"""threads.senders — who wrote, as distinct from who was involved

The message list showed a thread's `participants`, which the threader builds from
from + to + cc because the subject-fallback join matches on recipients. In a list
that meant every ordinary email read "Sender, You" — and the "+N" badge counted
the user themselves.

`senders` holds only the from addresses, newest writer first. Backfilled here so
existing threads do not have to wait to be touched again.

Revision ID: 0019
Revises: 0018
Create Date: 2026-09-18
"""

from __future__ import annotations

from collections.abc import Sequence

from alembic import op

revision: str = "0019"
down_revision: str | None = "0018"
branch_labels: str | Sequence[str] | None = None
depends_on: str | Sequence[str] | None = None


def upgrade() -> None:
    op.execute("ALTER TABLE threads ADD COLUMN senders jsonb NOT NULL DEFAULT '[]'")
    # Newest writer first, de-duplicated by lower-cased address, matching what
    # denormalize_thread computes from now on.
    op.execute(
        """
        WITH ranked AS (
            SELECT m.thread_id,
                   lower(a->>'email')                        AS email_key,
                   jsonb_build_object('name', coalesce(a->>'name', ''),
                                      'email', coalesce(a->>'email', '')) AS addr,
                   row_number() OVER (PARTITION BY m.thread_id, lower(a->>'email')
                                      ORDER BY m.internal_date DESC)       AS dup_rank,
                   max(m.internal_date) OVER (PARTITION BY m.thread_id, lower(a->>'email'))
                                                                           AS recency
            FROM messages m
            CROSS JOIN LATERAL jsonb_array_elements(m.from_addr) AS a
            WHERE m.thread_id IS NOT NULL AND coalesce(a->>'email', '') <> ''
        ),
        collected AS (
            SELECT thread_id, jsonb_agg(addr ORDER BY recency DESC) AS senders
            FROM ranked WHERE dup_rank = 1 GROUP BY thread_id
        )
        UPDATE threads t SET senders = c.senders
        FROM collected c WHERE c.thread_id = t.id
        """
    )


def downgrade() -> None:
    op.execute("ALTER TABLE threads DROP COLUMN IF EXISTS senders")