from datetime import datetime, timedelta, timezone

from fastapi import APIRouter, Depends
from fastapi.responses import JSONResponse
from sqlalchemy import func, select, text
from sqlalchemy.ext.asyncio import AsyncSession

from api.database import get_session, engine
from api.models.decision import Decision, DecisionStatus, DecisionType
from api.models.progress_event import ProgressEvent
from api.models.task import Task, TaskPriority, TaskStatus
from api.models.topic import Topic, TopicStatus
from api.models.workstream import Workstream, WorkstreamStatus
from api.models.workstream_dependency import WorkstreamDependency
from api.schemas.decision import DecisionRead
from api.schemas.progress_event import ProgressEventRead
from api.schemas.state import (
    DecisionTotals,
    NextStep,
    StateSummary,
    TaskTotals,
    Totals,
    TopicTotals,
    WorkstreamTotals,
)
from api.schemas.task import TaskRead
from api.schemas.topic import TopicWithWorkstreams
from api.schemas.workstream import WorkstreamRead, WorkstreamWithTaskCounts, WorkstreamWithDeps
from api.schemas.workstream_dependency import WorkstreamDepStub

router = APIRouter(prefix="/state", tags=["state"])


@router.get("/summary", response_model=StateSummary)
async def get_summary(session: AsyncSession = Depends(get_session)) -> StateSummary:
    # Run all queries sequentially on one session.
    # AsyncSession does not support concurrent operations (no gather on same session).

    topics_rows = await session.execute(
        select(Topic).where(Topic.status != TopicStatus.archived).order_by(Topic.created_at)
    )
    topics = list(topics_rows.scalars().all())

    blocking_rows = await session.execute(
        select(Decision)
        .where(Decision.decision_type == DecisionType.pending)
        .where(Decision.status.in_([DecisionStatus.open, DecisionStatus.escalated]))
        .order_by(Decision.deadline.asc().nullslast(), Decision.created_at)
    )
    blocking = list(blocking_rows.scalars().all())

    blocked_rows = await session.execute(
        select(Task).where(Task.status == TaskStatus.blocked).order_by(Task.created_at)
    )
    blocked = list(blocked_rows.scalars().all())

    recent_rows = await session.execute(
        select(ProgressEvent).order_by(ProgressEvent.created_at.desc()).limit(20)
    )
    recent = list(recent_rows.scalars().all())

    open_ws_rows = await session.execute(
        select(Workstream)
        .where(Workstream.status.in_([WorkstreamStatus.active, WorkstreamStatus.blocked]))
        .order_by(Workstream.due_date.asc().nullslast(), Workstream.created_at)
    )
    open_ws = list(open_ws_rows.scalars().all())

    # Task counts per workstream (used to enrich open_workstreams)
    task_per_ws: dict = {}
    for ws_id, tstat, cnt in await session.execute(
        select(Task.workstream_id, Task.status, func.count()).group_by(Task.workstream_id, Task.status)
    ):
        task_per_ws.setdefault(ws_id, {})[tstat] = cnt

    # Dependency graph for open workstreams
    open_ws_ids = [w.id for w in open_ws]
    dep_rows = []
    if open_ws_ids:
        dep_result = await session.execute(
            select(WorkstreamDependency).where(
                (WorkstreamDependency.from_workstream_id.in_(open_ws_ids))
                | (WorkstreamDependency.to_workstream_id.in_(open_ws_ids))
            )
        )
        dep_rows = list(dep_result.scalars().all())

    # Build a slug+title lookup for all workstreams referenced in deps
    dep_ws_ids = set()
    for d in dep_rows:
        dep_ws_ids.add(d.from_workstream_id)
        dep_ws_ids.add(d.to_workstream_id)
    ws_lookup: dict = {w.id: w for w in open_ws}
    extra_ids = dep_ws_ids - set(ws_lookup.keys())
    if extra_ids:
        extra_rows = await session.execute(
            select(Workstream).where(Workstream.id.in_(extra_ids))
        )
        for w in extra_rows.scalars():
            ws_lookup[w.id] = w

