"""Template CRUD for the exam-marker (/api/exam/templates...) — card S4-5.

All access is as-the-user (RLS-enforced; spec E1 fix) via ExamContext. Ownership is also
checked explicitly before mutating (E2: never trust a client-supplied id as authorization) —
defence in depth on top of RLS. A row the caller cannot see under RLS reads back as absent,
so cross-institute access surfaces as 404, never a data leak (IDOR-safe).

Hybrid persistence (R5.2): PUT /templates/{id} is a full-replace of the canvas children
(questions + response areas + boundaries); PATCH /questions/{qid} is the granular mark-scheme
edit path. Client-supplied UUIDs are preserved so Supabase ids stay aligned with the Neo4j
join keys (spec §2).
"""
from __future__ import annotations

import os
import uuid
from typing import Any, Dict, List, Optional, Tuple

from fastapi import APIRouter, BackgroundTasks, Depends, HTTPException, Request, UploadFile
from fastapi.responses import Response

from modules.database.services.exam_projection import project_template, project_template_safe
from modules.database.supabase.utils.client import SupabaseServiceRoleClient
from modules.database.supabase.utils.storage import StorageAdmin
from modules.logger_tool import initialise_logger
from routers.exam.dependencies import ExamContext, get_exam_context, lookup_exam_code
from routers.exam.schemas import (
    CreateTemplateRequest,
    PatchQuestionRequest,
    TemplateReplaceRequest,
    UpdateTemplateMetaRequest,
)

logger = initialise_logger(__name__, os.getenv("LOG_LEVEL"), os.getenv("LOG_PATH"), "default", True)

router = APIRouter()

SOURCE_CABINET_NAME = "Exam Marker Template Sources"
SOURCE_BUCKET_FALLBACK = "cc.users"


# ─── helpers ─────────────────────────────────────────────────────────────────

def _rows(result: Any) -> List[Dict[str, Any]]:
    data = getattr(result, "data", None)
    if not data:
        return []
    return data if isinstance(data, list) else [data]


def _first(result: Any) -> Optional[Dict[str, Any]]:
    rows = _rows(result)
    return rows[0] if rows else None


def _fetch_template_or_404(ctx: ExamContext, template_id: str) -> Dict[str, Any]:
    """Load a template the caller can see (RLS-scoped). Missing/forbidden → 404."""
    res = ctx.supabase.table("exam_templates").select("*").eq("id", template_id).limit(1).execute()
    row = _first(res)
    if not row:
        raise HTTPException(status_code=404, detail="Template not found")
    return row


def _require_owner(ctx: ExamContext, template: Dict[str, Any]) -> None:
    """Writes are limited to the owning teacher (R2.4)."""
    if template.get("teacher_id") != ctx.user_id:
        raise HTTPException(status_code=403, detail="Only the template owner can modify it")


def _require_source_visibility_or_404(ctx: ExamContext, template: Dict[str, Any]) -> None:
    """Institute boundary check — RLS already gates template visibility; this prevents cross-institute PDF leakage."""
    if template.get("institute_id") not in ctx.institute_ids:
        raise HTTPException(status_code=404, detail="Template not found")


def _template_has_recorded_marks(ctx: ExamContext, template_id: str) -> bool:
    """True if any mark_entry exists for a batch of this template (→ destructive PUT is unsafe)."""
    batches = _rows(
        ctx.supabase.table("marking_batches").select("id").eq("template_id", template_id).execute()
    )
    batch_ids = [b["id"] for b in batches]
    if not batch_ids:
        return False
    marks = _rows(
        ctx.supabase.table("mark_entries").select("id").in_("batch_id", batch_ids).limit(1).execute()
    )
    return bool(marks)



def _model_fields_set(model: Any) -> set[str]:
    """Return fields explicitly provided by the client (Pydantic v1/v2 compatible)."""
    if hasattr(model, "model_fields_set"):
        return set(model.model_fields_set)
    return set(getattr(model, "__fields_set__", set()))


def _model_dump(model: Any) -> Dict[str, Any]:
    """Dump a Pydantic model without pinning this router to v1/v2 APIs."""
    if hasattr(model, "model_dump"):
        return model.model_dump()
    return model.dict()


def _template_meta_updates(body: UpdateTemplateMetaRequest, *, include_explicit_nulls: bool = False) -> Dict[str, Any]:
    data = _model_dump(body)
    if include_explicit_nulls:
        fields = _model_fields_set(body)
        return {k: data[k] for k in fields if k in data}
    return {k: v for k, v in data.items() if v is not None}

