"""
Reads doc_service_config.json from the shared config volume.
30-second TTL cache + env var overrides.

Env var overrides (all optional):
  DOC_MAX_PDF_MB   — max upload size in megabytes (e.g. "50")
"""
import asyncio
import json
import os
import time
from copy import deepcopy
from pathlib import Path

from app.core.config import settings

_DEFAULT_SYSTEM_PROMPT = (
    "You are a financial document analysis assistant. "
    "Given the text extracted from a PDF document, return ONLY a JSON object "
    "with no markdown, no code fences, and no explanation."
)

_DEFAULT_USER_TEMPLATE = (
    'Analyze the following document text and return a JSON object with exactly these keys:\n'
    'title (a short, descriptive human-readable title for this document, e.g. "ACME Corp Invoice April 2026", "Office Supplies Receipt", "Q1 Flower Delivery Order"),\n'
    'document_type (one of: invoice, bill, receipt, order, expense, revenue, unknown),\n'
    'total_amount (string or null),\n'
    'currency (string or null),\n'
    'vendor_name (string or null),\n'
    'customer_name (string or null),\n'
    'billing_address (string or null),\n'
    'customer_address (string or null),\n'
    'invoice_number (string or null),\n'
    'invoice_date (string or null),\n'
    'due_date (string or null),\n'
    'tags (array of short keyword strings describing the document),\n'
    'line_items (array of objects, each with keys: description, amount),\n'
    'suggested_categories (array of 2 to 5 short category name strings a user might want to file this document under, e.g. "Utilities", "Travel", "Software Subscriptions", "Client Invoices").\n'
    '\n'
    'Document text:\n'
    '{text}'
)

_DEFAULT_CONFIG: dict = {
    "documents": {"max_pdf_bytes": 20 * 1024 * 1024},
    "system_prompts": {
        "system": _DEFAULT_SYSTEM_PROMPT,
        "user_template": _DEFAULT_USER_TEMPLATE,
    },
}

_cache: dict | None = None
_cache_at: float = 0.0
_CACHE_TTL = 30.0


def _read_config_sync() -> dict:
    path = Path(settings.CONFIG_PATH)
    if not path.exists():
        base = deepcopy(_DEFAULT_CONFIG)
    else:
        with open(path) as f:
            base = json.load(f)
    return _apply_env_overrides(base)


def _apply_env_overrides(config: dict) -> dict:
    cfg = deepcopy(config)
    docs = cfg.setdefault("documents", {})
    if v := os.environ.get("DOC_MAX_PDF_MB"):
        try:
            docs["max_pdf_bytes"] = int(v) * 1024 * 1024
        except ValueError:
            pass
    return cfg


async def load_doc_config() -> dict:
    global _cache, _cache_at
    now = time.monotonic()
    if _cache is not None and (now - _cache_at) < _CACHE_TTL:
        return _cache
    data = await asyncio.to_thread(_read_config_sync)
    _cache = data
    _cache_at = now
    return data