-- T007_optimize_queries.sql
-- Phase 1 Performance Optimization: Composite Indexes
-- Creates composite indexes for common query patterns to improve performance
-- Estimated improvement: 60-80% faster conversation and message queries

BEGIN;

-- Apply to all existing tenant schemas
DO $$
DECLARE
    tenant_schema TEXT;
BEGIN
    FOR tenant_schema IN
        SELECT schema_name
        FROM information_schema.schemata
        WHERE schema_name LIKE 'tenant_%' AND schema_name != 'tenant_template'
    LOOP
        -- Composite index for message queries
        -- Optimizes: SELECT * FROM messages WHERE conversation_id = ? ORDER BY created_at
        -- Common in: conversation_service.get_messages() with pagination
        -- Impact: Covers both filter and sort in single index scan
        EXECUTE format('
            CREATE INDEX IF NOT EXISTS idx_messages_conversation_created
              ON %I.messages
              USING btree (conversation_id, created_at ASC)
        ', tenant_schema);

        -- Composite index for conversation list queries
        -- Optimizes: SELECT * FROM conversations WHERE user_id = ? AND is_archived = false ORDER BY updated_at DESC
        -- Common in: conversation_service.list_conversations()
        -- Impact: Enables index-only scan for conversation lists
        EXECUTE format('
            CREATE INDEX IF NOT EXISTS idx_conversations_user_updated
              ON %I.conversations
              USING btree (user_id, is_archived, updated_at DESC)
        ', tenant_schema);

        RAISE NOTICE 'Applied T007 optimization indexes to schema: %', tenant_schema;
    END LOOP;
END $$;

COMMIT;

-- Performance Notes:
-- - Both indexes support common access patterns in the application
-- - No schema changes - purely additive optimization
-- - Safe to run multiple times (IF NOT EXISTS)
-- - Note: CONCURRENTLY cannot be used inside DO $$ blocks
--
-- Rollback (if needed):
-- DO $$
-- DECLARE tenant_schema TEXT;
-- BEGIN
--     FOR tenant_schema IN
--         SELECT schema_name FROM information_schema.schemata
--         WHERE schema_name LIKE 'tenant_%' AND schema_name != 'tenant_template'
--     LOOP
--         EXECUTE format('DROP INDEX IF EXISTS %I.idx_messages_conversation_created', tenant_schema);
--         EXECUTE format('DROP INDEX IF EXISTS %I.idx_conversations_user_updated', tenant_schema);
--     END LOOP;
-- END $$;