"""Parts inventory API.

JSON API plus a single self-contained frontend. Everything a bench lookup needs
lives behind /api; the browser app in static/ is the only consumer today, and
the future "what could I build with this?" feature is meant to be another
consumer of the same endpoints rather than a fork of them.
"""

import asyncio
import hashlib
import json
import math
import os
import sqlite3
from contextlib import asynccontextmanager
from typing import Annotated, Any, Literal

from fastapi import Depends, FastAPI, HTTPException, Query, Request, Response
from fastapi.exceptions import RequestValidationError
from fastapi.responses import HTMLResponse, JSONResponse
from fastapi.staticfiles import StaticFiles
from pydantic import AfterValidator, BaseModel, Field

from . import auth, db

STATIC_DIR = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "static")

CSP = (
    "default-src 'self'; "
    "img-src 'self' data:; "
    "style-src 'self' 'unsafe-inline'; "   # the UI sets inline style attributes
    "script-src 'self'; "
    "connect-src 'self'; "
    "frame-ancestors 'none'; "
    "base-uri 'none'; "
    "form-action 'self'"
)


@asynccontextmanager
async def lifespan(_app: FastAPI):
    db.init()
    yield


app = FastAPI(title="Parts Inventory", docs_url=None, redoc_url=None, lifespan=lifespan)


# --- validated field types --------------------------------------------------

def _required(v: str) -> str:
    v = v.strip()
    if not v:
        raise ValueError("must not be blank")
    return v


RequiredText = Annotated[str, AfterValidator(_required)]
Text = Annotated[str, AfterValidator(lambda v: v.strip())]


class SpecIn(BaseModel):
    key: RequiredText = Field(max_length=80)
    value: Text = Field(default="", max_length=400)


class PartIn(BaseModel):
    name: RequiredText = Field(max_length=200)
    description: Text = Field(default="", max_length=2000)
    category_id: int | None = None
    location_id: int | None = None
    manufacturer: Text = Field(default="", max_length=200)
    mpn: Text = Field(default="", max_length=120)
    quantity: float = Field(default=0, ge=0, allow_inf_nan=False)
    unit: RequiredText = Field(default="pcs", max_length=20)
    min_quantity: float | None = Field(default=None, ge=0, allow_inf_nan=False)
    cost_each: float | None = Field(default=None, ge=0, allow_inf_nan=False)
    datasheet_url: Text = Field(default="", max_length=1000)
    product_url: Text = Field(default="", max_length=1000)
    notes: Text = Field(default="", max_length=4000)
    specs: list[SpecIn] = []
    tags: list[str] = []


class PartPatch(BaseModel):
    name: RequiredText | None = Field(default=None, max_length=200)
    description: Text | None = Field(default=None, max_length=2000)
    category_id: int | None = None
    location_id: int | None = None
    manufacturer: Text | None = Field(default=None, max_length=200)
    mpn: Text | None = Field(default=None, max_length=120)
    quantity: float | None = Field(default=None, ge=0, allow_inf_nan=False)
    unit: RequiredText | None = Field(default=None, max_length=20)
    min_quantity: float | None = Field(default=None, ge=0, allow_inf_nan=False)
    cost_each: float | None = Field(default=None, ge=0, allow_inf_nan=False)
    datasheet_url: Text | None = Field(default=None, max_length=1000)
    product_url: Text | None = Field(default=None, max_length=1000)
    notes: Text | None = Field(default=None, max_length=4000)
    specs: list[SpecIn] | None = None
    tags: list[str] | None = None
    reason: Text = Field(default="edited", max_length=300)


