"""Chat orchestration: building requests, streaming replies, naming chats."""

from __future__ import annotations

import logging
from datetime import UTC, datetime, timedelta
from typing import Any

from sqlalchemy import func, select
from sqlalchemy.orm import Session as DBSession

from lembas.db.models import (
    KIND_MESSAGES,
    ROLE_ASSISTANT,
    ROLE_SYSTEM,
    ROLE_USER,
    Chat,
    Connection,
    Message,
    Model,
)
from lembas.services import files as files_service
from lembas.services.llm.openai_client import Endpoint, LLMError, complete

log = logging.getLogger(__name__)

# Sampling keys forwarded upstream. Anything else a user puts in params_json is
# ignored rather than passed through, so a typo cannot produce a 400 from the
# provider that looks like a LLeMbas bug.
FORWARDED_PARAMS = frozenset(
    {"temperature", "top_p", "max_tokens", "presence_penalty", "frequency_penalty",
     "seed", "stop"}
)

MAX_TITLE_LENGTH = 60

# What one title call may spend. A title is a handful of words; the rest of this
# is headroom for a model that thinks before it answers, which is most of the
# interesting local ones. Too small is not a shorter title -- it is no title at
# all, because the thinking consumes the budget and the content field comes back
# empty or holding an unclosed `<think>`.
TITLE_MAX_TOKENS = 512

# How long a temporary chat survives after the last thing said in it.
TEMPORARY_LIFETIME = timedelta(hours=24)


def resolve_endpoint(db: DBSession, chat: Chat) -> tuple[Endpoint, str]:
    """Find the connection and model a chat should use.

    Chats store the model id as text rather than a foreign key so history
    survives an admin deleting a connection, which means the mapping back to a
    live connection has to be resolved at send time and can legitimately fail.
    """
    if not chat.model_id:
        raise LLMError("This chat has no model selected.")

    connection: Connection | None = None
    if chat.connection_id:
        connection = db.get(Connection, chat.connection_id)

    if connection is None or not connection.enabled:
        # The original connection is gone or disabled. Any enabled connection
        # still offering this model id will do.
        model = db.scalar(
            select(Model)
            .join(Connection)
            .where(
                Model.model_id == chat.model_id,
                Model.enabled.is_(True),
                Connection.enabled.is_(True),
            )
            .order_by(Connection.position)
        )
        if model is None:
            raise LLMError(
                f"No enabled connection currently offers the model "
                f"'{chat.model_id}'. Pick another model for this chat."
            )
        connection = model.connection
        chat.connection_id = connection.id
        db.commit()

    return Endpoint.from_connection(connection), chat.model_id


def document_context(message: Message) -> str:
    """Extracted text from a message's non-image attachments.

    Wrapped in named tags so the model can tell one document from another, and
    tell all of them from what the user actually typed. Truncation is stated
    inline rather than silently, so a model asked about page 400 of a 300-page
    extract can say it did not see it.
    """
    blocks: list[str] = []
    for attachment in message.documents:
        if not attachment.extracted_text.strip():
            continue
        note = " (truncated)" if attachment.truncated else ""
        # Where it came from, when there is a where. A model handed `main.py`
        # cannot tell which of four it is looking at, and cannot name the file
        # back when asked to change something -- so a file read off a machine
        # says which machine and which path. Quotes are stripped rather than
        # escaped: these are attribute values in a tag the model reads, and a
        # path containing one would otherwise close it early.
        where = ""
        if attachment.source_path:
            where += f' path="{_attr(attachment.source_path)}"'
        if attachment.source_label:
            where += f' from="{_attr(attachment.source_label)}"'
        blocks.append(
            f'<document name="{_attr(attachment.filename)}"{where}{note}>\n'
            f"{attachment.extracted_text.strip()}\n"
            f"</document>"
        )
    return "\n\n".join(blocks)


def _attr(value: str) -> str:
    """A value safe to sit inside the double quotes of a tag we are writing."""
    return value.replace('"', "").replace("<", "").replace(">", "").replace("\n", " ")


def message_payload(message: Message, *, vision: bool) -> dict[str, Any]:
    """One history entry in the shape the endpoint expects.

