CREATE TABLE notification_channels (
    id uuid PRIMARY KEY,
    name text NOT NULL CHECK (char_length(name) BETWEEN 1 AND 160),
    channel_type text NOT NULL CHECK (channel_type IN ('memory', 'webhook', 'email')),
    enabled boolean NOT NULL DEFAULT true,
    secret_ref text NOT NULL CHECK (char_length(secret_ref) BETWEEN 1 AND 255),
    configuration jsonb NOT NULL DEFAULT '{}'::jsonb CHECK (jsonb_typeof(configuration) = 'object'),
    revision bigint NOT NULL DEFAULT 1 CHECK (revision > 0),
    created_at timestamptz NOT NULL DEFAULT now(),
    updated_at timestamptz NOT NULL DEFAULT now()
);

CREATE TABLE notification_outbox (
    id uuid PRIMARY KEY,
    idempotency_key text NOT NULL UNIQUE CHECK (char_length(idempotency_key) BETWEEN 1 AND 255),
    channel_id uuid NOT NULL REFERENCES notification_channels(id) ON DELETE RESTRICT,
    event_type text NOT NULL CHECK (event_type IN ('firing', 'recovery', 'unknown')),
    subject text NOT NULL CHECK (char_length(subject) BETWEEN 1 AND 240),
    body text NOT NULL CHECK (char_length(body) BETWEEN 1 AND 8000),
    status text NOT NULL DEFAULT 'pending' CHECK (status IN ('pending', 'delivering', 'retry', 'delivered', 'failed')),
    attempts integer NOT NULL DEFAULT 0 CHECK (attempts >= 0 AND attempts <= 10),
    next_attempt_at timestamptz NOT NULL DEFAULT now(),
    locked_until timestamptz,
    last_error text CHECK (last_error IS NULL OR char_length(last_error) <= 500),
    created_at timestamptz NOT NULL DEFAULT now(),
    updated_at timestamptz NOT NULL DEFAULT now(),
    delivered_at timestamptz
);

CREATE TABLE notification_deliveries (
    id uuid PRIMARY KEY,
    outbox_id uuid NOT NULL REFERENCES notification_outbox(id) ON DELETE CASCADE,
    attempt integer NOT NULL CHECK (attempt > 0),
    status text NOT NULL CHECK (status IN ('delivering', 'delivered', 'failed')),
    error text CHECK (error IS NULL OR char_length(error) <= 500),
    occurred_at timestamptz NOT NULL DEFAULT now(),
    UNIQUE (outbox_id, attempt)
);

CREATE INDEX notification_outbox_due_idx ON notification_outbox (next_attempt_at, id) WHERE status IN ('pending', 'retry');
CREATE INDEX notification_outbox_channel_idx ON notification_outbox (channel_id, status, updated_at DESC, id ASC);
CREATE INDEX notification_deliveries_history_idx ON notification_deliveries (outbox_id, occurred_at DESC, id ASC);