dcb

type AppendCondition struct {
	// FailIfEventsMatch is the query to check against. If any events matching
	// this query exist after the After position, the append fails.
	FailIfEventsMatch Query

	// After is the highest position the client was aware of when building
	// the decision model. Events at or before this position are ignored
	// when checking the condition. Use -1 or 0 to check all events.
	After int64
}

type CommandHandler[S any, C any] struct {
	Decider Decider[S, C]
	Store   EventStore
}

type Decider[S any, C any] struct {
	// Query returns the query needed to build the decision model for a command.
	Query func(cmd C) Query

	// Decide takes the current state and command, returning events or an error.
	Decide func(state S, cmd C) ([]Event, error)

	// Evolve applies a sequenced event to the current state.
	Evolve func(state S, event SequencedEvent) S

	// InitialState returns the zero state.
	InitialState func() S
}

type Event struct {
	// Type identifies the kind of event (e.g., "CourseCapacityChanged").
	Type string

	// Data is the event payload. Serialization is handled by the store.
	Data any

	// Tags attach domain metadata for query-based filtering.
	Tags []Tag
}

type EventStore interface {
	// Read returns events matching the query, optionally starting from a position.
	// Returns the matched events and the highest sequence position seen.
	// If no events match, returns an empty slice and position 0.
	Read(ctx context.Context, query Query, opts ...ReadOption) ([]SequencedEvent, int64, error)

	// Append persists one or more events atomically. If a condition is provided,
	// the append fails with ErrAppendConditionFailed if matching events exist
	// after the condition's After position.
	Append(ctx context.Context, events []Event, condition ...AppendCondition) error
}

type MemoryStore struct {
	// contains filtered or unexported fields
}

type Query struct {
	// contains filtered or unexported fields
}

type QueryItem struct {
	Types []string
	Tags  []Tag
}

type ReadOption func(*readOptions)

type SQLiteStore struct {
	// contains filtered or unexported fields
}

type SequencedEvent struct {
	// Position is the globally unique, monotonically increasing sequence position.
	Position int64

	// Type identifies the kind of event.
	Type string

	// Data is the deserialized event payload.
	Data any

	// Tags are the domain tags attached to this event.
	Tags []Tag

	// Timestamp is when the event was persisted.
	Timestamp time.Time
}

type Tag struct {
	Key   string
	Value string
}