use std::{
    str,
    borrow::Cow,
    collections::{HashMap, HashSet},
    fmt,
    path::PathBuf,
};

use rbx_tree::{RbxTree, RbxId, RbxInstanceProperties, RbxValue};
use serde_derive::{Serialize, Deserialize};

use crate::{
    path_map::PathMap,
    project::InstanceProjectNodeMetadata,
};

#[derive(Debug, Clone, Default, Serialize, Deserialize)]
pub struct InstanceChanges {
    pub added: HashSet<RbxId>,
    pub removed: HashSet<RbxId>,
    pub updated: HashSet<RbxId>,
}

impl fmt::Display for InstanceChanges {
    fn fmt(&self, output: &mut fmt::Formatter) -> fmt::Result {
        writeln!(output, "InstanceChanges {{")?;

        if !self.added.is_empty() {
            writeln!(output, "    Added:")?;
            for id in &self.added {
                writeln!(output, "        {}", id)?;
            }
        }

        if !self.removed.is_empty() {
            writeln!(output, "    Removed:")?;
            for id in &self.removed {
                writeln!(output, "        {}", id)?;
            }
        }

        if !self.updated.is_empty() {
            writeln!(output, "    Updated:")?;
            for id in &self.updated {
                writeln!(output, "        {}", id)?;
            }
        }

        writeln!(output, "}}")
    }
}

impl InstanceChanges {
    pub fn is_empty(&self) -> bool {
        self.added.is_empty() && self.removed.is_empty() && self.updated.is_empty()
    }
}

#[derive(Debug)]
pub struct RbxSnapshotInstance<'a> {
    pub name: Cow<'a, str>,
    pub class_name: Cow<'a, str>,
    pub properties: HashMap<String, RbxValue>,
    pub children: Vec<RbxSnapshotInstance<'a>>,
    pub source_path: Option<PathBuf>,
    pub metadata: Option<InstanceProjectNodeMetadata>,
}

pub fn snapshot_from_tree(tree: &RbxTree, id: RbxId) -> Option<RbxSnapshotInstance<'static>> {
    let instance = tree.get_instance(id)?;

    let mut children = Vec::new();
    for &child_id in instance.get_children_ids() {
        children.push(snapshot_from_tree(tree, child_id)?);
    }

    Some(RbxSnapshotInstance {
        name: Cow::Owned(instance.name.to_owned()),
        class_name: Cow::Owned(instance.class_name.to_owned()),
        properties: instance.properties.clone(),
        children,
        source_path: None,
        metadata: None,
    })
}

pub fn reify_root(
    snapshot: &RbxSnapshotInstance,
    path_map: &mut PathMap<RbxId>,
    instance_metadata_map: &mut HashMap<RbxId, InstanceProjectNodeMetadata>,
    changes: &mut InstanceChanges,
) -> RbxTree {
    let instance = reify_core(snapshot);
    let mut tree = RbxTree::new(instance);
    let root_id = tree.get_root_id();

    if let Some(source_path) = &snapshot.source_path {
        path_map.insert(source_path.clone(), root_id);
    }

    if let Some(metadata) = &snapshot.metadata {
        instance_metadata_map.insert(root_id, metadata.clone());
    }

    changes.added.insert(root_id);

    for child in &snapshot.children {
        reify_subtree(child, &mut tree, root_id, path_map, instance_metadata_map, changes);
    }

    tree
}

pub fn reify_subtree(
    snapshot: &RbxSnapshotInstance,
    tree: &mut RbxTree,
    parent_id: RbxId,
    path_map: &mut PathMap<RbxId>,
    instance_metadata_map: &mut HashMap<RbxId, InstanceProjectNodeMetadata>,
    changes: &mut InstanceChanges,
) {
    let instance = reify_core(snapshot);
    let id = tree.insert_instance(instance, parent_id);

    if let Some(source_path) = &snapshot.source_path {
        path_map.insert(source_path.clone(), id);
    }

    if let Some(metadata) = &snapshot.metadata {
        instance_metadata_map.insert(id, metadata.clone());
    }

    changes.added.insert(id);

    for child in &snapshot.children {
        reify_subtree(child, tree, id, path_map, instance_metadata_map, changes);
    }
}

pub fn reconcile_subtree(
    tree: &mut RbxTree,
    id: RbxId,
    snapshot: &RbxSnapshotInstance,
    path_map: &mut PathMap<RbxId>,
    instance_metadata_map: &mut HashMap<RbxId, InstanceProjectNodeMetadata>,
    changes: &mut InstanceChanges,
) {
    if let Some(source_path) = &snapshot.source_path {
        path_map.insert(source_path.clone(), id);
    }

    if let Some(metadata) = &snapshot.metadata {
        instance_metadata_map.insert(id, metadata.clone());
    }

