"""LLM-fallback CSV parser.

When the deterministic Trading 212 parser (``csv_import.parse_t212_csv``)
raises ``CSVImportError`` on an unrecognised format, this service kicks
in:

1. Detect the CSV dialect (delimiter, preamble offset).
2. Compute a fingerprint of the normalised header row.
3. Look up ``CsvFormatTemplate`` by fingerprint. On hit, replay the
   cached column-mapping deterministically. On miss, ask the LLM for a
   mapping, validate it, persist a new template, and apply it.

The LLM sees only headers + the first 3-5 sample rows. It returns a
column-mapping JSON, never transcribed numbers. The system never
auto-promotes a learned format to a hand-written parser — the operator
does that by inspecting collected ``sample_row`` values.
"""
from __future__ import annotations

import csv
import hashlib
import io
import json

import httpx
from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.db import utcnow
from app.logging import get_logger
from app.models import CsvFormatTemplate
from app.services.csv_import import CSVImportError, ParsedPie, ParsedPosition
from app.services.openrouter import LogResult, call_llm

# ---------------------------------------------------------------------------
# Module-level constants
# ---------------------------------------------------------------------------

# Cap for how many leading lines we'll scan looking for the header row.
# Real broker preambles are typically 1-10 lines.
_MAX_PREAMBLE_SCAN = 30

# Number of sample rows to send to the LLM and max token budget for the reply.
_LLM_SAMPLES = 5
_LLM_MAX_TOKENS = 400

# Required and optional keys in the LLM-returned column mapping.
_REQUIRED_MAPPING_KEYS = ("ticker_col", "qty_col")
_OPTIONAL_MAPPING_KEYS = ("name_col", "cost_col", "currency_col")

# Maximum CSV payload size accepted by parse_with_llm.
_MAX_CSV_BYTES = 1_048_576

log = get_logger("llm_csv_parser")


_SYSTEM_PROMPT = """\
You are an expert at recognising broker portfolio CSV formats.

You will be given the header row and 3-5 sample data rows from a CSV.
Identify which column contains each field. Return ONLY a single JSON
object, no prose, no markdown fences.

Schema (use the EXACT header string from the input; use null if no
column is a good match):

{
  "ticker_col":   "<header name or null>",
  "qty_col":      "<header name or null>",
  "name_col":     "<header name or null>",
  "cost_col":     "<header name or null>",   // average price per share
  "currency_col": "<header name or null>",
  "broker_label": "<short identifier like 'IBKR Activity Statement' or null>"
}

Rules:
- ticker_col and qty_col are required. If either is missing, return all nulls.
- Use the EXACT header string as it appears in the input — do not paraphrase.
- Output JSON ONLY. No prose, no code fences.
"""


class LLMParseError(CSVImportError):
    """Raised when the LLM call fails or returns an unusable mapping.

    Inherits from ``CSVImportError`` so route-level error handling can
    treat both deterministic and LLM-path failures uniformly when
    desired."""


def _fingerprint(headers: list[str]) -> str:
    """Stable hash of the header row.

    Lowercases each header, strips surrounding whitespace, joins with
    ``|`` (a character extremely unlikely to appear inside a real
    header), and returns the sha256 hex digest. Whitespace/case drift
    in the same broker's export does not change the fingerprint;
    adding or removing a column does."""
    normalised = "|".join(h.strip().lower() for h in headers)
    return hashlib.sha256(normalised.encode("utf-8")).hexdigest()


def _decode_raw(raw: bytes) -> str:
    """Best-effort UTF-8 decode with BOM strip and lossy fallback."""
    return raw.decode("utf-8-sig", errors="replace")


def _looks_numeric(value: str) -> bool:
    """True if ``value`` parses as a number after stripping common
    decoration (thousands separators, currency symbols, percent signs)."""
    s = value.strip().replace(",", "").replace("$", "").replace("€", "")
    s = s.replace("£", "").replace("%", "").lstrip("-+")
    if not s:
        return False
    try:
        float(s)
        return True
    except ValueError:
        return False


def _detect_dialect(raw: bytes) -> tuple[str, int]:
    """Detect (delimiter, preamble_rows).

    ``preamble_rows`` is the number of lines BEFORE the row we identify
    as the actual table header. The header row is the first line whose
    tokens are all non-numeric (so "Symbol,Quantity" is a header but
    "AAPL,100" is data). Falls back to assuming the first line is the
    header if no clear non-numeric line is found within the scan
    window.

