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#[derive(Debug, thiserror::Error)]
pub enum Error {
    #[error("todo")]
    ToDo,
}

/// A document id.
///
/// # Limit
///
/// <https://firebase.google.com/docs/firestore/quotas#collections_documents_and_fields>
///
/// > - Must be valid UTF-8 characters
/// > - Must be no longer than 1,500 bytes
/// > - Cannot contain a forward slash (/)
/// > - Cannot solely consist of a single period (.) or double periods (..)
/// > - Cannot match the regular expression __.*__
/// > - If you import Datastore entities into a Firestore database, numeric entity IDs are exposed as __id[0-9]+__
///
/// # Examples
///
/// ```rust
/// # fn main() -> anyhow::Result<()> {
/// use firestore_path::DocumentId;
/// use std::str::FromStr;
///
/// let document_id = DocumentId::from_str("chatroom1")?;
/// assert_eq!(document_id.as_ref(), "chatroom1");
/// assert_eq!(document_id.to_string(), "chatroom1");
/// #     Ok(())
/// # }
/// ```
///
#[derive(Clone, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct DocumentId(String);

impl std::convert::AsRef<str> for DocumentId {
    fn as_ref(&self) -> &str {
        self.0.as_ref()
    }
}

impl std::convert::TryFrom<&str> for DocumentId {
    type Error = Error;

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

impl std::convert::TryFrom<String> for DocumentId {
    type Error = Error;

    fn try_from(s: String) -> Result<Self, Self::Error> {
        // <https://firebase.google.com/docs/firestore/quotas#collections_documents_and_fields>
        if s.len() > 1_500 {
            return Err(Error::ToDo);
        }

        if s.contains('/') {
            return Err(Error::ToDo);
        }

        if s == "." || s == ".." {
            return Err(Error::ToDo);
        }

        if s.starts_with("__") && s.ends_with("__") {
            return Err(Error::ToDo);
        }

        // TODO: Datastore entities

        Ok(Self(s))
    }
}

impl std::fmt::Display for DocumentId {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        self.0.fmt(f)
    }
}

impl std::str::FromStr for DocumentId {
    type Err = Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Self::try_from(s)
    }
}

#[cfg(test)]
mod tests {
    use std::str::FromStr;

    use super::*;

    #[test]
    fn test() -> anyhow::Result<()> {
        let s = "chatroom1";
        let document_id = DocumentId::from_str(s)?;
        assert_eq!(document_id.to_string(), s);

        assert_eq!(document_id.as_ref(), s);
        Ok(())
    }

    #[test]
    fn test_impl_from_str_and_impl_try_from_string() -> anyhow::Result<()> {
        for (s, expected) in [
            ("chatroom1", true),
            ("x".repeat(1501).as_ref(), false),
            ("x".repeat(1500).as_ref(), true),
            ("chat/room1", false),
            (".", false),
            (".x", true),
            ("..", false),
            ("..x", true),
            ("__x__", false),
            ("__x", true),
            ("x__", true),
        ] {
            assert_eq!(DocumentId::from_str(s).is_ok(), expected);
            assert_eq!(DocumentId::try_from(s.to_string()).is_ok(), expected);
            if expected {
                assert_eq!(
                    DocumentId::from_str(s)?,
                    DocumentId::try_from(s.to_string())?
                );
                assert_eq!(DocumentId::from_str(s)?.to_string(), s);
            }
        }
        Ok(())
    }
}