-- Migration: Create UUID v7 generation function
-- Description: PostgreSQL function to generate UUID v7 (time-ordered UUIDs)
-- UUID v7 format: tttttttt-tttt-7xxx-yxxx-xxxxxxxxxxxx
-- Where: t = timestamp, 7 = version, y = variant, x = random

-- Enable pgcrypto extension for gen_random_bytes()
CREATE EXTENSION IF NOT EXISTS pgcrypto;

-- Create or replace the uuid_generate_v7 function
CREATE OR REPLACE FUNCTION uuid_generate_v7()
RETURNS uuid AS $$
DECLARE
    unix_ts_ms bigint;
    uuid_bytes bytea;
BEGIN
    -- Get current Unix timestamp in milliseconds
    unix_ts_ms := (EXTRACT(EPOCH FROM clock_timestamp()) * 1000)::bigint;
    
    -- Build the UUID bytes:
    -- First 6 bytes: timestamp (48 bits)
    -- Next 2 bytes: version (4 bits) + random (12 bits)
    -- Last 8 bytes: variant (2 bits) + random (62 bits)
    uuid_bytes := set_byte(
        set_byte(
            set_byte(
                set_byte(
                    set_byte(
                        set_byte(
                            gen_random_bytes(16),
                            0, (unix_ts_ms >> 40)::int
                        ),
                        1, (unix_ts_ms >> 32)::int
                    ),
                    2, (unix_ts_ms >> 24)::int
                ),
                3, (unix_ts_ms >> 16)::int
            ),
            4, (unix_ts_ms >> 8)::int
        ),
        5, unix_ts_ms::int
    );
    
    -- Set version 7 (0111) in byte 6
    uuid_bytes := set_byte(uuid_bytes, 6, (get_byte(uuid_bytes, 6) & 15) | 112);
    
    -- Set variant RFC 4122 (10xx) in byte 8
    uuid_bytes := set_byte(uuid_bytes, 8, (get_byte(uuid_bytes, 8) & 63) | 128);
    
    RETURN encode(uuid_bytes, 'hex')::uuid;
END;
$$ LANGUAGE plpgsql VOLATILE;

-- Comment
COMMENT ON FUNCTION uuid_generate_v7() IS 'Generates a UUID v7 (time-ordered) - RFC 9562 compliant';

-- Test the function
DO $$
BEGIN
    RAISE NOTICE 'UUID v7 test: %', uuid_generate_v7();
END $$;