"""Flows + approvals HTTP API."""

from __future__ import annotations

import json
from collections.abc import AsyncIterator, Iterator
from uuid import UUID

import httpx
from fastapi import APIRouter, Depends, HTTPException, Query
from fastapi.responses import StreamingResponse
from sqlmodel import Session

from app.db import get_engine, get_session
from app.settings import settings

from . import runner, store
from .lfx_client import (
    LfxClient,
    LfxConflict,
    LfxError,
    LfxInvalidFlow,
    LfxNotFound,
    LfxRunFailed,
    LfxUnavailable,
)
from .schemas import (
    ApprovalCreate,
    ApprovalRead,
    FlowDefinitionCreate,
    FlowDefinitionRead,
    FlowVersionCreate,
    FlowVersionRead,
    RunRead,
    RunRequest,
)

flows_router = APIRouter(prefix="/api/flows", tags=["flows"])
approvals_router = APIRouter(prefix="/api/approvals", tags=["approvals"])


def get_db() -> Iterator[Session]:
    yield from get_session()


def get_lfx() -> LfxClient:
    return LfxClient(settings.lfx_url, api_key=settings.lfx_api_key or None)


def _read_definition(d) -> FlowDefinitionRead:
    return FlowDefinitionRead(
        id=d.id,
        name=d.name,
        description=d.description,
        status=d.status,
        continuation_flow_id=d.continuation_flow_id,
        created_at=d.created_at,
    )


def _read_version(v) -> FlowVersionRead:
    return FlowVersionRead(
        id=v.id,
        flow_id=v.flow_id,
        version_no=v.version_no,
        langflow_json=v.langflow_json,
        lfx_flow_id=v.lfx_flow_id,
        deployed_at=v.deployed_at,
        author=v.author,
        created_at=v.created_at,
    )


def _read_run(r) -> RunRead:
    return RunRead(
        id=r.id,
        version_id=r.version_id,
        tenant_id=r.tenant_id,
        status=r.status,
        input=r.input,
        output=r.output,
        session_id=r.session_id,
        created_at=r.created_at,
        finished_at=r.finished_at,
    )


def _read_task(t) -> ApprovalRead:
    return ApprovalRead(
        id=t.id,
        run_id=t.run_id,
        version_id=t.version_id,
        tenant_id=t.tenant_id,
        title=t.title,
        payload=t.payload,
        continuation_flow_id=t.continuation_flow_id,
        approver=t.approver,
        status=t.status,
        decision_note=t.decision_note,
        created_at=t.created_at,
        decided_at=t.decided_at,
    )


@flows_router.post("", response_model=FlowDefinitionRead, status_code=201)
def create_flow(data: FlowDefinitionCreate, session: Session = Depends(get_db)):
    try:
        return _read_definition(store.create_definition(session, data))
    except store.ConflictError as exc:
        raise HTTPException(status_code=409, detail=str(exc)) from exc
    except store.InvalidError as exc:
        raise HTTPException(status_code=422, detail=str(exc)) from exc


@flows_router.get("", response_model=list[FlowDefinitionRead])
def list_flows(session: Session = Depends(get_db)):
    return [_read_definition(d) for d in store.list_definitions(session)]


@flows_router.get("/{flow_id}", response_model=FlowDefinitionRead)
def get_flow(flow_id: UUID, session: Session = Depends(get_db)):
    try:
        return _read_definition(store.get_definition(session, flow_id))
    except store.NotFoundError as exc:
        raise HTTPException(status_code=404, detail=str(exc)) from exc


@flows_router.post(
    "/{flow_id}/versions", response_model=FlowVersionRead, status_code=201
)
def create_version(
    flow_id: UUID, data: FlowVersionCreate, session: Session = Depends(get_db)
):
    try:
        return _read_version(store.create_version(session, flow_id, data))
    except store.NotFoundError as exc:
        raise HTTPException(status_code=404, detail=str(exc)) from exc
    except store.InvalidError as exc:
        raise HTTPException(status_code=422, detail=str(exc)) from exc


@flows_router.get("/{flow_id}/versions", response_model=list[FlowVersionRead])
def list_versions(flow_id: UUID, session: Session = Depends(get_db)):
    try:
        return [_read_version(v) for v in store.list_versions(session, flow_id)]
    except store.NotFoundError as exc:
        raise HTTPException(status_code=404, detail=str(exc)) from exc


@flows_router.post(
    "/{flow_id}/versions/{version_no}/deploy", response_model=FlowVersionRead
)
async def deploy_version(
    flow_id: UUID,
    version_no: int,
    session: Session = Depends(get_db),
    lfx: LfxClient = Depends(get_lfx),
):
    try:
        version = store.get_version_by_no(session, flow_id, version_no)
    except store.NotFoundError as exc:
        raise HTTPException(status_code=404, detail=str(exc)) from exc
    try:
        uploaded = await lfx.upload_flow(
            version.langflow_json, flow_id=str(version.id), replace=True
        )
    except LfxInvalidFlow as exc:
        raise HTTPException(status_code=422, detail=str(exc)) from exc
    except LfxConflict as exc:
        raise HTTPException(status_code=409, detail=str(exc)) from exc
    except LfxUnavailable as exc:
        raise HTTPException(status_code=503, detail=str(exc)) from exc
    except LfxError as exc:
        raise HTTPException(status_code=502, detail=str(exc)) from exc
    return _read_version(store.mark_deployed(session, version, uploaded.id))


def _resolve_version(session: Session, flow_id: UUID, version_no: int | None):
    if version_no is not None:
        return store.get_version_by_no(session, flow_id, version_no)
    return store.get_latest_deployed_version(session, flow_id)