# Columns a PATCH may legitimately set back to NULL. Everything else is NOT NULL
# in the schema, so an explicit null there is a client error, not a 500.
NULLABLE_COLUMNS = {"category_id", "location_id", "min_quantity", "cost_each"}
PART_COLUMNS = [
    "name", "description", "category_id", "location_id", "manufacturer", "mpn",
    "quantity", "unit", "min_quantity", "cost_each", "datasheet_url", "product_url", "notes",
]


class AdjustIn(BaseModel):
    delta: float = Field(allow_inf_nan=False)
    reason: Text = Field(default="", max_length=300)


class NodeIn(BaseModel):
    name: RequiredText = Field(max_length=120)
    parent_id: int | None = None
    unit: RequiredText = Field(default="pcs", max_length=20)
    spec_template: list[SpecIn] = []
    notes: Text = Field(default="", max_length=1000)
    sort_order: int = 0


class LoginIn(BaseModel):
    password: str = Field(max_length=500)


class PasswordChangeIn(BaseModel):
    current_password: str = Field(max_length=500)
    new_password: str = Field(max_length=500)


# --- helpers ----------------------------------------------------------------

def _specs_for(conn, part_ids: list[int]) -> dict[int, list[dict]]:
    if not part_ids:
        return {}
    marks = ",".join("?" * len(part_ids))
    rows = conn.execute(
        f"SELECT part_id, key, value FROM part_specs WHERE part_id IN ({marks}) ORDER BY position, key",
        part_ids,
    ).fetchall()
    out: dict[int, list[dict]] = {}
    for r in rows:
        out.setdefault(r["part_id"], []).append({"key": r["key"], "value": r["value"]})
    return out


def _tags_for(conn, part_ids: list[int]) -> dict[int, list[str]]:
    if not part_ids:
        return {}
    marks = ",".join("?" * len(part_ids))
    rows = conn.execute(
        f"""SELECT pt.part_id, t.name FROM part_tags pt
            JOIN tags t ON t.id = pt.tag_id
            WHERE pt.part_id IN ({marks}) ORDER BY t.name""",
        part_ids,
    ).fetchall()
    out: dict[int, list[str]] = {}
    for r in rows:
        out.setdefault(r["part_id"], []).append(r["name"])
    return out


def _serialise(rows, specs, tags, cat_paths, loc_paths) -> list[dict]:
    out = []
    for r in rows:
        d = dict(r)
        d["specs"] = specs.get(r["id"], [])
        d["tags"] = tags.get(r["id"], [])
        d["category_path"] = cat_paths.get(r["category_id"]) if r["category_id"] else None
        d["location_path"] = loc_paths.get(r["location_id"]) if r["location_id"] else None
        d["low_stock"] = (
            r["min_quantity"] is not None and r["quantity"] <= r["min_quantity"]
        )
        out.append(d)
    return out


def _write_specs(conn, part_id: int, specs: list[SpecIn]):
    conn.execute("DELETE FROM part_specs WHERE part_id = ?", (part_id,))
    seen = set()
    position = 0
    for s in specs:
        if s.key.lower() in seen:
            continue
        seen.add(s.key.lower())
        conn.execute(
            "INSERT INTO part_specs(part_id, key, value, position) VALUES (?,?,?,?)",
            (part_id, s.key, s.value, position),
        )
        position += 1


def _write_tags(conn, part_id: int, tags: list[str]):
    conn.execute("DELETE FROM part_tags WHERE part_id = ?", (part_id,))
    for raw in tags:
        name = raw.strip()
        if not name:
            continue
        conn.execute("INSERT OR IGNORE INTO tags(name) VALUES (?)", (name,))
        row = conn.execute("SELECT id FROM tags WHERE name = ? COLLATE NOCASE", (name,)).fetchone()
        if row:
            conn.execute(
                "INSERT OR IGNORE INTO part_tags(part_id, tag_id) VALUES (?,?)",
                (part_id, row["id"]),
            )


def _log_stock(conn, part_id: int, delta: float, after: float, reason: str):
    conn.execute(
        "INSERT INTO stock_log(part_id, delta, quantity_after, reason) VALUES (?,?,?,?)",
        (part_id, delta, after, reason),
    )


def _fetch_part(conn, part_id: int) -> dict:
    row = conn.execute("SELECT * FROM parts WHERE id = ?", (part_id,)).fetchone()
    if row is None:
        raise HTTPException(404, "Part not found")
    return _serialise(
        [row], _specs_for(conn, [part_id]), _tags_for(conn, [part_id]),
        db.tree_paths(conn, "categories"), db.tree_paths(conn, "locations"),
    )[0]


def _require_node(conn, table: str, node_id: int, label: str):
    if conn.execute(f"SELECT 1 FROM {table} WHERE id = ?", (node_id,)).fetchone() is None:
        raise HTTPException(404, f"{label} not found")


def _check_parent(conn, table: str, node_id: int, parent_id: int | None, label: str):
    """Reject re-parenting a node under itself or any of its own descendants.

