package nomad

import (
	"fmt"
	"io"
	"log"

	"github.com/hashicorp/go-memdb"
	"github.com/hashicorp/nomad/nomad/structs"
)

// The StateStore is responsible for maintaining all the Nomad
// state. It is manipulated by the FSM which maintains consistency
// through the use of Raft. The goals of the StateStore are to provide
// high concurrency for read operations without blocking writes, and
// to provide write availability in the face of reads. EVERY object
// returned as a result of a read against the state store should be
// considered a constant and NEVER modified in place.
type StateStore struct {
	logger *log.Logger
	db     *memdb.MemDB
}

// StateSnapshot is used to provide a point-in-time snapshot
type StateSnapshot struct {
	StateStore
}

// StateRestore is used to optimize the performance when
// restoring state by only using a single large transaction
// instead of thousands of sub transactions
type StateRestore struct {
	txn *memdb.Txn
}

// Abort is used to abort the restore operation
func (s *StateRestore) Abort() {
	s.txn.Abort()
}

// Commit is used to commit the restore operation
func (s *StateRestore) Commit() {
	s.txn.Commit()
}

// IndexEntry is used with the "index" table
// for managing the latest Raft index affecting a table.
type IndexEntry struct {
	Key   string
	Value uint64
}

// NewStateStore is used to create a new state store
func NewStateStore(logOutput io.Writer) (*StateStore, error) {
	// Create the MemDB
	db, err := memdb.NewMemDB(stateStoreSchema())
	if err != nil {
		return nil, fmt.Errorf("state store setup failed: %v", err)
	}

	// Create the state store
	s := &StateStore{
		logger: log.New(logOutput, "", log.LstdFlags),
		db:     db,
	}
	return s, nil
}

// Snapshot is used to create a point in time snapshot. Because
// we use MemDB, we just need to snapshot the state of the underlying
// database.
func (s *StateStore) Snapshot() (*StateSnapshot, error) {
	snap := &StateSnapshot{
		StateStore: StateStore{
			logger: s.logger,
			db:     s.db.Snapshot(),
		},
	}
	return snap, nil
}

// Restore is used to optimize the efficiency of rebuilding
// state by minimizing the number of transactions and checking
// overhead.
func (s *StateStore) Restore() (*StateRestore, error) {
	txn := s.db.Txn(true)
	return &StateRestore{txn}, nil
}

// RegisterNode is used to register a node or update a node definition
func (s *StateStore) RegisterNode(index uint64, node *structs.Node) error {
	txn := s.db.Txn(true)
	defer txn.Abort()

	// Check if the node already exists
	existing, err := txn.First("nodes", "id", node.ID)
	if err != nil {
		return fmt.Errorf("node lookup failed: %v", err)
	}

	// Setup the indexes correctly
	if existing != nil {
		node.CreateIndex = existing.(*structs.Node).CreateIndex
		node.ModifyIndex = index
	} else {
		node.CreateIndex = index
		node.ModifyIndex = index
	}

	// Insert the node
	if err := txn.Insert("nodes", node); err != nil {
		return fmt.Errorf("node insert failed: %v", err)
	}
	if err := txn.Insert("index", &IndexEntry{"nodes", index}); err != nil {
		return fmt.Errorf("index update failed: %v", err)
	}

	txn.Commit()
	return nil
}

// DeregisterNode is used to deregister a node
func (s *StateStore) DeregisterNode(index uint64, nodeID string) error {
	txn := s.db.Txn(true)
	defer txn.Abort()

	// Lookup the node
	existing, err := txn.First("nodes", "id", nodeID)
	if err != nil {
		return fmt.Errorf("node lookup failed: %v", err)
	}
	if existing == nil {
		return fmt.Errorf("node not found")
	}

	// Delete the node
	if err := txn.Delete("nodes", existing); err != nil {
		return fmt.Errorf("node delete failed: %v", err)
	}
	if err := txn.Insert("index", &IndexEntry{"nodes", index}); err != nil {
		return fmt.Errorf("index update failed: %v", err)
	}

	txn.Commit()
	return nil
}

// UpdateNodeStatus is used to update the status of a node
func (s *StateStore) UpdateNodeStatus(index uint64, nodeID string, status string) error {
	txn := s.db.Txn(true)
	defer txn.Abort()

