use std::borrow::Borrow;

use heromodels_core::{Index, Model};
use serde::{Deserialize, Serialize};

pub mod hero;
pub mod postgres;

pub trait Db {
    /// Error type returned by database operations.
    type Error: std::fmt::Debug;

    /// Open the collection for a specific model. This method must create the collection if it does not exist.
    fn collection<M: Model>(&self) -> Result<impl Collection<&str, M>, Error<Self::Error>>;
}

/// A collection stores a specific model under a specific key
pub trait Collection<K, V>
where
    K: Serialize,
    V: Serialize + for<'a> Deserialize<'a>,
{
    /// Error type for database operations
    type Error: std::fmt::Debug;

    /// Get all items where the given index field is equal to key.
    fn get<I, Q>(&self, key: &Q) -> Result<Vec<V>, Error<Self::Error>>
    where
        I: Index<Model = V>,
        I::Key: Borrow<Q>,
        Q: ToString + Serialize + core::fmt::Debug + Sync + ?Sized;

    /// Get an object from its ID. This does not use an index lookup
    fn get_by_id(&self, id: u32) -> Result<Option<V>, Error<Self::Error>>;

    /// Store an item in the DB and return the assigned ID and the updated model.
    ///
    /// # Important Notes
    /// - This method does not modify the original model passed as an argument.
    /// - For new models (with ID 0), an ID will be auto-generated by OurDB.
    /// - The returned model will have the correct ID and should be used instead of the original model.
    /// - The original model should not be used after calling this method, as it may have
    ///   an inconsistent state compared to what's in the database.
    /// - ID 0 is reserved for new models and should not be used for existing models.
    fn set(&self, value: &V) -> Result<(u32, V), Error<Self::Error>>;

    /// Delete all items from the db with a given index.
    fn delete<I, Q>(&self, key: &Q) -> Result<(), Error<Self::Error>>
    where
        I: Index<Model = V>,
        I::Key: Borrow<Q>,
        Q: ToString + Serialize + core::fmt::Debug + Sync + ?Sized;

    /// Delete an object with a given ID
    fn delete_by_id(&self, id: u32) -> Result<(), Error<Self::Error>>;

    /// Get all objects from the collection
    fn get_all(&self) -> Result<Vec<V>, Error<Self::Error>>;

    /// Begin a transaction for this collection
    fn begin_transaction(
        &self,
    ) -> Result<Box<dyn Transaction<Error = Self::Error>>, Error<Self::Error>>;
}

/// Errors returned by the DB implementation
#[derive(Debug)]
pub enum Error<E> {
    /// Error in the underlying database
    DB(E),
    /// Error decoding a stored model
    Decode(bincode::error::DecodeError),
    /// Error encoding a model for storage
    Encode(bincode::error::EncodeError),
    /// Invalid ID used (e.g., using ID 0 for an existing model)
    InvalidId(String),
    /// ID mismatch (e.g., expected ID 5 but got ID 6)
    IdMismatch(String),
    /// ID collision (e.g., trying to create a model with an ID that already exists)
    IdCollision(String),
    /// Type error (e.g., trying to get a model of the wrong type)
    TypeError,
}

impl<E> From<bincode::error::DecodeError> for Error<E> {
    fn from(value: bincode::error::DecodeError) -> Self {
        Error::Decode(value)
    }
}

impl<E> From<bincode::error::EncodeError> for Error<E> {
    fn from(value: bincode::error::EncodeError) -> Self {
        Error::Encode(value)
    }
}

impl<E: std::fmt::Debug + std::fmt::Display> std::fmt::Display for Error<E> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Error::DB(e) => write!(f, "Database error: {}", e),
            Error::Decode(e) => write!(f, "Failed to decode model: {}", e),
            Error::Encode(e) => write!(f, "Failed to encode model: {}", e),
            Error::InvalidId(s) => write!(f, "Invalid ID: {}", s),
            Error::IdMismatch(s) => write!(f, "ID Mismatch: {}", s),
            Error::IdCollision(s) => write!(f, "ID Collision: {}", s),
            Error::TypeError => write!(f, "Type error"),
        }
    }
}
/// A transaction that can be committed or rolled back
pub trait Transaction {
    /// Error type for transaction operations
    type Error: std::fmt::Debug;

    /// Begin a transaction
    fn begin(&self) -> Result<(), Error<Self::Error>>;

    /// Commit a transaction
    fn commit(&self) -> Result<(), Error<Self::Error>>;

    /// Roll back a transaction
    fn rollback(&self) -> Result<(), Error<Self::Error>>;

    /// Check if a transaction is active
    fn is_active(&self) -> bool;
}