package ethdb

import (
	"context"
	"errors"
	"unsafe"

	"github.com/ledgerwatch/turbo-geth/common/dbutils"
	"github.com/ledgerwatch/turbo-geth/metrics"
)

const ReadersLimit = 2000 // MDBX_READERS_LIMIT on 64bit system

var (
	ErrAttemptToDeleteNonDeprecatedBucket = errors.New("only buckets from dbutils.DeprecatedBuckets can be deleted")
	ErrUnknownBucket                      = errors.New("unknown bucket. add it to dbutils.Buckets")

	dbSize             = metrics.GetOrRegisterGauge("db/size", metrics.DefaultRegistry)
	tableScsLeaf       = metrics.GetOrRegisterGauge("table/scs/leaf", metrics.DefaultRegistry)       //nolint
	tableScsBranch     = metrics.GetOrRegisterGauge("table/scs/branch", metrics.DefaultRegistry)     //nolint
	tableScsOverflow   = metrics.GetOrRegisterGauge("table/scs/overflow", metrics.DefaultRegistry)   //nolint
	tableScsEntries    = metrics.GetOrRegisterGauge("table/scs/entries", metrics.DefaultRegistry)    //nolint
	tableStateLeaf     = metrics.GetOrRegisterGauge("table/state/leaf", metrics.DefaultRegistry)     //nolint
	tableStateBranch   = metrics.GetOrRegisterGauge("table/state/branch", metrics.DefaultRegistry)   //nolint
	tableStateOverflow = metrics.GetOrRegisterGauge("table/state/overflow", metrics.DefaultRegistry) //nolint
	tableStateEntries  = metrics.GetOrRegisterGauge("table/state/entries", metrics.DefaultRegistry)  //nolint
	tableLogLeaf       = metrics.GetOrRegisterGauge("table/log/leaf", metrics.DefaultRegistry)       //nolint
	tableLogBranch     = metrics.GetOrRegisterGauge("table/log/branch", metrics.DefaultRegistry)     //nolint
	tableLogOverflow   = metrics.GetOrRegisterGauge("table/log/overflow", metrics.DefaultRegistry)   //nolint
	tableLogEntries    = metrics.GetOrRegisterGauge("table/log/entries", metrics.DefaultRegistry)    //nolint
	tableTxLeaf        = metrics.GetOrRegisterGauge("table/tx/leaf", metrics.DefaultRegistry)        //nolint
	tableTxBranch      = metrics.GetOrRegisterGauge("table/tx/branch", metrics.DefaultRegistry)      //nolint
	tableTxOverflow    = metrics.GetOrRegisterGauge("table/tx/overflow", metrics.DefaultRegistry)    //nolint
	tableTxEntries     = metrics.GetOrRegisterGauge("table/tx/entries", metrics.DefaultRegistry)     //nolint
	tableGcLeaf        = metrics.GetOrRegisterGauge("table/gc/leaf", metrics.DefaultRegistry)        //nolint
	tableGcBranch      = metrics.GetOrRegisterGauge("table/gc/branch", metrics.DefaultRegistry)      //nolint
	tableGcOverflow    = metrics.GetOrRegisterGauge("table/gc/overflow", metrics.DefaultRegistry)    //nolint
	tableGcEntries     = metrics.GetOrRegisterGauge("table/gc/entries", metrics.DefaultRegistry)     //nolint
)

// KV low-level database interface - main target is - to provide common abstraction over top of LMDB and RemoteKV.
//
// Common pattern for short-living transactions:
//
//  if err := db.View(ctx, func(tx ethdb.Tx) error {
//     ... code which uses database in transaction
//  }); err != nil {
//		return err
// }
//
// Common pattern for long-living transactions:
//	tx, err := db.Begin(ethdb.RW)
//	if err != nil {
//		return err
//	}
//	defer tx.Rollback()
//
//	... code which uses database in transaction
//
//	err := tx.Commit()
//	if err != nil {
//		return err
//	}
//
type KV interface {
	View(ctx context.Context, f func(tx Tx) error) error
	Update(ctx context.Context, f func(tx RwTx) error) error
	Close()

	// Begin - creates transaction
	// 	tx may be discarded by .Rollback() method
	//
	// A transaction and its cursors must only be used by a single
	// 	thread (not goroutine), and a thread may only have a single transaction at a time.
	//  It happen automatically by - because this method calls runtime.LockOSThread() inside (Rollback/Commit releases it)
	//  By this reason application code can't call runtime.UnlockOSThread() - it leads to undefined behavior.
	//
	// If this `parent` is non-NULL, the new transaction
	//	will be a nested transaction, with the transaction indicated by parent
	//	as its parent. Transactions may be nested to any level. A parent
	//	transaction and its cursors may not issue any other operations than
	//	Commit and Rollback while it has active child transactions.
	Begin(ctx context.Context) (Tx, error)
	BeginRw(ctx context.Context) (RwTx, error)
	AllBuckets() dbutils.BucketsCfg