@flows_router.post("/{flow_id}/run", response_model=RunRead)
async def run_flow(
    flow_id: UUID,
    data: RunRequest,
    stream: bool = Query(default=False),
    session: Session = Depends(get_db),
    lfx: LfxClient = Depends(get_lfx),
):
    try:
        version = _resolve_version(session, flow_id, data.version_no)
    except store.NotFoundError as exc:
        raise HTTPException(status_code=404, detail=str(exc)) from exc
    except store.InvalidError as exc:
        raise HTTPException(status_code=422, detail=str(exc)) from exc
    if stream:
        return await _run_stream(session, lfx, version, data)
    try:
        run = await runner.execute_run(
            session,
            lfx,
            version,
            payload=data.input,
            tenant_id=data.tenant_id,
            session_id=data.session_id,
            callback_base_url=data.callback_base_url or settings.callback_base_url,
            continuation_flow_id=data.continuation_flow_id,
        )
    except LfxNotFound as exc:
        raise HTTPException(status_code=502, detail=f"LFX drift: {exc}") from exc
    except LfxUnavailable as exc:
        raise HTTPException(status_code=503, detail=str(exc)) from exc
    except LfxError as exc:
        raise HTTPException(status_code=502, detail=str(exc)) from exc
    return _read_run(run)


async def _run_stream(session: Session, lfx: LfxClient, version, data: RunRequest):
    if not version.lfx_flow_id:
        raise HTTPException(
            status_code=422, detail=f"version {version.id} is not deployed to LFX"
        )
    run = store.create_run(
        session,
        version,
        input=data.input,
        tenant_id=data.tenant_id,
        session_id=data.session_id,
    )
    envelope = runner.build_envelope(
        payload=data.input,
        run_id=run.id,
        callback_base_url=data.callback_base_url or settings.callback_base_url,
        continuation_flow_id=data.continuation_flow_id,
    )
    run_id = run.id
    lfx_flow_id = version.lfx_flow_id
    session_id = data.session_id or str(run.id)

    async def event_gen() -> AsyncIterator[str]:
        yield f"event: run\ndata: {json.dumps({'run_id': str(run_id)})}\n\n"
        try:
            async with httpx.AsyncClient(
                base_url=lfx.base_url, timeout=lfx.timeout, headers=lfx._headers()
            ) as client:
                async with client.stream(
                    "POST",
                    f"/flows/{lfx_flow_id}/stream",
                    json={"input_value": envelope, "session_id": session_id},
                ) as response:
                    if response.status_code == 404:
                        raise LfxNotFound(f"flow {lfx_flow_id} unknown to LFX")
                    response.raise_for_status()
                    async for chunk in response.aiter_text():
                        yield chunk
        except (LfxNotFound, httpx.HTTPError) as exc:
            yield f"event: error\ndata: {json.dumps({'error': str(exc)})}\n\n"
        # Finalize from a fresh session: the request session may be closed.
        with Session(get_engine()) as fresh:
            try:
                fresh_run = store.get_run(fresh, run_id)
                status = (
                    "pending_approval"
                    if runner._task_exists(fresh, run_id)
                    else "completed"
                )
                store.set_run_result(fresh, fresh_run, status, {"streamed": True})
            except store.NotFoundError:
                status = "failed"
        yield f"event: run_finished\ndata: {json.dumps({'run_id': str(run_id), 'status': status})}\n\n"

    return StreamingResponse(event_gen(), media_type="text/event-stream")


@flows_router.get("/{flow_id}/runs", response_model=list[RunRead])
def list_runs(flow_id: UUID, session: Session = Depends(get_db)):
    try:
        return [_read_run(r) for r in store.list_runs(session, flow_id)]
    except store.NotFoundError as exc:
        raise HTTPException(status_code=404, detail=str(exc)) from exc


@flows_router.get("/runs/{run_id}", response_model=RunRead)
def get_run(run_id: UUID, session: Session = Depends(get_db)):
    try:
        return _read_run(store.get_run(session, run_id))
    except store.NotFoundError as exc:
        raise HTTPException(status_code=404, detail=str(exc)) from exc


@approvals_router.post("", response_model=ApprovalRead, status_code=201)
def create_approval(data: ApprovalCreate, session: Session = Depends(get_db)):
    """Flow callback contract: report a terminal approval state for a run."""
    try:
        return _read_task(store.create_approval_task(session, data))
    except store.NotFoundError as exc:
        raise HTTPException(status_code=404, detail=str(exc)) from exc
    except store.ConflictError as exc:
        raise HTTPException(status_code=409, detail=str(exc)) from exc
    except store.InvalidError as exc:
        raise HTTPException(status_code=422, detail=str(exc)) from exc


@approvals_router.get("", response_model=list[ApprovalRead])
def list_approvals(
    tenant_id: str | None = Query(default=None),
    session: Session = Depends(get_db),
):
    return [_read_task(t) for t in store.list_approval_tasks(session, tenant_id)]