    Plain text stays a plain string: sending the multimodal list form to an
    endpoint that does not implement it is a reliable way to get a 400, and
    most local runners do not.
    """
    text = message.content.strip()

    documents = document_context(message)
    if documents:
        # Documents lead so the question that follows has its material already
        # in view, which is how these models are trained to read a prompt.
        text = f"{documents}\n\n{text}" if text else documents

    # Images ride on a *user* turn and nowhere else. Until image generation
    # existed no assistant message had ever carried one, so this was never a
    # distinction worth drawing -- and the moment one does, the multimodal list
    # form on an `assistant` turn is rejected outright by OpenAI and by most
    # local runners, which would break not that turn but every later one in the
    # chat. What follows from it, and is worth knowing rather than discovering:
    # a model cannot see the picture it made on a *subsequent* turn (tool
    # results are not replayed either), so "make it bluer" regenerates rather
    # than edits. Honest for a text-to-image workflow with no img2img path.
    images = message.images if (vision and message.role == ROLE_USER) else []
    if not images:
        return {"role": message.role, "content": text}

    parts: list[dict[str, Any]] = []
    if text:
        parts.append({"type": "text", "text": text})
    for attachment in images:
        uri = files_service.data_uri(attachment)
        if uri is None:
            # The row survived but the file did not. Better to say so than to
            # send a turn that silently lost its picture.
            log.warning("attachment %s has no file on disk", attachment.id)
            continue
        parts.append({"type": "image_url", "image_url": {"url": uri}})

    if not parts:
        return {"role": message.role, "content": text}
    return {"role": message.role, "content": parts}


def folder_system_prompt(db: DBSession, chat: Chat) -> str:
    """The nearest prompt on the chat's folder, or on a folder above it.

    Walks up rather than reading one level, because folders nest and a project's
    prompt belongs on the project rather than on each sub-folder of it. The
    nearest one wins, which is the same rule the ladder as a whole follows.

    Bounded and cycle-safe the way `api/folders.py:_depth_of` is. Reparenting
    already refuses to build a cycle, but this runs on the request path for
    every reply and a row written by something else must not be able to hang it.
    """
    from lembas.db.models import Folder

    folder = chat.folder
    seen: set[str] = set()
    while folder is not None and folder.id not in seen:
        seen.add(folder.id)
        if (folder.system_prompt or "").strip():
            return folder.system_prompt.strip()
        folder = db.get(Folder, folder.parent_id) if folder.parent_id else None
    return ""


def effective_system_prompt(db: DBSession, chat: Chat) -> str:
    """The system prompt a chat actually runs with.

    Four layers, most specific wins outright:

        chat  >  folder  >  model  >  instance

    Precedence rather than concatenation. Stacking them reads well in a
    settings screen and badly in practice: the moment two layers disagree the
    model gets contradictory instructions and nobody can tell which one is
    losing. With precedence, "why is it behaving like this" has one answer.

    The folder sits above the model because it is the more specific statement:
    a model's prompt describes the model wherever it is used, and a folder's
    describes this piece of work whichever model is pointed at it.
    """
    from lembas.services import settings_store

    if chat.system_prompt.strip():
        return chat.system_prompt.strip()

    if inherited := folder_system_prompt(db, chat):
        return inherited

    model = db.scalar(
        select(Model).where(Model.model_id == chat.model_id).order_by(Model.position)
    )
    if model is not None and (model.system_prompt or "").strip():
        return model.system_prompt.strip()

    return (settings_store.get(db, "system_prompt") or "").strip()


def build_messages(
    db: DBSession,
    chat: Chat,
    *,
    upto: Message | None = None,
    vision: bool = False,
    system_prompt: str | None = None,
) -> list[dict]:
    """Assemble the message list to send upstream.