    A direct self-parent is the obvious case; the indirect one (A under B, where
    B is already a child of A) is the one that actually corrupts the tree.
    """
    if parent_id is None:
        return
    if parent_id == node_id:
        raise HTTPException(400, f"A {label} cannot be its own parent")
    _require_node(conn, table, parent_id, f"Parent {label}")
    if parent_id in db.descendants(conn, table, node_id):
        raise HTTPException(400, f"A {label} cannot be moved beneath itself")


# --- error handling ---------------------------------------------------------

def _json_safe(value):
    """Make a validation-error payload encodable.

    FastAPI echoes the rejected value back in the error detail. When that value
    is Infinity or NaN — the very thing being rejected — the JSON encoder
    refuses it and a clean 422 turns into a serialisation failure. Stringify
    anything the encoder can't represent.
    """
    if isinstance(value, float):
        return value if math.isfinite(value) else str(value)
    if isinstance(value, dict):
        return {str(k): _json_safe(v) for k, v in value.items()}
    if isinstance(value, (list, tuple, set)):
        return [_json_safe(v) for v in value]
    if isinstance(value, (str, int, bool)) or value is None:
        return value
    return str(value)


@app.exception_handler(RequestValidationError)
def validation_error(request: Request, exc: RequestValidationError):
    return JSONResponse({"detail": _json_safe(exc.errors())}, status_code=422)


# --- middleware -------------------------------------------------------------

@app.middleware("http")
async def security_headers(request: Request, call_next):
    response = await call_next(request)
    headers = response.headers
    headers.setdefault("X-Content-Type-Options", "nosniff")
    headers.setdefault("X-Frame-Options", "DENY")
    headers.setdefault("Referrer-Policy", "no-referrer")
    headers.setdefault("Content-Security-Policy", CSP)
    if auth.is_https(request):
        headers.setdefault("Strict-Transport-Security", "max-age=31536000; includeSubDomains")
    if request.url.path.startswith("/static/"):
        # Asset URLs carry a content hash (see _index_html), so a versioned URL
        # is safe to cache forever and a deploy simply changes the URL. Without
        # the hash — someone hitting the bare path — it must not be cached, or
        # an intermediary can pin stale frontend code against a new API.
        if request.query_params.get("v"):
            headers["Cache-Control"] = "public, max-age=31536000, immutable"
        else:
            headers["Cache-Control"] = "no-cache"
    elif request.url.path.startswith("/api/"):
        headers["Cache-Control"] = "no-store"
    return response


# --- auth routes ------------------------------------------------------------

def _set_session_cookie(response: Response, request: Request, conn):
    response.set_cookie(
        auth.COOKIE_NAME,
        auth.issue_token(conn),
        max_age=auth.session_days() * 86400,
        httponly=True,
        samesite="lax",
        secure=auth.is_https(request),
        path="/",
    )


@app.get("/api/me")
def me(request: Request, conn=Depends(db.get_db)):
    if not auth.auth_enabled():
        return {"authenticated": True, "auth_required": False, "using_bootstrap_password": False}
    token = request.cookies.get(auth.COOKIE_NAME)
    authenticated = bool(token and auth.token_valid(token, conn))
    return {
        "authenticated": authenticated,
        "auth_required": True,
        # Surfaced so the UI can nag until the handed-over password is replaced.
        "using_bootstrap_password": authenticated and auth.using_bootstrap_password(conn),
        "min_password_length": auth.MIN_PASSWORD_LENGTH,
    }


