"""Tests for the provenance leaf rail (SHARD-WP-0007 T1)."""

from datetime import datetime, timezone

from shard_wiki.provenance import (
    Liveness,
    OverlayState,
    ProvenanceEnvelope,
    SpanProvenanceDelta,
    Staleness,
    effective,
)


def _base() -> ProvenanceEnvelope:
    return ProvenanceEnvelope(
        source_shard="shardA",
        liveness=Liveness.STATIC,
        staleness=Staleness.FRESH,
        source_rev="r1",
        observed_at=datetime(2026, 6, 15, tzinfo=timezone.utc),
    )


def test_no_delta_returns_base_identity():
    base = _base()
    assert effective(base) is base
    assert effective(base, SpanProvenanceDelta()) is base


def test_empty_delta_is_detected():
    assert SpanProvenanceDelta().is_empty()
    assert not SpanProvenanceDelta(source_shard="other").is_empty()


def test_single_field_override():
    base = _base()
    eff = effective(base, SpanProvenanceDelta(source_shard="shardB"))
    assert eff.source_shard == "shardB"
    # Untouched fields inherit from the page envelope.
    assert eff.source_rev == "r1"
    assert eff.liveness is Liveness.STATIC
    # Base is unchanged (frozen, pure composition).
    assert base.source_shard == "shardA"


def test_partial_delta_overrides_several_fields():
    base = _base()
    eff = effective(
        base,
        SpanProvenanceDelta(
            staleness=Staleness.STALE,
            overlay_state=OverlayState.DRAFT,
            divergence=("shardB:Home",),
        ),
    )
    assert eff.staleness is Staleness.STALE
    assert eff.overlay_state is OverlayState.DRAFT
    assert eff.divergence == ("shardB:Home",)
    assert eff.source_shard == "shardA"  # inherited


def test_divergence_empty_tuple_overrides_but_none_inherits():
    base = ProvenanceEnvelope(source_shard="s", divergence=("x",))
    # None → inherit the page's divergence.
    assert effective(base, SpanProvenanceDelta(divergence=None)).divergence == ("x",)
    # Explicit empty tuple → override (clear it).
    assert effective(base, SpanProvenanceDelta(divergence=())).divergence == ()


def test_envelope_is_hashable_and_value_equal():
    assert _base() == _base()
    assert len({_base(), _base()}) == 1