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use std::convert::Infallible;
use std::fmt::Display;
use std::num::ParseIntError;

use crate::ID;

/// Cursor type
///
/// A custom scalar that serializes as a string.
/// <https://relay.dev/graphql/connections.htm#sec-Cursor>
pub trait CursorType: Sized {
    /// Error type for `decode_cursor`.
    type Error: Display;

    /// Decode cursor from string.
    fn decode_cursor(s: &str) -> Result<Self, Self::Error>;

    /// Encode cursor to string.
    fn encode_cursor(&self) -> String;
}

impl CursorType for usize {
    type Error = ParseIntError;

    fn decode_cursor(s: &str) -> Result<Self, Self::Error> {
        s.parse()
    }

    fn encode_cursor(&self) -> String {
        self.to_string()
    }
}

impl CursorType for String {
    type Error = Infallible;

    fn decode_cursor(s: &str) -> Result<Self, Self::Error> {
        Ok(s.to_string())
    }

    fn encode_cursor(&self) -> String {
        self.clone()
    }
}

impl CursorType for ID {
    type Error = Infallible;

    fn decode_cursor(s: &str) -> Result<Self, Self::Error> {
        Ok(s.to_string().into())
    }

    fn encode_cursor(&self) -> String {
        self.to_string()
    }
}