/// In-memory registry of named projection schemas.
///
/// The registry is the store of all registered projections. In a running server,
/// one registry instance is shared (behind a Mutex or RwLock). Projections are
/// looked up by name to execute queries.
use std::collections::HashMap;

use crate::error::{ProjectionError, ProjectionResult};
use crate::schema::ProjectionSchema;

/// Holds all registered `ProjectionSchema`s, keyed by name.
#[derive(Default)]
pub struct ProjectionRegistry {
    schemas: HashMap<String, ProjectionSchema>,
}

impl ProjectionRegistry {
    pub fn new() -> Self {
        Self {
            schemas: HashMap::new(),
        }
    }

    /// Register a new schema. Fails if one with the same name already exists.
    pub fn register(&mut self, schema: ProjectionSchema) -> ProjectionResult<()> {
        if self.schemas.contains_key(&schema.name) {
            return Err(ProjectionError::AlreadyExists(schema.name.clone()));
        }
        if schema.name.is_empty() {
            return Err(ProjectionError::InvalidSchema("name must not be empty".into()));
        }
        self.schemas.insert(schema.name.clone(), schema);
        Ok(())
    }

    /// Replace an existing schema (upsert). Creates if not present.
    pub fn upsert(&mut self, schema: ProjectionSchema) -> ProjectionResult<()> {
        if schema.name.is_empty() {
            return Err(ProjectionError::InvalidSchema("name must not be empty".into()));
        }
        self.schemas.insert(schema.name.clone(), schema);
        Ok(())
    }

    /// Retrieve a schema by name.
    pub fn get(&self, name: &str) -> ProjectionResult<&ProjectionSchema> {
        self.schemas
            .get(name)
            .ok_or_else(|| ProjectionError::NotFound(name.to_string()))
    }

    /// List all schema names.
    pub fn list(&self) -> Vec<&ProjectionSchema> {
        let mut schemas: Vec<&ProjectionSchema> = self.schemas.values().collect();
        schemas.sort_by(|a, b| a.name.cmp(&b.name));
        schemas
    }

    /// Remove a schema by name. Returns true if it existed.
    pub fn remove(&mut self, name: &str) -> bool {
        self.schemas.remove(name).is_some()
    }

    /// Number of registered schemas.
    pub fn len(&self) -> usize {
        self.schemas.len()
    }

    /// True if no schemas are registered.
    pub fn is_empty(&self) -> bool {
        self.schemas.is_empty()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::schema::{NodeFilter, ProjectionType};

    fn make_schema(name: &str) -> ProjectionSchema {
        ProjectionSchema {
            name: name.to_string(),
            description: None,
            projection_type: ProjectionType::Relational,
            node_filter: NodeFilter::All,
            field_mappings: vec![],
        }
    }

    #[test]
    fn test_register_and_get() {
        let mut reg = ProjectionRegistry::new();
        reg.register(make_schema("users")).unwrap();
        let s = reg.get("users").unwrap();
        assert_eq!(s.name, "users");
    }

    #[test]
    fn test_register_duplicate_fails() {
        let mut reg = ProjectionRegistry::new();
        reg.register(make_schema("events")).unwrap();
        assert!(reg.register(make_schema("events")).is_err());
    }

    #[test]
    fn test_upsert_replaces() {
        let mut reg = ProjectionRegistry::new();
        reg.register(make_schema("s1")).unwrap();
        let mut updated = make_schema("s1");
        updated.description = Some("updated".into());
        reg.upsert(updated).unwrap();
        assert_eq!(reg.get("s1").unwrap().description.as_deref(), Some("updated"));
    }

    #[test]
    fn test_list_sorted() {
        let mut reg = ProjectionRegistry::new();
        reg.register(make_schema("zoo")).unwrap();
        reg.register(make_schema("alpha")).unwrap();
        reg.register(make_schema("mango")).unwrap();
        let names: Vec<&str> = reg.list().iter().map(|s| s.name.as_str()).collect();
        assert_eq!(names, vec!["alpha", "mango", "zoo"]);
    }

    #[test]
    fn test_remove() {
        let mut reg = ProjectionRegistry::new();
        reg.register(make_schema("temp")).unwrap();
        assert!(reg.remove("temp"));
        assert!(!reg.remove("temp"));
        assert!(reg.get("temp").is_err());
    }
}