trine-kv 0.2.0

use std::path::{Path, PathBuf};

use crate::{codec::CodecId, prefix::PrefixExtractor, runtime::RuntimeOptions};

/// Storage location and host backend selected for a database.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum StorageMode {
    /// Keep all data in memory and discard it when the handle closes.
    InMemory,
    /// Store data in a native filesystem directory.
    Persistent {
        /// Native filesystem database directory.
        path: PathBuf,
    },
    /// Store data through an explicit host-provided backend.
    HostPersistent {
        /// Host backend used for persistent storage.
        backend: HostStorageBackend,
    },
}

/// Host storage backend selected for non-native persistent modes.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum HostStorageBackend {
    /// Use a WASI preopened filesystem path.
    Wasi {
        /// WASI preopened filesystem path.
        path: PathBuf,
    },
    /// Use browser storage.
    Browser,
}

impl HostStorageBackend {
    pub(crate) const fn as_str(&self) -> &'static str {
        match self {
            Self::Wasi { .. } => "WASI persistent storage backend",
            Self::Browser => "browser persistent storage backend",
        }
    }
}

impl StorageMode {
    pub(crate) fn persistent_path(&self) -> Option<&Path> {
        match self {
            Self::Persistent { path }
            | Self::HostPersistent {
                backend: HostStorageBackend::Wasi { path },
            } => Some(path.as_path()),
            Self::InMemory
            | Self::HostPersistent {
                backend: HostStorageBackend::Browser,
            } => None,
        }
    }

    pub(crate) const fn is_wasi_persistent(&self) -> bool {
        matches!(
            self,
            Self::HostPersistent {
                backend: HostStorageBackend::Wasi { .. }
            }
        )
    }

    pub(crate) const fn is_browser_persistent(&self) -> bool {
        matches!(
            self,
            Self::HostPersistent {
                backend: HostStorageBackend::Browser
            }
        )
    }
}

impl Default for StorageMode {
    fn default() -> Self {
        Self::InMemory
    }
}

/// Durability requested for committed writes.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub enum DurabilityMode {
    /// Accept writes after buffering them in the storage backend.
    #[default]
    Buffered,
    /// Flush buffered bytes to the backend.
    Flush,
    /// Sync file data without requiring metadata sync where the backend allows it.
    SyncData,
    /// Sync file data and metadata where the backend allows it.
    SyncAll,
}

impl DurabilityMode {
    pub(crate) const fn as_str(self) -> &'static str {
        match self {
            Self::Buffered => "buffered",
            Self::Flush => "flush",
            Self::SyncData => "sync-data",
            Self::SyncAll => "sync-all",
        }
    }
}

/// Compression codec profile used for table blocks.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub enum CompressionProfile {
    /// Store table blocks without compression.
    None,
    /// Use the v1 fast LZ4 block codec.
    #[default]
    Fast,
}

impl CompressionProfile {
    #[must_use]
    pub(crate) const fn codec_id(self) -> CodecId {
        match self {
            Self::None => CodecId::None,
            Self::Fast => CodecId::FastLz4Block,
        }
    }
}

/// Point-read filter policy for table keys.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum FilterPolicy {
    /// Do not write table key filters.
    Disabled,
    /// Write Bloom filters with the requested bit budget per key.
    Bloom {
        /// Bloom-filter bit budget per key.
        bits_per_key: u8,
    },
}

impl Default for FilterPolicy {
    fn default() -> Self {
        Self::Bloom { bits_per_key: 10 }
    }
}

/// Prefix-read filter policy for extracted key prefixes.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum PrefixFilterPolicy {
    /// Do not write prefix filters.
    Disabled,
    /// Write Bloom filters with the requested bit budget per prefix.
    Bloom {
        /// Bloom-filter bit budget per extracted prefix.
        bits_per_prefix: u8,
    },
}

impl Default for PrefixFilterPolicy {
    fn default() -> Self {
        Self::Bloom {
            bits_per_prefix: 10,
        }
    }
}

/// Search strategy used inside table indexes.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub enum IndexSearchPolicy {
    /// Scan index entries linearly.
    Linear,
    /// Search index entries with binary search.
    Binary,
    /// Let Trine choose based on index size.
    #[default]
    Auto,
}

/// Startup policy when repairable temporary files are found.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub enum FailOnCorruptionPolicy {
    /// Report the files as corruption and leave them untouched.
    #[default]
    FailClosed,
    /// Delete safe temporary files and write a recovery report.
    RepairSafeTemporaryFiles,
}

