-- Lessons under an exam-prep unit module (mirrors LMS lessons under modules; avoids collision with public.lessons / sqlc).
CREATE TABLE exam_prep.unit_module_lessons (
    id BIGSERIAL PRIMARY KEY,
    unit_module_id BIGINT NOT NULL REFERENCES exam_prep.unit_modules (id) ON DELETE CASCADE,
    title VARCHAR(255) NOT NULL,
    video_url TEXT,
    thumbnail TEXT,
    description TEXT,
    sort_order INTEGER NOT NULL DEFAULT 0,
    created_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMPTZ
);

CREATE UNIQUE INDEX uq_exam_prep_unit_module_lessons_sort ON exam_prep.unit_module_lessons (unit_module_id, sort_order);

CREATE INDEX idx_exam_prep_unit_module_lessons_module_id ON exam_prep.unit_module_lessons (unit_module_id);
CREATE INDEX idx_exam_prep_unit_module_lessons_module_created ON exam_prep.unit_module_lessons (unit_module_id, created_at DESC);