package store

import (
	"context"
)

// KV represents a key-value pair from the store.
type KV struct {
	Key     string
	Value   []byte
	Version int64 // etcd ModRevision or similar versioning
}

// EventType defines the type of change observed by a Watch.
type EventType int

const (
	// EventTypePut indicates a key was created or updated.
	EventTypePut EventType = iota
	// EventTypeDelete indicates a key was deleted.
	EventTypeDelete
)

// WatchEvent represents a single event from a Watch operation.
type WatchEvent struct {
	Type   EventType
	KV     KV
	PrevKV *KV // Previous KV, if available and applicable (e.g., for updates)
}

// Compare is used in transactions to check a key's version.
type Compare struct {
	Key             string
	ExpectedVersion int64 // 0 means key should not exist. >0 means key must have this version.
}

// OpType defines the type of operation in a transaction.
type OpType int

const (
	// OpPut represents a put operation.
	OpPut OpType = iota
	// OpDelete represents a delete operation.
	OpDelete
	// OpGet is not typically used in Txn success/fail ops but included for completeness if needed.
	OpGet
)

// Op represents an operation to be performed within a transaction.
type Op struct {
	Type  OpType
	Key   string
	Value []byte // Used for OpPut
}

// StateStore defines the interface for interacting with the underlying key-value store.
// It's designed based on RFC 5.1.
type StateStore interface {
	// Put stores a key-value pair.
	Put(ctx context.Context, key string, value []byte) error
	// Get retrieves a key-value pair. Returns an error if key not found.
	Get(ctx context.Context, key string) (*KV, error)
	// Delete removes a key.
	Delete(ctx context.Context, key string) error
	// List retrieves all key-value pairs matching a prefix.
	List(ctx context.Context, prefix string) ([]KV, error)
	// Watch observes changes to a key or prefix, starting from a given revision.
	// startRevision = 0 means watch from current.
	Watch(ctx context.Context, keyOrPrefix string, startRevision int64) (<-chan WatchEvent, error)
	// Close releases any resources held by the store client.
	Close() error

	// Campaign attempts to acquire leadership for the given leaderID.
	// It returns a leadershipCtx that is cancelled when leadership is lost or Resign is called.
	// leaseTTLSeconds specifies the TTL for the leader's lease.
	Campaign(ctx context.Context, leaderID string, leaseTTLSeconds int64) (leadershipCtx context.Context, err error)
	// Resign relinquishes leadership if currently held.
	// The context passed should ideally be the one associated with the current leadership term or a parent.
	Resign(ctx context.Context) error
	// GetLeader retrieves the ID of the current leader.
	GetLeader(ctx context.Context) (leaderID string, err error)

	// DoTransaction executes a list of operations atomically if all checks pass.
	// checks are conditions that must be true.
	// onSuccess operations are performed if checks pass.
	// onFailure operations are performed if checks fail (not typically supported by etcd Txn else).
	// Returns true if the transaction was committed (onSuccess ops were applied).
	DoTransaction(ctx context.Context, checks []Compare, onSuccess []Op, onFailure []Op) (committed bool, err error)
}