use std::{cmp, collections::HashMap, convert::TryFrom};

use conduit::{err, utils, Config, Result};
use rocksdb::{
	statistics::StatsLevel, BlockBasedOptions, Cache, DBCompactionStyle, DBCompressionType, DBRecoveryMode, Env,
	LogLevel, Options, UniversalCompactOptions, UniversalCompactionStopStyle,
};

/// Create database-wide options suitable for opening the database. This also
/// sets our default column options in case of opening a column with the same
/// resulting value. Note that we require special per-column options on some
/// columns, therefor columns should only be opened after passing this result
/// through cf_options().
pub(crate) fn db_options(config: &Config, env: &mut Env, row_cache: &Cache, col_cache: &Cache) -> Result<Options> {
	const DEFAULT_STATS_LEVEL: StatsLevel = if cfg!(debug_assertions) {
		StatsLevel::ExceptDetailedTimers
	} else {
		StatsLevel::DisableAll
	};

	let mut opts = Options::default();

	// Logging
	set_logging_defaults(&mut opts, config);

	// Processing
	opts.set_enable_pipelined_write(true);
	opts.set_max_background_jobs(num_threads::<i32>(config)?);
	opts.set_max_subcompactions(num_threads::<u32>(config)?);
	opts.set_max_file_opening_threads(0);
	if config.rocksdb_compaction_prio_idle {
		env.lower_thread_pool_cpu_priority();
	}

	// IO
	opts.set_manual_wal_flush(true);
	if config.rocksdb_direct_io {
		opts.set_use_direct_reads(true);
		opts.set_use_direct_io_for_flush_and_compaction(true);
	}
	if config.rocksdb_optimize_for_spinning_disks {
		// speeds up opening DB on hard drives
		opts.set_skip_checking_sst_file_sizes_on_db_open(true);
		opts.set_skip_stats_update_on_db_open(true);
		//opts.set_max_file_opening_threads(threads.try_into().unwrap());
	}
	if config.rocksdb_compaction_ioprio_idle {
		env.lower_thread_pool_io_priority();
	}

	// Blocks
	let mut table_opts = table_options(config);
	table_opts.set_block_cache(col_cache);
	opts.set_block_based_table_factory(&table_opts);
	opts.set_row_cache(row_cache);

	// Buffers
	opts.set_write_buffer_size(2 * 1024 * 1024);
	opts.set_max_write_buffer_number(2);
	opts.set_min_write_buffer_number(1);

	// Files
	opts.set_max_total_wal_size(96 * 1024 * 1024);
	set_level_defaults(&mut opts, config);

	// Compression
	set_compression_defaults(&mut opts, config);

	// Misc
	opts.create_if_missing(true);
	opts.set_disable_auto_compactions(!config.rocksdb_compaction);

	opts.set_statistics_level(match config.rocksdb_stats_level {
		0 => StatsLevel::DisableAll,
		1 => DEFAULT_STATS_LEVEL,
		2 => StatsLevel::ExceptHistogramOrTimers,
		3 => StatsLevel::ExceptTimers,
		4 => StatsLevel::ExceptDetailedTimers,
		5 => StatsLevel::ExceptTimeForMutex,
		6_u8..=u8::MAX => StatsLevel::All,
	});

	// Default: https://github.com/facebook/rocksdb/wiki/WAL-Recovery-Modes#ktoleratecorruptedtailrecords
	//
	// Unclean shutdowns of a Matrix homeserver are likely to be fine when
	// recovered in this manner as it's likely any lost information will be
	// restored via federation.
	opts.set_wal_recovery_mode(match config.rocksdb_recovery_mode {
		0 => DBRecoveryMode::AbsoluteConsistency,
		1 => DBRecoveryMode::TolerateCorruptedTailRecords,
		2 => DBRecoveryMode::PointInTime,
		3 => DBRecoveryMode::SkipAnyCorruptedRecord,
		4_u8..=u8::MAX => unimplemented!(),
	});

	opts.set_env(env);
	Ok(opts)
}

/// Adjust options for the specific column by name. Provide the result of
/// db_options() as the argument to this function and use the return value in
/// the arguments to open the specific column.
pub(crate) fn cf_options(
	cfg: &Config, name: &str, mut opts: Options, cache: &mut HashMap<String, Cache>,
) -> Result<Options> {
	// Columns with non-default compaction options
	match name {
		"backupid_algorithm"
		| "backupid_etag"
		| "backupkeyid_backup"
		| "roomid_shortroomid"
		| "shorteventid_shortstatehash"
		| "shorteventid_eventid"
		| "shortstatekey_statekey"
		| "shortstatehash_statediff"
		| "userdevicetxnid_response"
		| "userfilterid_filter" => set_for_sequential_small_uc(&mut opts, cfg),
		&_ => {},
	}

