"""Session management for conversation history."""

import json
import os
import re
import shutil
from contextlib import suppress
from dataclasses import dataclass, field
from datetime import datetime
from pathlib import Path
from typing import Any

from loguru import logger

from nanobot.config.paths import get_legacy_sessions_dir
from nanobot.utils.helpers import (
    ensure_dir,
    estimate_message_tokens,
    find_legal_message_start,
    image_placeholder_text,
    safe_filename,
)

FILE_MAX_MESSAGES = 2000
_MESSAGE_TIME_PREFIX_RE = re.compile(r"^\[Message Time: [^\]]+\]\n?")
_LOCAL_IMAGE_BREADCRUMB_RE = re.compile(r"^\[image: (?:/|~)[^\]]+\]\s*$")
_TOOL_CALL_ECHO_RE = re.compile(r'^\s*(?:generate_image|message)\([^)]*\)\s*$')


def _sanitize_assistant_replay_text(content: str) -> str:
    """Remove internal replay artifacts that the model may have copied before.

    These strings are useful as runtime/session metadata, but when they appear
    in assistant examples they become demonstrations for the model to repeat.
    """
    content = _MESSAGE_TIME_PREFIX_RE.sub("", content, count=1)
    lines = [
        line
        for line in content.splitlines()
        if not _LOCAL_IMAGE_BREADCRUMB_RE.match(line)
        and not _TOOL_CALL_ECHO_RE.match(line)
    ]
    return "\n".join(lines).strip()


@dataclass
class Session:
    """A conversation session."""

    key: str  # channel:chat_id
    messages: list[dict[str, Any]] = field(default_factory=list)
    created_at: datetime = field(default_factory=datetime.now)
    updated_at: datetime = field(default_factory=datetime.now)
    metadata: dict[str, Any] = field(default_factory=dict)
    last_consolidated: int = 0  # Number of messages already consolidated to files

    @staticmethod
    def _annotate_message_time(message: dict[str, Any], content: Any) -> Any:
        """Expose persisted turn timestamps to the model for relative-date reasoning.

        Annotating *every* assistant turn trains the model (via in-context
        demonstrations) to start its own replies with the same
        ``[Message Time: ...]`` prefix, which leaks metadata back to the user.
        We therefore only annotate user turns. User-side stamps are enough to
        pin adjacent assistant replies for relative-time reasoning, including
        proactive messages the user replies to later.
        """
        timestamp = message.get("timestamp")
        if not timestamp or not isinstance(content, str):
            return content
        role = message.get("role")
        if role != "user":
            return content
        return f"[Message Time: {timestamp}]\n{content}"

    def add_message(self, role: str, content: str, **kwargs: Any) -> None:
        """Add a message to the session."""
        msg = {
            "role": role,
            "content": content,
            "timestamp": datetime.now().isoformat(),
            **kwargs
        }
        self.messages.append(msg)
        self.updated_at = datetime.now()

    def get_history(
        self,
        max_messages: int = 120,
        *,
        max_tokens: int = 0,
        include_timestamps: bool = False,
    ) -> list[dict[str, Any]]:
        """Return unconsolidated messages for LLM input.

        History is sliced by message count first (``max_messages``), then by
        token budget from the tail (``max_tokens``) when provided.
        """
        unconsolidated = self.messages[self.last_consolidated:]
        max_messages = max_messages if max_messages > 0 else 120
        sliced = unconsolidated[-max_messages:]

        # Avoid starting mid-turn when possible, except for proactive
        # assistant deliveries that the user may be replying to.
        for i, message in enumerate(sliced):
            if message.get("role") == "user":
                start = i
                if i > 0 and sliced[i - 1].get("_channel_delivery"):
                    start = i - 1
                sliced = sliced[start:]
                break

        # Drop orphan tool results at the front.
        start = find_legal_message_start(sliced)
        if start:
            sliced = sliced[start:]

        out: list[dict[str, Any]] = []
        for message in sliced:
            content = message.get("content", "")
            role = message.get("role")
            if role == "assistant" and isinstance(content, str):
                content = _sanitize_assistant_replay_text(content)
            # Synthesize an ``[image: path]`` breadcrumb from the persisted
            # ``media`` kwarg so LLM replay still sees *something* where the
            # image used to be. Without this, an image-only user turn
            # replays as an empty user message — the assistant's reply then
            # looks like it's responding to nothing.
            media = message.get("media")
            if role == "user" and isinstance(media, list) and media and isinstance(content, str):
                breadcrumbs = "\n".join(
                    image_placeholder_text(p) for p in media if isinstance(p, str) and p
                )
                content = f"{content}\n{breadcrumbs}" if content else breadcrumbs
            if include_timestamps:
                content = self._annotate_message_time(message, content)
            if role == "assistant" and isinstance(content, str) and not content.strip():
                if not any(key in message for key in ("tool_calls", "reasoning_content", "thinking_blocks")):
                    continue
            entry: dict[str, Any] = {"role": message["role"], "content": content}
            for key in ("tool_calls", "tool_call_id", "name", "reasoning_content", "thinking_blocks"):
                if key in message:
                    entry[key] = message[key]
            out.append(entry)