/// Options used when opening a database.
///
/// `DbOptions` controls where data is stored, whether missing storage is
/// created, the default write durability, bucket defaults, runtime behavior,
/// maintenance thresholds, and startup recovery policy. Path-like calls to
/// [`crate::Db::open`] and [`crate::Db::open_sync`] are converted with
/// [`DbOptions::new`], which selects persistent native filesystem storage.
///
/// # Examples
///
/// ```rust
/// use trine_kv::{Db, DbOptions, DurabilityMode};
///
/// # fn main() -> trine_kv::Result<()> {
/// let persistent = Db::open_sync(
///     DbOptions::new("target/doc-example-options")
///         .with_durability(DurabilityMode::SyncAll),
/// )?;
///
/// let memory = Db::open_sync(DbOptions::memory())?;
/// assert_eq!(persistent.options().read_only, false);
/// assert_eq!(memory.options().read_only, false);
/// # Ok(())
/// # }
/// ```
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct DbOptions {
    /// Storage location and host backend.
    pub storage_mode: StorageMode,
    /// Create the database directory and metadata when missing.
    pub create_if_missing: bool,
    /// Open without allowing writes or maintenance that mutates storage.
    pub read_only: bool,
    /// Options used when the built-in default bucket is first created.
    pub default_bucket_options: BucketOptions,
    /// Default durability used by write helpers that do not pass `WriteOptions`.
    pub durability: DurabilityMode,
    /// Active memtable target size before flush.
    pub write_buffer_bytes: usize,
    /// Maximum queued immutable memtables before writes apply backpressure.
    pub max_immutable_memtables: usize,
    /// Target size for newly written table files.
    pub target_table_bytes: usize,
    /// Per-level size multiplier used by compaction.
    pub level_size_multiplier: usize,
    /// Maximum L0 table count before compaction is requested.
    pub max_l0_files: usize,
    /// Approximate bytes reserved for cached table blocks.
    pub block_cache_bytes: usize,
    /// Number of background workers used by maintenance-capable runtimes.
    pub background_worker_count: usize,
    /// Runtime used for async, blocking, and background work.
    pub runtime: RuntimeOptions,
    /// Startup policy for safe temporary files left by interrupted writes.
    pub fail_on_corruption: FailOnCorruptionPolicy,
    /// Enable garbage collection of obsolete blob bytes.
    pub blob_gc_enabled: bool,
    /// Minimum discardable-byte ratio required before a blob file is collected.
    pub blob_gc_discardable_ratio: BlobGcRatio,
    /// Minimum blob file size considered for garbage collection.
    pub blob_gc_min_file_bytes: u64,
}

impl DbOptions {
    /// Default active memtable target size.
    pub const DEFAULT_WRITE_BUFFER_BYTES: usize = 64 * 1024 * 1024;
    /// Default target size for table files.
    pub const DEFAULT_TARGET_TABLE_BYTES: usize = 64 * 1024 * 1024;
    /// Default block-cache byte budget.
    pub const DEFAULT_BLOCK_CACHE_BYTES: usize = 256 * 1024 * 1024;
    /// Default minimum blob file size for garbage collection.
    pub const DEFAULT_BLOB_GC_MIN_FILE_BYTES: u64 = 64 * 1024 * 1024;

    /// Creates persistent database options for `path`.
    ///
    /// This is the path-first constructor used by `Db::open(path)` and
    /// `Db::open_sync(path)`. It selects [`StorageMode::Persistent`], sets
    /// safety-first default durability for confirmed writes, and leaves
    /// `create_if_missing` enabled.
    ///
    /// # Parameters
    ///
    /// - `path`: native filesystem database directory.
    #[must_use]
    pub fn new(path: impl Into<PathBuf>) -> Self {
        Self::persistent(path)
    }

    /// Creates in-memory database options.
    ///
    /// In-memory databases keep memtables, tables, metadata, and WAL state only
    /// in process memory. Closing the handle drops all data. This is useful for
    /// tests, temporary indexes, and caches that can be rebuilt.
    #[must_use]
    pub fn memory() -> Self {
        Self::default()
    }

    /// Creates persistent native-filesystem options for `path`.
    ///
    /// This is equivalent to [`DbOptions::new`].
    #[must_use]
    pub fn persistent(path: impl Into<PathBuf>) -> Self {
        Self {
            storage_mode: StorageMode::Persistent { path: path.into() },
            durability: DurabilityMode::SyncAll,
            ..Self::default()
        }
    }

    /// Creates persistent WASI host-filesystem options for `path`.
    #[must_use]
    pub fn wasi_persistent(path: impl Into<PathBuf>) -> Self {
        Self {
            storage_mode: StorageMode::HostPersistent {
                backend: HostStorageBackend::Wasi { path: path.into() },
            },
            background_worker_count: 0,
            durability: DurabilityMode::Flush,
            runtime: RuntimeOptions::inline(),
            ..Self::default()
        }
    }