@app.post("/api/login")
async def login(body: LoginIn, response: Response, request: Request, conn=Depends(db.get_db)):
    if not auth.auth_enabled():
        return {"authenticated": True, "auth_required": False}

    retry_after = auth.login_retry_after()
    if retry_after:
        raise HTTPException(
            429, "Too many failed attempts", headers={"Retry-After": str(retry_after)}
        )

    if not auth.check_password(conn, body.password):
        auth.record_failure()
        # Async sleep, so a burst of guesses can't tie up the worker threadpool
        # that real requests need.
        await asyncio.sleep(0.5)
        raise HTTPException(401, "Incorrect password")

    auth.clear_failures()
    _set_session_cookie(response, request, conn)
    return {
        "authenticated": True,
        "auth_required": True,
        "using_bootstrap_password": auth.using_bootstrap_password(conn),
    }


@app.post("/api/password", dependencies=[Depends(auth.require_auth)])
async def change_password(
    body: PasswordChangeIn, response: Response, request: Request, conn=Depends(db.get_db)
):
    """Change the password from inside the app.

    Requires the current password even though the caller already holds a valid
    session: a borrowed browser tab should not be enough to lock the owner out.
    """
    if not auth.auth_enabled():
        raise HTTPException(400, "Authentication is disabled, so there is no password to change")

    if not auth.check_password(conn, body.current_password):
        auth.record_failure()
        await asyncio.sleep(0.5)
        raise HTTPException(403, "Current password is incorrect")

    problem = auth.password_problem(body.new_password)
    if problem:
        raise HTTPException(422, problem)
    if body.new_password == body.current_password:
        raise HTTPException(422, "New password must be different from the current one")

    auth.clear_failures()
    # Bumps the session epoch, so every cookie issued before now stops working.
    auth.set_password(conn, body.new_password)
    # Re-issue for the caller, so changing the password doesn't log you out of
    # the tab you changed it in.
    _set_session_cookie(response, request, conn)
    return {"changed": True, "other_sessions_signed_out": True}


@app.post("/api/sessions/revoke", dependencies=[Depends(auth.require_auth)])
def revoke_sessions(response: Response, request: Request, conn=Depends(db.get_db)):
    """Sign out every other device, keeping this one signed in."""
    auth.bump_epoch(conn)
    _set_session_cookie(response, request, conn)
    return {"revoked": True}


@app.post("/api/logout")
def logout(response: Response):
    response.delete_cookie(auth.COOKIE_NAME, path="/")
    return {"authenticated": False}


# --- parts ------------------------------------------------------------------

@app.get("/api/parts", dependencies=[Depends(auth.require_auth)])
def list_parts(
    conn=Depends(db.get_db),
    q: str = "",
    category_id: int | None = None,
    location_id: int | None = None,
    tag: str = "",
    low_stock: bool = False,
    sort: Literal["relevance", "name", "quantity", "updated", "created", "location"] = "relevance",
    limit: int = Query(default=200, ge=1, le=1000),
    offset: int = Query(default=0, ge=0),
):
    where: list[str] = []
    params: list[Any] = []
    joins = ""
    order = "p.name COLLATE NOCASE ASC"

    q = q.strip()
    if q:
        match = db.fts_query(q)
        if match:
            joins += " JOIN parts_fts ON parts_fts.rowid = p.id "
            where.append("parts_fts MATCH ?")
            params.append(match)
            if sort == "relevance":
                order = "parts_fts.rank ASC, p.name COLLATE NOCASE ASC"

    if category_id is not None:
        ids = db.descendants(conn, "categories", category_id)
        where.append(f"p.category_id IN ({','.join('?' * len(ids))})")
        params.extend(ids)

    if location_id is not None:
        ids = db.descendants(conn, "locations", location_id)
        where.append(f"p.location_id IN ({','.join('?' * len(ids))})")
        params.extend(ids)

    if tag.strip():
        where.append(
            "p.id IN (SELECT pt.part_id FROM part_tags pt JOIN tags t ON t.id = pt.tag_id "
            "WHERE t.name = ? COLLATE NOCASE)"
        )
        params.append(tag.strip())