    Raises ``LLMParseError`` on empty input."""
    if not raw or not raw.strip():
        raise LLMParseError("empty CSV")

    text = _decode_raw(raw)
    # csv.Sniffer is happy with ~4KB. Anything more and it gets slow.
    sample = text[:4096]
    try:
        dialect = csv.Sniffer().sniff(sample, delimiters=",;\t|")
        delimiter = dialect.delimiter
    except csv.Error:
        # Most broker exports are comma-delimited; default rather than
        # error out — the caller will still validate column shapes.
        delimiter = ","

    rows = list(csv.reader(io.StringIO(text), delimiter=delimiter))
    # Build a flat list of (index, non_empty_tokens) for rows within scan limit
    parsed = []
    for i, row in enumerate(rows):
        if i >= _MAX_PREAMBLE_SCAN:
            break
        non_empty = [c.strip() for c in row if c.strip()]
        parsed.append((i, non_empty))

    # Find the first all-alpha candidate row that is followed by a data
    # row (one that contains at least one numeric token). This
    # distinguishes real header rows from preamble metadata rows that
    # also happen to be all-text.
    for idx, (i, non_empty) in enumerate(parsed):
        if len(non_empty) < 2:
            continue
        all_alpha = all(not _looks_numeric(c) for c in non_empty)
        if not all_alpha:
            continue
        # Check whether the next non-empty row looks like data (has a numeric)
        for _, next_non_empty in parsed[idx + 1:]:
            if not next_non_empty:
                continue
            if any(_looks_numeric(c) for c in next_non_empty):
                return delimiter, i
            # Next row is also all-alpha → keep scanning
            break
    return delimiter, 0


def _validate_mapping(
    mapping: dict, headers: list[str], first_row: list[str],
) -> None:
    """Verify the LLM-returned mapping is sane.

    - ``ticker_col`` and ``qty_col`` are required (non-null).
    - Every named column must exist in ``headers``.
    - The value at ``qty_col`` on ``first_row`` must parse as a number.
    - The value at ``cost_col`` on ``first_row`` (if present) must parse
      as a number.

    Raises ``LLMParseError`` on any failure, with a message that names
    the specific problem (helpful for log forensics and for the
    user-facing 400)."""
    for key in _REQUIRED_MAPPING_KEYS:
        if not mapping.get(key):
            raise LLMParseError(
                f"LLM mapping missing required column: {key.replace('_col', '')}"
            )

    headers_set = set(headers)
    for key in _REQUIRED_MAPPING_KEYS + _OPTIONAL_MAPPING_KEYS:
        col = mapping.get(key)
        if col is not None and col not in headers_set:
            raise LLMParseError(
                f"LLM mapping references unknown column: {col!r}"
            )

    # Numeric sanity check: qty and (if present) cost must parse on row 1.
    header_index = {h: i for i, h in enumerate(headers)}
    qty_col = mapping["qty_col"]
    qty_value = first_row[header_index[qty_col]] if header_index[qty_col] < len(first_row) else ""
    if not _looks_numeric(qty_value):
        raise LLMParseError(
            f"LLM mapping qty_col={qty_col!r} maps to non-numeric value {qty_value!r}"
        )

    cost_col = mapping.get("cost_col")
    if cost_col is not None:
        cost_value = first_row[header_index[cost_col]] if header_index[cost_col] < len(first_row) else ""
        if cost_value and not _looks_numeric(cost_value):
            raise LLMParseError(
                f"LLM mapping cost_col={cost_col!r} maps to non-numeric value {cost_value!r}"
            )


def _parse_number(value: str) -> float | None:
    """Permissive float parse: strips thousands separators, currency
    symbols, percent signs. Returns None on failure (so callers can
    decide whether to skip or raise)."""
    s = value.strip().replace(",", "").replace("$", "")
    s = s.replace("€", "").replace("£", "").replace("%", "")
    if not s:
        return None
    try:
        return float(s)
    except ValueError:
        return None


def _apply_mapping(
    headers: list[str],
    data_rows: list[list[str]],
    mapping: dict,
) -> ParsedPie:
    """Iterate ``data_rows`` and produce a ``ParsedPie``.

    Rows that lack a parseable quantity (blank, non-numeric, zero) are
    silently skipped — broker exports often include summary or
    placeholder rows after the position list. ``name_col`` falls back
    to the ticker symbol when null."""
    idx = {h: i for i, h in enumerate(headers)}
    ticker_col = mapping["ticker_col"]
    qty_col = mapping["qty_col"]
    name_col = mapping.get("name_col")
    cost_col = mapping.get("cost_col")

    positions: list[ParsedPosition] = []
    invested_total = 0.0
    invested_seen = False

    for row in data_rows:
        if not any(c.strip() for c in row):
            continue
        ticker_raw = row[idx[ticker_col]] if idx[ticker_col] < len(row) else ""
        ticker = ticker_raw.strip().upper()
        if not ticker:
            continue
        qty_raw = row[idx[qty_col]] if idx[qty_col] < len(row) else ""
        qty = _parse_number(qty_raw)
        if qty is None or qty <= 0:
            continue
        avg_cost: float | None = None
        if cost_col is not None and idx[cost_col] < len(row):
            avg_cost = _parse_number(row[idx[cost_col]])
        invested_value: float | None = None
        if avg_cost is not None:
            invested_value = qty * avg_cost
            invested_total += invested_value
            invested_seen = True
        name = ""
        if name_col is not None and idx[name_col] < len(row):
            name = row[idx[name_col]].strip()
        if not name:
            name = ticker
        positions.append(ParsedPosition(
            slice=ticker,
            name=name,
            invested_value=invested_value,
            current_value=None,
            result=None,
            quantity=qty,
        ))