    /// Creates read-only WASI host-filesystem options for `path`.
    #[must_use]
    pub fn wasi_persistent_read_only(path: impl Into<PathBuf>) -> Self {
        Self::wasi_persistent(path).read_only()
    }

    /// Creates browser persistent options.
    #[must_use]
    pub fn browser_persistent() -> Self {
        Self {
            storage_mode: StorageMode::HostPersistent {
                backend: HostStorageBackend::Browser,
            },
            background_worker_count: 0,
            durability: DurabilityMode::Flush,
            runtime: RuntimeOptions::inline(),
            ..Self::default()
        }
    }

    /// Creates read-only browser persistent options.
    #[must_use]
    pub fn browser_persistent_read_only() -> Self {
        Self::browser_persistent().read_only()
    }

    /// Creates read-only native-filesystem options for `path`.
    #[must_use]
    pub fn persistent_read_only(path: impl Into<PathBuf>) -> Self {
        Self::persistent(path).read_only()
    }

    /// Sets the default durability for writes that do not pass `WriteOptions`.
    ///
    /// This affects helpers such as [`crate::Db::put_sync`] and
    /// [`crate::Db::put`]. Calls that pass [`WriteOptions`] use their explicit
    /// durability instead.
    #[must_use]
    pub const fn with_durability(mut self, durability: DurabilityMode) -> Self {
        self.durability = durability;
        self
    }

    /// Sets the options used by the built-in default bucket.
    ///
    /// Named buckets still use the options passed to `Db::bucket_with_options`.
    #[must_use]
    pub fn with_default_bucket_options(mut self, options: BucketOptions) -> Self {
        self.default_bucket_options = options;
        self
    }

    /// Marks these options read-only and disables creation of missing storage.
    ///
    /// Read-only handles can read existing persistent data, but reject writes,
    /// flushes, compactions, and repairs that would mutate storage.
    #[must_use]
    pub const fn read_only(mut self) -> Self {
        self.read_only = true;
        self.create_if_missing = false;
        self
    }
}

impl Default for DbOptions {
    fn default() -> Self {
        Self {
            storage_mode: StorageMode::InMemory,
            create_if_missing: true,
            read_only: false,
            default_bucket_options: BucketOptions::default(),
            durability: DurabilityMode::Buffered,
            write_buffer_bytes: Self::DEFAULT_WRITE_BUFFER_BYTES,
            max_immutable_memtables: 4,
            target_table_bytes: Self::DEFAULT_TARGET_TABLE_BYTES,
            level_size_multiplier: 10,
            max_l0_files: 8,
            block_cache_bytes: Self::DEFAULT_BLOCK_CACHE_BYTES,
            background_worker_count: 1,
            runtime: RuntimeOptions::default(),
            fail_on_corruption: FailOnCorruptionPolicy::FailClosed,
            blob_gc_enabled: true,
            blob_gc_discardable_ratio: BlobGcRatio::HALF,
            blob_gc_min_file_bytes: Self::DEFAULT_BLOB_GC_MIN_FILE_BYTES,
        }
    }
}

/// Ratio threshold used by blob garbage collection.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct BlobGcRatio {
    millionths: u32,
}

impl BlobGcRatio {
    /// A 50% discardable-byte threshold.
    pub const HALF: Self = Self {
        millionths: 500_000,
    };
    /// A 100% discardable-byte threshold.
    pub const FULL: Self = Self {
        millionths: 1_000_000,
    };

    /// Creates a ratio from millionths, where `1_000_000` means 100%.
    #[must_use]
    pub const fn from_millionths(millionths: u32) -> Self {
        Self { millionths }
    }

    /// Returns this ratio in millionths.
    #[must_use]
    pub const fn millionths(self) -> u32 {
        self.millionths
    }

    pub(crate) fn should_collect(self, discardable_bytes: u64, total_bytes: u64) -> bool {
        if total_bytes == 0 {
            return false;
        }
        u128::from(discardable_bytes).saturating_mul(1_000_000)
            >= u128::from(total_bytes).saturating_mul(u128::from(self.millionths))
    }
}

impl Default for BlobGcRatio {
    fn default() -> Self {
        Self::HALF
    }
}

/// Policy for merging blob values back into table levels during compaction.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub enum BlobLevelMergePolicy {
    /// Keep blob values in blob files during compaction.
    Disabled,
    /// Let Trine decide based on level and value size.
    #[default]
    Auto,
    /// Always merge blob values back into table files when compacting.
    Always,
}