def _parse_storage_loc(storage_loc: str) -> Tuple[str, str]:
    bucket, sep, path = (storage_loc or "").partition("/")
    if not bucket or not sep or not path:
        raise ValueError(f"Invalid storage_loc: {storage_loc!r}")
    return bucket, path


def _lookup_exam_storage_loc(exam_id: str) -> Optional[str]:
    try:
        sb = SupabaseServiceRoleClient().supabase
        res = sb.table("eb_exams").select("storage_loc").eq("id", exam_id).limit(1).execute()
        row = _first(res)
        return row.get("storage_loc") if row else None
    except Exception as exc:
        logger.warning(f"storage_loc lookup failed for exam_id={exam_id}: {exc}")
        return None


async def _parse_create_template_request(request: Request) -> tuple[CreateTemplateRequest, Optional[UploadFile]]:
    content_type = request.headers.get("content-type", "")
    if "multipart/form-data" in content_type:
        form = await request.form()
        payload: Dict[str, Any] = {}
        for key in ("title", "subject", "exam_id", "exam_code", "source_file_id", "page_count", "institute_id"):
            value = form.get(key)
            if value is not None and value != "":
                payload[key] = value
        upload = form.get("source_pdf")
        if upload is not None and not hasattr(upload, "read"):
            raise HTTPException(status_code=400, detail="source_pdf must be a file upload")
        if upload is not None and payload.get("source_file_id"):
            raise HTTPException(status_code=400, detail="Use either source_file_id or source_pdf, not both")
        return CreateTemplateRequest(**payload), upload

    try:
        data = await request.json()
    except Exception as exc:
        raise HTTPException(status_code=400, detail=f"Invalid request body: {exc}")
    return CreateTemplateRequest(**data), None


async def _upload_template_source_file(
    ctx: ExamContext,
    institute_id: str,
    upload: UploadFile,
) -> str:
    file_bytes = await upload.read()
    if not file_bytes:
        raise HTTPException(status_code=400, detail="Uploaded PDF is empty")
    if upload.content_type and upload.content_type != "application/pdf":
        raise HTTPException(status_code=400, detail="Uploaded file must be a PDF")

    service = SupabaseServiceRoleClient()
    storage = StorageAdmin()

    cabinet_name = SOURCE_CABINET_NAME
    existing = _first(
        service.supabase.table("file_cabinets")
        .select("id")
        .eq("user_id", ctx.user_id)
        .eq("name", cabinet_name)
        .limit(1)
        .execute()
    )
    if existing:
        cabinet_id = existing["id"]
    else:
        created_cabinet = _first(
            service.supabase.table("file_cabinets")
            .insert({"user_id": ctx.user_id, "name": cabinet_name})
            .execute()
        )
        if not created_cabinet:
            raise HTTPException(status_code=500, detail="Failed to create upload cabinet")
        cabinet_id = created_cabinet["id"]

    file_id = str(uuid.uuid4())
    safe_name = os.path.basename(upload.filename or "template.pdf")
    # Use the shared users bucket (exists on all envs). Per-institute private buckets
    # (cc.institutes.<id>.private) are a future multi-tenant provisioning concern and are NOT
    # created on dev .94 — using one here failed with "Bucket not found". The institute is already
    # namespaced in the storage path + enforced by RLS on the files row.
    bucket = SOURCE_BUCKET_FALLBACK
    storage_path = f"exam-marker/{institute_id or 'noinst'}/{cabinet_id}/{file_id}/{safe_name}"

    try:
        storage.upload_file(bucket, storage_path, file_bytes, "application/pdf", upsert=True)
    except Exception as exc:
        raise HTTPException(status_code=500, detail=f"Storage upload failed: {exc}")

    inserted = _first(
        service.supabase.table("files").insert(
            {
                "id": file_id,
                "cabinet_id": cabinet_id,
                "name": safe_name,
                "path": storage_path,
                "bucket": bucket,
                "mime_type": "application/pdf",
                "uploaded_by": ctx.user_id,
                "size_bytes": len(file_bytes),
                "source": "classroomcopilot-web",
                "is_directory": False,
                "relative_path": safe_name,
                "processing_status": "uploaded",
            }
        ).execute()
    )
    if not inserted:
        raise HTTPException(status_code=500, detail="Failed to create file record")

    return file_id


# ─── templates ───────────────────────────────────────────────────────────────


@router.post("/templates")
async def create_template(
    request: Request,
    ctx: ExamContext = Depends(get_exam_context),
) -> Dict[str, Any]:
    body, upload = await _parse_create_template_request(request)
    institute_id = ctx.resolve_institute(body.institute_id)

