use ::anyhow::Result;
use ::chrono::prelude::*;
use ::log::{debug, error, info};
use ::serde_derive::{Deserialize, Serialize};
use ::std::collections::BTreeMap;
use ::std::collections::HashMap;
use ::std::fs;
use ::std::path::{Path, PathBuf};
use ::std::sync::{Arc, Mutex};
use ::std::time::SystemTime;

use crate::settings::Settings;
use crate::task::{Task, TaskResult, TaskStatus};

pub type SharedState = Arc<Mutex<State>>;

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct State {
    max_id: usize,
    pub settings: Settings,
    pub running: bool,
    pub tasks: BTreeMap<usize, Task>,
    /// Represents whether the group is currently paused or running
    pub groups: HashMap<String, bool>,
}

impl State {
    pub fn new(settings: &Settings) -> State {
        // Create a default group state.
        let mut groups = HashMap::new();
        for group in settings.daemon.groups.keys() {
            groups.insert(group.into(), true);
        }

        let mut state = State {
            max_id: 0,
            settings: settings.clone(),
            running: true,
            tasks: BTreeMap::new(),
            groups,
        };
        state.restore();
        state.save();
        state
    }

    pub fn add_task(&mut self, mut task: Task) -> usize {
        task.id = self.max_id;
        self.tasks.insert(self.max_id, task);
        self.max_id += 1;
        self.save();
        self.max_id - 1
    }

    pub fn change_status(&mut self, id: usize, new_status: TaskStatus) {
        if let Some(ref mut task) = self.tasks.get_mut(&id) {
            task.status = new_status;
            self.save();
        };
    }

    pub fn set_enqueue_at(&mut self, id: usize, enqueue_at: Option<DateTime<Local>>) {
        if let Some(ref mut task) = self.tasks.get_mut(&id) {
            task.enqueue_at = enqueue_at;
        }
    }

    /// Check if the given group already exists.
    /// If it doesn't exist yet, create a state entry and a new settings entry.
    pub fn create_group(&mut self, group: &str) -> Result<()> {
        if self.settings.daemon.groups.get(group).is_none() {
            self.settings.daemon.groups.insert(group.into(), 1);
        }
        if self.groups.get(group).is_none() {
            self.groups.insert(group.into(), true);
        }

        self.save();
        self.settings.save()
    }

    /// Remove a group.
    /// Also go through all tasks and set the removed group to `None`.
    pub fn remove_group(&mut self, group: &str) -> Result<()> {
        self.settings.daemon.groups.remove(group);
        self.groups.remove(group);

        // Reset all tasks with removed group to the default
        for (_, task) in self.tasks.iter_mut() {
            if let Some(group_name) = &task.group {
                if group_name == group {
                    task.group = None;
                }
            }
        }

        self.save();
        self.settings.save()
    }

    /// Set the running status for all groups including the default queue
    pub fn set_status_for_all_groups(&mut self, status: bool) {
        self.running = status;
        let keys = self.groups.keys().cloned().collect::<Vec<String>>();
        for key in keys {
            self.groups.insert(key, status);
        }
        self.save()
    }

    /// Get all task ids of a specific group
    pub fn task_ids_in_group_with_stati(
        &mut self,
        group: &Option<String>,
        stati: Vec<TaskStatus>,
    ) -> Vec<usize> {
        self.tasks
            .iter()
            .filter(|(_, task)| stati.contains(&task.status))
            .filter(|(_, task)| group == &task.group)
            .map(|(id, _)| *id)
            .collect()
    }

    /// This checks, whether the given task_ids are in the specified statuses.
    /// The first result is the list of task_ids that match these statuses.
    /// The second result is the list of task_ids that don't match these statuses.
    ///
    /// Additionally, a list of task_ids can be specified to only run the check
    /// on a subset of all tasks.
    pub fn tasks_in_statuses(
        &mut self,
        statuses: Vec<TaskStatus>,
        task_ids: Option<Vec<usize>>,
    ) -> (Vec<usize>, Vec<usize>) {
        let task_ids = match task_ids {
            Some(ids) => ids,
            None => self.tasks.keys().cloned().collect(),
        };

        let mut matching = Vec::new();
        let mut mismatching = Vec::new();

        // Filter all task id's that match the provided statuses.
        for task_id in task_ids.iter() {
            // Check whether the task exists and save all non-existing task ids.
            match self.tasks.get(&task_id) {
                None => {
                    mismatching.push(*task_id);
                    continue;
                }
                Some(task) => {
                    // Check whether the task status matches the specified statuses.
                    if statuses.contains(&task.status) {
                        matching.push(*task_id);
                    } else {
                        mismatching.push(*task_id);
                    }
                }
            };
        }

        (matching, mismatching)
    }

    pub fn reset(&mut self) {
        self.backup();
        self.max_id = 0;
        self.tasks = BTreeMap::new();
        self.set_status_for_all_groups(true);
    }

    /// Convenience wrapper around save_to_file.
    pub fn save(&mut self) {
        self.save_to_file(false);
    }

    /// Save the current current state in a file with a timestamp.
    /// At the same time remove old state logs from the log directory.
    /// This function is called, when large changes to the state are applied, e.g. clean/reset.
    pub fn backup(&mut self) {
        self.save_to_file(true);
        if let Err(error) = self.rotate() {
            error!("Failed to rotate files: {:?}", error);
        };
    }

