"""Per-source result shaping for `/search` -- module 5 phase 4 (kb/phases/kb-m5-faza4.md,
§4 response shape, §6/decision 3 links). `kb_retrieval.retrieval` only ever touches
`document_chunk`/`document_summary`; the join to `envelope` (for `source` and link/metadata
fields) is new HTTP-layer code that belongs to kb-query, not the shared retrieval package.

Paperless link format verified live 2026-07-22: `curl -I https://paper.kapala.org/documents/1/details`
-> 302 to `/accounts/login/?next=/documents/1/details` (unauthenticated, but confirms the route
exists and is handled by the Angular app, not a 404) -- the plan's candidate format.

Gmail has nothing to link to (plan §2 decision 3: `envelope_id` **is** the Message-ID already,
nothing to extract) -- `mail_ui_url` stays a reserved `null` until kb-00's future mail-UI.
"""
from __future__ import annotations

from typing import Optional

PAPERLESS_LINK_TEMPLATE = "https://paper.kapala.org/documents/{doc_id}/details"


def _extract_headers(entities: list) -> dict:
    for entity in entities or []:
        if isinstance(entity, dict) and entity.get("type") == "headers":
            return entity
    return {}


def _format_from(headers: dict) -> Optional[str]:
    frm = headers.get("from")
    if not isinstance(frm, dict):
        return None
    name = frm.get("name")
    address = frm.get("address")
    if name and address:
        return f"{name} <{address}>"
    return address or name


def _paperless_link(envelope_id: str) -> str:
    # envelope_id is "paperless:<id>" (paperless_adapter.py:126) -- the raw Paperless doc id
    # is everything after the first colon.
    doc_id = envelope_id.split(":", 1)[1] if ":" in envelope_id else envelope_id
    return PAPERLESS_LINK_TEMPLATE.format(doc_id=doc_id)


def build_result(chunk: dict, envelope: Optional[dict]) -> dict:
    """One `/search` result item: retrieval hit (`chunk`) + its envelope metadata (`envelope`,
    `None` if the envelope vanished between chunk-embedding and this query -- shouldn't happen
    on a read-only corpus, but the join must not crash on it)."""
    source = (envelope or {}).get("source", "unknown")
    result = {
        "envelope_id": chunk["envelope_id"],
        "source": source,
        "dist": chunk["dist"],
        "chunk_index": chunk["chunk_index"],
        "text": chunk["text"],
    }

    if source == "paperless":
        result["link"] = _paperless_link(chunk["envelope_id"])
        return result

    if source == "gmail":
        headers = _extract_headers((envelope or {}).get("entities", []))
        result["subject"] = headers.get("subject")
        result["from"] = _format_from(headers)
        result["date"] = headers.get("date_raw")
        result["link"] = None
        result["mail_ui_url"] = None
        return result

    result["link"] = None
    return result