        if max_tokens > 0 and out:
            kept: list[dict[str, Any]] = []
            used = 0
            for message in reversed(out):
                tokens = estimate_message_tokens(message)
                if kept and used + tokens > max_tokens:
                    break
                kept.append(message)
                used += tokens
            kept.reverse()

            # Keep history aligned to the first visible user turn.
            first_user = next((i for i, m in enumerate(kept) if m.get("role") == "user"), None)
            if first_user is not None:
                kept = kept[first_user:]
            else:
                # Tight token budgets can otherwise leave assistant-only tails.
                # If a user turn exists in the unsliced output, recover the
                # nearest one even if it slightly exceeds the token budget.
                recovered_user = next(
                    (i for i in range(len(out) - 1, -1, -1) if out[i].get("role") == "user"),
                    None,
                )
                if recovered_user is not None:
                    kept = out[recovered_user:]

            # And keep a legal tool-call boundary at the front.
            start = find_legal_message_start(kept)
            if start:
                kept = kept[start:]
            out = kept
        return out

    def clear(self) -> None:
        """Clear all messages and reset session to initial state."""
        self.messages = []
        self.last_consolidated = 0
        self.updated_at = datetime.now()
        self.metadata.pop("_last_summary", None)

    def retain_recent_legal_suffix(self, max_messages: int) -> None:
        """Keep a legal recent suffix constrained by a hard message cap."""
        if max_messages <= 0:
            self.clear()
            return
        if len(self.messages) <= max_messages:
            return

        retained = list(self.messages[-max_messages:])

        # Prefer starting at a user turn when one exists within the tail.
        first_user = next((i for i, m in enumerate(retained) if m.get("role") == "user"), None)
        if first_user is not None:
            retained = retained[first_user:]
        else:
            # If the tail is assistant/tool-only, anchor to the latest user in
            # the full session and take a capped forward window from there.
            latest_user = next(
                (i for i in range(len(self.messages) - 1, -1, -1)
                 if self.messages[i].get("role") == "user"),
                None,
            )
            if latest_user is not None:
                retained = list(self.messages[latest_user: latest_user + max_messages])

        # Mirror get_history(): avoid persisting orphan tool results at the front.
        start = find_legal_message_start(retained)
        if start:
            retained = retained[start:]

        # Hard-cap guarantee: never keep more than max_messages.
        if len(retained) > max_messages:
            retained = retained[-max_messages:]
            start = find_legal_message_start(retained)
            if start:
                retained = retained[start:]

        dropped = len(self.messages) - len(retained)
        self.messages = retained
        self.last_consolidated = max(0, self.last_consolidated - dropped)
        self.updated_at = datetime.now()

    def enforce_file_cap(
        self,
        on_archive: Any = None,
        limit: int = FILE_MAX_MESSAGES,
    ) -> None:
        """Bound session message growth by archiving and trimming old prefixes."""
        if limit <= 0 or len(self.messages) <= limit:
            return

        before = list(self.messages)
        before_last_consolidated = self.last_consolidated
        before_count = len(before)
        self.retain_recent_legal_suffix(limit)
        dropped_count = before_count - len(self.messages)
        if dropped_count <= 0:
            return

        dropped = before[:dropped_count]
        already_consolidated = min(before_last_consolidated, dropped_count)
        archive_chunk = dropped[already_consolidated:]
        if archive_chunk and on_archive:
            on_archive(archive_chunk)
        logger.info(
            "Session file cap hit for {}: dropped {}, raw-archived {}, kept {}",
            self.key,
            dropped_count,
            len(archive_chunk),
            len(self.messages),
        )


class SessionManager:
    """
    Manages conversation sessions.

    Sessions are stored as JSONL files in the sessions directory.
    """

    def __init__(self, workspace: Path):
        self.workspace = workspace
        self.sessions_dir = ensure_dir(self.workspace / "sessions")
        self.legacy_sessions_dir = get_legacy_sessions_dir()
        self._cache: dict[str, Session] = {}

    @staticmethod
    def safe_key(key: str) -> str:
        """Public helper used by HTTP handlers to map an arbitrary key to a stable filename stem."""
        return safe_filename(key.replace(":", "_"))

    def _get_session_path(self, key: str) -> Path:
        """Get the file path for a session."""
        return self.sessions_dir / f"{self.safe_key(key)}.jsonl"

    def _get_legacy_session_path(self, key: str) -> Path:
        """Legacy global session path (~/.nanobot/sessions/)."""
        return self.legacy_sessions_dir / f"{self.safe_key(key)}.jsonl"

    def get_or_create(self, key: str) -> Session:
        """
        Get an existing session or create a new one.