    if low_stock:
        where.append("p.min_quantity IS NOT NULL AND p.quantity <= p.min_quantity")

    if sort == "name":
        order = "p.name COLLATE NOCASE ASC"
    elif sort == "quantity":
        order = "p.quantity ASC, p.name COLLATE NOCASE ASC"
    elif sort == "updated":
        order = "p.updated_at DESC, p.id DESC"
    elif sort == "created":
        order = "p.created_at DESC, p.id DESC"
    elif sort == "location":
        order = "l.name COLLATE NOCASE ASC, p.name COLLATE NOCASE ASC"

    clause = (" WHERE " + " AND ".join(where)) if where else ""
    base = f"FROM parts p LEFT JOIN locations l ON l.id = p.location_id {joins} {clause}"

    total = conn.execute(f"SELECT COUNT(*) AS n {base}", params).fetchone()["n"]
    rows = conn.execute(
        f"SELECT p.* {base} ORDER BY {order} LIMIT ? OFFSET ?", params + [limit, offset]
    ).fetchall()

    ids = [r["id"] for r in rows]
    items = _serialise(
        rows, _specs_for(conn, ids), _tags_for(conn, ids),
        db.tree_paths(conn, "categories"), db.tree_paths(conn, "locations"),
    )
    return {"total": total, "limit": limit, "offset": offset, "items": items}


@app.post("/api/parts", dependencies=[Depends(auth.require_auth)], status_code=201)
def create_part(body: PartIn, conn=Depends(db.get_db)):
    if body.category_id is not None:
        _require_node(conn, "categories", body.category_id, "Category")
    if body.location_id is not None:
        _require_node(conn, "locations", body.location_id, "Location")
    cur = conn.execute(
        """INSERT INTO parts(name, description, category_id, location_id, manufacturer, mpn,
                             quantity, unit, min_quantity, cost_each, datasheet_url,
                             product_url, notes)
           VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?)""",
        (
            body.name, body.description, body.category_id, body.location_id,
            body.manufacturer, body.mpn, body.quantity, body.unit,
            body.min_quantity, body.cost_each, body.datasheet_url,
            body.product_url, body.notes,
        ),
    )
    part_id = cur.lastrowid
    _write_specs(conn, part_id, body.specs)
    _write_tags(conn, part_id, body.tags)
    if body.quantity:
        _log_stock(conn, part_id, body.quantity, body.quantity, "initial stock")
    db.reindex_part(conn, part_id)
    return _fetch_part(conn, part_id)


@app.get("/api/parts/{part_id}", dependencies=[Depends(auth.require_auth)])
def get_part(part_id: int, conn=Depends(db.get_db)):
    return _fetch_part(conn, part_id)


@app.patch("/api/parts/{part_id}", dependencies=[Depends(auth.require_auth)])
def update_part(part_id: int, body: PartPatch, conn=Depends(db.get_db)):
    fields = body.model_dump(exclude_unset=True)
    fields.pop("specs", None)
    fields.pop("tags", None)
    reason = fields.pop("reason", "edited") or "edited"

    for col, value in fields.items():
        if value is None and col not in NULLABLE_COLUMNS:
            raise HTTPException(422, f"'{col}' cannot be null")
    if fields.get("category_id") is not None:
        _require_node(conn, "categories", fields["category_id"], "Category")
    if fields.get("location_id") is not None:
        _require_node(conn, "locations", fields["location_id"], "Location")

    # Setting quantity is a read-modify-write like any adjustment, and has to be
    # logged the same way — "every change is recorded" has to mean every change,
    # or the history is worse than useless.
    db.begin_immediate(conn)
    row = conn.execute("SELECT quantity FROM parts WHERE id = ?", (part_id,)).fetchone()
    if row is None:
        raise HTTPException(404, "Part not found")

    sets, params = [], []
    for col in PART_COLUMNS:
        if col in fields:
            sets.append(f"{col} = ?")
            params.append(fields[col])
    if sets:
        sets.append("updated_at = datetime('now')")
        conn.execute(f"UPDATE parts SET {', '.join(sets)} WHERE id = ?", params + [part_id])

    if "quantity" in fields and fields["quantity"] != row["quantity"]:
        new_qty = fields["quantity"]
        _log_stock(conn, part_id, new_qty - row["quantity"], new_qty, reason)

    if body.specs is not None:
        _write_specs(conn, part_id, body.specs)
    if body.tags is not None:
        _write_tags(conn, part_id, body.tags)
    db.reindex_part(conn, part_id)
    return _fetch_part(conn, part_id)


