CREATE TABLE alert_instances (
    id uuid PRIMARY KEY,
    rule_id uuid NOT NULL REFERENCES alert_rules(id) ON DELETE RESTRICT,
    rule_version_id uuid NOT NULL REFERENCES alert_rule_versions(id) ON DELETE RESTRICT,
    fingerprint text NOT NULL CHECK (length(fingerprint) BETWEEN 1 AND 160),
    entity_id uuid REFERENCES entities(id) ON DELETE RESTRICT,
    current_state text NOT NULL DEFAULT 'inactive' CHECK (current_state IN ('inactive', 'pending', 'firing', 'acknowledged', 'resolved', 'unknown')),
    retained_state text NOT NULL DEFAULT 'inactive' CHECK (retained_state IN ('inactive', 'pending', 'firing', 'acknowledged', 'resolved', 'unknown')),
    active_since timestamptz,
    recovery_since timestamptz,
    last_evaluated_at timestamptz NOT NULL,
    last_known_at timestamptz,
    last_value jsonb NOT NULL DEFAULT 'null'::jsonb,
    reason text NOT NULL DEFAULT '' CHECK (length(reason) <= 500),
    source_health jsonb NOT NULL DEFAULT '{}'::jsonb,
    acknowledged_by text,
    acknowledged_at timestamptz,
    revision bigint NOT NULL DEFAULT 1 CHECK (revision > 0),
    created_at timestamptz NOT NULL DEFAULT now(),
    updated_at timestamptz NOT NULL DEFAULT now(),
    UNIQUE (rule_id, fingerprint)
);

CREATE TABLE alert_occurrences (
    id uuid PRIMARY KEY,
    instance_id uuid NOT NULL REFERENCES alert_instances(id) ON DELETE RESTRICT,
    evaluation_key text NOT NULL CHECK (length(evaluation_key) BETWEEN 1 AND 160),
    event_type text NOT NULL CHECK (event_type IN ('evaluation', 'transition', 'acknowledge')),
    from_state text NOT NULL CHECK (from_state IN ('inactive', 'pending', 'firing', 'acknowledged', 'resolved', 'unknown')),
    to_state text NOT NULL CHECK (to_state IN ('inactive', 'pending', 'firing', 'acknowledged', 'resolved', 'unknown')),
    observed_at timestamptz NOT NULL,
    value jsonb NOT NULL DEFAULT 'null'::jsonb,
    reason text NOT NULL DEFAULT '' CHECK (length(reason) <= 500),
    source_health jsonb NOT NULL DEFAULT '{}'::jsonb,
    created_at timestamptz NOT NULL DEFAULT now(),
    UNIQUE (instance_id, evaluation_key)
);

CREATE INDEX alert_instances_state_idx ON alert_instances (current_state, last_evaluated_at DESC, id ASC);
CREATE INDEX alert_instances_rule_idx ON alert_instances (rule_id, current_state, updated_at DESC, id ASC);
CREATE INDEX alert_occurrences_history_idx ON alert_occurrences (instance_id, observed_at DESC, id ASC);