use std::sync::Arc;

use crate::{loader::LoaderError, ResourceState, UntypedResHandle};

#[derive(Clone)]
pub enum DependencyState {
    Loading,
    Error {
        /// The resource that had the error.
        handle: UntypedResHandle,
        /// The error that the resource ran into when loading.
        error: Arc<LoaderError>,
    },
    Ready,
}

impl DependencyState {
    /// Creates a DependencyState from a resource by retrieving its state. Does not include
    /// the states of the dependencies.
    pub fn shallow_from_res(handle: &UntypedResHandle) -> DependencyState {
        let res = handle.read();
        match &res.state {
            ResourceState::Loading => DependencyState::Loading,
            ResourceState::Error(er) => DependencyState::Error {
                handle: handle.clone(),
                error: er.clone(),
            },
            ResourceState::Ready(_) => DependencyState::Ready,
        }
    }

    /// Retrieve the state of the handle and its dependencies, does not recursively retrieve.
    pub fn from_res(handle: &UntypedResHandle) -> DependencyState {
        let res = handle.read();
        match &res.state {
            ResourceState::Loading => DependencyState::Loading,
            ResourceState::Error(er) => DependencyState::Error {
                handle: handle.clone(),
                error: er.clone(),
            },
            ResourceState::Ready(res) => {
                let mut lowest_state = DependencyState::Ready;
                
                for dep in res.dependencies() {
                    let state = DependencyState::shallow_from_res(&dep);

                    // try to find the "lowest" dependency. Meaning the state of a dependency
                    // that would stop the parent from being ready.
                    if state.is_loading() {
                        lowest_state = state;
                        break;
                    } else if state.is_error() {
                        lowest_state = state;
                        break;
                    }

                    // anything else would be loaded, so no need to update `lowest_state`
                }

                lowest_state
            },
        }
    }

    /// Retrieve the state of the handle and its dependencies, does not recursively retrieve.
    pub fn from_res_recurse(handle: &UntypedResHandle) -> DependencyState {
        let res = handle.read();
        match &res.state {
            ResourceState::Loading => DependencyState::Loading,
            ResourceState::Error(er) => DependencyState::Error {
                handle: handle.clone(),
                error: er.clone(),
            },
            ResourceState::Ready(res) => {
                let mut lowest_state = DependencyState::Ready;
                
                for dep in res.dependencies() {
                    let state = DependencyState::from_res_recurse(&dep);

                    // try to find the "lowest" dependency. Meaning the state of a dependency
                    // that would stop the parent from being ready.
                    if state.is_loading() {
                        lowest_state = state;
                        break;
                    } else if state.is_error() {
                        lowest_state = state;
                        break;
                    }

                    // anything else would be loaded, so no need to update `lowest_state`
                }

                lowest_state
            },
        }
    }

    pub fn is_ready(&self) -> bool {
        matches!(self, DependencyState::Ready)
    }

    pub fn is_error(&self) -> bool {
        matches!(self, DependencyState::Error { handle: _, error: _ })
    }

    pub fn is_loading(&self) -> bool {
        matches!(self, DependencyState::Loading)
    }
}