context_for_display_keep(
            session.context_messages,
            full_messages,
            keep,
        )
    session.truncation_watermark = _truncation_watermark_for(session.messages)
    session.truncation_boundary = session.truncation_watermark
    return old_msg_count, old_ctx_count


def retry_last(session_id: str) -> dict[str, Any]:
    """Truncate the session to before the last user message, return its text.

    Mirrors gateway/run.py:_handle_retry_command. Caller (webui frontend)
    is expected to put the returned text back in the composer and call
    send() to resume the conversation -- the agent's gateway calls its own
    _handle_message; the webui has no equivalent in-process pipeline.

    Raises:
        KeyError: session not found
        ValueError: no user message in transcript
    """
    # Acquire the per-session agent lock as the outermost lock so that the
    # read-modify-write of s.messages is serialised with the periodic
    # checkpoint thread, cancel_stream, and all other session writers.
    # Lock ordering: _agent_lock → LOCK → _write_session_index (LOCK).
    with _get_session_agent_lock(session_id):
        # get_session() and Session.save() both acquire the module-level LOCK
        # internally (the latter via _write_session_index()), and LOCK is a
        # non-reentrant threading.Lock — so they MUST be called outside our
        # own `with LOCK:` block to avoid self-deadlocking.
        #
        # The race we close is the read-modify-write of s.messages: two
        # concurrent /api/session/retry calls could otherwise both compute the
        # same last_user_idx from the same history and double-truncate. We
        # serialize just the in-memory mutation; persistence happens inside
        # the per-session lock so the checkpoint thread cannot race us.
        #
        # Stale-object guard: on a cache miss, two concurrent get_session()
        # calls can each load and cache a *different* Session instance for the
        # same session_id (the second store clobbers the first). Re-bind to
        # the canonical cached instance inside the lock so the mutation lands
        # on the object the next reader will see, not a stale parallel copy.
        s = get_session(session_id)  # raises KeyError if missing
        with LOCK:
            s = SESSIONS.get(session_id, s)
            history = s.messages or []
            last_user_idx = None
            for i in range(len(history) - 1, -1, -1):
                if history[i].get('role') == 'user':
                    last_user_idx = i
                    break
            if last_user_idx is None:
                raise ValueError('No previous message to retry.')

            last_user_text = _extract_text(history[last_user_idx].get('content', ''))
            removed_count = len(history) - last_user_idx
            s.messages = history[:last_user_idx]
            s.truncation_watermark = _truncation_watermark_for(s.messages)
            # Persist the original truncate cutoff so empty-sidecar recovery
            # can distinguish legitimate prefix from deleted suffix.
            s.truncation_boundary = s.truncation_watermark
            if isinstance(getattr(s, 'context_messages', None), list) and s.context_messages:
                truncated_context = _truncate_at_last_user(s.context_messages)
                if truncated_context is not None:
                    s.context_messages = truncated_context
        s.save()
    return {'last_user_text': last_user_text, 'removed_count': removed_count}


def undo_last(session_id: str) -> dict[str, Any]:
    """Remove the most recent user message and everything after it.

    Mirrors gateway/run.py:_handle_undo_command. Returns a preview of the
    removed text so the UI can confirm to the user.

    Raises:
        KeyError: session not found
        ValueError: no user message in transcript
    """
    # Acquire the per-session agent lock as the outermost lock so that the
    # read-modify-write of s.messages is serialised with the periodic
    # checkpoint thread, cancel_stream, and all other session writers.
    # Lock ordering: _agent_lock → LOCK → _write_session_index (LOCK).
    with _get_session_agent_lock(session_id):
        s = get_session(session_id)  # acquires LOCK transiently
        with LOCK:
            # Stale-object guard — see retry_last for the rationale.
            s = SESSIONS.get(session_id, s)
            history = s.messages or []
            last_user_idx = None
            for i in range(len(history) - 1, -1, -1):
                if history[i].get('role') == 'user':
                    last_user_idx = i
                    break
            if last_user_idx is None:
                raise ValueError('Nothing to undo.')

