package sysadmin

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"strconv"
	"time"
)

// 设置读写错误；HTTP 适配层据此映射状态码。
var (
	ErrUnknownSetting      = errors.New("sysadmin: unknown setting key")
	ErrSettingReadOnly     = errors.New("sysadmin: setting is read-only")
	ErrInvalidSettingValue = errors.New("sysadmin: invalid setting value")
	ErrStoreUnavailable    = errors.New("sysadmin: settings store unavailable")
)

// 设置值类型。
const (
	SettingTypeString = "string"
	SettingTypeBool   = "bool"
	SettingTypeNumber = "number"
)

// SettingSpec 白名单注册表条目；只有登记在册的 key 才可读写。
type SettingSpec struct {
	Key             string
	Label           string
	Group           string
	Type            string
	Default         any
	Writable        bool
	RequiresRestart bool
	EnvVar          string // 可选 env 中间层：DB > env > default
	Description     string
}

// Setting 设置视图，字段对齐前端 camelCase 契约。
type Setting struct {
	Key             string     `json:"key"`
	Label           string     `json:"label"`
	Group           string     `json:"group"`
	Type            string     `json:"type"`
	Value           any        `json:"value"`
	Default         any        `json:"default"`
	Writable        bool       `json:"writable"`
	RequiresRestart bool       `json:"requiresRestart"`
	Description     string     `json:"description"`
	UpdatedAt       *time.Time `json:"updatedAt,omitempty"`
	UpdatedBy       *int64     `json:"updatedBy,omitempty"`
}

// defaultSettingSpecs 一期白名单：先做机制，键空间可后续扩展。
func defaultSettingSpecs() []SettingSpec {
	return []SettingSpec{
		{Key: "ui.maintenance_notice", Label: "维护公告", Group: "ui", Type: SettingTypeString, Default: "", Writable: true, RequiresRestart: false, Description: "全站维护公告横幅文案；空字符串表示关闭"},
		{Key: "ui.read_only_mode", Label: "只读模式提示", Group: "ui", Type: SettingTypeBool, Default: false, Writable: true, RequiresRestart: false, Description: "开启后前端进入只读提示模式，阻断写操作入口"},
		{Key: "chat.default_session_role", Label: "新会话默认职责", Group: "chat", Type: SettingTypeString, Default: "engineer", Writable: true, RequiresRestart: false, Description: "未显式指定职责时新会话的默认角色"},
		{Key: "tasks.default_auto_repair", Label: "任务默认自动修复", Group: "tasks", Type: SettingTypeBool, Default: false, Writable: true, RequiresRestart: false, Description: "独立任务运行未传 auto_repair 时的默认值"},
		{Key: "kb.default_search_limit", Label: "KB 检索默认条数", Group: "kb", Type: SettingTypeNumber, Default: 8.0, Writable: true, RequiresRestart: false, Description: "知识库检索未指定 limit 时的默认返回条数"},
		{Key: "notifications.stage_advance_reminder", Label: "阶段推进提醒总开关", Group: "notification", Type: SettingTypeBool, Default: true, Writable: true, RequiresRestart: false, Description: "阶段就绪 24h 提醒的总开关（一期先落机制）"},
	}
}

func (s *Service) findSpec(key string) (SettingSpec, bool) {
	for _, spec := range s.specs {
		if spec.Key == key {
			return spec, true
		}
	}
	return SettingSpec{}, false
}

// ListSettings 返回白名单全部设置；读优先级 DB > env > default。
func (s *Service) ListSettings(ctx context.Context) ([]Setting, error) {
	out := make([]Setting, 0, len(s.specs))
	for _, spec := range s.specs {
		setting, err := s.resolve(ctx, spec)
		if err != nil {
			return nil, err
		}
		out = append(out, setting)
	}
	return out, nil
}

// UpdateSetting 校验并写入白名单设置，返回更新后的视图。
func (s *Service) UpdateSetting(ctx context.Context, key string, raw json.RawMessage, updatedBy int64) (Setting, error) {
	spec, ok := s.findSpec(key)
	if !ok {
		return Setting{}, ErrUnknownSetting
	}
	if !spec.Writable {
		return Setting{}, ErrSettingReadOnly
	}
	if err := validateSettingValue(spec.Type, raw); err != nil {
		return Setting{}, err
	}
	if s.store == nil {
		return Setting{}, ErrStoreUnavailable
	}
	if _, err := s.store.Upsert(ctx, key, raw, updatedBy); err != nil {
		return Setting{}, err
	}
	return s.resolve(ctx, spec)
}

// resolve 按 DB > env > default 解析单个设置的当前值。
func (s *Service) resolve(ctx context.Context, spec SettingSpec) (Setting, error) {
	setting := Setting{
		Key:             spec.Key,
		Label:           spec.Label,
		Group:           spec.Group,
		Type:            spec.Type,
		Value:           spec.Default,
		Default:         spec.Default,
		Writable:        spec.Writable,
		RequiresRestart: spec.RequiresRestart,
		Description:     spec.Description,
	}
	if spec.EnvVar != "" {
		if raw, set := os.LookupEnv(spec.EnvVar); set {
			if v, err := parseSettingValue(spec.Type, raw); err == nil {
				setting.Value = v
			}
		}
	}
	if s.store == nil {
		return setting, nil
	}
	raw, updatedBy, updatedAt, err := s.store.Get(ctx, spec.Key)
	if err != nil {
		if errors.Is(err, ErrSettingNotFound) {
			return setting, nil
		}
		return Setting{}, err
	}
	var value any
	if err := json.Unmarshal(raw, &value); err != nil {
		return Setting{}, fmt.Errorf("sysadmin: decode stored value for %s: %w", spec.Key, err)
	}
	setting.Value = value
	setting.UpdatedBy = updatedBy
	setting.UpdatedAt = updatedAt
	return setting, nil
}

// validateSettingValue 按声明类型校验 JSON 值。
func validateSettingValue(valueType string, raw json.RawMessage) error {
	if len(raw) == 0 {
		return ErrInvalidSettingValue
	}
	switch valueType {
	case SettingTypeString:
		var v string
		if err := json.Unmarshal(raw, &v); err != nil {
			return ErrInvalidSettingValue
		}
	case SettingTypeBool:
		var v bool
		if err := json.Unmarshal(raw, &v); err != nil {
			return ErrInvalidSettingValue
		}
	case SettingTypeNumber:
		var v float64
		if err := json.Unmarshal(raw, &v); err != nil {
			return ErrInvalidSettingValue
		}
	default:
		return ErrInvalidSettingValue
	}
	return nil
}

// parseSettingValue 将 env 字符串按类型解析。
func parseSettingValue(valueType, raw string) (any, error) {
	switch valueType {
	case SettingTypeString:
		return raw, nil
	case SettingTypeBool:
		v, err := strconv.ParseBool(raw)
		if err != nil {
			return nil, err
		}
		return v, nil
	case SettingTypeNumber:
		v, err := strconv.ParseFloat(raw, 64)
		if err != nil {
			return nil, err
		}
		return v, nil
	default:
		return nil, ErrInvalidSettingValue
	}
}