        Args:
            key: Session key (usually channel:chat_id).

        Returns:
            The session.
        """
        if key in self._cache:
            return self._cache[key]

        session = self._load(key)
        if session is None:
            session = Session(key=key)

        self._cache[key] = session
        return session

    def _load(self, key: str) -> Session | None:
        """Load a session from disk."""
        path = self._get_session_path(key)
        if not path.exists():
            legacy_path = self._get_legacy_session_path(key)
            if legacy_path.exists():
                try:
                    shutil.move(str(legacy_path), str(path))
                    logger.info("Migrated session {} from legacy path", key)
                except Exception:
                    logger.exception("Failed to migrate session {}", key)

        if not path.exists():
            return None

        try:
            messages = []
            metadata = {}
            created_at = None
            updated_at = None
            last_consolidated = 0

            with open(path, encoding="utf-8") as f:
                for line in f:
                    line = line.strip()
                    if not line:
                        continue

                    data = json.loads(line)

                    if data.get("_type") == "metadata":
                        metadata = data.get("metadata", {})
                        created_at = datetime.fromisoformat(data["created_at"]) if data.get("created_at") else None
                        updated_at = datetime.fromisoformat(data["updated_at"]) if data.get("updated_at") else None
                        last_consolidated = data.get("last_consolidated", 0)
                    else:
                        messages.append(data)

            return Session(
                key=key,
                messages=messages,
                created_at=created_at or datetime.now(),
                updated_at=updated_at or datetime.now(),
                metadata=metadata,
                last_consolidated=last_consolidated
            )
        except Exception as e:
            logger.warning("Failed to load session {}: {}", key, e)
            repaired = self._repair(key)
            if repaired is not None:
                logger.info("Recovered session {} from corrupt file ({} messages)", key, len(repaired.messages))
            return repaired

    def _repair(self, key: str) -> Session | None:
        """Attempt to recover a session from a corrupt JSONL file."""
        path = self._get_session_path(key)
        if not path.exists():
            return None

        try:
            messages: list[dict[str, Any]] = []
            metadata: dict[str, Any] = {}
            created_at: datetime | None = None
            updated_at: datetime | None = None
            last_consolidated = 0
            skipped = 0

            with open(path, encoding="utf-8") as f:
                for line in f:
                    line = line.strip()
                    if not line:
                        continue
                    try:
                        data = json.loads(line)
                    except json.JSONDecodeError:
                        skipped += 1
                        continue

                    if data.get("_type") == "metadata":
                        metadata = data.get("metadata", {})
                        if data.get("created_at"):
                            with suppress(ValueError, TypeError):
                                created_at = datetime.fromisoformat(data["created_at"])
                        if data.get("updated_at"):
                            with suppress(ValueError, TypeError):
                                updated_at = datetime.fromisoformat(data["updated_at"])
                        last_consolidated = data.get("last_consolidated", 0)
                    else:
                        messages.append(data)

            if skipped:
                logger.warning("Skipped {} corrupt lines in session {}", skipped, key)

            if not messages and not metadata:
                return None

            return Session(
                key=key,
                messages=messages,
                created_at=created_at or datetime.now(),
                updated_at=updated_at or datetime.now(),
                metadata=metadata,
                last_consolidated=last_consolidated
            )
        except Exception as e:
            logger.warning("Repair failed for session {}: {}", key, e)
            return None

    @staticmethod
    def _session_payload(session: Session) -> dict[str, Any]:
        return {
            "key": session.key,
            "created_at": session.created_at.isoformat(),
            "updated_at": session.updated_at.isoformat(),
            "metadata": session.metadata,
            "messages": session.messages,
        }

    def save(self, session: Session, *, fsync: bool = False) -> None:
        """Save a session to disk atomically.