    if body.exam_id and body.source_file_id:
        raise HTTPException(status_code=400, detail="Use either exam_id or source_file_id, not both")

    exam_code = body.exam_code
    if body.exam_id and not exam_code:
        exam_code = lookup_exam_code(body.exam_id)

    source_file_id = body.source_file_id
    if upload is not None:
        source_file_id = await _upload_template_source_file(ctx, institute_id, upload)

    row = {
        "title": body.title,
        "subject": body.subject,
        "exam_id": body.exam_id,
        "exam_code": exam_code,
        "source_file_id": source_file_id,
        "page_count": body.page_count,
        "institute_id": institute_id,
        "teacher_id": ctx.user_id,
        "status": "draft",
    }
    row = {k: v for k, v in row.items() if v is not None}

    res = ctx.supabase.table("exam_templates").insert(row).execute()
    created = _first(res)
    if not created:
        raise HTTPException(status_code=500, detail="Failed to create template")
    logger.info(f"Exam template created: {created.get('id')} by {ctx.user_id}")
    return created


@router.get("/catalogue")
async def list_catalogue_papers() -> Dict[str, Any]:
    """Lightweight exam-board paper catalogue for the create dialog."""
    try:
        sb = SupabaseServiceRoleClient().supabase
        res = (
            sb.table("eb_exams")
            .select("id, exam_code, spec_code, paper_code, tier, session, type_code, storage_loc")
            .eq("type_code", "QP")
            .order("exam_code")
            .execute()
        )
        return {"papers": _rows(res)}
    except Exception as exc:
        raise HTTPException(status_code=502, detail=f"Could not load catalogue papers: {exc}")


@router.get("/templates")
async def list_templates(
    include_archived: bool = False,
    institute_id: Optional[str] = None,
    ctx: ExamContext = Depends(get_exam_context),
) -> Dict[str, Any]:
    # RLS already scopes to the caller's institutes; the optional filter narrows within that.
    q = ctx.supabase.table("exam_templates").select("*")
    if institute_id:
        q = q.eq("institute_id", institute_id)
    if not include_archived:
        q = q.neq("status", "archived")
    res = q.order("updated_at", desc=True).execute()
    return {"templates": _rows(res)}


@router.get("/templates/{template_id}")
async def get_template(
    template_id: str,
    ctx: ExamContext = Depends(get_exam_context),
) -> Dict[str, Any]:
    template = _fetch_template_or_404(ctx, template_id)
    questions = _rows(
        ctx.supabase.table("exam_questions").select("*").eq("template_id", template_id).order("order").execute()
    )
    response_areas = _rows(
        ctx.supabase.table("exam_response_areas").select("*").eq("template_id", template_id).execute()
    )
    boundaries = _rows(
        ctx.supabase.table("exam_boundaries").select("*").eq("template_id", template_id).execute()
    )
    layout = _rows(
        ctx.supabase.table("exam_template_layout")
        .select("*")
        .eq("template_id", template_id)
        .order("page_index")
        .execute()
    )
    return {
        **template,
        "questions": questions,
        "response_areas": response_areas,
        "boundaries": boundaries,
        "layout": layout,
    }


@router.get("/templates/{template_id}/source-pdf")
async def get_template_source_pdf(
    template_id: str,
    ctx: ExamContext = Depends(get_exam_context),
) -> Response:
    template = _fetch_template_or_404(ctx, template_id)
    _require_source_visibility_or_404(ctx, template)

    bucket: Optional[str] = None
    path: Optional[str] = None

    if template.get("exam_id"):
        storage_loc = _lookup_exam_storage_loc(template["exam_id"])
        if not storage_loc:
            raise HTTPException(status_code=404, detail="Template source not found")
        try:
            bucket, path = _parse_storage_loc(storage_loc)
        except ValueError:
            raise HTTPException(status_code=404, detail="Template source not found")
    elif template.get("source_file_id"):
        # Resolve the file row via service role (authz already done above: the caller proved they
        # can see this template, and source_file_id is the template's own file). Reading `files`
        # as-the-user trips a pre-existing broken RLS policy on cabinet_memberships
        # (42P17 infinite recursion) — documented service-role exception, like the catalogue lookup.
        file_row = _first(
            SupabaseServiceRoleClient().supabase.table("files")
            .select("bucket, path, mime_type, name")
            .eq("id", template["source_file_id"])
            .limit(1)
            .execute()
        )
        if not file_row or not file_row.get("bucket") or not file_row.get("path"):
            raise HTTPException(status_code=404, detail="Template source not found")
        bucket = file_row["bucket"]
        path = file_row["path"]
    else:
        raise HTTPException(status_code=404, detail="Template source not found")

    if not bucket or not path:
        raise HTTPException(status_code=404, detail="Template source not found")

    try:
        pdf_bytes = StorageAdmin().download_file(bucket, path)
    except Exception as exc:
        logger.warning(f"Template source download failed for template {template_id}: {exc}")
        raise HTTPException(status_code=404, detail="Template source not found")

    return Response(content=pdf_bytes, media_type="application/pdf")