	// Columns with non-default table/cache configs
	match name {
		"shorteventid_eventid" => set_table_with_new_cache(
			&mut opts,
			cfg,
			cache,
			name,
			cache_size(cfg, cfg.shorteventid_cache_capacity, 64)?,
		),

		"eventid_shorteventid" => set_table_with_new_cache(
			&mut opts,
			cfg,
			cache,
			name,
			cache_size(cfg, cfg.eventidshort_cache_capacity, 64)?,
		),

		"shorteventid_authchain" => {
			set_table_with_new_cache(
				&mut opts,
				cfg,
				cache,
				name,
				cache_size(cfg, cfg.auth_chain_cache_capacity, 192)?,
			);
		},

		"shortstatekey_statekey" => set_table_with_new_cache(
			&mut opts,
			cfg,
			cache,
			name,
			cache_size(cfg, cfg.shortstatekey_cache_capacity, 1024)?,
		),

		"statekey_shortstatekey" => set_table_with_new_cache(
			&mut opts,
			cfg,
			cache,
			name,
			cache_size(cfg, cfg.statekeyshort_cache_capacity, 1024)?,
		),

		"eventid_outlierpdu" => {
			set_table_with_new_cache(&mut opts, cfg, cache, name, cache_size(cfg, cfg.pdu_cache_capacity, 1536)?);
		},

		"pduid_pdu" => set_table_with_shared_cache(&mut opts, cfg, cache, name, "eventid_outlierpdu"),

		&_ => {},
	}

	Ok(opts)
}

fn set_logging_defaults(opts: &mut Options, config: &Config) {
	let rocksdb_log_level = match config.rocksdb_log_level.as_ref() {
		"debug" => LogLevel::Debug,
		"info" => LogLevel::Info,
		"warn" => LogLevel::Warn,
		"fatal" => LogLevel::Fatal,
		_ => LogLevel::Error,
	};

	opts.set_log_level(rocksdb_log_level);
	opts.set_max_log_file_size(config.rocksdb_max_log_file_size);
	opts.set_log_file_time_to_roll(config.rocksdb_log_time_to_roll);
	opts.set_keep_log_file_num(config.rocksdb_max_log_files);
	opts.set_stats_dump_period_sec(0);

	if config.rocksdb_log_stderr {
		opts.set_stderr_logger(rocksdb_log_level, "rocksdb");
	}
}

fn set_compression_defaults(opts: &mut Options, config: &Config) {
	let rocksdb_compression_algo = match config.rocksdb_compression_algo.as_ref() {
		"snappy" => DBCompressionType::Snappy,
		"zlib" => DBCompressionType::Zlib,
		"bz2" => DBCompressionType::Bz2,
		"lz4" => DBCompressionType::Lz4,
		"lz4hc" => DBCompressionType::Lz4hc,
		"none" => DBCompressionType::None,
		_ => DBCompressionType::Zstd,
	};

	if config.rocksdb_bottommost_compression {
		opts.set_bottommost_compression_type(rocksdb_compression_algo);
		opts.set_bottommost_zstd_max_train_bytes(0, true);

		// -14 w_bits is only read by zlib.
		opts.set_bottommost_compression_options(-14, config.rocksdb_bottommost_compression_level, 0, 0, true);
	}

	// -14 w_bits is only read by zlib.
	opts.set_compression_options(-14, config.rocksdb_compression_level, 0, 0);
	opts.set_compression_type(rocksdb_compression_algo);
}

#[allow(dead_code)]
fn set_for_random_small_uc(opts: &mut Options, config: &Config) {
	let uco = uc_options(config);
	set_for_random_small(opts, config);
	opts.set_universal_compaction_options(&uco);
	opts.set_compaction_style(DBCompactionStyle::Universal);
}

fn set_for_sequential_small_uc(opts: &mut Options, config: &Config) {
	let uco = uc_options(config);
	set_for_sequential_small(opts, config);
	opts.set_universal_compaction_options(&uco);
	opts.set_compaction_style(DBCompactionStyle::Universal);
}