    # Index: workstream_id → (depends_on stubs, blocks stubs)
    dep_index: dict = {w.id: {"depends_on": [], "blocks": []} for w in open_ws}
    for d in dep_rows:
        from_id, to_id = d.from_workstream_id, d.to_workstream_id
        if from_id in dep_index and to_id in ws_lookup:
            dep_index[from_id]["depends_on"].append(WorkstreamDepStub(
                dep_id=d.id,
                workstream_id=to_id,
                workstream_slug=ws_lookup[to_id].slug,
                workstream_title=ws_lookup[to_id].title,
                description=d.description,
            ))
        if to_id in dep_index and from_id in ws_lookup:
            dep_index[to_id]["blocks"].append(WorkstreamDepStub(
                dep_id=d.id,
                workstream_id=from_id,
                workstream_slug=ws_lookup[from_id].slug,
                workstream_title=ws_lookup[from_id].title,
                description=d.description,
            ))

    # Totals — one GROUP BY per table
    topic_counts = {r[0]: r[1] for r in await session.execute(
        select(Topic.status, func.count()).group_by(Topic.status)
    )}
    ws_counts = {r[0]: r[1] for r in await session.execute(
        select(Workstream.status, func.count()).group_by(Workstream.status)
    )}
    task_counts = {r[0]: r[1] for r in await session.execute(
        select(Task.status, func.count()).group_by(Task.status)
    )}
    dec_counts = {r[0]: r[1] for r in await session.execute(
        select(Decision.status, func.count()).group_by(Decision.status)
    )}

    totals = Totals(
        topics=TopicTotals(
            active=topic_counts.get(TopicStatus.active, 0),
            paused=topic_counts.get(TopicStatus.paused, 0),
            archived=topic_counts.get(TopicStatus.archived, 0),
            total=sum(topic_counts.values()),
        ),
        workstreams=WorkstreamTotals(
            active=ws_counts.get(WorkstreamStatus.active, 0),
            blocked=ws_counts.get(WorkstreamStatus.blocked, 0),
            completed=ws_counts.get(WorkstreamStatus.completed, 0),
            archived=ws_counts.get(WorkstreamStatus.archived, 0),
            total=sum(ws_counts.values()),
        ),
        tasks=TaskTotals(
            todo=task_counts.get(TaskStatus.todo, 0),
            in_progress=task_counts.get(TaskStatus.in_progress, 0),
            blocked=task_counts.get(TaskStatus.blocked, 0),
            done=task_counts.get(TaskStatus.done, 0),
            cancelled=task_counts.get(TaskStatus.cancelled, 0),
            total=sum(task_counts.values()),
        ),
        decisions=DecisionTotals(
            open=dec_counts.get(DecisionStatus.open, 0),
            resolved=dec_counts.get(DecisionStatus.resolved, 0),
            escalated=dec_counts.get(DecisionStatus.escalated, 0),
            superseded=dec_counts.get(DecisionStatus.superseded, 0),
            total=sum(dec_counts.values()),
        ),
    )

    next_steps = await _derive_next_steps(session)

    return StateSummary(
        generated_at=datetime.now(tz=timezone.utc),
        totals=totals,
        topics=[TopicWithWorkstreams.model_validate(t) for t in topics],
        blocking_decisions=[DecisionRead.model_validate(d) for d in blocking],
        blocked_tasks=[TaskRead.model_validate(t) for t in blocked],
        recent_progress=[ProgressEventRead.model_validate(e) for e in recent],
        next_steps=next_steps,
        open_workstreams=[
            WorkstreamWithDeps(
                **WorkstreamRead.model_validate(w).model_dump(),
                tasks_total=sum(task_per_ws.get(w.id, {}).values()),
                tasks_todo=task_per_ws.get(w.id, {}).get(TaskStatus.todo, 0),
                tasks_in_progress=task_per_ws.get(w.id, {}).get(TaskStatus.in_progress, 0),
                tasks_blocked=task_per_ws.get(w.id, {}).get(TaskStatus.blocked, 0),
                tasks_done=task_per_ws.get(w.id, {}).get(TaskStatus.done, 0),
                depends_on=dep_index.get(w.id, {}).get("depends_on", []),
                blocks=dep_index.get(w.id, {}).get("blocks", []),
            )
            for w in open_ws
        ],
    )


_PRIORITY_RANK = {
    TaskPriority.critical: 0,
    TaskPriority.high: 1,
    TaskPriority.medium: 2,
    TaskPriority.low: 3,
}


async def _derive_next_steps(session: AsyncSession) -> list[NextStep]:
    """Derive contextual next-action suggestions from current hub state.

