package discovery

import (
	"context"
	"slices"
	"sync"
)

// MockDiscovery is an in-memory Discovery implementation for tests.
// It allows deterministic injection of host additions/removals without
// depending on Kubernetes API machinery.
type MockDiscovery struct {
	mu      sync.RWMutex
	hosts   []string
	events  chan HostChange
	closed  bool
	started bool
}

// NewMockDiscovery creates a mock discovery with an initial host list.
func NewMockDiscovery(initial []string) *MockDiscovery {
	cp := make([]string, len(initial))
	copy(cp, initial)
	return &MockDiscovery{
		hosts:  cp,
		events: make(chan HostChange, 32),
	}
}

// Discover returns the current host snapshot.
func (m *MockDiscovery) Discover() ([]string, error) {
	m.mu.RLock()
	defer m.mu.RUnlock()
	cp := make([]string, len(m.hosts))
	copy(cp, m.hosts)
	return cp, nil
}

// Watch returns a channel that will receive HostChange events.
// The channel is buffered; AddHost/RemoveHost push events non-blockingly.
func (m *MockDiscovery) Watch() (<-chan HostChange, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.closed {
		return nil, context.Canceled
	}
	m.started = true
	return m.events, nil
}

// AddHost inserts a new host (if absent) and emits an Added event.
func (m *MockDiscovery) AddHost(host string) {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.closed {
		return
	}
	if slices.Contains(m.hosts, host) {
		return
	}
	m.hosts = append(m.hosts, host)
	if m.started {
		m.events <- HostChange{Host: host, IsReady: true}
	}
}

// RemoveHost removes a host (if present) and emits a Deleted event.
func (m *MockDiscovery) RemoveHost(host string) {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.closed {
		return
	}
	idx := -1
	for i, h := range m.hosts {
		if h == host {
			idx = i
			break
		}
	}
	if idx == -1 {
		return
	}
	m.hosts = append(m.hosts[:idx], m.hosts[idx+1:]...)
	if m.started {
		m.events <- HostChange{Host: host, IsReady: false}
	}
}

// Close closes the event channel (idempotent).
func (m *MockDiscovery) Close() {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.closed {
		return
	}
	m.closed = true
	close(m.events)
}