nxtgauge-backend-rust/crates/db/migrations/20260608030000_ai_ab_tests.up.sql

-- Phase 4: A/B testing tables for Ask Ash prompt variations.

BEGIN;

CREATE TABLE IF NOT EXISTS ai_ab_tests (
    id            BIGSERIAL PRIMARY KEY,
    name          TEXT NOT NULL UNIQUE,
    description   TEXT,
    -- Each variant is an arbitrary JSON blob the request handler decides how
    -- to interpret (e.g. {"persona":"job_seekers","system_prompt_override":"..."})
    variant_a     JSONB NOT NULL,
    variant_b     JSONB NOT NULL,
    -- 0.0 → all traffic to A, 1.0 → all traffic to B, 0.5 → 50/50.
    -- DOUBLE PRECISION because sqlx's default feature set doesn't include
    -- bigdecimal/rust_decimal; double has plenty of precision for 0-1.
    traffic_split DOUBLE PRECISION NOT NULL DEFAULT 0.50
        CHECK (traffic_split >= 0.0 AND traffic_split <= 1.0),
    active        BOOLEAN NOT NULL DEFAULT TRUE,
    created_at    TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

CREATE TABLE IF NOT EXISTS ai_ab_assignments (
    id              BIGSERIAL PRIMARY KEY,
    test_id         BIGINT NOT NULL REFERENCES ai_ab_tests(id) ON DELETE CASCADE,
    user_id         UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    -- References ai_conversations.id which is UUID.
    conversation_id UUID REFERENCES ai_conversations(id) ON DELETE SET NULL,
    variant         TEXT NOT NULL CHECK (variant IN ('A', 'B')),
    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

-- Hot path: "what variant was user X assigned to test Y?"
CREATE INDEX IF NOT EXISTS idx_ai_ab_assignments_user
    ON ai_ab_assignments (user_id, test_id);

-- Hot path: aggregate results per test
CREATE INDEX IF NOT EXISTS idx_ai_ab_assignments_variant
    ON ai_ab_assignments (test_id, variant, created_at DESC);

COMMIT;