"""Keep one gallery highlight link per name and capture year."""

from datetime import datetime, timezone
import json
from pathlib import Path
import re


def field(content, name):
    match = re.search(rf"^{re.escape(name)}: (.+)$", content.split("---", 2)[1], re.MULTILINE)
    if not match:
        return None
    value = match.group(1).strip()
    return json.loads(value) if value.startswith('"') else value


def normalize_highlights(art):
    """Place each link on the newest photo in its named, dated group."""
    groups = {}
    for path in Path(art).glob("*.md"):
        content = path.read_text()
        name = field(content, "highlight_name") or field(content, "anchor")
        date = field(content, "date")
        if not name or not date:
            continue
        taken = datetime.fromisoformat(str(date))
        if taken.tzinfo is None:
            taken = taken.replace(tzinfo=timezone.utc)
        groups.setdefault((name, taken.year), []).append((taken, path, content))

    changed = []
    for (name, _), entries in groups.items():
        # An old single anchor is already the only link; a newer named photo
        # moves the link without changing any photo's capture date or position.
        newest = max(entries, key=lambda entry: (entry[0], entry[1].name))[1]
        if len(entries) == 1 and field(entries[0][2], "anchor") == name:
            continue
        for _, path, content in entries:
            old = content
            had_anchor = field(content, "anchor") is not None
            if (path == newest and had_anchor and
                    all(field(other[2], "anchor") is None for other in entries if other[1] != path)):
                continue
            if had_anchor:
                content = re.sub(r"^anchor: .+\n", "", content, count=1, flags=re.MULTILINE)
            if path == newest:
                content = content.replace("categories: art\n", "categories: art\n" +
                                          f"anchor: {json.dumps(name, ensure_ascii=False)}\n", 1)
            elif had_anchor:
                title = field(content, "title")
                if title and title.startswith("photo-") and f'id="{title}"' not in content:
                    content = content.replace("---\n\n", f'---\n\n<div id="{title}"></div>\n\n', 1)
            if content != old:
                path.write_text(content)
                changed.append(path)
    return changed