-- =============================================================================
-- Migration: 2026-09-11-message-export-policy.sql
-- Description: 为 chat_messages 新增正文类型、权威导出策略、版本与 SHA256 哈希
-- =============================================================================

-- 1. 结构变更：新增消息导出权威列
ALTER TABLE chat_messages
    ADD COLUMN IF NOT EXISTS content_kind TEXT NOT NULL DEFAULT '',
    ADD COLUMN IF NOT EXISTS export_policy TEXT NOT NULL DEFAULT 'none',
    ADD COLUMN IF NOT EXISTS content_revision INT NOT NULL DEFAULT 1,
    ADD COLUMN IF NOT EXISTS content_sha256 TEXT NOT NULL DEFAULT '';

-- 2. 导出策略枚举约束检查 (full | copy_only | none)
DO $$
BEGIN
    IF NOT EXISTS (
        SELECT 1 FROM pg_constraint WHERE conname = 'chk_chat_export_policy'
    ) THEN
        ALTER TABLE chat_messages
            ADD CONSTRAINT chk_chat_export_policy
            CHECK (export_policy IN ('full', 'copy_only', 'none'));
    END IF;
END $$;

-- 3. 索引优化：快速基于消息与版本校验
CREATE INDEX IF NOT EXISTS idx_chat_messages_export_policy
    ON chat_messages(id, export_policy);

CREATE EXTENSION IF NOT EXISTS pgcrypto;

-- 4. 存量消息安全保守回填：旧消息默认为 none，仅纯文本 assistant 消息标记为 copy_only
UPDATE chat_messages
SET 
    content_kind = CASE
        WHEN role = 'user' THEN 'conversational_text'
        WHEN role = 'system' THEN 'system_notice'
        WHEN role = 'assistant' AND (metadata ? 'interactive_card') THEN 'action_card'
        WHEN role = 'assistant' AND length(trim(content)) > 0 THEN 'document_text'
        ELSE 'conversational_text'
    END,
    export_policy = CASE
        WHEN role = 'assistant' AND NOT (metadata ? 'interactive_card') AND length(trim(content)) >= 10 THEN 'full'
        WHEN role = 'assistant' AND length(trim(content)) > 0 THEN 'copy_only'
        ELSE 'none'
    END,
    content_revision = 1,
    content_sha256 = CASE 
        WHEN length(content) > 0 THEN encode(sha256(convert_to(content, 'UTF8')), 'hex')
        ELSE ''
    END
WHERE export_policy = 'none' AND role = 'assistant' AND length(trim(content)) > 0;