-- Migration: Create UUID v7 generation function
-- Description: PostgreSQL function to generate UUID v7 (time-ordered UUIDs)
-- Uses gen_random_uuid() as base, then overrides first 6 bytes with timestamp

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

-- Simple UUID v7 function that works with PostgreSQL's type system
CREATE OR REPLACE FUNCTION uuid_generate_v7()
RETURNS uuid AS $$
DECLARE
    v_time double precision;
    v_secs bigint;
    v_msec int;
    v_random bytea;
    v_uuid bytea;
    v_timestamp bytea;
BEGIN
    -- Get current time
    v_time := extract(epoch from clock_timestamp());
    v_secs := floor(v_time);
    v_msec := floor((v_time - v_secs) * 1000);
    
    -- Generate random bytes for the rest
    v_random := gen_random_bytes(10);
    
    -- Build timestamp bytes (6 bytes = 48 bits)
    v_timestamp := decode(lpad(to_hex(v_secs * 1000 + v_msec), 12, '0'), 'hex');
    
    -- Combine: timestamp (6 bytes) + random (10 bytes)
    v_uuid := v_timestamp || v_random;
    
    -- Set version 7 (0111) in byte 6 (bits 4-7)
    v_uuid := set_byte(v_uuid, 6, (get_byte(v_uuid, 6) & 15) | 112);
    
    -- Set variant RFC 4122 (10xx) in byte 8
    v_uuid := set_byte(v_uuid, 8, (get_byte(v_uuid, 8) & 63) | 128);
    
    RETURN encode(v_uuid, '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 $$
BEGIN
    RAISE NOTICE 'UUID v7 test: %', uuid_generate_v7();
END $$;