@app.delete("/api/parts/{part_id}", dependencies=[Depends(auth.require_auth)])
def delete_part(part_id: int, conn=Depends(db.get_db)):
    cur = conn.execute("DELETE FROM parts WHERE id = ?", (part_id,))
    if cur.rowcount == 0:
        raise HTTPException(404, "Part not found")
    conn.execute("DELETE FROM parts_fts WHERE rowid = ?", (part_id,))
    return {"deleted": part_id}


@app.post("/api/parts/{part_id}/adjust", dependencies=[Depends(auth.require_auth)])
def adjust_part(part_id: int, body: AdjustIn, conn=Depends(db.get_db)):
    # Read and write under one write lock. Without it, concurrent adjustments
    # read the same starting quantity and silently overwrite each other, leaving
    # the stock log disagreeing with the stock.
    db.begin_immediate(conn)
    row = conn.execute("SELECT quantity FROM parts WHERE id = ?", (part_id,)).fetchone()
    if row is None:
        raise HTTPException(404, "Part not found")

    before = row["quantity"]
    after = round(max(0.0, before + body.delta), 4)
    # Log what actually happened. Asking for -999 against a stock of 7 removes
    # 7, and recording -999 would make the ledger unsummable.
    applied = round(after - before, 4)

    conn.execute(
        "UPDATE parts SET quantity = ?, updated_at = datetime('now') WHERE id = ?",
        (after, part_id),
    )
    _log_stock(conn, part_id, applied, after, body.reason)
    return _fetch_part(conn, part_id)


@app.get("/api/parts/{part_id}/history", dependencies=[Depends(auth.require_auth)])
def part_history(part_id: int, conn=Depends(db.get_db), limit: int = Query(default=50, ge=1, le=500)):
    if conn.execute("SELECT 1 FROM parts WHERE id = ?", (part_id,)).fetchone() is None:
        raise HTTPException(404, "Part not found")
    rows = conn.execute(
        "SELECT * FROM stock_log WHERE part_id = ? ORDER BY id DESC LIMIT ?", (part_id, limit)
    ).fetchall()
    return {"items": [dict(r) for r in rows]}


# --- categories & locations -------------------------------------------------

def _node_payload(conn, table: str) -> list[dict]:
    paths = db.tree_paths(conn, table)
    rows = conn.execute(
        f"SELECT * FROM {table} ORDER BY sort_order, name COLLATE NOCASE"
    ).fetchall()
    column = "category_id" if table == "categories" else "location_id"
    direct = {
        r["k"]: r["n"]
        for r in conn.execute(
            f"SELECT {column} AS k, COUNT(*) AS n FROM parts GROUP BY k"
        ).fetchall()
        if r["k"] is not None
    }
    # Counts roll up: "Electronics" reports everything filed under its children
    # too, matching what clicking it as a filter actually returns.
    children: dict[int, list[int]] = {}
    for r in rows:
        children.setdefault(r["parent_id"], []).append(r["id"])

    def rollup(node_id: int, seen: set[int]) -> int:
        total = direct.get(node_id, 0)
        for child in children.get(node_id, []):
            if child not in seen:
                total += rollup(child, seen | {node_id})
        return total

    out = []
    for r in rows:
        d = dict(r)
        d["path"] = paths.get(r["id"], r["name"])
        d["part_count"] = rollup(r["id"], set())
        d["direct_count"] = direct.get(r["id"], 0)
        if table == "categories":
            try:
                d["spec_template"] = json.loads(r["spec_template"] or "[]")
            except (TypeError, ValueError):
                d["spec_template"] = []
        out.append(d)
    out.sort(key=lambda d: d["path"].lower())
    return out


def _template_json(specs: list[SpecIn]) -> str:
    return json.dumps([{"key": s.key} for s in specs])