	// Lookup the node
	existing, err := txn.First("nodes", "id", nodeID)
	if err != nil {
		return fmt.Errorf("node lookup failed: %v", err)
	}
	if existing == nil {
		return fmt.Errorf("node not found")
	}

	// Copy the existing node
	existingNode := existing.(*structs.Node)
	copyNode := new(structs.Node)
	*copyNode = *existingNode

	// Update the status in the copy
	copyNode.Status = status
	copyNode.ModifyIndex = index

	// Insert the node
	if err := txn.Insert("nodes", copyNode); err != nil {
		return fmt.Errorf("node update failed: %v", err)
	}
	if err := txn.Insert("index", &IndexEntry{"nodes", index}); err != nil {
		return fmt.Errorf("index update failed: %v", err)
	}

	txn.Commit()
	return nil
}

// GetNodeByID is used to lookup a node by ID
func (s *StateStore) GetNodeByID(nodeID string) (*structs.Node, error) {
	txn := s.db.Txn(false)

	existing, err := txn.First("nodes", "id", nodeID)
	if err != nil {
		return nil, fmt.Errorf("node lookup failed: %v", err)
	}

	if existing != nil {
		return existing.(*structs.Node), nil
	}
	return nil, nil
}

// Nodes returns an iterator over all the nodes
func (s *StateStore) Nodes() (memdb.ResultIterator, error) {
	txn := s.db.Txn(false)

	// Walk the entire nodes table
	iter, err := txn.Get("nodes", "id")
	if err != nil {
		return nil, err
	}
	return iter, nil
}

// RegisterJob is used to register a job or update a job definition
func (s *StateStore) RegisterJob(index uint64, job *structs.Job) error {
	txn := s.db.Txn(true)
	defer txn.Abort()

	// Check if the job already exists
	existing, err := txn.First("jobs", "id", job.ID)
	if err != nil {
		return fmt.Errorf("job lookup failed: %v", err)
	}

	// Setup the indexes correctly
	if existing != nil {
		job.CreateIndex = existing.(*structs.Job).CreateIndex
		job.ModifyIndex = index
	} else {
		job.CreateIndex = index
		job.ModifyIndex = index
	}

	// Insert the job
	if err := txn.Insert("jobs", job); err != nil {
		return fmt.Errorf("job insert failed: %v", err)
	}
	if err := txn.Insert("index", &IndexEntry{"jobs", index}); err != nil {
		return fmt.Errorf("index update failed: %v", err)
	}

	txn.Commit()
	return nil
}

// DeregisterJob is used to deregister a job
func (s *StateStore) DeregisterJob(index uint64, jobID string) error {
	txn := s.db.Txn(true)
	defer txn.Abort()

	// Lookup the node
	existing, err := txn.First("jobs", "id", jobID)
	if err != nil {
		return fmt.Errorf("job lookup failed: %v", err)
	}
	if existing == nil {
		return fmt.Errorf("job not found")
	}

	// Delete the node
	if err := txn.Delete("jobs", existing); err != nil {
		return fmt.Errorf("job delete failed: %v", err)
	}
	if err := txn.Insert("index", &IndexEntry{"jobs", index}); err != nil {
		return fmt.Errorf("index update failed: %v", err)
	}

	txn.Commit()
	return nil
}

// GetJobByID is used to lookup a job by its ID
func (s *StateStore) GetJobByID(id string) (*structs.Job, error) {
	txn := s.db.Txn(false)

	existing, err := txn.First("jobs", "id", id)
	if err != nil {
		return nil, fmt.Errorf("job lookup failed: %v", err)
	}

	if existing != nil {
		return existing.(*structs.Job), nil
	}
	return nil, nil
}

// Jobs returns an iterator over all the jobs
func (s *StateStore) Jobs() (memdb.ResultIterator, error) {
	txn := s.db.Txn(false)

