"""Tests for the BackLinks derived view (SHARD-WP-0010 T2)."""

from shard_wiki.adapters import FolderAdapter
from shard_wiki.model import Identity
from shard_wiki.union import UnionGraph
from shard_wiki.views import build_backlinks


def _shard(tmp_path, name, files):
    root = tmp_path / name
    for rel, text in files.items():
        p = root / rel
        p.parent.mkdir(parents=True, exist_ok=True)
        p.write_text(text, encoding="utf-8")
    return FolderAdapter(name, root)


def test_link_yields_backlink_with_provenance(tmp_path):
    u = UnionGraph("space")
    u.attach(_shard(tmp_path, "shardA", {"A.md": "see [[B]]", "B.md": "target"}))
    index = build_backlinks(u)
    assert index.sources("B") == frozenset({Identity("shardA", "A")})
    (bl,) = index.to("B")
    assert bl.source_shard == "shardA"  # entry carries source provenance


def test_red_links_create_no_backlinks(tmp_path):
    u = UnionGraph("space")
    u.attach(_shard(tmp_path, "shardA", {"A.md": "see [[Ghost]]"}))
    index = build_backlinks(u)
    assert index.to("Ghost") == ()  # unresolved target → no backlink
    assert "Ghost" not in index.names()


def test_chorus_target_aggregates_backlinks(tmp_path):
    # "Home" exists in two shards (a chorus); links to it from anywhere aggregate under one name.
    u = UnionGraph("space")
    u.attach(_shard(tmp_path, "shardA", {"Home.md": "A home", "A.md": "[[Home]]"}))
    u.attach(_shard(tmp_path, "shardB", {"Home.md": "B home", "B.md": "[[Home]]"}))
    index = build_backlinks(u)
    assert index.sources("Home") == frozenset(
        {Identity("shardA", "A"), Identity("shardB", "B")}
    )


def test_backlinks_span_shards(tmp_path):
    u = UnionGraph("space")
    u.attach(_shard(tmp_path, "shardA", {"Index.md": "x"}))
    u.attach(_shard(tmp_path, "shardB", {"B.md": "links [[Index]]"}))
    index = build_backlinks(u)
    assert index.sources("Index") == frozenset({Identity("shardB", "B")})