use serde::{Deserialize, Serialize};
use std::{convert::Infallible, str::FromStr};

/// Include/exclude fields from item collections.
///
/// By default, STAC API endpoints that return Item objects return every field
/// of those Items. However, Item objects can have hundreds of fields, or large
/// geometries, and even smaller Item objects can add up when large numbers of
/// them are in results. Frequently, not all fields in an Item are used, so this
/// specification provides a mechanism for clients to request that servers to
/// explicitly include or exclude certain fields.
#[derive(Debug, Serialize, Deserialize, Default, PartialEq)]
pub struct Fields {
    /// Fields to include.
    #[serde(skip_serializing_if = "Vec::is_empty")]
    pub include: Vec<String>,

    /// Fields to exclude.
    #[serde(skip_serializing_if = "Vec::is_empty")]
    pub exclude: Vec<String>,
}

impl FromStr for Fields {
    type Err = Infallible;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let mut include = Vec::new();
        let mut exclude = Vec::new();
        for field in s.split(",").filter(|s| !s.is_empty()) {
            if field.starts_with('-') {
                exclude.push(field[1..].to_string());
            } else {
                include.push(field.to_string());
            }
        }
        Ok(Fields { include, exclude })
    }
}

#[cfg(test)]
mod tests {
    use super::Fields;

    #[test]
    fn empty() {
        assert_eq!(Fields::default(), "".parse().unwrap());
    }

    #[test]
    fn includes() {
        assert_eq!(
            Fields {
                include: vec![
                    "id".to_string(),
                    "type".to_string(),
                    "geometry".to_string(),
                    "bbox".to_string(),
                    "properties".to_string(),
                    "links".to_string(),
                    "assets".to_string(),
                ],
                exclude: Vec::new()
            },
            "id,type,geometry,bbox,properties,links,assets"
                .parse()
                .unwrap()
        )
    }

    #[test]
    fn exclude() {
        assert_eq!(
            Fields {
                include: Vec::new(),
                exclude: vec!["geometry".to_string()]
            },
            "-geometry".parse().unwrap()
        );
    }
}