@router.put("/templates/{template_id}")
async def replace_template(
    template_id: str,
    body: TemplateReplaceRequest,
    background_tasks: BackgroundTasks,
    ctx: ExamContext = Depends(get_exam_context),
) -> Dict[str, Any]:
    """Full-replace canvas save (R5.2). Replaces questions/response_areas/boundaries wholesale.

    Note: the delete-then-insert spans several PostgREST calls and is therefore not atomic;
    acceptable for the small (~20-question) payloads this carries. A transactional RPC is a
    later hardening step if concurrent canvas saves become a concern.
    """
    template = _fetch_template_or_404(ctx, template_id)
    _require_owner(ctx, template)

    # Data-loss guard: the wholesale question delete below cascades to mark_entries
    # (mark_entries.question_id → exam_questions ON DELETE CASCADE). Refuse a structural
    # full-replace once any marks have been recorded against this template's batches, so
    # re-saving the setup canvas mid-marking can't silently wipe a teacher's marking work.
    # (Mark-scheme tweaks use PATCH /questions/{id}, which is unaffected.)
    if _template_has_recorded_marks(ctx, template_id):
        raise HTTPException(
            status_code=409,
            detail="Template has recorded marks; structural full-replace is blocked. "
                   "Edit questions individually via PATCH /questions/{id}.",
        )

    # Optional template-level metadata update alongside the canvas.
    if body.meta:
        updates = _template_meta_updates(body.meta)
        if updates:
            ctx.supabase.table("exam_templates").update(updates).eq("id", template_id).execute()

    sb = ctx.supabase
    # Clear existing children. Order matters: response_areas/boundaries reference questions, so
    # remove them first (we delete by template_id rather than rely on cascade for predictability).
    sb.table("exam_response_areas").delete().eq("template_id", template_id).execute()
    sb.table("exam_boundaries").delete().eq("template_id", template_id).execute()
    sb.table("exam_template_layout").delete().eq("template_id", template_id).execute()
    sb.table("exam_questions").delete().eq("template_id", template_id).execute()

    # Re-insert, preserving client-supplied UUIDs (Neo4j join keys, spec §2).
    if body.questions:
        q_rows = []
        for q in body.questions:
            r = {
                "template_id": template_id,
                "parent_id": q.parent_id,
                "label": q.label,
                "order": q.order,
                "max_marks": q.max_marks,
                "answer_type": q.answer_type,
                "mcq_options": q.mcq_options,
                "mark_scheme": q.mark_scheme,
                "is_container": q.is_container,
                "spec_ref": q.spec_ref,
                "bounds": q.bounds,   # drawn Part box (73); null for derived main questions
                "page": q.page,
                "source": q.source,
                "confirmed": q.confirmed,
                "confidence": q.confidence,
                "derivation": q.derivation,
            }
            if q.id:
                r["id"] = q.id
            q_rows.append({k: v for k, v in r.items() if v is not None})
        sb.table("exam_questions").insert(q_rows).execute()

    if body.response_areas:
        ra_rows = []
        for ra in body.response_areas:
            r = {
                "template_id": template_id,
                "question_id": ra.question_id,
                "page": ra.page,
                "bounds": ra.bounds,
                "kind": ra.kind,
                "response_form": ra.response_form,
                "context_type": ra.context_type,   # 73: optional Context differentiation
                "source": ra.source,
                "confirmed": ra.confirmed,
                "confidence": ra.confidence,
                "mark_subtype": ra.mark_subtype,
                "derivation": ra.derivation,
            }
            if ra.id:
                r["id"] = ra.id
            ra_rows.append({k: v for k, v in r.items() if v is not None})
        sb.table("exam_response_areas").insert(ra_rows).execute()

    if body.boundaries:
        b_rows = []
        for b in body.boundaries:
            r = {
                "template_id": template_id,
                "question_id": b.question_id,
                "label": b.label,
                "page_index": b.page_index,
                "y": b.y,
                "bounds": b.bounds,
                "source": b.source,
                "confirmed": b.confirmed,
                "confidence": b.confidence,
                "derivation": b.derivation,
            }
            if b.id:
                r["id"] = b.id
            b_rows.append({k: v for k, v in r.items() if v is not None})
        sb.table("exam_boundaries").insert(b_rows).execute()

