"""Session-context rendering for the Scribe plugin's SessionStart hook.

The plugin's hook curls `GET /api/plugin/context` at session start and injects
the returned text as `additionalContext`, giving Scribe the same push channel
that superpowers and file-memory have. This module renders that text.

Design note — altitude: we inject rule *titles* grouped by topic (a compact
index), NOT every rule's full statement. The 48 always-on statements run well
past the 10k-char `additionalContext` cap, and the push channel's job is to make
Claude *aware* the rules exist and *reach* for them — not to dump them. Full
text stays one `get_rule(id)` / `list_always_on_rules()` call away. Titles are
mostly self-describing ("`dev` is home", "No GitHub — Fabled-Git only"), so the
index alone already steers behavior.
"""
from __future__ import annotations

from sqlalchemy import select

from scribe.models import async_session
from scribe.models.rulebook import RulebookTopic
from scribe.services import notes as notes_svc
from scribe.services import projects as projects_svc
from scribe.services import rulebooks as rulebooks_svc

# Defensive cap below Claude Code's 10k additionalContext limit.
_MAX_CHARS = 9000


async def _topic_titles(topic_ids: set[int]) -> dict[int, str]:
    """Map topic_id -> title for the given ids (live topics only)."""
    if not topic_ids:
        return {}
    async with async_session() as session:
        rows = await session.execute(
            select(RulebookTopic.id, RulebookTopic.title).where(
                RulebookTopic.id.in_(topic_ids),
                RulebookTopic.deleted_at.is_(None),
            )
        )
        return {tid: title for tid, title in rows.all()}


async def build_session_context(
    user_id: int, project_id: int = 0, unbound_repo: str = ""
) -> dict:
    """Render the SessionStart context for a user, optionally project-scoped.

    Args:
        user_id: the operator.
        project_id: the resolved active project (0 = none). The endpoint
            resolves this from the working repo's remote, not from config.
        unbound_repo: when the hook sent a repo remote that maps to no project,
            its normalized key — triggers a one-line "bind this repo" hint so
            the binding is self-healing.

    Returns {"context": str, "rule_count": int, "project": dict | None}.
    `context` is markdown ready to drop into `additionalContext`; it is capped
    at _MAX_CHARS with an explicit truncation note so the hook can pass it
    through verbatim.
    """
    rules = await rulebooks_svc.list_always_on_rules(user_id)
    topic_map = await _topic_titles({r.topic_id for r in rules if r.topic_id})

    lines: list[str] = [
        "# Scribe — standing session context (auto-injected by the Scribe plugin)",
        "",
        "You are working with Scribe, the operator's self-hosted second brain. "
        "The always-on rules below are BINDING this session. Titles only — full "
        "text via `list_always_on_rules()` or `get_rule(id)`.",
        "",
        "## Always-on rules (by topic)",
    ]

    # rules already arrive ordered by rulebook/topic/order, so grouping by
    # consecutive topic_id preserves the intended sequence.
    current_topic: int | None = object()  # sentinel distinct from any id/None
    for r in rules:
        if r.topic_id != current_topic:
            current_topic = r.topic_id
            heading = topic_map.get(r.topic_id, "ungrouped") if r.topic_id else "ungrouped"
            lines.append(f"### {heading}")
        lines.append(f"- [{r.id}] {r.title}")

    project_dict: dict | None = None
    if project_id:
        project = await projects_svc.get_project(user_id, project_id)
        if project is not None:
            _, open_count = await notes_svc.list_notes(
                user_id, is_task=True, status="todo", project_id=project_id, limit=1,
            )
            goal = (getattr(project, "goal", "") or "").strip()
            project_dict = {"id": project.id, "title": project.title}
            lines += [
                "",
                f"## Active project: {project.title} (id {project.id})",
                f"Goal: {goal[:200]}" if goal else "",
                f"Open todo tasks: {open_count}",
            ]
    elif unbound_repo:
        lines += [
            "",
            "## Repository not yet bound",
            f"This repo (`{unbound_repo}`) isn't mapped to a Scribe project, so "
            "no project context was loaded. Bind it once with "
            f'`bind_repo(repo_url="{unbound_repo}", project_id=<id>)` '
            "(call `list_projects` to find the id) and future sessions here will "
            "auto-load that project's context.",
        ]

    lines += [
        "",
        "Reflex: search Scribe (search / list_tasks / list_notes, scoped to the "
        "active project) before answering or starting work; prefer UPDATING an "
        "existing note/rule over creating a new one.",
    ]

    context = "\n".join(line for line in lines if line is not None)
    if len(context) > _MAX_CHARS:
        context = context[:_MAX_CHARS].rstrip() + "\n\n…(truncated — call list_always_on_rules())"

    return {"context": context, "rule_count": len(rules), "project": project_dict}