use std::error::Error;
use base64::Engine;
use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct Cursor {
    pub page: u64
}

impl TryFrom<Cursor> for String {
    type Error = Box<dyn Error>;

    fn try_from(value: Cursor) -> Result<Self, Self::Error> {
        // Serialize it to json
        let json_str = serde_json::to_string(&value)?;
        // Then base64-encode the json
        let base64_str = base64::engine::general_purpose::STANDARD.encode(json_str);
        Ok(base64_str)
    }
}

impl TryFrom<String> for Cursor {
    type Error = Box<dyn Error>;

    fn try_from(value: String) -> Result<Self, Self::Error> {
        if value.is_empty() {
            // If empty, it's page 0
            return Ok(Cursor {
                page: 0
            })
        }
        // Base64-decode the value
        let json_bytes = base64::engine::general_purpose::STANDARD.decode(value)?;
        // Convert it into a string
        let json_str = String::from_utf8(json_bytes)?;
        // Deserialize it from json
        let cursor = serde_json::from_str(&json_str)?;
        Ok(cursor)
    }
}