@app.get("/api/categories", dependencies=[Depends(auth.require_auth)])
def list_categories(conn=Depends(db.get_db)):
    return {"items": _node_payload(conn, "categories")}


@app.post("/api/categories", dependencies=[Depends(auth.require_auth)], status_code=201)
def create_category(body: NodeIn, conn=Depends(db.get_db)):
    if body.parent_id is not None:
        _require_node(conn, "categories", body.parent_id, "Parent category")
    try:
        cur = conn.execute(
            "INSERT INTO categories(name, parent_id, unit, spec_template, sort_order) VALUES (?,?,?,?,?)",
            (body.name, body.parent_id, body.unit, _template_json(body.spec_template), body.sort_order),
        )
    except sqlite3.IntegrityError:
        raise HTTPException(409, "A category with that name already exists here")
    return {"id": cur.lastrowid}


@app.patch("/api/categories/{cat_id}", dependencies=[Depends(auth.require_auth)])
def update_category(cat_id: int, body: NodeIn, conn=Depends(db.get_db)):
    # Before the first read: the affected-parts scan and the reindex that
    # follows it have to see one consistent tree, or a concurrent write can slip
    # between them and leave the search index describing the old taxonomy.
    db.begin_immediate(conn)
    _require_node(conn, "categories", cat_id, "Category")
    _check_parent(conn, "categories", cat_id, body.parent_id, "category")
    affected = db.parts_under(conn, "categories", cat_id)
    try:
        conn.execute(
            "UPDATE categories SET name=?, parent_id=?, unit=?, spec_template=?, sort_order=? WHERE id=?",
            (body.name, body.parent_id, body.unit, _template_json(body.spec_template),
             body.sort_order, cat_id),
        )
    except sqlite3.IntegrityError:
        raise HTTPException(409, "A category with that name already exists here")
    # The category path is part of every affected part's search text.
    db.reindex_parts(conn, affected)
    return {"id": cat_id}


@app.delete("/api/categories/{cat_id}", dependencies=[Depends(auth.require_auth)])
def delete_category(cat_id: int, conn=Depends(db.get_db)):
    # Before the first read: the affected-parts scan and the reindex that
    # follows it have to see one consistent tree, or a concurrent write can slip
    # between them and leave the search index describing the old taxonomy.
    db.begin_immediate(conn)
    _require_node(conn, "categories", cat_id, "Category")
    # Capture the parts first: ON DELETE SET NULL means they survive as
    # uncategorised rather than vanish, but their indexed path must be rebuilt.
    affected = db.parts_under(conn, "categories", cat_id)
    conn.execute("DELETE FROM categories WHERE id = ?", (cat_id,))
    db.reindex_parts(conn, affected)
    return {"deleted": cat_id}


@app.get("/api/locations", dependencies=[Depends(auth.require_auth)])
def list_locations(conn=Depends(db.get_db)):
    return {"items": _node_payload(conn, "locations")}


@app.post("/api/locations", dependencies=[Depends(auth.require_auth)], status_code=201)
def create_location(body: NodeIn, conn=Depends(db.get_db)):
    if body.parent_id is not None:
        _require_node(conn, "locations", body.parent_id, "Parent location")
    try:
        cur = conn.execute(
            "INSERT INTO locations(name, parent_id, notes, sort_order) VALUES (?,?,?,?)",
            (body.name, body.parent_id, body.notes, body.sort_order),
        )
    except sqlite3.IntegrityError:
        raise HTTPException(409, "A location with that name already exists here")
    return {"id": cur.lastrowid}


