// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.

use std::cell::RefCell;
use std::cmp::Ordering;
use std::num::NonZeroU32;
use std::rc::Rc;

use async_trait::async_trait;
use deno_core::error::AnyError;
use deno_core::OpState;
use num_bigint::BigInt;

use crate::codec::canonicalize_f64;

#[async_trait(?Send)]
pub trait DatabaseHandler {
  type DB: Database + 'static;

  async fn open(
    &self,
    state: Rc<RefCell<OpState>>,
    path: Option<String>,
  ) -> Result<Self::DB, AnyError>;
}

#[async_trait(?Send)]
pub trait Database {
  async fn snapshot_read(
    &self,
    requests: Vec<ReadRange>,
    options: SnapshotReadOptions,
  ) -> Result<Vec<ReadRangeOutput>, AnyError>;

  async fn atomic_write(
    &self,
    write: AtomicWrite,
  ) -> Result<Option<CommitResult>, AnyError>;
}

/// Options for a snapshot read.
pub struct SnapshotReadOptions {
  pub consistency: Consistency,
}

/// The consistency of a read.
#[derive(Eq, PartialEq, Copy, Clone, Debug)]
pub enum Consistency {
  Strong,
  Eventual,
}

/// A key is for a KV pair. It is a vector of KeyParts.
///
/// The ordering of the keys is defined by the ordering of the KeyParts. The
/// first KeyPart is the most significant, and the last KeyPart is the least
/// significant.
#[derive(Eq, PartialEq, Ord, PartialOrd, Clone, Debug)]
pub struct Key(pub Vec<KeyPart>);

/// A key part is single item in a key. It can be a boolean, a double float, a
/// variable precision signed integer, a UTF-8 string, or an arbitrary byte
/// array.
///
/// The ordering of a KeyPart is dependent on the type of the KeyPart.
///
/// Between different types, the ordering is as follows: arbitrary byte array <
/// UTF-8 string < variable precision signed integer < double float < false < true.
///
/// Within a type, the ordering is as follows:
/// - For a **boolean**, false is less than true.
/// - For a **double float**, the ordering must follow -NaN < -Infinity < -100.0 < -1.0 < -0.5 < -0.0 < 0.0 < 0.5 < 1.0 < 100.0 < Infinity < NaN.
/// - For a **variable precision signed integer**, the ordering must follow mathematical ordering.
/// - For a **UTF-8 string**, the ordering must follow the UTF-8 byte ordering.
/// - For an **arbitrary byte array**, the ordering must follow the byte ordering.
///
/// This means that the key part `1.0` is less than the key part `2.0`, but is
/// greater than the key part `0n`, because `1.0` is a double float and `0n`
/// is a variable precision signed integer, and the ordering types obviously has
/// precedence over the ordering within a type.
#[derive(Clone, Debug)]
pub enum KeyPart {
  Bytes(Vec<u8>),
  String(String),
  Int(BigInt),
  Float(f64),
  False,
  True,
}

impl KeyPart {
  fn tag_ordering(&self) -> u8 {
    match self {
      KeyPart::Bytes(_) => 0,
      KeyPart::String(_) => 1,
      KeyPart::Int(_) => 2,
      KeyPart::Float(_) => 3,
      KeyPart::False => 4,
      KeyPart::True => 5,
    }
  }
}

impl Eq for KeyPart {}

impl PartialEq for KeyPart {
  fn eq(&self, other: &Self) -> bool {
    self.cmp(other) == Ordering::Equal
  }
}

impl Ord for KeyPart {
  fn cmp(&self, other: &Self) -> Ordering {
    match (self, other) {
      (KeyPart::Bytes(b1), KeyPart::Bytes(b2)) => b1.cmp(b2),
      (KeyPart::String(s1), KeyPart::String(s2)) => {
        s1.as_bytes().cmp(s2.as_bytes())
      }
      (KeyPart::Int(i1), KeyPart::Int(i2)) => i1.cmp(i2),
      (KeyPart::Float(f1), KeyPart::Float(f2)) => {
        canonicalize_f64(*f1).total_cmp(&canonicalize_f64(*f2))
      }
      _ => self.tag_ordering().cmp(&other.tag_ordering()),
    }
  }
}

impl PartialOrd for KeyPart {
  fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
    Some(self.cmp(other))
  }
}

/// A request to read a range of keys from the database. If `end` is `None`,
/// then the range is from `start` shall also be used as the end of the range.
///
/// The range is inclusive of the start and exclusive of the end. The start may
/// not be greater than the end.
///
/// The range is limited to `limit` number of entries.
pub struct ReadRange {
  pub start: Vec<u8>,
  pub end: Vec<u8>,
  pub limit: NonZeroU32,
  pub reverse: bool,
}

/// A response to a `ReadRange` request.
pub struct ReadRangeOutput {
  pub entries: Vec<KvEntry>,
}

/// A versionstamp is a 10 byte array that is used to represent the version of
/// a key in the database.
type Versionstamp = [u8; 10];

/// A key-value entry with a versionstamp.
pub struct KvEntry {
  pub key: Vec<u8>,
  pub value: Value,
  pub versionstamp: Versionstamp,
}