#[allow(dead_code)]
fn set_for_random_small(opts: &mut Options, config: &Config) {
	set_for_random(opts, config);

	opts.set_write_buffer_size(1024 * 128);
	opts.set_target_file_size_base(1024 * 128);
	opts.set_target_file_size_multiplier(2);
	opts.set_max_bytes_for_level_base(1024 * 512);
	opts.set_max_bytes_for_level_multiplier(2.0);
}

fn set_for_sequential_small(opts: &mut Options, config: &Config) {
	set_for_sequential(opts, config);

	opts.set_write_buffer_size(1024 * 512);
	opts.set_target_file_size_base(1024 * 512);
	opts.set_target_file_size_multiplier(2);
	opts.set_max_bytes_for_level_base(1024 * 1024);
	opts.set_max_bytes_for_level_multiplier(2.0);
}

fn set_for_random(opts: &mut Options, config: &Config) {
	set_level_defaults(opts, config);

	let pri = "compaction_pri=kOldestSmallestSeqFirst";
	opts.set_options_from_string(pri)
		.expect("set compaction priority string");

	opts.set_max_bytes_for_level_base(8 * 1024 * 1024);
	opts.set_max_bytes_for_level_multiplier(1.0);
	opts.set_max_bytes_for_level_multiplier_additional(&[0, 1, 1, 3, 7, 15, 31]);
}

fn set_for_sequential(opts: &mut Options, config: &Config) {
	set_level_defaults(opts, config);

	let pri = "compaction_pri=kOldestLargestSeqFirst";
	opts.set_options_from_string(pri)
		.expect("set compaction priority string");

	opts.set_target_file_size_base(2 * 1024 * 1024);
	opts.set_target_file_size_multiplier(2);

	opts.set_max_bytes_for_level_base(32 * 1024 * 1024);
	opts.set_max_bytes_for_level_multiplier(1.0);
	opts.set_max_bytes_for_level_multiplier_additional(&[0, 1, 1, 3, 7, 15, 31]);
}

fn set_level_defaults(opts: &mut Options, _config: &Config) {
	opts.set_level_zero_file_num_compaction_trigger(2);

	opts.set_target_file_size_base(1024 * 1024);
	opts.set_target_file_size_multiplier(2);

	opts.set_level_compaction_dynamic_level_bytes(false);
	opts.set_max_bytes_for_level_base(16 * 1024 * 1024);
	opts.set_max_bytes_for_level_multiplier(2.0);

	opts.set_ttl(21 * 24 * 60 * 60);
}

fn uc_options(_config: &Config) -> UniversalCompactOptions {
	let mut opts = UniversalCompactOptions::default();

	opts.set_stop_style(UniversalCompactionStopStyle::Total);
	opts.set_max_size_amplification_percent(10000);
	opts.set_compression_size_percent(-1);
	opts.set_size_ratio(1);

	opts.set_min_merge_width(2);
	opts.set_max_merge_width(16);

	opts
}

fn set_table_with_new_cache(
	opts: &mut Options, config: &Config, cache: &mut HashMap<String, Cache>, name: &str, size: usize,
) {
	cache.insert(name.to_owned(), Cache::new_lru_cache(size));
	set_table_with_shared_cache(opts, config, cache, name, name);
}

fn set_table_with_shared_cache(
	opts: &mut Options, config: &Config, cache: &HashMap<String, Cache>, _name: &str, cache_name: &str,
) {
	let mut table = table_options(config);
	table.set_block_cache(
		cache
			.get(cache_name)
			.expect("existing cache to share with this column"),
	);
	opts.set_block_based_table_factory(&table);
}

fn cache_size(config: &Config, base_size: u32, entity_size: usize) -> Result<usize> {
	let ents = f64::from(base_size) * config.cache_capacity_modifier;

	#[allow(clippy::as_conversions, clippy::cast_sign_loss, clippy::cast_possible_truncation)]
	(ents as usize)
		.checked_mul(entity_size)
		.ok_or_else(|| err!(Config("cache_capacity_modifier", "Cache size is too large.")))
}

fn table_options(_config: &Config) -> BlockBasedOptions {
	let mut opts = BlockBasedOptions::default();

	opts.set_block_size(4 * 1024);
	opts.set_metadata_block_size(4 * 1024);

	opts.set_optimize_filters_for_memory(true);
	opts.set_cache_index_and_filter_blocks(true);
	opts.set_pin_top_level_index_and_filter(true);

	opts
}

fn num_threads<T: TryFrom<usize>>(config: &Config) -> Result<T> {
	const MIN_PARALLELISM: usize = 2;

	let requested = if config.rocksdb_parallelism_threads != 0 {
		config.rocksdb_parallelism_threads
	} else {
		utils::available_parallelism()
	};

	utils::math::try_into::<T, usize>(cmp::max(MIN_PARALLELISM, requested))
}