stac 0.17.2

use serde::{Deserialize, Deserializer, Serialize};
use std::{
    convert::Infallible,
    fmt::{Display, Formatter},
    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(Clone, Debug, Serialize, Default, PartialEq)]
pub struct Fields {
    /// Fields to include.
    #[serde(skip_serializing_if = "Vec::is_empty", default)]
    pub include: Vec<String>,

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

impl Fields {
    fn from_iter<I>(fields: I) -> Fields
    where
        I: IntoIterator<Item = String>,
    {
        let mut include = Vec::new();
        let mut exclude = Vec::new();
        for field in fields {
            if let Some(field) = field.strip_prefix('-') {
                exclude.push(field.to_string());
            } else if let Some(field) = field.strip_prefix('+') {
                include.push(field.to_string());
            } else {
                include.push(field);
            }
        }
        Fields { include, exclude }
    }
}

impl FromStr for Fields {
    type Err = Infallible;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Ok(Fields::from_iter(
            s.split(',')
                .filter(|s| !s.is_empty())
                .map(ToString::to_string),
        ))
    }
}

impl<'de> Deserialize<'de> for Fields {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        #[derive(Deserialize)]
        #[serde(untagged)]
        enum Repr {
            List(Vec<String>),
            Struct {
                #[serde(default)]
                include: Vec<String>,
                #[serde(default)]
                exclude: Vec<String>,
            },
        }

        Ok(match Repr::deserialize(deserializer)? {
            Repr::List(fields) => Fields::from_iter(fields),
            Repr::Struct { include, exclude } => Fields { include, exclude },
        })
    }
}

impl Display for Fields {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        let mut fields = Vec::new();
        for include in &self.include {
            fields.push(include.to_string());
        }
        for exclude in &self.exclude {
            fields.push(format!("-{exclude}"));
        }
        write!(f, "{}", fields.join(","))
    }
}

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

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

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

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

    #[test]
    fn permissive_deserialization() {
        let _ = serde_json::from_str::<Fields>("{}").unwrap();
    }

    #[test]
    fn deserialize_struct() {
        assert_eq!(
            Fields {
                include: vec!["foo".to_string()],
                exclude: vec!["bar".to_string()],
            },
            serde_json::from_str(r#"{"include": ["foo"], "exclude": ["bar"]}"#).unwrap()
        );
    }

    #[test]
    fn deserialize_list() {
        assert_eq!(
            Fields {
                include: vec!["foo".to_string(), "baz".to_string()],
                exclude: vec!["bar".to_string()],
            },
            serde_json::from_str(r#"["foo", "-bar", "+baz"]"#).unwrap()
        );
    }

    #[test]
    fn deserialize_empty_list() {
        assert_eq!(Fields::default(), serde_json::from_str("[]").unwrap());
    }
}