package conditions

import (
	"context"
	"encoding/json"
	"errors"
	"sort"
	"sync"
	"time"
)

// InMemory is a store and a history held in this process: for tests, and for nothing else — a
// condition kept here is forgotten by a restart, which is the fault the store exists to remove.
type InMemory struct {
	mu       sync.Mutex
	values   map[string]Entry
	revision uint64
	events   []Event
	// fail, when set, is what every read and write answers: a store that is away. It is set only
	// through SetFail, under the lock, because the keeper's telling goroutine reads it while a test
	// takes the store away.
	fail error
}

// NewInMemory is an empty store.
func NewInMemory() *InMemory { return &InMemory{values: map[string]Entry{}} }

// SetFail makes every read and write answer err from now on, or none when err is nil.
func (m *InMemory) SetFail(err error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	m.fail = err
}

func (m *InMemory) Get(_ context.Context, key string) (Entry, bool, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.fail != nil {
		return Entry{}, false, m.fail
	}
	e, ok := m.values[key]
	return e, ok, nil
}

func (m *InMemory) Create(_ context.Context, key string, value []byte) error {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.fail != nil {
		return m.fail
	}
	if _, ok := m.values[key]; ok {
		return ErrMoved
	}
	m.revision++
	m.values[key] = Entry{Value: value, Revision: m.revision}
	return nil
}

func (m *InMemory) Update(_ context.Context, key string, value []byte, revision uint64) error {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.fail != nil {
		return m.fail
	}
	if e, ok := m.values[key]; !ok || e.Revision != revision {
		return ErrMoved
	}
	m.revision++
	m.values[key] = Entry{Value: value, Revision: m.revision}
	return nil
}

func (m *InMemory) Delete(_ context.Context, key string, revision uint64) error {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.fail != nil {
		return m.fail
	}
	if e, ok := m.values[key]; !ok || e.Revision != revision {
		return ErrMoved
	}
	delete(m.values, key)
	return nil
}

func (m *InMemory) All(context.Context) (map[string]Entry, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.fail != nil {
		return nil, m.fail
	}
	out := make(map[string]Entry, len(m.values))
	for k, v := range m.values {
		out[k] = v
	}
	return out, nil
}

func (m *InMemory) Append(_ context.Context, e Event) error {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.fail != nil {
		return m.fail
	}
	m.events = append(m.events, e)
	return nil
}

func (m *InMemory) Since(_ context.Context, since time.Time) ([]Event, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.fail != nil {
		return nil, m.fail
	}
	var out []Event
	for _, e := range m.events {
		if !e.At.Before(since) {
			out = append(out, e)
		}
	}
	sort.SliceStable(out, func(i, j int) bool { return out[i].At.Before(out[j].At) })
	return out, nil
}

// Told is a teller that remembers what it was told, for tests.
type Told struct {
	mu     sync.Mutex
	Events []Event
	Names  []string
	// fail, when set, is what every publish answers; set only through SetFail, under the lock.
	fail error
}

// SetFail makes every publish answer err from now on, or none when err is nil.
func (t *Told) SetFail(err error) {
	t.mu.Lock()
	defer t.mu.Unlock()
	t.fail = err
}

func (t *Told) PublishSeatEvent(_ context.Context, seat, event string, body []byte) error {
	t.mu.Lock()
	defer t.mu.Unlock()
	if t.fail != nil {
		return t.fail
	}
	if seat != Seat {
		return errors.New("told under the wrong seat: " + seat)
	}
	var e Event
	if err := json.Unmarshal(body, &e); err != nil {
		return err
	}
	t.Events = append(t.Events, e)
	t.Names = append(t.Names, event)
	return nil
}

// Said is a copy of what was told so far.
func (t *Told) Said() []Event {
	t.mu.Lock()
	defer t.mu.Unlock()
	return append([]Event(nil), t.Events...)
}