"""
Bilingual output: interleave source paragraphs with their translation.

Given the ORIGINAL document and the TRANSLATED document (same structure —
the pipeline only rewrites run texts), produce a copy of the translated
document where each translated body paragraph is preceded by its source
paragraph in gray italic. Tables, headers and footers keep the translated
version only (duplicating them would double the layout).
"""

from pathlib import Path
from typing import Optional

from docx import Document
from docx.text.paragraph import Paragraph
from docx.oxml import OxmlElement
from docx.oxml.ns import qn
from docx.shared import Pt, RGBColor

from core.logging import get_logger

logger = get_logger(__name__)


def make_bilingual_docx(
    source_path: Path, translated_path: Path, output_path: Path
) -> Optional[Path]:
    """Create a bilingual .docx (source paragraph above its translation).

    Returns the output path, or None when the pairing failed (structure
    mismatch) — callers fall back to the translated-only file.
    """
    source_path = Path(source_path)
    translated_path = Path(translated_path)
    output_path = Path(output_path)

    try:
        src = Document(str(source_path))
        tr = Document(str(translated_path))
    except Exception as e:
        logger.warning("bilingual_open_failed", error=str(e))
        return None

    src_children = list(src.element.body)
    tr_children = list(tr.element.body)

    # The pipeline preserves structure exactly; a drift beyond a small
    # tolerance means pairing by index is unsafe → bail out.
    if abs(len(src_children) - len(tr_children)) > 0:
        logger.warning(
            "bilingual_structure_mismatch",
            source_elements=len(src_children),
            translated_elements=len(tr_children),
        )
        if len(src_children) != len(tr_children):
            return None

    inserted = 0
    for src_el, tr_el in zip(src_children, tr_children):
        if tr_el.tag != qn("w:p") or src_el.tag != qn("w:p"):
            continue
        src_text = "".join(
            t.text or "" for t in src_el.iter(qn("w:t"))
        ).strip()
        if not src_text:
            continue

        # Insert a NEW paragraph directly above the translated one, inside
        # the translated document (keeps styles/sections untouched).
        new_p = OxmlElement("w:p")
        tr_el.addprevious(new_p)
        para = Paragraph(new_p, tr)
        run = para.add_run(src_text)
        run.font.size = Pt(9)
        run.font.italic = True
        run.font.color.rgb = RGBColor(0x80, 0x80, 0x80)
        inserted += 1

    if inserted == 0:
        logger.info("bilingual_nothing_inserted")
        return None

    try:
        tr.save(str(output_path))
    except Exception as e:
        logger.warning("bilingual_save_failed", error=str(e))
        return None

    logger.info("bilingual_docx_created", paragraphs=inserted)
    return output_path