	// Walk the entire jobs table
	iter, err := txn.Get("jobs", "id")
	if err != nil {
		return nil, err
	}
	return iter, nil
}

// UpsertEvaluation is used to upsert an evaluation
func (s *StateStore) UpsertEvals(index uint64, evals []*structs.Evaluation) error {
	txn := s.db.Txn(true)
	defer txn.Abort()

	// Do a nested upsert
	for _, eval := range evals {
		if err := s.nestedUpsertEval(txn, index, eval); err != nil {
			return err
		}
	}

	txn.Commit()
	return nil
}

// nestedUpsertEvaluation is used to nest an evaluation upsert within a transaction
func (s *StateStore) nestedUpsertEval(txn *memdb.Txn, index uint64, eval *structs.Evaluation) error {
	// Lookup the evaluation
	existing, err := txn.First("evals", "id", eval.ID)
	if err != nil {
		return fmt.Errorf("eval lookup failed: %v", err)
	}

	// Update the indexes
	if existing != nil {
		eval.CreateIndex = existing.(*structs.Evaluation).CreateIndex
		eval.ModifyIndex = index
	} else {
		eval.CreateIndex = index
		eval.ModifyIndex = index
	}

	// Insert the eval
	if err := txn.Insert("evals", eval); err != nil {
		return fmt.Errorf("eval insert failed: %v", err)
	}
	if err := txn.Insert("index", &IndexEntry{"evals", index}); err != nil {
		return fmt.Errorf("index update failed: %v", err)
	}
	return nil
}

// DeleteEval is used to delete an evaluation
func (s *StateStore) DeleteEval(index uint64, evalID string) error {
	txn := s.db.Txn(true)
	defer txn.Abort()

	// Lookup the node
	existing, err := txn.First("evals", "id", evalID)
	if err != nil {
		return fmt.Errorf("eval lookup failed: %v", err)
	}
	if existing == nil {
		return fmt.Errorf("eval not found")
	}

	// Delete the node
	if err := txn.Delete("evals", existing); err != nil {
		return fmt.Errorf("eval delete failed: %v", err)
	}
	if err := txn.Insert("index", &IndexEntry{"evals", index}); err != nil {
		return fmt.Errorf("index update failed: %v", err)
	}

	txn.Commit()
	return nil
}

// GetEvalByID is used to lookup an eval by its ID
func (s *StateStore) GetEvalByID(id string) (*structs.Evaluation, error) {
	txn := s.db.Txn(false)

	existing, err := txn.First("evals", "id", id)
	if err != nil {
		return nil, fmt.Errorf("eval lookup failed: %v", err)
	}

	if existing != nil {
		return existing.(*structs.Evaluation), nil
	}
	return nil, nil
}

// Evals returns an iterator over all the evaluations
func (s *StateStore) Evals() (memdb.ResultIterator, error) {
	txn := s.db.Txn(false)

	// Walk the entire table
	iter, err := txn.Get("evals", "id")
	if err != nil {
		return nil, err
	}
	return iter, nil
}

// UpdateAllocations is used to evict a set of allocations
// and allocate new ones at the same time.
func (s *StateStore) UpdateAllocations(index uint64, evicts []string,
	allocs []*structs.Allocation) error {
	txn := s.db.Txn(true)
	defer txn.Abort()

	// Handle evictions first
	for _, evict := range evicts {
		existing, err := txn.First("allocs", "id", evict)
		if err != nil {
			return fmt.Errorf("alloc lookup failed: %v", err)
		}
		if existing == nil {
			continue
		}
		if err := txn.Delete("allocs", existing); err != nil {
			return fmt.Errorf("alloc delete failed: %v", err)
		}
	}

	// Handle the allocations
	for _, alloc := range allocs {
		existing, err := txn.First("allocs", "id", alloc.ID)
		if err != nil {
			return fmt.Errorf("alloc lookup failed: %v", err)
		}
		if existing == nil {
			alloc.CreateIndex = index
			alloc.ModifyIndex = index
		} else {
			alloc.CreateIndex = existing.(*structs.Allocation).CreateIndex
			alloc.ModifyIndex = index
		}
		if err := txn.Insert("allocs", alloc); err != nil {
			return fmt.Errorf("alloc insert failed: %v", err)
		}
	}