        When *fsync* is ``True`` the final file and its parent directory are
        explicitly flushed to durable storage.  This is intentionally off by
        default (the OS page-cache is sufficient for normal operation) but
        should be enabled during graceful shutdown so that filesystems with
        write-back caching (e.g. rclone VFS, NFS, FUSE mounts) do not lose
        the most recent writes.
        """
        path = self._get_session_path(session.key)
        tmp_path = path.with_suffix(".jsonl.tmp")

        try:
            with open(tmp_path, "w", encoding="utf-8") as f:
                metadata_line = {
                    "_type": "metadata",
                    "key": session.key,
                    "created_at": session.created_at.isoformat(),
                    "updated_at": session.updated_at.isoformat(),
                    "metadata": session.metadata,
                    "last_consolidated": session.last_consolidated
                }
                f.write(json.dumps(metadata_line, ensure_ascii=False) + "\n")
                for msg in session.messages:
                    f.write(json.dumps(msg, ensure_ascii=False) + "\n")
                if fsync:
                    f.flush()
                    os.fsync(f.fileno())

            os.replace(tmp_path, path)

            if fsync:
                # fsync the directory so the rename is durable.
                # On Windows, opening a directory with O_RDONLY raises
                # PermissionError — skip the dir sync there (NTFS
                # journals metadata synchronously).
                with suppress(PermissionError):
                    fd = os.open(str(path.parent), os.O_RDONLY)
                    try:
                        os.fsync(fd)
                    finally:
                        os.close(fd)
        except BaseException:
            tmp_path.unlink(missing_ok=True)
            raise

        self._cache[session.key] = session

    def flush_all(self) -> int:
        """Re-save every cached session with fsync for durable shutdown.

        Returns the number of sessions flushed.  Errors on individual
        sessions are logged but do not prevent other sessions from being
        flushed.
        """
        flushed = 0
        for key, session in list(self._cache.items()):
            try:
                self.save(session, fsync=True)
                flushed += 1
            except Exception:
                logger.warning("Failed to flush session {}", key, exc_info=True)
        return flushed

    def invalidate(self, key: str) -> None:
        """Remove a session from the in-memory cache."""
        self._cache.pop(key, None)

    def delete_session(self, key: str) -> bool:
        """Remove a session from disk and the in-memory cache.

        Returns True if a JSONL file was found and unlinked.
        """
        path = self._get_session_path(key)
        self.invalidate(key)
        if not path.exists():
            return False
        try:
            path.unlink()
            return True
        except OSError as e:
            logger.warning("Failed to delete session file {}: {}", path, e)
            return False

    def read_session_file(self, key: str) -> dict[str, Any] | None:
        """Load a session from disk without caching; intended for read-only HTTP endpoints.

        Returns ``{"key", "created_at", "updated_at", "metadata", "messages"}`` or
        ``None`` when the session file does not exist or fails to parse.
        """
        path = self._get_session_path(key)
        if not path.exists():
            return None
        try:
            messages: list[dict[str, Any]] = []
            metadata: dict[str, Any] = {}
            created_at: str | None = None
            updated_at: str | None = None
            stored_key: str | None = None
            with open(path, encoding="utf-8") as f:
                for line in f:
                    line = line.strip()
                    if not line:
                        continue
                    data = json.loads(line)
                    if data.get("_type") == "metadata":
                        metadata = data.get("metadata", {})
                        created_at = data.get("created_at")
                        updated_at = data.get("updated_at")
                        stored_key = data.get("key")
                    else:
                        messages.append(data)
            return {
                "key": stored_key or key,
                "created_at": created_at,
                "updated_at": updated_at,
                "metadata": metadata,
                "messages": messages,
            }
        except Exception as e:
            logger.warning("Failed to read session {}: {}", key, e)
            repaired = self._repair(key)
            if repaired is not None:
                logger.info("Recovered read-only session view {} from corrupt file", key)
                return self._session_payload(repaired)
            return None

    def list_sessions(self) -> list[dict[str, Any]]:
        """
        List all sessions.

        Returns:
            List of session info dicts.
        """
        sessions = []

        for path in self.sessions_dir.glob("*.jsonl"):
            fallback_key = path.stem.replace("_", ":", 1)
            try:
                # Read just the metadata line
                with open(path, encoding="utf-8") as f:
                    first_line = f.readline().strip()
                    if first_line:
                        data = json.loads(first_line)
                        if data.get("_type") == "metadata":
                            key = data.get("key") or path.stem.replace("_", ":", 1)
                            metadata = data.get("metadata", {})
                            title = metadata.get("title") if isinstance(metadata, dict) else None
                            sessions.append({
                                "key": key,
                                "created_at": data.get("created_at"),
                                "updated_at": data.get("updated_at"),
                                "title": title if isinstance(title, str) else "",
                                "path": str(path)
                            })
            except Exception:
                repaired = self._repair(fallback_key)
                if repaired is not None:
                    sessions.append({
                        "key": repaired.key,
                        "created_at": repaired.created_at.isoformat(),
                        "updated_at": repaired.updated_at.isoformat(),
                        "title": (
                            repaired.metadata.get("title")
                            if isinstance(repaired.metadata.get("title"), str)
                            else ""
                        ),
                        "path": str(path)
                    })
                continue

        return sorted(sessions, key=lambda x: x.get("updated_at", ""), reverse=True)