    `upto` excludes the placeholder assistant row being generated into, and
    everything after it. `system_prompt` overrides what would otherwise be
    resolved, which is how the harness gets in front of the authored prompt
    without this function knowing anything about tools.
    """
    from lembas.services import compaction as compaction_service
    from lembas.services import prompts as prompts_service

    payload: list[dict[str, Any]] = []
    system = effective_system_prompt(db, chat) if system_prompt is None else system_prompt
    if system:
        payload.append({"role": ROLE_SYSTEM, "content": system})

    # Compacted turns are replaced by a summary carried in two turns rather than
    # one. A leading `assistant` breaks templates that require the first
    # non-system message to be `user`; a lone leading `user` produces user, user
    # whenever the kept history starts on a user turn -- which it always does,
    # because the cutoff lands on a finished reply. The pair alternates
    # correctly in both directions and keeps exactly one system message.
    cutoff = compaction_service.cutoff_message(db, chat)
    if cutoff is not None:
        lead = prompts_service.resolve(db, "task.compact_lead").strip()
        ack = prompts_service.resolve(db, "task.compact_ack").strip()
        summary = chat.compact_summary.strip()
        payload.append(
            {"role": ROLE_USER, "content": f"{lead}\n\n{summary}" if lead else summary}
        )
        if ack:
            payload.append({"role": ROLE_ASSISTANT, "content": ack})

    history = db.scalars(
        select(Message).where(Message.chat_id == chat.id).order_by(Message.created_at)
    ).all()

    # The Messages conversation never ends, so it cannot all be sent. Only the
    # most recent turns go; everything before them stays on screen and out of
    # the request. One branch, and the bound is applied before the loop rather
    # than inside it so the filters below still see a contiguous tail.
    #
    # Not compaction: that summarises with a model call and a threshold, on a
    # conversation somebody decided to shorten. This is mechanical, lossless and
    # permanent, which is why `compaction.should_compact` refuses this kind --
    # two mechanisms fighting over one transcript is how you get a summary of a
    # summary.
    if chat.kind == KIND_MESSAGES:
        from lembas.services import messages as messages_service

        history = history[-messages_service.LIVE_CHUNK :]

    for message in history:
        if upto is not None and message.id == upto.id:
            break
        if cutoff is not None and compaction_service.moment(
            message
        ) <= compaction_service.moment(cutoff):
            continue
        # Typed while the previous reply was still being written, and not yet
        # handed to a model. It is in the transcript and it is not in the
        # request; delivery is what moves it from one to the other.
        if message.queued:
            continue
        # Skip turns that failed or produced nothing -- but a message carrying
        # only an attachment has no text and must still be sent.
        if message.error:
            continue
        if not message.content.strip() and not message.attachments:
            continue
        payload.append(message_payload(message, vision=vision))

    return payload


def model_for(db: DBSession, chat: Chat) -> Model | None:
    """The Model row a chat is using, or None if it has gone.

    Looked up by id rather than held as a foreign key, for the same reason
    resolve_endpoint does: chats store the model as text so history survives an
    administrator deleting a connection.
    """
    return db.scalar(
        select(Model).where(Model.model_id == chat.model_id).order_by(Model.position)
    )


def model_supports(db: DBSession, chat: Chat, capability: str) -> bool:
    """Whether the chat's current model is marked as having a capability."""
    model = model_for(db, chat)
    return bool(model and (model.capabilities_json or {}).get(capability))


def build_request(
    db: DBSession,
    chat: Chat,
    *,
    upto: Message | None = None,
    tools: list[dict[str, Any]] | None = None,
    user=None,
    force_tool: str = "",
) -> dict[str, Any]:
    """The whole request body, tools and harness included.

    Composed here rather than in the generation loop so that "what gets sent"
    has one answer, and so the harness cannot be forgotten by a future caller
    that offers tools.
    """
    from lembas.services import harness as harness_service
    from lembas.services import prompts as prompts_service

    params = {
        key: value
        for key, value in (chat.params_json or {}).items()
        if key in FORWARDED_PARAMS and value not in (None, "")
    }
    # Images are only sent to a model an administrator has marked as having
    # vision. Sending them to one that has not is not a graceful degradation:
    # most endpoints reject the whole request.
    vision = model_supports(db, chat, "vision")

    if user is None:
        from lembas.db.models import User

        user = db.get(User, chat.user_id)