    return ParsedPie(
        name=None,
        positions=tuple(positions),
        invested=(invested_total if invested_seen else None),
        value=None,
        result=None,
    )


def _build_user_prompt(headers: list[str], samples: list[list[str]]) -> str:
    lines = ["headers: " + json.dumps(headers)]
    lines.append("samples:")
    for s in samples[:_LLM_SAMPLES]:
        lines.append("  " + ",".join(s))
    return "\n".join(lines)


async def _extract_mapping_via_llm(
    client: httpx.AsyncClient,
    headers: list[str],
    samples: list[list[str]],
) -> tuple[dict, LogResult]:
    """Single LLM call returning ``(mapping_dict, LogResult)``.

    The LLM is asked for a strict JSON object (no markdown). We attempt
    to parse the returned content; ``LLMParseError`` wraps any failure
    in a way callers can surface to the user."""
    messages = [
        {"role": "system", "content": _SYSTEM_PROMPT},
        {"role": "user", "content": _build_user_prompt(headers, samples)},
    ]
    try:
        result = await call_llm(client, messages, max_tokens=_LLM_MAX_TOKENS)
    except Exception as e:
        raise LLMParseError(f"LLM provider failed: {e}") from e

    content = (result.content or "").strip()
    # Strip code fences if the model added them despite instructions.
    if content.startswith("```"):
        content = content.strip("`")
        # Drop optional 'json' language tag.
        if content.lstrip().lower().startswith("json"):
            content = content.lstrip()[4:]
        content = content.strip()
    try:
        mapping = json.loads(content)
    except json.JSONDecodeError as e:
        raise LLMParseError(f"LLM did not return valid JSON: {e}") from e
    if not isinstance(mapping, dict):
        raise LLMParseError("LLM JSON was not an object")
    return mapping, result


async def parse_with_llm(raw: bytes, session: AsyncSession) -> ParsedPie:
    """Cache-first LLM-fallback CSV parse.

    On cache hit, applies the stored mapping deterministically and
    increments ``use_count``. On cache miss, calls the LLM, validates
    the returned mapping against the first data row, and persists a
    new ``CsvFormatTemplate``. Raises ``LLMParseError`` on any
    failure; the caller (route layer) maps that to a 400."""
    if len(raw) > _MAX_CSV_BYTES:
        raise LLMParseError("CSV too large (1 MB max)")
    if not raw or not raw.strip():
        raise LLMParseError("empty CSV")

    delimiter, preamble_rows = _detect_dialect(raw)
    text = _decode_raw(raw)

    reader = csv.reader(io.StringIO(text), delimiter=delimiter)
    rows = list(reader)
    if preamble_rows >= len(rows):
        raise LLMParseError("no header row found in CSV")
    headers = [c.strip() for c in rows[preamble_rows]]
    data_rows = rows[preamble_rows + 1:]
    if not headers:
        raise LLMParseError("empty header row")

    first_data_row = next(
        (r for r in data_rows if any(c.strip() for c in r)), None,
    )
    if first_data_row is None:
        raise LLMParseError("CSV contains a header but no data rows")

    fp = _fingerprint(headers)
    existing = (await session.execute(
        select(CsvFormatTemplate).where(CsvFormatTemplate.fingerprint == fp)
    )).scalar_one_or_none()

    if existing is not None:
        log.info("csv.format.cache_hit", fingerprint=fp,
                 broker_label=existing.broker_label, use_count=existing.use_count)
        pie = _apply_mapping(headers, data_rows, existing.mapping)
        if not pie.positions:
            raise LLMParseError(
                "cached mapping produced no positions — the broker may have "
                "changed their CSV shape; ask the operator to evict the "
                "stale template"
            )
        existing.use_count += 1
        existing.last_used_at = utcnow()
        await session.commit()
        return pie

    log.info("csv.format.cache_miss", fingerprint=fp,
             header_count=len(headers))
    samples = [r for r in data_rows[:_LLM_SAMPLES] if any(c.strip() for c in r)]
    async with httpx.AsyncClient(follow_redirects=True, timeout=30) as client:
        mapping, llm_log = await _extract_mapping_via_llm(client, headers, samples)
    _validate_mapping(mapping, headers, first_data_row)

    pie = _apply_mapping(headers, data_rows, mapping)
    if not pie.positions:
        raise LLMParseError(
            "LLM mapping validated but produced no positions — the file "
            "may not contain portfolio data"
        )

    now = utcnow()
    session.add(CsvFormatTemplate(
        fingerprint=fp,
        headers=headers,
        sample_row=first_data_row,
        mapping=mapping,
        preamble_rows=preamble_rows,
        delimiter=delimiter,
        broker_label=mapping.get("broker_label"),
        first_seen_at=now,
        last_used_at=now,
        use_count=1,
        llm_model=llm_log.model,
        llm_cost_usd=llm_log.cost_usd,
    ))
    await session.commit()
    return pie