package config

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"io"
	"os"
	"path/filepath"
	"reflect"
	"strings"
	"sync"
	"time"

	apierrors "git.yuntuo.hk/k2safe/go-omni/errors"
	"git.yuntuo.hk/k2safe/go-omni/logx"
	"gopkg.in/yaml.v3"
)

// DecodeFile merges a bounded JSON/YAML document into defaults. It uses JSON
// field names for both formats, rejects unknown fields and accepts durations
// such as "3s". Application-specific validation remains with the caller.
func DecodeFile[T any](path string, defaults T) (T, error) {
	result, err := decodeFile(path, defaults)
	if err != nil {
		var zero T
		return zero, &DecodeError{cause: err}
	}
	return result, nil
}

// DecodeError keeps input values out of public diagnostics while preserving
// errors.Is/As for explicitly handled underlying I/O and syntax errors.
type DecodeError struct{ cause error }

func (e *DecodeError) Error() string {
	return "config: cannot decode file; check its path, format, field names and value types"
}
func (e *DecodeError) Unwrap() error { return e.cause }
func decodeFile[T any](path string, defaults T) (T, error) {
	var zero T
	f, err := os.Open(path)
	if err != nil {
		return zero, err
	}
	defer f.Close()
	data, err := io.ReadAll(io.LimitReader(f, (1<<20)+1))
	if err != nil {
		return zero, err
	}
	if len(data) > 1<<20 {
		return zero, errors.New("config: file exceeds 1 MiB")
	}
	var value any
	switch strings.ToLower(filepath.Ext(path)) {
	case ".yaml", ".yml":
		dec := yaml.NewDecoder(bytes.NewReader(data))
		if err := dec.Decode(&value); err != nil {
			return zero, err
		}
		var extra any
		if err := dec.Decode(&extra); err != io.EOF {
			return zero, errors.New("config: one YAML document required")
		}
	case ".json":
		if err := apierrors.DecodeCatalogJSON(data, &value); err != nil {
			return zero, err
		}
	default:
		return zero, errors.New("config: expected .json, .yaml or .yml")
	}
	if _, ok := value.(map[string]any); !ok {
		return zero, errors.New("config: root must be an object")
	}
	value, err = durations(value, reflect.TypeOf(defaults))
	if err != nil {
		return zero, err
	}
	encoded, err := json.Marshal(value)
	if err != nil {
		return zero, err
	}
	// Clone configuration without serializing borrowed json:"-" capabilities.
	var result T
	original, err := cloneConfiguration(reflect.ValueOf(&defaults).Elem(), 0)
	if err != nil {
		return zero, err
	}
	reflect.ValueOf(&result).Elem().Set(original)
	dec := json.NewDecoder(bytes.NewReader(encoded))
	dec.DisallowUnknownFields()
	if err = dec.Decode(&result); err != nil {
		return zero, err
	}
	return result, nil
}
func durations(v any, t reflect.Type) (any, error) {
	if t == nil {
		return v, nil
	}
	for t.Kind() == reflect.Pointer {
		t = t.Elem()
	}
	if t == reflect.TypeOf(time.Duration(0)) {
		if s, ok := v.(string); ok {
			d, err := time.ParseDuration(s)
			return int64(d), err
		}
		return v, nil
	}
	if t.Kind() == reflect.Struct {
		if m, ok := v.(map[string]any); ok {
			for n := 0; n < t.NumField(); n++ {
				field := t.Field(n)
				name := strings.Split(field.Tag.Get("json"), ",")[0]
				if name == "-" {
					continue
				}
				if name == "" {
					name = field.Name
				}
				if item, exists := m[name]; exists {
					converted, err := durations(item, field.Type)
					if err != nil {
						return nil, err
					}
					m[name] = converted
				}
			}
		}
	}
	if t.Kind() == reflect.Map && t.Key().Kind() == reflect.String {
		if values, ok := v.(map[string]any); ok {
			for key, value := range values {
				converted, err := durations(value, t.Elem())
				if err != nil {
					return nil, err
				}
				values[key] = converted
			}
		}
	}
	if t.Kind() == reflect.Slice {
		if items, ok := v.([]any); ok {
			for n, item := range items {
				converted, err := durations(item, t.Elem())
				if err != nil {
					return nil, err
				}
				items[n] = converted
			}
		}
	}
	return v, nil
}
func LoadFile(path, prefix string) (Config, error) {
	cfg, err := DecodeFile(path, Default())
	if err != nil {
		return Config{}, err
	}
	return ApplyEnv(cfg, prefix)
}

// Reloader only accepts log.level changes. Static changes and invalid files
// leave the current snapshot and logger untouched. Watch does not own a goroutine.
type Reloader struct {
	mu           sync.Mutex
	path, prefix string
	current      Config
	logger       *logx.Logger
}

func NewReloader(path, prefix string, logger *logx.Logger) (*Reloader, error) {
	cfg, err := LoadFile(path, prefix)
	if err != nil {
		return nil, err
	}
	if err = logger.SetLevel(cfg.Log.Level); err != nil {
		return nil, err
	}
	return &Reloader{path: path, prefix: prefix, current: cfg, logger: logger}, nil
}
func (r *Reloader) Reload() error {
	r.mu.Lock()
	defer r.mu.Unlock()
	next, err := LoadFile(r.path, r.prefix)
	if err != nil {
		return err
	}
	comparable := next
	comparable.Log.Level = r.current.Log.Level
	if !reflect.DeepEqual(comparable, r.current) {
		return errors.New("config: static fields changed; restart required")
	}
	if err = r.logger.SetLevel(next.Log.Level); err != nil {
		return err
	}
	r.current = next
	return nil
}
func (r *Reloader) Snapshot() Config {
	r.mu.Lock()
	defer r.mu.Unlock()
	cfg := r.current
	cfg.Response = r.current.Response.Clone()
	cfg.Errors = r.current.Errors.Clone()
	cfg.TrustedProxies = append([]string(nil), cfg.TrustedProxies...)
	cfg.Log.RedactKeys = append([]string(nil), cfg.Log.RedactKeys...)
	return cfg
}
func (r *Reloader) Watch(ctx context.Context, interval time.Duration, onError func(error)) error {
	if ctx == nil || interval < 100*time.Millisecond {
		return errors.New("config: context and interval >=100ms required")
	}
	ticker := time.NewTicker(interval)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-ticker.C:
			if err := r.Reload(); err != nil && onError != nil {
				onError(err)
			}
		}
	}
}