    # The harness describes the tools; the authored prompt describes the
    # behaviour. See services/harness.py for why these are joined rather than
    # being two competing layers.
    system = harness_service.join(
        harness_service.compose(db, user, tools, chat),
        effective_system_prompt(db, chat),
        lead=prompts_service.render(db, "seam.authored_lead", {}),
    )

    body: dict[str, Any] = {
        "model": chat.model_id,
        "messages": build_messages(
            db, chat, upto=upto, vision=vision, system_prompt=system
        ),
        **params,
    }
    if tools:
        body["tools"] = tools
        # Making the model call one particular tool, for `/image` -- the whole
        # of what that command is. Only ever sent alongside a tools array and
        # only when something asked for it, so a provider strict about unknown
        # parameters sees exactly the request it always did until somebody types
        # a slash command.
        #
        # An endpoint that ignores `tool_choice` is not a failure here: the turn
        # still carries the instruction in words, so the model is being steered
        # twice and the weaker half is the one that can be dropped.
        if force_tool and any(
            (tool.get("function") or {}).get("name") == force_tool for tool in tools
        ):
            body["tool_choice"] = {"type": "function", "function": {"name": force_tool}}

    apply_effort(body, (chat.params_json or {}).get("reasoning_effort"))
    return body


# Reasoning effort, and why it goes out twice.
#
# There is no one field that works. OpenAI and vLLM read a plain
# `reasoning_effort`. llama.cpp reads it too and, per its own documentation,
# "other values (e.g. 'low', 'max') have no effect" -- its maintainer is blunter
# still: "llama-server cannot support reasoning_effort at all", and the field
# "simply gets dropped without error or logging". What *does* reach a gpt-oss
# behind llama.cpp is `chat_template_kwargs`, which it accepts per request.
#
# So both are sent, and only when an effort has actually been chosen. That
# second half is what keeps this from being a regression: a chat nobody has set
# an effort on sends neither field and is byte-for-byte what it was. An endpoint
# strict about unknown parameters will refuse the extra one -- but on a chat
# somebody deliberately set an effort on, not on every chat in the instance.
EFFORTS = ("low", "medium", "high")


def resolved_effort(chat) -> str:
    """The effort this chat will actually send, or "" for none.

    Its own value, and nothing else. The model's default is a **seed** applied
    when the chat is created (`api/chats.py:_new_chat`) and on a model change,
    and is deliberately not consulted here for two reasons. A chat's request
    should be a function of the chat row alone -- the same rule that has PDF
    text extracted once at upload and knowledge attachments copied. And a
    fallback would break "off": `update_chat` stores `None` for a cleared
    effort, a fallback would resurrect the model's default underneath it, and
    the off option would silently do nothing.

    The picker shows exactly this, which is the whole point of it existing:
    "Effort: default" named no level and was true of nothing in particular.
    """
    value = (getattr(chat, "params_json", None) or {}).get("reasoning_effort")
    return value if value in EFFORTS else ""


def apply_effort(body: dict[str, Any], effort: str | None) -> None:
    """Put a chosen reasoning effort into a request body, in both forms."""
    if not effort or effort not in EFFORTS:
        return
    body["reasoning_effort"] = effort
    kwargs = dict(body.get("chat_template_kwargs") or {})
    kwargs["reasoning_effort"] = effort
    body["chat_template_kwargs"] = kwargs


def default_model(db: DBSession, user=None) -> tuple[str, str] | None:
    """The model a new chat should start with, as (model_id, connection_id).

    Preference order: the user's own choice, then the instance default, then
    whatever is first in the admin's ordering. Each is checked against what the
    user may actually reach, so a default they have lost access to falls
    through rather than producing a chat they cannot use.
    """
    from lembas.security import permissions
    from lembas.services import settings_store

    reachable = permissions.models_visible_to(db, user)
    if not reachable:
        return None

    by_id = {model.model_id: model for model in reachable}

    preferred = (user.settings_json or {}).get("default_model") if user is not None else None
    if preferred and preferred in by_id:
        return preferred, by_id[preferred].connection_id

    instance_default = settings_store.get(db, "default_model")
    if instance_default and instance_default in by_id:
        return instance_default, by_id[instance_default].connection_id

    # First in the administrator's ordering. Pinning is a sidebar shortcut, not
    # a reordering, so it deliberately does not influence this.
    chosen = sorted(reachable, key=lambda m: (m.position, m.model_id))[0]
    return chosen.model_id, chosen.connection_id


def available_models(db: DBSession, user=None) -> list[Model]:
    """Models this user may start a chat with, in the administrator's order.