	// Update the indexes
	if err := txn.Insert("index", &IndexEntry{"allocs", index}); err != nil {
		return fmt.Errorf("index update failed: %v", err)
	}

	txn.Commit()
	return nil
}

// GetAllocByID is used to lookup an allocation by its ID
func (s *StateStore) GetAllocByID(id string) (*structs.Allocation, error) {
	txn := s.db.Txn(false)

	existing, err := txn.First("allocs", "id", id)
	if err != nil {
		return nil, fmt.Errorf("alloc lookup failed: %v", err)
	}

	if existing != nil {
		return existing.(*structs.Allocation), nil
	}
	return nil, nil
}

// AllocsByNode returns all the allocations by node
func (s *StateStore) AllocsByNode(node string) ([]*structs.Allocation, error) {
	txn := s.db.Txn(false)

	// Get an iterator over the node allocations
	iter, err := txn.Get("allocs", "node", node)
	if err != nil {
		return nil, err
	}

	var out []*structs.Allocation
	for {
		raw := iter.Next()
		if raw == nil {
			break
		}
		out = append(out, raw.(*structs.Allocation))
	}
	return out, nil
}

// AllocsByJob returns all the allocations by job id
func (s *StateStore) AllocsByJob(jobID string) ([]*structs.Allocation, error) {
	txn := s.db.Txn(false)

	// Get an iterator over the node allocations
	iter, err := txn.Get("allocs", "job", jobID)
	if err != nil {
		return nil, err
	}

	var out []*structs.Allocation
	for {
		raw := iter.Next()
		if raw == nil {
			break
		}
		out = append(out, raw.(*structs.Allocation))
	}
	return out, nil
}

// Allocs returns an iterator over all the evaluations
func (s *StateStore) Allocs() (memdb.ResultIterator, error) {
	txn := s.db.Txn(false)

	// Walk the entire table
	iter, err := txn.Get("allocs", "id")
	if err != nil {
		return nil, err
	}
	return iter, nil
}

// GetIndex finds the matching index value
func (s *StateStore) GetIndex(name string) (uint64, error) {
	txn := s.db.Txn(false)

	// Lookup the first matching index
	out, err := txn.First("index", "id", name)
	if err != nil {
		return 0, err
	}
	if out == nil {
		return 0, nil
	}
	return out.(*IndexEntry).Value, nil
}

// Indexes returns an iterator over all the indexes
func (s *StateStore) Indexes() (memdb.ResultIterator, error) {
	txn := s.db.Txn(false)

	// Walk the entire nodes table
	iter, err := txn.Get("index", "id")
	if err != nil {
		return nil, err
	}
	return iter, nil
}

// NodeRestore is used to restore a node
func (r *StateRestore) NodeRestore(node *structs.Node) error {
	if err := r.txn.Insert("nodes", node); err != nil {
		return fmt.Errorf("node insert failed: %v", err)
	}
	return nil
}

// JobRestore is used to restore a job
func (r *StateRestore) JobRestore(job *structs.Job) error {
	if err := r.txn.Insert("jobs", job); err != nil {
		return fmt.Errorf("job insert failed: %v", err)
	}
	return nil
}

// EvalRestore is used to restore an evaluation
func (r *StateRestore) EvalRestore(eval *structs.Evaluation) error {
	if err := r.txn.Insert("evals", eval); err != nil {
		return fmt.Errorf("eval insert failed: %v", err)
	}
	return nil
}

// AllocRestore is used to restore an allocation
func (r *StateRestore) AllocRestore(alloc *structs.Allocation) error {
	if err := r.txn.Insert("allocs", alloc); err != nil {
		return fmt.Errorf("alloc insert failed: %v", err)
	}
	return nil
}

// IndexRestore is used to restore an index
func (r *StateRestore) IndexRestore(idx *IndexEntry) error {
	if err := r.txn.Insert("index", idx); err != nil {
		return fmt.Errorf("index insert failed: %v", err)
	}
	return nil
}