#![allow(dead_code)] // REMOVE THIS LINE after fully implementing this functionality

mod leveled;
mod simple_leveled;
mod tiered;

use std::sync::Arc;
use std::time::Duration;

use anyhow::Result;
pub use leveled::{LeveledCompactionController, LeveledCompactionOptions, LeveledCompactionTask};
use serde::{Deserialize, Serialize};
pub use simple_leveled::{
    SimpleLeveledCompactionController, SimpleLeveledCompactionOptions, SimpleLeveledCompactionTask,
};
pub use tiered::{TieredCompactionController, TieredCompactionOptions, TieredCompactionTask};

use crate::lsm_storage::{LsmStorageInner, LsmStorageState};
use crate::table::SsTable;

#[derive(Debug, Serialize, Deserialize)]
pub enum CompactionTask {
    Leveled(LeveledCompactionTask),
    Tiered(TieredCompactionTask),
    Simple(SimpleLeveledCompactionTask),
    ForceFullCompaction(Vec<usize>),
}

impl CompactionTask {
    fn compact_to_bottom_level(&self) -> bool {
        match self {
            CompactionTask::ForceFullCompaction(_) => true,
            CompactionTask::Leveled(task) => task.is_lower_level_bottom_level,
            CompactionTask::Simple(task) => task.is_lower_level_bottom_level,
            CompactionTask::Tiered(task) => task.bottom_tier_included,
        }
    }
}

pub(crate) enum CompactionController {
    Leveled(LeveledCompactionController),
    Tiered(TieredCompactionController),
    Simple(SimpleLeveledCompactionController),
    NoCompaction,
}

impl CompactionController {
    pub fn generate_compaction_task(&self, snapshot: &LsmStorageState) -> Option<CompactionTask> {
        match self {
            CompactionController::Leveled(ctrl) => ctrl
                .generate_compaction_task(&snapshot)
                .map(CompactionTask::Leveled),
            CompactionController::Simple(ctrl) => ctrl
                .generate_compaction_task(&snapshot)
                .map(CompactionTask::Simple),
            CompactionController::Tiered(ctrl) => ctrl
                .generate_compaction_task(&snapshot)
                .map(CompactionTask::Tiered),
            CompactionController::NoCompaction => unreachable!(),
        }
    }

    pub fn apply_compaction_result(
        &self,
        snapshot: &LsmStorageState,
        task: &CompactionTask,
        output: &[usize],
    ) -> (LsmStorageState, Vec<usize>) {
        match (self, task) {
            (CompactionController::Leveled(ctrl), CompactionTask::Leveled(task)) => {
                ctrl.apply_compaction_result(&snapshot, task, output)
            }
            (CompactionController::Simple(ctrl), CompactionTask::Simple(task)) => {
                ctrl.apply_compaction_result(&snapshot, task, output)
            }
            (CompactionController::Tiered(ctrl), CompactionTask::Tiered(task)) => {
                ctrl.apply_compaction_result(&snapshot, task, output)
            }
            _ => unreachable!(),
        }
    }
}

impl CompactionController {
    pub fn flush_to_l0(&self) -> bool {
        if let Self::Leveled(_) | Self::Simple(_) | Self::NoCompaction = self {
            true
        } else {
            false
        }
    }
}

pub enum CompactionOptions {
    /// Leveled compaction with partial compaction + dynamic level support (= RocksDB's Leveled
    /// Compaction)
    Leveled(LeveledCompactionOptions),
    /// Tiered compaction (= RocksDB's universal compaction)
    Tiered(TieredCompactionOptions),
    /// Simple leveled compaction
    Simple(SimpleLeveledCompactionOptions),
    /// In no compaction mode (week 1), always flush to L0
    NoCompaction,
}

impl LsmStorageInner {
    fn compact(&self, _task: &CompactionTask) -> Result<Vec<Arc<SsTable>>> {
        unimplemented!()
    }

    pub fn force_full_compaction(&self) -> Result<()> {
        unimplemented!()
    }

    fn trigger_compaction(&self) -> Result<()> {
        unimplemented!()
    }

    pub(crate) fn spawn_compaction_thread(
        self: &Arc<Self>,
        rx: crossbeam_channel::Receiver<()>,
    ) -> Result<Option<std::thread::JoinHandle<()>>> {
        if let CompactionOptions::Leveled(_)
        | CompactionOptions::Simple(_)
        | CompactionOptions::Tiered(_) = self.options.compaction_options
        {
            let this = self.clone();
            let handle = std::thread::spawn(move || {
                let ticker = crossbeam_channel::tick(Duration::from_millis(50));
                loop {
                    crossbeam_channel::select! {
                        recv(ticker) -> _ => if let Err(e) = this.trigger_compaction() {
                            eprintln!("compaction failed: {}", e);
                        },
                        recv(rx) -> _ => return
                    }
                }
            });
            return Ok(Some(handle));
        }
        Ok(None)
    }
}