"""
Aaron AI Stage 1 encoding helpers — single canonical implementation of:
  - extract_text(filepath) — four-extension text extraction
  - chunk_text(text, chunk_size, overlap) — word-based chunking
  - chunk_and_embed(text, source, embedder, filepath, folder) — produce ready-to-write rows
  - write_embeddings_batch(conn, batch) — server-side NOW() canonical INSERT

Used by watcher.py, ingest.py, corpus_integrity.py, and api.py /api/corpus/retry.
Replaces four separate extract reimplementations and two extract-chunk-embed paths.
"""

import hashlib
import json
import logging
from pathlib import Path

from docx import Document as DocxDocument
from pypdf import PdfReader
from pptx import Presentation

log = logging.getLogger("encoding")

SUPPORTED = {".docx", ".pdf", ".pptx", ".txt", ".md"}
DEFAULT_CHUNK_SIZE = 500
DEFAULT_CHUNK_OVERLAP = 50


def extract_text(filepath: Path) -> str:
    """Return the text of a supported file. Returns "" on any failure or
    unsupported extension. Does not write to ingest_failures — caller decides."""
    suffix = filepath.suffix.lower()
    try:
        if suffix == ".docx":
            doc = DocxDocument(filepath)
            return "\n".join(p.text for p in doc.paragraphs if p.text.strip())
        elif suffix == ".pdf":
            reader = PdfReader(filepath)
            return "".join(
                page.extract_text() + "\n"
                for page in reader.pages if page.extract_text()
            )
        elif suffix == ".pptx":
            prs = Presentation(filepath)
            return "\n".join(
                shape.text for slide in prs.slides
                for shape in slide.shapes
                if hasattr(shape, "text") and shape.text.strip()
            )
        elif suffix in {".txt", ".md"}:
            return filepath.read_text(encoding="utf-8", errors="ignore")
    except Exception as e:
        log.warning(f"Text extraction failed for {filepath.name}: {e}")
    return ""


def chunk_text(text: str,
               chunk_size: int = DEFAULT_CHUNK_SIZE,
               overlap: int = DEFAULT_CHUNK_OVERLAP) -> list[str]:
    """Word-based chunking. Empty chunks filtered."""
    words = text.split()
    chunks = []
    start = 0
    while start < len(words):
        chunk = " ".join(words[start:start + chunk_size])
        if chunk.strip():
            chunks.append(chunk)
        start += chunk_size - overlap
    return chunks


def _chunk_id(filepath, source: str, index: int) -> str:
    basis = str(filepath) if filepath else source
    return f"{hashlib.md5(basis.encode()).hexdigest()[:8]}_{index}"


def chunk_and_embed(text: str,
                    source: str,
                    embedder,
                    filepath=None,
                    folder=None) -> list[dict]:
    """Chunk text, embed each chunk, return rows ready for write_embeddings_batch."""
    chunks = chunk_text(text)
    if not chunks:
        return []
    embeddings = embedder.encode(chunks).tolist()
    rows = []
    for i, (chunk, emb) in enumerate(zip(chunks, embeddings)):
        rows.append({
            "id": _chunk_id(filepath, source, i),
            "document": chunk,
            "embedding": emb,
            "source": source,
            "type": "document",
            "metadata": {
                "source": source,
                "filepath": str(filepath) if filepath else source,
                "folder": folder,
            },
        })
    return rows


def write_embeddings_batch(conn, batch: list[dict]) -> int:
    """Single canonical INSERT. Sets created_at = NOW() server-side. Commits.

    Every row dict must supply 'type'. created_at is SQL-supplied (NOW()), so
    callers do not need to provide it. The application-layer assertion is the
    primary enforcement point for type — the column lacks NOT NULL because
    historical NULLs were resolved by the Improvement #2 backfill, and a
    Python-level raise gives a faster, more debuggable failure than a
    Postgres constraint error.
    """
    if not batch:
        return 0
    cur = conn.cursor()
    for row in batch:
        if not row.get("type"):
            raise ValueError(
                f"row {row.get('id')!r} missing 'type'; writers must supply it "
                f"(see Improvement #2 in docs/birdai-component-inventory)"
            )
        cur.execute("""
            INSERT INTO embeddings (id, document, embedding, source, type, created_at, metadata)
            VALUES (%s, %s, %s::vector, %s, %s, NOW(), %s)
            ON CONFLICT (id) DO UPDATE SET
                document   = EXCLUDED.document,
                embedding  = EXCLUDED.embedding,
                source     = EXCLUDED.source,
                type       = EXCLUDED.type,
                created_at = COALESCE(embeddings.created_at, EXCLUDED.created_at),
                metadata   = EXCLUDED.metadata
        """, (row["id"], row["document"], row["embedding"],
              row["source"], row["type"], json.dumps(row["metadata"])))
    conn.commit()
    return len(batch)