"""Cross-tenant referential integrity: composite FKs on (tenant_id, contact_id).

Revision ID: 0036_cross_tenant_fk
Revises: 0035_comm_search_index
Create Date: 2026-07-25

Changes:
1. Add UNIQUE (tenant_id, id) on contacts — prerequisite for composite FK.
2. Replace contactpersons.contact_id FK with composite (tenant_id, contact_id)
   → contacts(tenant_id, id).
3. Replace contact_merge_history.source_contact_id FK with composite
   (tenant_id, source_contact_id) → contacts(tenant_id, id).
4. Replace contact_merge_history.target_contact_id FK with composite
   (tenant_id, target_contact_id) → contacts(tenant_id, id).
"""

from __future__ import annotations

from typing import Union

import sqlalchemy as sa
from alembic import op

# revision identifiers
revision: str = "0036_cross_tenant_fk"
down_revision: Union[str, None] = "0035_comm_search_index"
branch_labels: Union[str, None] = None
depends_on: Union[str, None] = None


def _constraint_exists(name: str) -> str:
    """Return SQL that checks if a constraint exists."""
    return (
        f"SELECT 1 FROM information_schema.table_constraints "
        f"WHERE constraint_name = '{name}'"
    )


def _fk_exists(name: str) -> str:
    """Return SQL that checks if a foreign key constraint exists."""
    return (
        f"SELECT 1 FROM information_schema.table_constraints "
        f"WHERE constraint_name = '{name}' AND constraint_type = 'FOREIGN KEY'"
    )


def upgrade() -> None:
    conn = op.get_bind()

    # ── 1. Add UNIQUE (tenant_id, id) on contacts ──────────────────────────
    unique_name = "uq_contacts_tenant_id"
    result = conn.execute(sa.text(_constraint_exists(unique_name))).fetchone()
    if result is None:
        op.execute(
            f"ALTER TABLE contacts ADD CONSTRAINT {unique_name} "
            f"UNIQUE (tenant_id, id)"
        )

    # ── 2. contactpersons: replace single-column FK with composite FK ──────
    # Find and drop the existing FK on contactpersons.contact_id
    old_cp_fk_result = conn.execute(
        sa.text(
            "SELECT conname FROM pg_constraint c "
            "JOIN pg_class cls ON c.conrelid = cls.oid "
            "JOIN pg_namespace nsp ON c.connamespace = nsp.oid "
            "WHERE cls.relname = 'contactpersons' "
            "AND nsp.nspname = 'public' "
            "AND c.contype = 'f' "
            "AND EXISTS ("
            "  SELECT 1 FROM pg_attribute a "
    "  WHERE a.attrelid = c.conrelid AND a.attname = 'contact_id' "
    "  AND a.attnum = ANY(c.conkey)"
            ")"
        )
    ).fetchone()

    if old_cp_fk_result is not None:
        old_cp_fk_name = old_cp_fk_result[0]
        op.execute(f"ALTER TABLE contactpersons DROP CONSTRAINT IF EXISTS {old_cp_fk_name}")

    # Add composite FK on contactpersons (tenant_id, contact_id) → contacts(tenant_id, id)
    cp_composite_fk = "fk_contactpersons_tenant_contact"
    result = conn.execute(sa.text(_fk_exists(cp_composite_fk))).fetchone()
    if result is None:
        op.execute(
            f"ALTER TABLE contactpersons ADD CONSTRAINT {cp_composite_fk} "
            f"FOREIGN KEY (tenant_id, contact_id) "
            f"REFERENCES contacts (tenant_id, id) ON DELETE CASCADE"
        )