/// Options fixed for a bucket when the bucket is created.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct BucketOptions {
    /// Allow empty user keys.
    pub allow_empty_keys: bool,
    /// Compression profile used for table blocks.
    pub compression: CompressionProfile,
    /// Target uncompressed data-block size.
    pub block_bytes: usize,
    /// Point-read filter policy for table keys.
    pub filter_policy: FilterPolicy,
    /// Prefix extractor used by prefix filters.
    pub prefix_extractor: PrefixExtractor,
    /// Prefix-read filter policy.
    pub prefix_filter_policy: PrefixFilterPolicy,
    /// Search strategy used inside table indexes.
    pub index_search_policy: IndexSearchPolicy,
    /// Values at or above this size are stored in blob files.
    pub blob_threshold_bytes: usize,
    /// Policy for merging blob values during compaction.
    pub blob_level_merge_policy: BlobLevelMergePolicy,
}

impl BucketOptions {
    /// Default target data-block size.
    pub const DEFAULT_BLOCK_BYTES: usize = 16 * 1024;
    /// Default threshold for storing values in blob files.
    pub const DEFAULT_BLOB_THRESHOLD_BYTES: usize = 1024 * 1024;

    /// Sets the prefix extractor for this bucket.
    #[must_use]
    pub fn with_prefix_extractor(mut self, prefix_extractor: PrefixExtractor) -> Self {
        self.prefix_extractor = prefix_extractor;
        self
    }

    /// Sets the value-size threshold for blob storage.
    #[must_use]
    pub const fn with_blob_threshold_bytes(mut self, blob_threshold_bytes: usize) -> Self {
        self.blob_threshold_bytes = blob_threshold_bytes;
        self
    }

    /// Sets the blob-level merge policy.
    #[must_use]
    pub const fn with_blob_level_merge_policy(mut self, policy: BlobLevelMergePolicy) -> Self {
        self.blob_level_merge_policy = policy;
        self
    }

    /// Enables or disables blob-level merge with a boolean convenience flag.
    #[must_use]
    pub const fn with_blob_level_merge_enabled(mut self, enabled: bool) -> Self {
        self.blob_level_merge_policy = if enabled {
            BlobLevelMergePolicy::Always
        } else {
            BlobLevelMergePolicy::Disabled
        };
        self
    }
}

impl Default for BucketOptions {
    fn default() -> Self {
        Self {
            allow_empty_keys: true,
            compression: CompressionProfile::Fast,
            block_bytes: Self::DEFAULT_BLOCK_BYTES,
            filter_policy: FilterPolicy::default(),
            prefix_extractor: PrefixExtractor::default(),
            prefix_filter_policy: PrefixFilterPolicy::default(),
            index_search_policy: IndexSearchPolicy::Auto,
            blob_threshold_bytes: Self::DEFAULT_BLOB_THRESHOLD_BYTES,
            blob_level_merge_policy: BlobLevelMergePolicy::Auto,
        }
    }
}

/// Per-write options passed to commit operations.
///
/// `WriteOptions` lets a single write or batch request a durability level
/// different from the database default. The options are evaluated when the
/// write is accepted; changing a `WriteOptions` value later has no effect on an
/// already committed write.
///
/// # Examples
///
/// ```rust
/// use trine_kv::{Db, WriteOptions};
///
/// # fn main() -> trine_kv::Result<()> {
/// let db = Db::open_sync(trine_kv::DbOptions::memory())?;
/// let commit = db.put_with_options_sync(b"k", b"v", WriteOptions::sync_all())?;
/// assert!(commit.sequence().get() > 0);
/// # Ok(())
/// # }
/// ```
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub struct WriteOptions {
    /// Durability requested for this write.
    pub durability: DurabilityMode,
}

impl WriteOptions {
    /// Creates write options with an explicit durability mode.
    ///
    /// # Parameters
    ///
    /// - `durability`: durability requested for the write or batch.
    #[must_use]
    pub const fn new(durability: DurabilityMode) -> Self {
        Self { durability }
    }

    /// Creates buffered write options.
    ///
    /// The write may return after bytes are accepted by the storage backend but
    /// before a flush or sync is requested. This is the lowest-latency and
    /// weakest durability mode.
    #[must_use]
    pub const fn buffered() -> Self {
        Self::new(DurabilityMode::Buffered)
    }

    /// Creates flush write options.
    ///
    /// The write requests a backend flush for accepted WAL bytes. Exact meaning
    /// depends on the selected backend capabilities.
    #[must_use]
    pub const fn flush() -> Self {
        Self::new(DurabilityMode::Flush)
    }

    /// Creates data-sync write options.
    ///
    /// The write requests durable file data without requiring metadata sync
    /// where the backend can distinguish those operations.
    #[must_use]
    pub const fn sync_data() -> Self {
        Self::new(DurabilityMode::SyncData)
    }

    /// Creates full-sync write options.
    ///
    /// The write requests the strongest durability mode supported by the
    /// backend for WAL data and required metadata.
    #[must_use]
    pub const fn sync_all() -> Self {
        Self::new(DurabilityMode::SyncAll)
    }
}