    if body.layout:
        layout_rows = []
        for item in body.layout:
            r = {
                "template_id": template_id,
                "page_index": item.page_index,
                "role": item.role,
                "margin_left": item.margin_left,
                "margin_right": item.margin_right,
                "margin_top": item.margin_top,
                "margin_bottom": item.margin_bottom,
                "margins_enabled": item.margins_enabled,
                "source": item.source,
                "confirmed": item.confirmed,
                "confidence": item.confidence,
                "derivation": item.derivation,
                "meta": item.meta,
            }
            if item.id:
                r["id"] = item.id
            layout_rows.append({k: v for k, v in r.items() if v is not None})
        sb.table("exam_template_layout").insert(layout_rows).execute()

    logger.info(
        f"Exam template {template_id} replaced: {len(body.questions)} questions, "
        f"{len(body.response_areas)} regions, {len(body.boundaries)} boundaries, "
        f"{len(body.layout)} layout rows"
    )
    # R3.5.4: a successful save enqueues a graph projection into cc.public.exams. BackgroundTasks
    # is acceptable for Sprint 4 (durability via a real queue is a later step); failures are
    # swallowed so the canvas save itself never fails on a graph hiccup.
    background_tasks.add_task(project_template_safe, template_id)
    return await get_template(template_id, ctx)


@router.patch("/templates/{template_id}")
async def patch_template_meta(
    template_id: str,
    body: UpdateTemplateMetaRequest,
    ctx: ExamContext = Depends(get_exam_context),
) -> Dict[str, Any]:
    """Metadata-only template update.

    Unlike PUT /templates/{id}, this never deletes/re-inserts questions, response areas or
    boundaries, so it is safe after marking has started. RLS scopes the initial read and
    owner-only writes are enforced explicitly like the structural save path.
    """
    updates = _template_meta_updates(body, include_explicit_nulls=True)
    if not updates:
        raise HTTPException(status_code=400, detail="No fields to update")

    template = _fetch_template_or_404(ctx, template_id)
    _require_owner(ctx, template)

    res = ctx.supabase.table("exam_templates").update(updates).eq("id", template_id).execute()
    updated = _first(res)
    if not updated:
        raise HTTPException(status_code=404, detail="Template not found")
    return updated


@router.delete("/templates/{template_id}")
async def archive_template(
    template_id: str,
    ctx: ExamContext = Depends(get_exam_context),
) -> Dict[str, Any]:
    """Soft-delete: status='archived' (R5.2). Never hard-deletes a teacher's work."""
    template = _fetch_template_or_404(ctx, template_id)
    _require_owner(ctx, template)
    ctx.supabase.table("exam_templates").update({"status": "archived"}).eq("id", template_id).execute()
    return {"status": "archived", "id": template_id}


@router.post("/templates/{template_id}/neo4j-sync")
async def neo4j_sync(
    template_id: str,
    ctx: ExamContext = Depends(get_exam_context),
) -> Dict[str, Any]:
    """Manual graph-projection trigger (R5.3) for dev/backfill — runs synchronously and returns
    counts. Auth/ownership is checked as-the-user; the projection itself uses service role
    (R3.5.1, the documented graph-writer path)."""
    template = _fetch_template_or_404(ctx, template_id)
    _require_owner(ctx, template)
    try:
        counts = project_template(template_id)
    except Exception as exc:
        logger.error(f"Manual neo4j-sync failed for template {template_id}: {exc}")
        raise HTTPException(status_code=502, detail=f"Projection failed: {exc}")
    return {"status": "ok", "projection": counts}


# ─── questions (granular edit path, R5.2) ────────────────────────────────────


@router.patch("/questions/{question_id}")
async def patch_question(
    question_id: str,
    body: PatchQuestionRequest,
    ctx: ExamContext = Depends(get_exam_context),
) -> Dict[str, Any]:
    updates = {k: v for k, v in _model_dump(body).items() if v is not None}
    if not updates:
        raise HTTPException(status_code=400, detail="No fields to update")

    # RLS (exam_questions_all) enforces that the question belongs to a template owned by the
    # caller; an out-of-scope id updates zero rows → 404, so no explicit pre-fetch is needed.
    res = ctx.supabase.table("exam_questions").update(updates).eq("id", question_id).execute()
    updated = _first(res)
    if not updated:
        raise HTTPException(status_code=404, detail="Question not found")
    return updated