// Package adapter defines the cross-platform IM channel adaptation contract for
// Cyrene v2. It declares the normalized message model, the per-platform adapter
// interface, the capability declaration, and the strongly typed identity (actor)
// metadata that the channel layer uses for owner detection and group-chat
// isolation.
//
// The contract is intentionally platform-neutral: concrete adapters (qq-obv11,
// weixin-ilink, telegram, webhook) are implemented behind this interface in
// milestone M6, not here. The design authority is DevDocs/design/08-渠道接入.md
// (sections 0-2) and DevDocs/design/02-会话与上下文模型.md (section 3).
package adapter

import (
	"errors"
	"fmt"
	"time"
)

// ChannelType classifies where a message originated or is destined.
type ChannelType string

const (
	// ChannelDirect is a one-to-one private conversation.
	ChannelDirect ChannelType = "direct"
	// ChannelGroup is a group / room conversation.
	ChannelGroup ChannelType = "group"
)

// Valid reports whether ct is one of the known channel kinds.
func (ct ChannelType) Valid() bool {
	switch ct {
	case ChannelDirect, ChannelGroup:
		return true
	default:
		return false
	}
}

// ContentType classifies the primary payload of a message.
type ContentType string

const (
	// ContentText is a plain-text chat message.
	ContentText ContentType = "text"
	// ContentImage is an image attachment.
	ContentImage ContentType = "image"
	// ContentVoice is a voice/audio clip.
	ContentVoice ContentType = "voice"
	// ContentFile is an arbitrary file attachment.
	ContentFile ContentType = "file"
	// ContentAction is a non-chat action signal (typing, join/leave, recall).
	ContentAction ContentType = "action"
)

// Valid reports whether ct is one of the known content kinds.
func (ct ContentType) Valid() bool {
	switch ct {
	case ContentText, ContentImage, ContentVoice, ContentFile, ContentAction:
		return true
	default:
		return false
	}
}

// MediaKind classifies an individual media attachment. It is broader than
// ContentType so attachments can also carry video or other payloads.
type MediaKind string

const (
	// MediaImage is an image file.
	MediaImage MediaKind = "image"
	// MediaVoice is an audio/voice file.
	MediaVoice MediaKind = "voice"
	// MediaVideo is a video file.
	MediaVideo MediaKind = "video"
	// MediaFile is an arbitrary file.
	MediaFile MediaKind = "file"
)

// Media is a single attachment carried by a UnifiedMessage. URL and Data are
// mutually exclusive representations: prefer URL for remote media to
// keep payloads out of memory.
type Media struct {
	// Kind classifies the attachment.
	Kind MediaKind
	// URL is the remote location of the media when not inlined.
	URL string
	// Name is the original file name, when known.
	Name string
	// Size is the media size in bytes.
	Size int64
	// MIMEType is the media content type, when known.
	MIMEType string
	// Data carries inlined bytes for small, locally produced payloads.
	Data []byte
}

// Mention is a reference to a user inside a message body.
type Mention struct {
	UserID   string
	UserName string
}

// UnifiedMessage is the normalized, platform-neutral representation of an IM
// event or inbound message. Every channel adapter converts its native payload
// into UnifiedMessage so the runtime can reason about them uniformly.
//
// SenderID/SenderName are kept per design/08 section 0; Sender carries the
// strongly typed identity metadata (Role, group flags) used for owner detection
// and group isolation. The strategy engine (M6) decides access from Sender, not
// from the free-text SenderName.
type UnifiedMessage struct {
	Platform    string
	ChannelID   string
	ChannelType ChannelType
	SenderID    string
	SenderName  string
	Sender      Actor
	Content     string
	ContentType ContentType
	Media       []Media
	Mentions    []Mention
	ReplyToID   string
	ReplyToText string
	GroupID     string
	GroupName   string
	ThreadID    string
	MessageID   string
	Timestamp   time.Time
	// RawData is the opaque native payload the message was converted from.
	RawData []byte
}

// UnifiedResponse is the normalized outbound payload for SendMessage. It may
// carry several messages so an adapter can burst a reply.
type UnifiedResponse struct {
	// Messages are the reply messages to deliver.
	Messages []UnifiedMessage
	// ReplyTo is an optional context identifier the messages reply to.
	ReplyTo string
	// Hint is an optional human hint surfaced by the runtime.
	Hint string
}

// Validate reports whether the message is well-formed for downstream handling.
// It checks the enum fields and requires a group id on group messages.
func (m UnifiedMessage) Validate() error {
	if !m.ChannelType.Valid() {
		return fmt.Errorf("adapter: invalid channel type %q", m.ChannelType)
	}
	if !m.ContentType.Valid() {
		return fmt.Errorf("adapter: invalid content type %q", m.ContentType)
	}
	if m.ChannelType == ChannelGroup && m.GroupID == "" {
		return errors.New("adapter: group message missing group id")
	}
	return nil
}

// IsGroup reports whether the message belongs to a group conversation.
func (m UnifiedMessage) IsGroup() bool { return m.ChannelType == ChannelGroup }