@app.patch("/api/locations/{loc_id}", dependencies=[Depends(auth.require_auth)])
def update_location(loc_id: int, body: NodeIn, conn=Depends(db.get_db)):
    # Before the first read: the affected-parts scan and the reindex that
    # follows it have to see one consistent tree, or a concurrent write can slip
    # between them and leave the search index describing the old taxonomy.
    db.begin_immediate(conn)
    _require_node(conn, "locations", loc_id, "Location")
    _check_parent(conn, "locations", loc_id, body.parent_id, "location")
    affected = db.parts_under(conn, "locations", loc_id)
    try:
        conn.execute(
            "UPDATE locations SET name=?, parent_id=?, notes=?, sort_order=? WHERE id=?",
            (body.name, body.parent_id, body.notes, body.sort_order, loc_id),
        )
    except sqlite3.IntegrityError:
        raise HTTPException(409, "A location with that name already exists here")
    db.reindex_parts(conn, affected)
    return {"id": loc_id}


@app.delete("/api/locations/{loc_id}", dependencies=[Depends(auth.require_auth)])
def delete_location(loc_id: int, conn=Depends(db.get_db)):
    # Before the first read: the affected-parts scan and the reindex that
    # follows it have to see one consistent tree, or a concurrent write can slip
    # between them and leave the search index describing the old taxonomy.
    db.begin_immediate(conn)
    _require_node(conn, "locations", loc_id, "Location")
    affected = db.parts_under(conn, "locations", loc_id)
    conn.execute("DELETE FROM locations WHERE id = ?", (loc_id,))
    db.reindex_parts(conn, affected)
    return {"deleted": loc_id}


@app.get("/api/tags", dependencies=[Depends(auth.require_auth)])
def list_tags(conn=Depends(db.get_db)):
    rows = conn.execute(
        """SELECT t.name, COUNT(pt.part_id) AS n FROM tags t
           LEFT JOIN part_tags pt ON pt.tag_id = t.id
           GROUP BY t.id ORDER BY t.name COLLATE NOCASE"""
    ).fetchall()
    return {"items": [dict(r) for r in rows]}


@app.get("/api/stats", dependencies=[Depends(auth.require_auth)])
def stats(conn=Depends(db.get_db)):
    row = conn.execute(
        """SELECT COUNT(*) AS parts,
                  COALESCE(SUM(quantity * COALESCE(cost_each, 0)), 0) AS value,
                  SUM(CASE WHEN min_quantity IS NOT NULL AND quantity <= min_quantity
                           THEN 1 ELSE 0 END) AS low
           FROM parts"""
    ).fetchone()
    return {
        "parts": row["parts"],
        "low_stock": row["low"] or 0,
        "estimated_value": round(row["value"] or 0, 2),
    }


@app.get("/healthz")
def healthz():
    return {"ok": True}


# --- frontend ---------------------------------------------------------------

app.mount("/static", StaticFiles(directory=STATIC_DIR), name="static")

_index_cache: str | None = None


def _index_html() -> str:
    """index.html with a content hash appended to each asset URL.

    Cloudflare sits in front of this and will happily serve a cached app.js for
    hours. Versioned URLs mean a deploy changes the URL itself, so a stale copy
    can never be paired with a newer API.
    """
    global _index_cache
    if _index_cache is None:
        with open(os.path.join(STATIC_DIR, "index.html"), encoding="utf-8") as fh:
            html = fh.read()
        for asset in ("app.css", "app.js"):
            with open(os.path.join(STATIC_DIR, asset), "rb") as fh:
                digest = hashlib.sha256(fh.read()).hexdigest()[:10]
            html = html.replace(f"/static/{asset}", f"/static/{asset}?v={digest}")
        _index_cache = html
    return _index_cache


def _index_response(status_code: int = 200) -> HTMLResponse:
    return HTMLResponse(
        _index_html(), status_code=status_code, headers={"Cache-Control": "no-store"}
    )


@app.get("/")
def index():
    return _index_response()


@app.exception_handler(404)
def not_found(request: Request, exc):
    path = request.url.path
    if path.startswith("/api/") or path.startswith("/static/") or path == "/healthz":
        return JSONResponse({"detail": "Not found"}, status_code=404)
    return _index_response()