    /// Save the current state to disk.
    /// We do this to restore in case of a crash.
    /// If log == true, the file will be saved with a time stamp.
    ///
    /// In comparison to the daemon -> client communication, the state is saved
    /// as JSON for better readability and debug purposes.
    fn save_to_file(&mut self, log: bool) {
        let serialized = serde_json::to_string(&self);
        if let Err(error) = serialized {
            error!("Failed to serialize state: {:?}", error);
            return;
        }

        let serialized = serialized.unwrap();

        let path = Path::new(&self.settings.daemon.pueue_directory);
        let (temp, real) = if log {
            let path = path.join("log");
            let now: DateTime<Utc> = Utc::now();
            let time = now.format("%Y-%m-%d_%H-%M-%S");
            (
                path.join(format!("{}_state.json.partial", time)),
                path.join(format!("{}_state.json", time)),
            )
        } else {
            (path.join("state.json.partial"), path.join("state.json"))
        };

        // Write to temporary log file first, to prevent loss due to crashes.
        if let Err(error) = fs::write(&temp, serialized) {
            error!(
                "Failed to write log to directory. File permissions? Error: {:?}",
                error
            );
            return;
        }

        // Overwrite the original with the temp file, if everything went fine.
        if let Err(error) = fs::rename(&temp, &real) {
            error!(
                "Failed to overwrite old log file. File permissions? Error: {:?}",
                error
            );
            return;
        }

        if log {
            debug!("State backup created at: {:?}", real);
        } else {
            debug!("State saved at: {:?}", real);
        }
    }

    /// Restore the last state from a previous session.
    /// The state is stored as json in the log directory.
    fn restore(&mut self) {
        let path = Path::new(&self.settings.daemon.pueue_directory).join("state.json");

        // Ignore if the file doesn't exist. It doesn't have to.
        if !path.exists() {
            info!(
                "Couldn't find state from previous session at location: {:?}",
                path
            );
            return;
        }
        info!("Start restoring state");

        // Try to load the file.
        let data = fs::read_to_string(&path);
        if let Err(error) = data {
            error!("Failed to read previous state log: {:?}", error);
            return;
        }
        let data = data.unwrap();

        // Try to deserialize the state file.
        let deserialized: Result<State, serde_json::error::Error> = serde_json::from_str(&data);
        if let Err(error) = deserialized {
            error!("Failed to deserialize previous state log: {:?}", error);
            return;
        }
        let mut state = deserialized.unwrap();

        // Restore the state from the file.
        // While restoring the tasks, check for any invalid/broken stati.
        for (task_id, task) in state.tasks.iter_mut() {
            // Handle ungraceful shutdowns while executing tasks.
            if task.status == TaskStatus::Running || task.status == TaskStatus::Paused {
                info!(
                    "Setting task {} with previous status {:?} to new status {:?}",
                    task.id,
                    task.status,
                    TaskResult::Killed
                );
                task.status = TaskStatus::Done;
                task.result = Some(TaskResult::Killed);
            }
            // Crash during editing of the task command.
            if task.status == TaskStatus::Locked {
                task.status = TaskStatus::Stashed;
            }
            // If there are any queued tasks, pause the daemon.
            // This should prevent any unwanted execution of tasks due to a system crash.
            if task.status == TaskStatus::Queued {
                info!("Pausing daemon to prevent unwanted execution of previous tasks");
                state.running = false;
            }

            self.tasks.insert(*task_id, task.clone());
        }

        if !self.running {
            // If the daemon isn't running, stop all groups.
            for group in self.settings.daemon.groups.keys() {
                self.groups.insert(group.into(), false);
            }
        } else {
            // If the daemon running, apply all running group states from the previous state.
            for (group, running) in state.groups.iter() {
                if self.groups.contains_key(group) {
                    self.groups.insert(group.into(), *running);
                }
            }
        }

        // Go trough all tasks and set all groups that are no longer
        // listed in the configuration file to the default.
        for (_, task) in self.tasks.iter_mut() {
            if let Some(group) = &task.group {
                if !self.groups.contains_key(group) {
                    task.group = None;
                }
            }
        }

        self.running = state.running;
        self.max_id = state.max_id;
    }

    /// Remove old logs that aren't needed any longer.
    fn rotate(&mut self) -> Result<()> {
        let path = Path::new(&self.settings.daemon.pueue_directory);
        let path = path.join("log");

        // Get all log files in the directory with their respective system time.
        let mut entries: BTreeMap<SystemTime, PathBuf> = BTreeMap::new();
        let mut directory_list = fs::read_dir(path)?;
        while let Some(Ok(entry)) = directory_list.next() {
            let path = entry.path();

            let metadata = entry.metadata()?;
            let time = metadata.modified()?;
            entries.insert(time, path);
        }

        // Remove all files above the threshold.
        // Old files are removed first (implictly by the BTree order).
        let mut number_entries = entries.len();
        let mut iter = entries.iter();
        while number_entries > 10 {
            if let Some((_, path)) = iter.next() {
                fs::remove_file(path)?;
                number_entries -= 1;
            }
        }

        Ok(())
    }
}