"""Seam adapter: parsed-document artifact → the pipeline's internal `Chunk`.

**This is the only file that knows the seam's shape.** Every stage downstream
depends on `models.Chunk` alone, so when the artifact contract settles with
Sofhia the change lands here and nowhere else.

The seam is still under discussion (KNOWLEDGE_PIPELINE_TODO.md §3), so this
reads defensively: it accepts either the draft's field names or the prototype's,
takes plain dicts, and tolerates missing optional structure. It deliberately
does **not** accept a file path — extraction never opens a document. That
constraint is the point of the split, not an implementation detail.

Two things it must never do:
  - reflow, strip or whitespace-normalise `text`. Span validation locates quoted
    spans literally inside it; cleaning the text makes the lookup fail and the
    field go silently null, which presents as a bad model.
  - infer a page number it was not given. A wrong page sends the reviewer to the
    wrong part of the document, which is worse than no page at all.
"""

from __future__ import annotations

import hashlib
import json
from typing import Any

from .models import Chunk, ParsedDoc

# Field names accepted for the same concept. `page_idx`/`page_idxs` are the
# parsing half's contract; the rest are earlier drafts and the prototype's shape,
# kept so old fixtures still load.
#
# Page numbers are 0-BASED throughout, exactly as the parser reports them. No
# conversion happens anywhere in this pipeline: converting to 1-based is the
# review UI's job, done once at display time. An off-by-one here would be
# invisible until an expert opened the wrong page.
_PAGE_KEYS = ("page_idx", "page_start", "page")
_PAGES_KEYS = ("page_idxs", "pages", "page_list")
_PAGE_END_KEYS = ("page_idx_end", "page_end")


def chunk_from_dict(raw: dict[str, Any], doc_id: str, ordinal: int = 0) -> Chunk:
    """Map one artifact item onto the internal chunk.

    `kind`/`is_tabular` are reconciled: the draft carries a `kind` discriminator
    while the prototype carried booleans. Either is accepted.
    """
    kind = raw.get("kind")
    pages = _first(raw, _PAGES_KEYS) or []
    page_start = _first(raw, _PAGE_KEYS)
    if page_start is None:
        page_start = min(pages) if pages else 0
    page_end = _first(raw, _PAGE_END_KEYS)
    if page_end is None:
        page_end = max(pages) if pages else page_start

    return Chunk(
        chunk_id=raw.get("chunk_id") or f"{doc_id}#{ordinal:04d}",
        doc_id=raw.get("doc_id") or doc_id,
        text=raw["text"],  # verbatim, never cleaned
        page_start=int(page_start),
        page_end=int(page_end),
        ordinal=int(raw.get("ordinal", ordinal)),
        section_no=raw.get("section_no"),
        heading=raw.get("heading"),
        has_formula=bool(raw.get("has_formula", kind == "equation")),
        is_tabular=bool(raw.get("is_tabular", kind == "table")),
        bold_spans=list(raw.get("bold_spans") or []),
    )


def parsed_doc_from_artifact(
    artifact: Any,
    doc_id: str | None = None,
    source_ref: str = "",
    parser_name: str = "unknown",
    parser_version: str = "",
) -> ParsedDoc:
    """Build a `ParsedDoc` from either shape of the artifact.

    Accepts a bare `list[chunk]` (the draft's current shape) or a mapping with a
    `chunks` key (the shape proposed for the document-level envelope). When the
    envelope lands, its `content_hash`/`n_pages`/`version` are preferred over
    the values derived here.
    """
    if hasattr(artifact, "model_dump"):  # a ParsedDocument from the parsing half
        artifact = artifact.model_dump(mode="json")

    if isinstance(artifact, dict):
        items = artifact.get("chunks") or []
        doc_id = doc_id or artifact.get("doc_id")
        source_ref = source_ref or artifact.get("source_path") or artifact.get("source_ref") or ""
        parser_name = artifact.get("parser_name") or parser_name
        parser_version = artifact.get("parser_version") or parser_version
        # The backend matters as much as the version: the same MinerU build can
        # emit different text from `pipeline` and `vlm`, so a shift in extraction
        # output has to be attributable to one or the other.
        backend = artifact.get("parser_backend")
        if backend:
            parser_version = f"{parser_version}/{backend}" if parser_version else backend
        declared_hash = artifact.get("content_hash")
        declared_pages = artifact.get("n_pages")
    else:
        items = list(artifact)
        declared_hash, declared_pages = None, None

    if not doc_id:
        doc_id = (items[0].get("doc_id") if items else None) or "unknown"

    chunks = [chunk_from_dict(raw, doc_id, i) for i, raw in enumerate(items)]
    pages = {p for c in chunks for p in (c.page_start, c.page_end)}

    return ParsedDoc(
        doc_id=doc_id,
        source_ref=source_ref,
        content_hash=declared_hash or content_hash(chunks),
        n_pages=int(declared_pages) if declared_pages else (max(pages) + 1 if pages else 0),
        chunks=chunks,
        parser_name=parser_name,
        parser_version=parser_version,
        used_heading_split=any(c.section_no for c in chunks),
    )


def content_hash(chunks: list[Chunk]) -> str:
    """Stable hash of the chunk text, so a re-parse that changed nothing can be
    detected and the expensive stages skipped."""
    blob = json.dumps([c.text for c in chunks], ensure_ascii=False).encode()
    return hashlib.sha256(blob).hexdigest()[:16]


def _first(raw: dict[str, Any], keys: tuple[str, ...]) -> Any:
    for key in keys:
        if raw.get(key) is not None:
            return raw[key]
    return None