    Pinning does NOT hoist a model up this list: pinned models get their own
    shortcuts in the sidebar, and a picker whose order silently differs from
    the one configured in the admin screen is just confusing.
    """
    from lembas.security import permissions

    reachable = permissions.models_visible_to(db, user)
    return sorted(reachable, key=lambda m: (m.position, m.model_id))


def fallback_title(text: str) -> str:
    """Derive a chat title from the opening message, without calling a model."""
    cleaned = " ".join(text.split())
    if not cleaned:
        return "New chat"
    if len(cleaned) <= MAX_TITLE_LENGTH:
        return cleaned
    # Prefer a word boundary, but only if it does not cut the title in half.
    clipped = cleaned[:MAX_TITLE_LENGTH]
    space = clipped.rfind(" ")
    if space > MAX_TITLE_LENGTH * 0.6:
        clipped = clipped[:space]
    return clipped.rstrip(" ,.;:-") + "…"


async def generate_title(
    endpoint: Endpoint, model_id: str, question: str, answer: str, *, template: str
) -> str:
    """Ask the model for a short chat title.

    Best-effort by design: any failure falls back to trimming the first
    message. Naming a chat is never worth surfacing an error for.

    `template` is passed in rather than read here because this runs after the
    generation's session has closed -- see `generation._run`. An empty one means
    an administrator cleared the fragment, which is how auto-titling is turned
    off: no request is made at all.
    """
    from lembas.services import prompts as prompts_service

    if not template.strip():
        return fallback_title(question)

    from lembas.services.reasoning import strip_reasoning

    prompt = prompts_service.substitute(
        template, {"question": question[:500], "answer": answer[:500]}
    )
    body = {
        "model": model_id,
        "messages": [{"role": ROLE_USER, "content": prompt}],
        # Enough that a model which thinks before answering can do both. It was
        # 24, which is ample for six words and nowhere near enough for a
        # reasoning model: the whole budget went on thinking and the reply came
        # back either empty or as an unclosed `<think>`, so every chat on such a
        # model silently fell back to its first prompt and looked as though
        # titling had never run.
        "max_tokens": TITLE_MAX_TOKENS,
        "temperature": 0.2,
    }
    # Deliberately *not* `apply_effort(body, "low")`, tempting as it is: naming
    # a chat does not reward deliberation and a low effort would make this call
    # much cheaper. But `reasoning_effort` and `chat_template_kwargs` appear
    # only when somebody has opted in, precisely so a provider strict about
    # unknown parameters sees exactly the request it always did — and sending
    # them here would put them on every instance's title call, where a 400 is
    # caught and turned into a fallback title. That is titling silently
    # switching itself off, which is the failure this whole change is fixing.
    # The token budget above is what makes room for the thinking instead.
    try:
        raw = await complete(endpoint, body)
    except LLMError as exc:
        log.debug("auto-title failed, using fallback: %s", exc)
        return fallback_title(question)

    # `complete` hands back `message.content` as it arrived. A model that emits
    # `<think>` tags inline puts them in exactly that field, so without this the
    # title was "<think>Okay, the user wants a short title for". Reasoning sent
    # in a separate `reasoning_content` field is ignored by `complete` already.
    answered, _thinking = strip_reasoning(raw)

    title = " ".join(answered.split()).strip().strip('"“”\'')
    # Small models sometimes ignore the instruction and answer the question
    # instead; an over-long reply is a better signal of that than anything else.
    if not title or len(title) > MAX_TITLE_LENGTH * 1.5:
        return fallback_title(question)
    return title[:MAX_TITLE_LENGTH]


def create_message(
    db: DBSession,
    chat: Chat,
    role: str,
    content: str = "",
    *,
    complete_: bool = True,
    model_id: str = "",
    queued: bool = False,
    machine: bool = False,
) -> Message:
    message = Message(
        chat_id=chat.id,
        role=role,
        content=content,
        complete=complete_,
        model_id=model_id,
        queued=queued,
        machine=machine,
    )
    db.add(message)
    db.commit()
    return message


async def summarise_for_compaction(
    endpoint: Endpoint,
    model_id: str,
    *,
    transcript: str,
    previous_summary: str,
    template: str,
) -> str:
    """Ask the model to summarise the earlier turns.

