package mdb

import (
	"fmt"
	"net/http"
	"os"
	"sync"
	"sync/atomic"
	"time"

	"git.crumpington.com/public/jldb/lib/errs"
	"git.crumpington.com/public/jldb/lib/rep"
	"git.crumpington.com/public/jldb/mdb/change"
	"git.crumpington.com/public/jldb/mdb/pfile"
)

type Config struct {
	RootDir        string
	Primary        bool
	ReplicationPSK string
	NetTimeout     time.Duration // Default is 1 minute.

	// WAL settings.
	WALSegMinCount  int64 // Minimum Change sets in a segment. Default is 1024.
	WALSegMaxAgeSec int64 // Maximum age of a segment. Default is 1 hour.
	WALSegGCAgeSec  int64 // Segment age for garbage collection. Default is 7 days.

	// Necessary for secondary.
	PrimaryEndpoint string

	// MaxConcurrentUpdates restricts the number of concurently running updates,
	// and also limits the maximum number of changes that may be aggregated in
	// the WAL.
	//
	// Default is 32.
	MaxConcurrentUpdates int
}

func (c Config) repConfig() rep.Config {
	return rep.Config{
		RootDir:         repDirPath(c.RootDir),
		Primary:         c.Primary,
		ReplicationPSK:  c.ReplicationPSK,
		NetTimeout:      c.NetTimeout,
		WALSegMinCount:  c.WALSegMinCount,
		WALSegMaxAgeSec: c.WALSegMaxAgeSec,
		WALSegGCAgeSec:  c.WALSegGCAgeSec,
		PrimaryEndpoint: c.PrimaryEndpoint,
	}
}

type Database struct {
	rep     *rep.Replicator
	rootDir string
	conf    Config

	pf  *pfile.File
	idx *pfile.Index

	changes []change.Change

	// The Snapshot stored here is read-only. It will be replaced as needed by
	// the txAggregator (primary), or the follower (secondary).
	snapshot    *atomic.Pointer[Snapshot]
	collections map[uint64]collection

	stop chan struct{}
	done *sync.WaitGroup

	txModPool chan txMod

	modChan chan txMod
}

func New(conf Config) *Database {
	if conf.MaxConcurrentUpdates <= 0 {
		conf.MaxConcurrentUpdates = 32
	}

	db := &Database{
		rootDir:     conf.RootDir,
		conf:        conf,
		snapshot:    &atomic.Pointer[Snapshot]{},
		collections: map[uint64]collection{},
		stop:        make(chan struct{}),
		done:        &sync.WaitGroup{},
		txModPool:   make(chan txMod, conf.MaxConcurrentUpdates),
		modChan:     make(chan txMod),
	}

	db.snapshot.Store(newSnapshot())

	for i := 0; i < conf.MaxConcurrentUpdates; i++ {
		db.txModPool <- txMod{Resp: make(chan error, 1)}
	}

	return db
}

func (db *Database) Open() (err error) {
	if err := os.MkdirAll(db.rootDir, 0700); err != nil {
		return errs.IO.WithErr(err)
	}

	db.rep, err = rep.Open(
		rep.App{
			SendState:       db.repSendState,
			RecvState:       db.repRecvState,
			InitStorage:     db.repInitStorage,
			Replay:          db.repReplay,
			LoadFromStorage: db.repLoadFromStorage,
			Apply:           db.repApply,
		},
		db.conf.repConfig())
	if err != nil {
		return err
	}

	if db.conf.Primary {
		db.done.Add(1)
		go db.runTXAggreagtor()
	}
	return nil
}

func (db *Database) Close() error {
	select {
	case <-db.stop:
		return nil
	default:
	}

	close(db.stop)
	db.rep.Close()
	db.done.Wait()

	db.snapshot = nil
	db.collections = nil

	return nil
}

func (db *Database) Snapshot() *Snapshot {
	return db.snapshot.Load()
}

func (db *Database) Update(update func(tx *Snapshot) error) error {
	if !db.conf.Primary {
		return errs.ReadOnly.WithMsg("cannot update secondary directly")
	}

	mod := <-db.txModPool
	mod.Update = update

	db.modChan <- mod
	err := <-mod.Resp
	db.txModPool <- mod

	return err
}

func (db *Database) Info() Info {
	tx := db.Snapshot()
	repInfo := db.rep.Info()

	return Info{
		SeqNum:             tx.seqNum,
		TimestampMS:        tx.timestampMS,
		WALFirstSeqNum:     repInfo.WALFirstSeqNum,
		WALLastSeqNum:      repInfo.WALLastSeqNum,
		WALLastTimestampMS: repInfo.WALLastTimestampMS,
	}
}

func (db *Database) addCollection(id uint64, c collection, collectionState any) {
	if _, ok := db.collections[id]; ok {
		panic(fmt.Sprintf("Collection %s uses duplicate ID %d.", c.Name(), id))
	}
	db.collections[id] = c
	db.snapshot.Load().addCollection(id, collectionState)
}

func (db *Database) Handle(w http.ResponseWriter, r *http.Request) {
	db.rep.Handle(w, r)
}