    if reconcile_instance_properties(tree.get_instance_mut(id).unwrap(), snapshot) {
        changes.updated.insert(id);
    }

    reconcile_instance_children(tree, id, snapshot, path_map, instance_metadata_map, changes);
}

fn reify_core(snapshot: &RbxSnapshotInstance) -> RbxInstanceProperties {
    let mut properties = HashMap::new();

    for (key, value) in &snapshot.properties {
        properties.insert(key.clone(), value.clone());
    }

    let instance = RbxInstanceProperties {
        name: snapshot.name.to_string(),
        class_name: snapshot.class_name.to_string(),
        properties,
    };

    instance
}

fn reconcile_instance_properties(instance: &mut RbxInstanceProperties, snapshot: &RbxSnapshotInstance) -> bool {
    let mut has_diffs = false;

    if instance.name != snapshot.name {
        instance.name = snapshot.name.to_string();
        has_diffs = true;
    }

    if instance.class_name != snapshot.class_name {
        instance.class_name = snapshot.class_name.to_string();
        has_diffs = true;
    }

    let mut property_updates = HashMap::new();

    for (key, instance_value) in &instance.properties {
        match snapshot.properties.get(key) {
            Some(snapshot_value) => {
                if snapshot_value != instance_value {
                    property_updates.insert(key.clone(), Some(snapshot_value.clone()));
                }
            },
            None => {
                property_updates.insert(key.clone(), None);
            },
        }
    }

    for (key, snapshot_value) in &snapshot.properties {
        if property_updates.contains_key(key) {
            continue;
        }

        match instance.properties.get(key) {
            Some(instance_value) => {
                if snapshot_value != instance_value {
                    property_updates.insert(key.clone(), Some(snapshot_value.clone()));
                }
            },
            None => {
                property_updates.insert(key.clone(), Some(snapshot_value.clone()));
            },
        }
    }

    has_diffs = has_diffs || !property_updates.is_empty();

    for (key, change) in property_updates.drain() {
        match change {
            Some(value) => instance.properties.insert(key, value),
            None => instance.properties.remove(&key),
        };
    }

    has_diffs
}

fn reconcile_instance_children(
    tree: &mut RbxTree,
    id: RbxId,
    snapshot: &RbxSnapshotInstance,
    path_map: &mut PathMap<RbxId>,
    instance_metadata_map: &mut HashMap<RbxId, InstanceProjectNodeMetadata>,
    changes: &mut InstanceChanges,
) {
    let mut visited_snapshot_indices = HashSet::new();

    let mut children_to_update: Vec<(RbxId, &RbxSnapshotInstance)> = Vec::new();
    let mut children_to_add: Vec<&RbxSnapshotInstance> = Vec::new();
    let mut children_to_remove: Vec<RbxId> = Vec::new();

    let children_ids = tree.get_instance(id).unwrap().get_children_ids();

    // Find all instances that were removed or updated, which we derive by
    // trying to pair up existing instances to snapshots.
    for &child_id in children_ids {
        let child_instance = tree.get_instance(child_id).unwrap();

        // Locate a matching snapshot for this instance
        let mut matching_snapshot = None;
        for (snapshot_index, child_snapshot) in snapshot.children.iter().enumerate() {
            if visited_snapshot_indices.contains(&snapshot_index) {
                continue;
            }

            // We assume that instances with the same name are probably pretty
            // similar. This heuristic is similar to React's reconciliation
            // strategy.
            if child_snapshot.name == child_instance.name {
                visited_snapshot_indices.insert(snapshot_index);
                matching_snapshot = Some(child_snapshot);
                break;
            }
        }

        match matching_snapshot {
            Some(child_snapshot) => {
                children_to_update.push((child_instance.get_id(), child_snapshot));
            },
            None => {
                children_to_remove.push(child_instance.get_id());
            },
        }
    }

    // Find all instancs that were added, which is just the snapshots we didn't
    // match up to existing instances above.
    for (snapshot_index, child_snapshot) in snapshot.children.iter().enumerate() {
        if !visited_snapshot_indices.contains(&snapshot_index) {
            children_to_add.push(child_snapshot);
        }
    }

    for child_snapshot in &children_to_add {
        reify_subtree(child_snapshot, tree, id, path_map, instance_metadata_map, changes);
    }

    for child_id in &children_to_remove {
        if let Some(subtree) = tree.remove_instance(*child_id) {
            for id in subtree.iter_all_ids() {
                instance_metadata_map.remove(&id);
                changes.removed.insert(id);
            }
        }
    }

    for (child_id, child_snapshot) in &children_to_update {
        reconcile_subtree(tree, *child_id, child_snapshot, path_map, instance_metadata_map, changes);
    }
}