    `template` is passed in for the same reason `generate_title`'s is: this runs
    after the generation's session has closed, and opening another one there is
    how you get a session that outlives its scope. An empty template means an
    administrator cleared the fragment, and nothing is asked of anyone.
    """
    from lembas.services import prompts as prompts_service

    if not template.strip() or not transcript.strip():
        return ""

    prompt = prompts_service.substitute(
        template, {"transcript": transcript, "previous_summary": previous_summary}
    )
    raw = await complete(
        endpoint,
        {
            "model": model_id,
            "messages": [{"role": ROLE_USER, "content": prompt}],
            "max_tokens": 1200,
            # Low, but not zero: this is recall, not invention.
            "temperature": 0.3,
        },
    )
    return raw.strip()


def delete_chats(db: DBSession, chats) -> int:
    """Delete chats, and the files their attachments point at.

    **The one way to delete a chat.** `db.delete(chat)` cascades to its messages
    and to its attachment *rows*, and leaves every file on disk -- a generated
    image, an uploaded PDF, a photo -- with nothing that will ever look at them
    again: `sweep_orphans` only considers uploads that were never attached.

    `files_service.remove_files_for_chats` was written for exactly this and was
    called from one place, the temporary sweep. The delete button, a schedule's
    task chat, a helper's hidden chat and deleting an account all went straight
    to `db.delete`, so four of the five ways a chat can end leaked its files.
    That is `sharing.forget_principal` again: a helper that exists, is correct,
    and is not called on the path that needs it.

    The order matters and is why this is a function rather than a note. The
    files have to be unlinked **while the rows still say which they are**, so it
    happens before the delete and in the same session.

    Does not commit -- the caller decides, because some of them are deleting
    other things in the same transaction.
    """
    live = [chat for chat in chats if chat is not None]
    if not live:
        return 0
    files_service.remove_files_for_chats(db, [chat.id for chat in live])
    for chat in live:
        db.delete(chat)
    return len(live)


def sweep_temporary(db: DBSession, older_than: timedelta = TEMPORARY_LIFETIME) -> int:
    """Delete temporary chats nobody has touched for a day.

    Age is measured from the newest message rather than from the chat row's own
    timestamps. `created_at` would destroy a conversation still in use at hour
    23, and `updated_at` does not move when a message is inserted -- `onupdate`
    fires on an UPDATE of the chat, and adding a message is not one.

    Startup only, like files.sweep_orphans beside it. A server that runs for a
    month sweeps once; that is the trade the existing sweep already makes, and a
    scheduler is a whole new concern for a single-worker application.
    """
    cutoff = datetime.now(UTC) - older_than
    newest = (
        select(Message.chat_id, func.max(Message.created_at).label("last"))
        .group_by(Message.chat_id)
        .subquery()
    )
    stale = list(
        db.scalars(
            select(Chat)
            .outerjoin(newest, newest.c.chat_id == Chat.id)
            .where(
                Chat.temporary.is_(True),
                func.coalesce(newest.c.last, Chat.created_at) < cutoff,
            )
        )
    )
    if not stale:
        return 0

    delete_chats(db, stale)
    db.commit()
    log.info("swept %d temporary chat(s)", len(stale))
    return len(stale)


def user_chats(db: DBSession, user_id: str, *, folder_id: str | None = None) -> list[Chat]:
    query = select(Chat).where(
        Chat.user_id == user_id, Chat.archived.is_(False), Chat.temporary.is_(False)
    )
    if folder_id is not None:
        query = query.where(Chat.folder_id == folder_id)
    return list(db.scalars(query.order_by(Chat.pinned.desc(), Chat.updated_at.desc())))


__all__ = [
    "ROLE_ASSISTANT",
    "ROLE_USER",
    "available_models",
    "build_request",
    "create_message",
    "default_model",
    "fallback_title",
    "generate_title",
    "resolve_endpoint",
    "user_chats",
]