            removed_text = _extract_text(history[last_user_idx].get('content', ''))
            removed_count = len(history) - last_user_idx
            s.messages = history[:last_user_idx]
            s.truncation_watermark = _truncation_watermark_for(s.messages)
            # Persist the original truncate cutoff.
            s.truncation_boundary = s.truncation_watermark
            if isinstance(getattr(s, 'context_messages', None), list) and s.context_messages:
                truncated_context = _truncate_at_last_user(s.context_messages)
                if truncated_context is not None:
                    s.context_messages = truncated_context
        s.save()  # outside LOCK -- save() re-acquires LOCK via _write_session_index()
    preview = (removed_text[:40] + '...') if len(removed_text) > 40 else removed_text
    return {
        'removed_count': removed_count,
        'removed_preview': preview,
    }


def session_status(session_id: str) -> dict[str, Any]:
    """Return a snapshot of session state for /status.

    Webui equivalent of gateway/run.py:_handle_status_command. The agent's
    "agent_running" comes from `session_key in self._running_agents`; the
    webui equivalent is whether the session has an active stream
    (active_stream_id is set).
    """
    s = get_session(session_id)
    inp = int(s.input_tokens or 0)
    out = int(s.output_tokens or 0)
    profile = getattr(s, 'profile', None) or 'default'
    try:
        from api.profiles import get_hermes_home_for_profile
        hermes_home = str(get_hermes_home_for_profile(profile))
    except Exception:
        hermes_home = ''
    return {
        'session_id': s.session_id,
        'title': s.title,
        'model': s.model,
        'profile': profile,
        'hermes_home': hermes_home,
        'workspace': s.workspace,
        'personality': s.personality,
        'message_count': len(s.messages or []),
        'created_at': s.created_at,
        'updated_at': s.updated_at,
        'agent_running': bool(getattr(s, 'active_stream_id', None)),
        # Expose the stream id itself (not just the agent_running bool) so a
        # hidden-tab poller can attach the live renderer to a server-initiated
        # turn (self-wake / cron / restart hook) without opening the persistent
        # per-session SSE while the tab is hidden. See messages.js hidden-tab
        # active-stream poll. Additive field — existing consumers ignore it.
        #
        # CRITICAL: only expose a stream id that is actually LIVE in this
        # process. After a restart/crash the persisted active_stream_id is stale
        # (the in-memory STREAMS/ACTIVE_RUNS were wiped) — handing that dead id
        # to the poller would make it attach a renderer to a stream that never
        # produces tokens (a permanent fake "thinking" state). Mirror
        # _clear_stale_stream_state's liveness test: a stream counts as live
        # only if it's in STREAMS (SSE channel open) or ACTIVE_RUNS (worker
        # bookkeeping). Otherwise report None so the poller waits for a REAL
        # server_turn_started instead of latching a ghost.
        'active_stream_id': _live_active_stream_id(s),
        'input_tokens': inp,
        'output_tokens': out,
        'total_tokens': inp + out,
        'estimated_cost': s.estimated_cost,
    }


def session_usage(session_id: str) -> dict[str, Any]:
    """Return token usage and cost for /usage.

    Mirrors gateway/run.py:_handle_usage_command's basic counters. The
    agent shows additional fields (rate-limit headroom etc.) that depend
    on provider API responses we don't have in webui -- those are deferred.
    """
    s = get_session(session_id)
    inp = int(s.input_tokens or 0)
    out = int(s.output_tokens or 0)
    return {
        'input_tokens': inp,
        'output_tokens': out,
        'total_tokens': inp + out,
        'estimated_cost': s.estimated_cost,
        'model': s.model,
    }


def _extract_text(content: Any) -> str:
    """Flatten message content to plain text. Agent stores either a string
    or a list of {type, text|...} parts; webui needs the user-typed text."""
    if isinstance(content, str):
        return content
    if isinstance(content, list):
        parts = []
        for p in content:
            if isinstance(p, dict) and p.get('type') == 'text':
                parts.append(p.get('text', ''))
        return ' '.join(parts)
    return str(content)