package uuids

import (
    "encoding/hex"
    "fmt"
    "regexp"
)

// MarshalText is a wrapper around [UUID.String].
func (uuid UUID) MarshalText() ([]byte, error) {
    if uuid.IsZero() {
        return []byte(UUID{}.String()), nil
    }

    return []byte(uuid.String()), nil
}

var reParse = regexp.MustCompile(`^([0-9A-Fa-f]{8})-([0-9A-Fa-f]{4})-([0-9A-Fa-f]{4})-([0-9A-Fa-f]{4})-([0-9A-Fa-f]{12})$`)

// UnmarshalText parses a hexadecimal UUID representation
// of [UUID.String]'s flavour.
// Both upper-case and lower-case hexadecimal digits are recognized.
//
// TODO(jfrech): 2024-04-30: Emit a better error.
func (uuid *UUID) UnmarshalText(text []byte) error {
    *uuid = UUID{}

    parse := func(s string) (UUID, error) {
        smatchs := reParse.FindStringSubmatch(s)
        if len(smatchs) != 1+5 {
            return UUID{}, fmt.Errorf("not a UUID: %q", s)
        }

        uuid, err := hex.DecodeString(smatchs[1] + smatchs[2] + smatchs[3] + smatchs[4] + smatchs[5])
        if err != nil {
            panic("unreachable: " + err.Error())
        } else if len(uuid) != Size {
            panic("unreachable")
        }

        return UUID(uuid), nil
    }

    u, err := parse(string(text))
    if err != nil {
        return err
    }

    *uuid = u
    return nil
}