	CollectMetrics()
}

type TxFlags uint

const (
	RW TxFlags = 0x00 // default
	RO TxFlags = 0x02
)

type Tx interface {
	// Cursor - creates cursor object on top of given bucket. Type of cursor - depends on bucket configuration.
	// If bucket was created with lmdb.DupSort flag, then cursor with interface CursorDupSort created
	// Otherwise - object of interface Cursor created
	//
	// Cursor, also provides a grain of magic - it can use a declarative configuration - and automatically break
	// long keys into DupSort key/values. See docs for `bucket.go:BucketConfigItem`
	Cursor(bucket string) Cursor
	CursorDupSort(bucket string) CursorDupSort // CursorDupSort - can be used if bucket has lmdb.DupSort flag
	GetOne(bucket string, key []byte) (val []byte, err error)
	HasOne(bucket string, key []byte) (bool, error)

	Commit(ctx context.Context) error // Commit all the operations of a transaction into the database.
	Rollback()                        // Rollback - abandon all the operations of the transaction instead of saving them.

	BucketSize(name string) (uint64, error)

	Comparator(bucket string) dbutils.CmpFunc

	// ReadSequence - allows to create a linear sequence of unique positive integers for each table.
	// Can be called for a read transaction to retrieve the current sequence value, and the increment must be zero.
	// Sequence changes become visible outside the current write transaction after it is committed, and discarded on abort.
	// Starts from 0.
	ReadSequence(bucket string) (uint64, error)

	CHandle() unsafe.Pointer // Pointer to the underlying C transaction handle (e.g. *C.MDB_txn)
}

type RwTx interface {
	Tx

	RwCursor(bucket string) RwCursor
	RwCursorDupSort(bucket string) RwCursorDupSort

	IncrementSequence(bucket string, amount uint64) (uint64, error)
}

// BucketMigrator used for buckets migration, don't use it in usual app code
type BucketMigrator interface {
	DropBucket(string) error
	CreateBucket(string) error
	ExistsBucket(string) bool
	ClearBucket(string) error
	ExistingBuckets() ([]string, error)
}

// Cursor - class for navigating through a database
// CursorDupSort are inherit this class
//
// If methods (like First/Next/Seek) return error, then returned key SHOULD not be nil (can be []byte{} for example).
// Then looping code will look as:
// c := kv.Cursor(bucketName)
// for k, v, err := c.First(); k != nil; k, v, err = c.Next() {
//    if err != nil {
//        return err
//    }
//    ... logic
// }
type Cursor interface {
	First() ([]byte, []byte, error)               // First - position at first key/data item
	Seek(seek []byte) ([]byte, []byte, error)     // Seek - position at first key greater than or equal to specified key
	SeekExact(key []byte) ([]byte, []byte, error) // SeekExact - position at first key greater than or equal to specified key
	Next() ([]byte, []byte, error)                // Next - position at next key/value (can iterate over DupSort key/values automatically)
	Prev() ([]byte, []byte, error)                // Prev - position at previous key
	Last() ([]byte, []byte, error)                // Last - position at last key and last possible value
	Current() ([]byte, []byte, error)             // Current - return key/data at current cursor position

	Count() (uint64, error) // Count - fast way to calculate amount of keys in bucket. It counts all keys even if Prefix was set.

	Close()
}

type RwCursor interface {
	Cursor

	Put(k, v []byte) error           // Put - based on order
	Append(k []byte, v []byte) error // Append - append the given key/data pair to the end of the database. This option allows fast bulk loading when keys are already known to be in the correct order.
	Delete(k, v []byte) error        // Delete - short version of SeekExact+DeleteCurrent or SeekBothExact+DeleteCurrent

	// DeleteCurrent This function deletes the key/data pair to which the cursor refers.
	// This does not invalidate the cursor, so operations such as MDB_NEXT
	// can still be used on it.
	// Both MDB_NEXT and MDB_GET_CURRENT will return the same record after
	// this operation.
	DeleteCurrent() error
}

type CursorDupSort interface {
	Cursor

	// SeekBothExact -
	// second parameter can be nil only if searched key has no duplicates, or return error
	SeekBothExact(key, value []byte) ([]byte, []byte, error)
	SeekBothRange(key, value []byte) ([]byte, error)
	FirstDup() ([]byte, error)          // FirstDup - position at first data item of current key
	NextDup() ([]byte, []byte, error)   // NextDup - position at next data item of current key
	NextNoDup() ([]byte, []byte, error) // NextNoDup - position at first data item of next key
	LastDup() ([]byte, error)           // LastDup - position at last data item of current key

	CountDuplicates() (uint64, error) // CountDuplicates - number of duplicates for the current key
}

type RwCursorDupSort interface {
	CursorDupSort
	RwCursor

	DeleteCurrentDuplicates() error    // DeleteCurrentDuplicates - deletes all of the data items for the current key
	AppendDup(key, value []byte) error // AppendDup - same as Append, but for sorted dup data
}

type HasStats interface {
	DiskSize(context.Context) (uint64, error) // db size
}