package config

import (
	"context"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sync"
	"time"

	"go.uber.org/zap"

	"github.com/geo-platform/tenant-api/internal/shared/config/runtime"
	runtimeenv "github.com/geo-platform/tenant-api/internal/shared/config/runtime/env"
	runtimefile "github.com/geo-platform/tenant-api/internal/shared/config/runtime/file"
)

type Store struct {
	path string

	mu           sync.RWMutex
	cfg          *Config
	files        []string
	runtime      runtime.Config
	watchedFiles map[string]fileSnapshot
	updates      chan struct{}

	ctx    context.Context
	cancel context.CancelFunc
}

type ReloadEvent struct {
	Previous *Config
	Current  *Config
	Files    []string
	Changes  []FieldChange
}

func NewStore(configPath string) (*Store, error) {
	cfg, files, err := loadWithFiles(configPath)
	if err != nil {
		return nil, err
	}

	ctx, cancel := context.WithCancel(context.Background())
	store := &Store{
		path:         configPath,
		cfg:          cfg,
		files:        normalizeConfigFiles(files),
		watchedFiles: snapshotFiles(nil),
		updates:      make(chan struct{}, 1),
		ctx:          ctx,
		cancel:       cancel,
	}
	store.watchedFiles = snapshotFiles(store.watchFiles())
	store.runtime = store.newRuntimeConfig()
	return store, nil
}

func NewStaticStore(cfg *Config) (*Store, error) {
	if cfg == nil {
		return nil, errors.New("config is nil")
	}
	return &Store{cfg: cfg}, nil
}

func (s *Store) Current() *Config {
	if s == nil {
		return nil
	}
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.cfg
}

func (s *Store) Watch(ctx context.Context, logger *zap.Logger, onReload func(ReloadEvent)) error {
	if s == nil {
		return errors.New("config store is nil")
	}
	if s.runtime == nil {
		s.runtime = s.newRuntimeConfig()
	}

	if err := s.runtime.Load(); err != nil {
		return fmt.Errorf("load config runtime source: %w", err)
	}
	if err := s.runtime.Watch("", func(string, runtime.Value) {
		s.notifyReload()
	}); err != nil {
		_ = s.runtime.Close()
		return fmt.Errorf("watch config runtime source: %w", err)
	}

	if logger != nil {
		logger.Info("config hot reload watcher started", zap.Strings("files", s.files))
	}

	for {
		select {
		case <-ctx.Done():
			return nil
		case <-s.ctx.Done():
			return nil
		case <-s.updates:
			s.reload(logger, onReload)
		}
	}
}

func (s *Store) Close() {
	if s == nil {
		return
	}
	if s.cancel != nil {
		s.cancel()
	}
	if s.runtime != nil {
		_ = s.runtime.Close()
	}
}

func (s *Store) reload(logger *zap.Logger, onReload func(ReloadEvent)) {
	next, files, err := loadWithFiles(s.path)
	if err != nil {
		if logger != nil {
			logger.Warn("config reload rejected", zap.Error(err))
		}
		return
	}

	files = normalizeConfigFiles(files)
	s.mu.Lock()
	previous := s.cfg
	s.cfg = next
	s.files = files
	s.watchedFiles = snapshotFiles(s.watchFiles())
	s.mu.Unlock()

	changes := Diff(previous, next)
	if logger != nil {
		logger.Info("config reloaded",
			zap.Strings("files", files),
			zap.Strings("hot_changes", ChangePaths(changes, true)),
			zap.Strings("restart_required_changes", ChangePaths(changes, false)),
		)
	}
	if onReload != nil {
		onReload(ReloadEvent{
			Previous: previous,
			Current:  next,
			Files:    files,
			Changes:  changes,
		})
	}
}

func (s *Store) newRuntimeConfig() runtime.Config {
	return runtime.New(runtime.WithSource(
		runtimefile.NewSource(s.watchRoot(), s.watchNames()...),
		runtimeenv.NewSource(),
	))
}

func (s *Store) watchRoot() string {
	for _, candidate := range candidateConfigPaths(s.path, false) {
		if candidate == "" {
			continue
		}
		return filepath.Dir(candidate)
	}
	return filepath.Dir(s.path)
}

func (s *Store) notifyReload() {
	if !s.consumeFileChange() {
		return
	}
	select {
	case s.updates <- struct{}{}:
	default:
	}
}

func (s *Store) consumeFileChange() bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	next := snapshotFiles(s.watchFiles())
	if len(s.watchedFiles) == 0 {
		s.watchedFiles = next
		return true
	}
	changed := !fileSnapshotsEqual(s.watchedFiles, next)
	if changed {
		s.watchedFiles = next
	}
	return changed
}

func (s *Store) watchNames() []string {
	names := make([]string, 0, 4)
	seen := make(map[string]struct{})
	for _, local := range []bool{false, true} {
		for _, candidate := range candidateConfigPaths(s.path, local) {
			if candidate == "" {
				continue
			}
			name := filepath.Base(candidate)
			if _, ok := seen[name]; ok {
				continue
			}
			seen[name] = struct{}{}
			names = append(names, name)
		}
	}
	return names
}

func (s *Store) watchFiles() []string {
	files := make([]string, 0, 4)
	seen := make(map[string]struct{})
	for _, local := range []bool{false, true} {
		for _, candidate := range candidateConfigPaths(s.path, local) {
			if candidate == "" {
				continue
			}
			abs, err := filepath.Abs(candidate)
			if err == nil {
				candidate = abs
			}
			candidate = filepath.Clean(candidate)
			if _, ok := seen[candidate]; ok {
				continue
			}
			seen[candidate] = struct{}{}
			files = append(files, candidate)
		}
	}
	return files
}

func normalizeConfigFiles(files []string) []string {
	seen := make(map[string]struct{}, len(files))
	normalized := make([]string, 0, len(files))
	for _, file := range files {
		if file == "" {
			continue
		}
		abs, err := filepath.Abs(file)
		if err == nil {
			file = abs
		}
		file = filepath.Clean(file)
		if _, ok := seen[file]; ok {
			continue
		}
		seen[file] = struct{}{}
		normalized = append(normalized, file)
	}
	return normalized
}

type fileSnapshot struct {
	size    int64
	modTime time.Time
	exists  bool
}

func snapshotFiles(files []string) map[string]fileSnapshot {
	snapshots := make(map[string]fileSnapshot, len(files))
	for _, file := range normalizeConfigFiles(files) {
		info, err := os.Stat(file)
		if err != nil {
			snapshots[file] = fileSnapshot{}
			continue
		}
		snapshots[file] = fileSnapshot{
			size:    info.Size(),
			modTime: info.ModTime(),
			exists:  true,
		}
	}
	return snapshots
}

func fileSnapshotsEqual(a, b map[string]fileSnapshot) bool {
	if len(a) != len(b) {
		return false
	}
	for key, left := range a {
		right, ok := b[key]
		if !ok || left != right {
			return false
		}
	}
	return true
}