-- =============================================
-- Education 模块 — 收藏夹 DDL (PostgreSQL)
-- Ticket #10: 学生收藏题目
-- Migration: 007
-- Prerequisites: 000-education-schema.sql (base tables)
-- =============================================

-- =============================================
-- Preconditions
-- =============================================
-- Operator is expected to verify:
--   SELECT COUNT(*) FROM information_schema.tables
--     WHERE table_catalog = current_database()
--       AND table_name = 'education_favorite';
-- Result MUST be 0 before executing this migration.

-- =============================================
-- 收藏表
-- =============================================
-- Purpose: Student favorites for questions with safe snapshots.
--   Each (tenant, user, target_type, target_id) is a unique entry.
--   Logical deletion: setting deleted=true marks as unfavorited.
--   Re-adding after deletion reactivates the row via ON CONFLICT ... DO UPDATE.
--
-- target_type values: 'QUESTION' (extensible enum)
--
-- Snapshot fields (stem, type, difficulty, options, content_version):
--   populated at creation time from the visible question's safe fields.
--   These snapshots preserve the question state as it appeared when favorited,
--   and remain stable even if the source question later changes or becomes unavailable.
--
-- available flag:
--   FALSE when the source question becomes hidden/unpublished after being
--   favorited. Existing favorites with available=FALSE remain listable but
--   display an "unavailable" indicator. New favorites cannot be created for
--   unavailable resources.
--
-- Indexes:
--   uk_tenant_user_target — per (tenant, user, target_type, target_id) uniqueness.
--     INSERT ... ON CONFLICT DO UPDATE is the primary reactivation path.
--   idx_tenant_user — covers listing queries filtered by current tenant+user.
--   idx_tenant_user_target_type — covers target-type-filtered listing.
CREATE TABLE education_favorite (
    id               BIGINT       GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
    tenant_id        BIGINT       NOT NULL,
    user_id          BIGINT       NOT NULL,
    target_type      VARCHAR(32)  NOT NULL,
    target_id        VARCHAR(64)  NOT NULL,
    -- safe snapshot fields
    stem             TEXT         DEFAULT NULL,
    type             VARCHAR(32)  DEFAULT NULL,
    difficulty       VARCHAR(32)  DEFAULT NULL,
    options          JSONB        DEFAULT NULL,
    content_version  VARCHAR(64)  NOT NULL DEFAULT '',
    -- availability
    available        BOOLEAN      NOT NULL DEFAULT true,
    -- audit
    creator          VARCHAR(64)  DEFAULT '',
    create_time      TIMESTAMP    NOT NULL DEFAULT CURRENT_TIMESTAMP,
    updater          VARCHAR(64)  DEFAULT '',
    update_time      TIMESTAMP    NOT NULL DEFAULT CURRENT_TIMESTAMP,
    deleted          BOOLEAN      NOT NULL DEFAULT false,
    CONSTRAINT uk_tenant_user_target UNIQUE (tenant_id, user_id, target_type, target_id)
);

COMMENT ON TABLE education_favorite IS '教育-收藏夹';
COMMENT ON COLUMN education_favorite.id IS '主键';
COMMENT ON COLUMN education_favorite.tenant_id IS '租户编号';
COMMENT ON COLUMN education_favorite.user_id IS '学生用户编号';
COMMENT ON COLUMN education_favorite.target_type IS '目标类型：QUESTION';
COMMENT ON COLUMN education_favorite.target_id IS '目标 ID（题目 ID）';
COMMENT ON COLUMN education_favorite.stem IS '题干快照';
COMMENT ON COLUMN education_favorite.type IS '题型快照';
COMMENT ON COLUMN education_favorite.difficulty IS '难度快照';
COMMENT ON COLUMN education_favorite.options IS '选项快照 JSON（不含 isCorrect）';
COMMENT ON COLUMN education_favorite.content_version IS '题目内容版本';
COMMENT ON COLUMN education_favorite.available IS '源资源是否可用';
COMMENT ON COLUMN education_favorite.creator IS '创建者';
COMMENT ON COLUMN education_favorite.create_time IS '创建时间';
COMMENT ON COLUMN education_favorite.updater IS '更新者';
COMMENT ON COLUMN education_favorite.update_time IS '更新时间';
COMMENT ON COLUMN education_favorite.deleted IS '是否删除';

CREATE INDEX idx_tenant_user ON education_favorite (tenant_id, user_id);
CREATE INDEX idx_tenant_user_target_type ON education_favorite (tenant_id, user_id, target_type);

-- =============================================
-- Post-migration verification queries
-- =============================================
-- Verify new table exists:
--   \d education_favorite
-- Verify unique constraint is enforced:
--   SELECT * FROM pg_indexes WHERE tablename = 'education_favorite' AND indexname = 'uk_tenant_user_target';
-- Verify no orphan data (should be 0 after fresh migration):
--   SELECT COUNT(*) FROM education_favorite;