/// A serialized value for a KV pair as stored in the database. All values
/// **can** be serialized into the V8 representation, but not all values are.
///
/// The V8 representation is an opaque byte array that is only meaningful to
/// the V8 engine. It is guaranteed to be backwards compatible. Because this
/// representation is opaque, it is not possible to inspect or modify the value
/// without deserializing it.
///
/// The inability to inspect or modify the value without deserializing it means
/// that these values can not be quickly modified when performing atomic
/// read-modify-write operations on the database (because the database may not
/// have the ability to deserialize the V8 value into a modifiable value).
///
/// Because of this constraint, there are more specialized representations for
/// certain types of values that can be used in atomic read-modify-write
/// operations. These specialized representations are:
///
/// - **Bytes**: an arbitrary byte array.
/// - **U64**: a 64-bit unsigned integer.
pub enum Value {
  V8(Vec<u8>),
  Bytes(Vec<u8>),
  U64(u64),
}

/// A request to perform an atomic check-modify-write operation on the database.
///
/// The operation is performed atomically, meaning that the operation will
/// either succeed or fail. If the operation fails, then the database will be
/// left in the same state as before the operation was attempted. If the
/// operation succeeds, then the database will be left in a new state.
///
/// The operation is performed by first checking the database for the current
/// state of the keys, defined by the `checks` field. If the current state of
/// the keys does not match the expected state, then the operation fails. If
/// the current state of the keys matches the expected state, then the
/// mutations are applied to the database.
///
/// All checks and mutations are performed atomically.
///
/// The mutations are performed in the order that they are specified in the
/// `mutations` field. The order of checks is not specified, and is also not
/// important because this ordering is un-observable.
pub struct AtomicWrite {
  pub checks: Vec<KvCheck>,
  pub mutations: Vec<KvMutation>,
  pub enqueues: Vec<Enqueue>,
}

/// A request to perform a check on a key in the database. The check is not
/// performed on the value of the key, but rather on the versionstamp of the
/// key.
pub struct KvCheck {
  pub key: Vec<u8>,
  pub versionstamp: Option<Versionstamp>,
}

/// A request to perform a mutation on a key in the database. The mutation is
/// performed on the value of the key.
///
/// The type of mutation is specified by the `kind` field. The action performed
/// by each mutation kind is specified in the docs for [MutationKind].
pub struct KvMutation {
  pub key: Vec<u8>,
  pub kind: MutationKind,
}

/// A request to enqueue a message to the database. This message is delivered
/// to a listener of the queue at least once.
///
/// ## Retry
///
/// When the delivery of a message fails, it is retried for a finite number
/// of times. Each retry happens after a backoff period. The backoff periods
/// are specified by the `backoff_schedule` field in milliseconds. If
/// unspecified, the default backoff schedule of the platform (CLI or Deploy)
/// is used.
///
/// If all retry attempts failed, the message is written to the KV under all
/// keys specified in `keys_if_undelivered`.
pub struct Enqueue {
  pub payload: Vec<u8>,
  pub deadline_ms: u64,
  pub keys_if_undelivered: Vec<Vec<u8>>,
  pub backoff_schedule: Option<Vec<u32>>,
}

/// The type of mutation to perform on a key in the database.
///
/// ## Set
///
/// The set mutation sets the value of the key to the specified value. It
/// discards the previous value of the key, if any.
///
/// This operand supports all [Value] types.
///
/// ## Delete
///
/// The delete mutation deletes the value of the key.
///
/// ## Sum
///
/// The sum mutation adds the specified value to the existing value of the key.
///
/// This operand supports only value types [Value::U64]. The existing value in
/// the database must match the type of the value specified in the mutation. If
/// the key does not exist in the database, then the value specified in the
/// mutation is used as the new value of the key.
///
/// ## Min
///
/// The min mutation sets the value of the key to the minimum of the existing
/// value of the key and the specified value.
///
/// This operand supports only value types [Value::U64]. The existing value in
/// the database must match the type of the value specified in the mutation. If
/// the key does not exist in the database, then the value specified in the
/// mutation is used as the new value of the key.
///
/// ## Max
///
/// The max mutation sets the value of the key to the maximum of the existing
/// value of the key and the specified value.
///
/// This operand supports only value types [Value::U64]. The existing value in
/// the database must match the type of the value specified in the mutation. If
/// the key does not exist in the database, then the value specified in the
/// mutation is used as the new value of the key.
pub enum MutationKind {
  Set(Value),
  Delete,
  Sum(Value),
  Min(Value),
  Max(Value),
}

impl MutationKind {
  pub fn value(&self) -> Option<&Value> {
    match self {
      MutationKind::Set(value) => Some(value),
      MutationKind::Sum(value) => Some(value),
      MutationKind::Min(value) => Some(value),
      MutationKind::Max(value) => Some(value),
      MutationKind::Delete => None,
    }
  }
}

/// The result of a successful commit of an atomic write operation.
pub struct CommitResult {
  /// The new versionstamp of the data that was committed.
  pub versionstamp: Versionstamp,
}