    Two signal sources:
    1. Recently resolved decisions (last 7 days) → first open task in same workstream
    2. Workstreams whose every dependency is now completed → first todo task in that workstream
    """
    steps: list[NextStep] = []
    seen_task_ids: set = set()

    # ── Signal 1: recently resolved decisions ────────────────────────────────
    cutoff = datetime.now(tz=timezone.utc) - timedelta(days=7)
    resolved_rows = await session.execute(
        select(Decision)
        .where(Decision.status == DecisionStatus.resolved)
        .where(Decision.decided_at >= cutoff)
        .where(Decision.workstream_id.isnot(None))
        .order_by(Decision.decided_at.desc())
    )
    for decision in resolved_rows.scalars().all():
        open_tasks_rows = await session.execute(
            select(Task)
            .where(Task.workstream_id == decision.workstream_id)
            .where(Task.status.in_([TaskStatus.todo, TaskStatus.in_progress]))
        )
        open_tasks = list(open_tasks_rows.scalars().all())
        if not open_tasks:
            continue
        task = min(open_tasks, key=lambda t: (_PRIORITY_RANK.get(t.priority, 99), t.created_at))
        if task.id in seen_task_ids:
            continue
        ws = await session.get(Workstream, decision.workstream_id)
        topic = await session.get(Topic, ws.topic_id) if ws else None
        steps.append(NextStep(
            type="resolved_decision",
            domain=topic.domain if topic else None,
            workstream_id=ws.id if ws else None,
            workstream_title=ws.title if ws else None,
            workstream_slug=ws.slug if ws else None,
            task_id=task.id,
            task_title=task.title,
            message=(
                f"Decision '{decision.title}' was resolved → "
                f"'{task.title}' is the next open task in '{ws.title if ws else '?'}'"
            ),
        ))
        seen_task_ids.add(task.id)

    # ── Signal 2: cleared dependencies ──────────────────────────────────────
    all_dep_rows = await session.execute(select(WorkstreamDependency))
    all_deps = list(all_dep_rows.scalars().all())

    # Group from_workstream_id → set of to_workstream_ids
    dep_map: dict = {}
    for d in all_deps:
        dep_map.setdefault(d.from_workstream_id, set()).add(d.to_workstream_id)

    for from_ws_id, to_ws_ids in dep_map.items():
        # All targets must be completed
        all_done = True
        for to_id in to_ws_ids:
            to_ws = await session.get(Workstream, to_id)
            if to_ws is None or to_ws.status != WorkstreamStatus.completed:
                all_done = False
                break
        if not all_done:
            continue

        from_ws = await session.get(Workstream, from_ws_id)
        if from_ws is None or from_ws.status not in (WorkstreamStatus.active, WorkstreamStatus.blocked):
            continue

        todo_rows = await session.execute(
            select(Task)
            .where(Task.workstream_id == from_ws_id)
            .where(Task.status == TaskStatus.todo)
        )
        todo_tasks = list(todo_rows.scalars().all())
        if not todo_tasks:
            continue
        task = min(todo_tasks, key=lambda t: (_PRIORITY_RANK.get(t.priority, 99), t.created_at))
        if task.id in seen_task_ids:
            continue
        topic = await session.get(Topic, from_ws.topic_id)
        blocker_slugs = ", ".join(
            (await session.get(Workstream, tid)).slug
            for tid in to_ws_ids
            if await session.get(Workstream, tid)
        )
        steps.append(NextStep(
            type="dependency_cleared",
            domain=topic.domain if topic else None,
            workstream_id=from_ws.id,
            workstream_title=from_ws.title,
            workstream_slug=from_ws.slug,
            task_id=task.id,
            task_title=task.title,
            message=(
                f"All dependencies of '{from_ws.title}' are completed ({blocker_slugs}) → "
                f"'{task.title}' is ready to start"
            ),
        ))
        seen_task_ids.add(task.id)

    return steps


@router.get("/next_steps", response_model=list[NextStep])
async def get_next_steps(session: AsyncSession = Depends(get_session)) -> list[NextStep]:
    """Derive contextual next-action suggestions from current hub state.

    Returns suggestions based on:
    - Recently resolved decisions → first open task in the same workstream
    - Workstreams whose every dependency workstream is now completed → first todo task
    """
    return await _derive_next_steps(session)


@router.get("/health")
async def health_check() -> dict:
    try:
        async with engine.connect() as conn:
            await conn.execute(text("SELECT 1"))
        return {"status": "ok", "db": "connected"}
    except Exception as exc:
        return JSONResponse(
            status_code=503,
            content={"status": "error", "db": str(exc)},
        )