    # ── 3. contact_merge_history: replace source_contact_id FK ─────────────
    old_src_fk_result = conn.execute(
        sa.text(
            "SELECT conname FROM pg_constraint c "
            "JOIN pg_class cls ON c.conrelid = cls.oid "
            "JOIN pg_namespace nsp ON c.connamespace = nsp.oid "
            "WHERE cls.relname = 'contact_merge_history' "
            "AND nsp.nspname = 'public' "
            "AND c.contype = 'f' "
            "AND EXISTS ("
            "  SELECT 1 FROM pg_attribute a "
    "  WHERE a.attrelid = c.conrelid AND a.attname = 'source_contact_id' "
    "  AND a.attnum = ANY(c.conkey)"
            ")"
        )
    ).fetchone()

    if old_src_fk_result is not None:
        old_src_fk_name = old_src_fk_result[0]
        op.execute(f"ALTER TABLE contact_merge_history DROP CONSTRAINT IF EXISTS {old_src_fk_name}")

    src_composite_fk = "fk_merge_history_tenant_source"
    result = conn.execute(sa.text(_fk_exists(src_composite_fk))).fetchone()
    if result is None:
        op.execute(
            f"ALTER TABLE contact_merge_history ADD CONSTRAINT {src_composite_fk} "
            f"FOREIGN KEY (tenant_id, source_contact_id) "
            f"REFERENCES contacts (tenant_id, id) ON DELETE SET NULL"
        )

    # ── 4. contact_merge_history: replace target_contact_id FK ──────────────
    old_tgt_fk_result = conn.execute(
        sa.text(
            "SELECT conname FROM pg_constraint c "
            "JOIN pg_class cls ON c.conrelid = cls.oid "
            "JOIN pg_namespace nsp ON c.connamespace = nsp.oid "
            "WHERE cls.relname = 'contact_merge_history' "
            "AND nsp.nspname = 'public' "
            "AND c.contype = 'f' "
            "AND EXISTS ("
            "  SELECT 1 FROM pg_attribute a "
    "  WHERE a.attrelid = c.conrelid AND a.attname = 'target_contact_id' "
    "  AND a.attnum = ANY(c.conkey)"
            ")"
        )
    ).fetchone()

    if old_tgt_fk_result is not None:
        old_tgt_fk_name = old_tgt_fk_result[0]
        op.execute(f"ALTER TABLE contact_merge_history DROP CONSTRAINT IF EXISTS {old_tgt_fk_name}")

    tgt_composite_fk = "fk_merge_history_tenant_target"
    result = conn.execute(sa.text(_fk_exists(tgt_composite_fk))).fetchone()
    if result is None:
        op.execute(
            f"ALTER TABLE contact_merge_history ADD CONSTRAINT {tgt_composite_fk} "
            f"FOREIGN KEY (tenant_id, target_contact_id) "
            f"REFERENCES contacts (tenant_id, id) ON DELETE CASCADE"
        )


def downgrade() -> None:
    conn = op.get_bind()

    # Restore single-column FKs and remove composite FKs

    # ── contact_merge_history: target ──
    op.execute("ALTER TABLE contact_merge_history DROP CONSTRAINT IF EXISTS fk_merge_history_tenant_target")
    op.execute(
        "ALTER TABLE contact_merge_history ADD CONSTRAINT "
        "contact_merge_history_target_contact_id_fkey "
        "FOREIGN KEY (target_contact_id) REFERENCES contacts (id) ON DELETE CASCADE"
    )

    # ── contact_merge_history: source ──
    op.execute("ALTER TABLE contact_merge_history DROP CONSTRAINT IF EXISTS fk_merge_history_tenant_source")
    op.execute(
        "ALTER TABLE contact_merge_history ADD CONSTRAINT "
        "contact_merge_history_source_contact_id_fkey "
        "FOREIGN KEY (source_contact_id) REFERENCES contacts (id) ON DELETE SET NULL"
    )

    # ── contactpersons ──
    op.execute("ALTER TABLE contactpersons DROP CONSTRAINT IF EXISTS fk_contactpersons_tenant_contact")
    op.execute(
        "ALTER TABLE contactpersons ADD CONSTRAINT "
        "contactpersons_contact_id_fkey "
        "FOREIGN KEY (contact_id) REFERENCES contacts (id) ON DELETE CASCADE"
    )

    # ── Remove unique (tenant_id, id) on contacts ──
    op.execute("ALTER TABLE contacts DROP CONSTRAINT IF EXISTS uq_contacts_tenant_id")