package ownwire_sdk

import (
	"context"
	"encoding/json"
	"fmt"
	"sync"
)

type ClientOptions struct {
	Url          string
	Conn         Conn
	Handshaker   Handshaker
	EventsBuffer int
}

type Client struct {
	url       string
	conn      Conn
	handshaker Handshaker

	events_ch chan Event

	mu         sync.Mutex
	state      SessionState
	ready      bool
	closed     bool
	close_ch   chan struct{}
	read_cancel context.CancelFunc
}

type conn_closer interface {
	Close() error
}

func NewClient(opts ClientOptions) *Client {
	events_buffer := opts.EventsBuffer
	if events_buffer == 0 {
		events_buffer = 64
	}

	handshaker := opts.Handshaker.EnsureDefaults()

	return &Client{
		url:        opts.Url,
		conn:       opts.Conn,
		handshaker: handshaker,
		events_ch:  make(chan Event, events_buffer),
		close_ch:   make(chan struct{}),
	}
}

func (c *Client) Events() <-chan Event {
	return c.events_ch
}

func (c *Client) Connect(ctx context.Context, resume_session_id string) error {
	c.mu.Lock()
	if c.ready {
		c.mu.Unlock()
		return nil
	}
	c.mu.Unlock()

	conn := c.conn
	if conn == nil {
		if c.url == "" {
			return fmt.Errorf("no Url configured and no Conn provided")
		}

		ws_conn, err := DialWs(ctx, c.url)
		if err != nil {
			return err
		}
		conn = ws_conn

		c.mu.Lock()
		c.conn = conn
		c.mu.Unlock()
	}

	state, pending, err := c.handshaker.Run(ctx, conn, resume_session_id)
	if err != nil {
		return err
	}

	read_ctx, read_cancel := context.WithCancel(context.Background())

	c.mu.Lock()
	c.state = state
	c.ready = true
	c.read_cancel = read_cancel
	c.mu.Unlock()

	c.emit(Event{Kind: EventOpened})

	go c.read_loop(read_ctx, pending)

	return nil
}

func (c *Client) Close() {
	c.mu.Lock()
	if c.closed {
		c.mu.Unlock()
		return
	}
	c.closed = true

	read_cancel := c.read_cancel
	conn := c.conn
	close(c.close_ch)
	c.mu.Unlock()

	if read_cancel != nil {
		read_cancel()
	}

	if closer, ok := conn.(conn_closer); ok {
		_ = closer.Close()
	}

	c.emit(Event{Kind: EventClosed})
}

func (c *Client) Send(ctx context.Context, content string, metadata string) error {
	c.mu.Lock()
	if !c.ready {
		c.mu.Unlock()
		return fmt.Errorf("client not connected")
	}

	c.state.SeqOut++
	seq_num := c.state.SeqOut

	shared_key := c.state.SharedKey
	session_id_bytes := c.state.SessionIdBytes
	conn := c.conn
	c.mu.Unlock()

	payload := outgoing_frame{
		Content:     content,
		Metadata:    metadata,
		SeqNum:      seq_num,
		IsEncrypted: true,
		Salt:        "",
	}

	enc, err := EncryptAESGCM(shared_key, session_id_bytes, []byte(content), seq_num, false)
	if err != nil {
		return err
	}

	payload.Content = enc.ContentB64
	payload.Salt = enc.SaltHex

	buf, err := json.Marshal(payload)
	if err != nil {
		return err
	}

	return conn.WriteText(ctx, string(buf))
}

func (c *Client) read_loop(ctx context.Context, pending []string) {
	for _, s := range pending {
		c.handle_incoming_text(s)
	}

	for {
		select {
		case <-c.close_ch:
			return
		default:
		}

		s, err := c.conn.ReadText(ctx)
		if err != nil {
			c.emit(Event{Kind: EventError, Err: err})
			return
		}

		c.handle_incoming_text(s)
	}
}

func (c *Client) handle_incoming_text(s string) {
	if len(s) > 0 && s[0] == '/' {
		// Ignore unknown commands after handshake for now.
		return
	}

	var in incoming_frame
	if err := json.Unmarshal([]byte(s), &in); err != nil {
		return
	}

	c.mu.Lock()
	if !c.ready {
		c.mu.Unlock()
		return
	}

	shared_key := c.state.SharedKey
	session_id_bytes := c.state.SessionIdBytes
	c.mu.Unlock()

	content := in.Content

	if in.IsEncrypted {
		plain, err := DecryptAESGCM(shared_key, session_id_bytes, in.Content, in.Salt, in.SeqNum, in.IsResponse)
		if err != nil {
			c.emit(Event{Kind: EventError, Err: err})
			return
		}
		content = string(plain)
	}

	c.mu.Lock()
	if in.SeqNum > c.state.SeqInMax {
		c.state.SeqInMax = in.SeqNum
	}
	c.mu.Unlock()

	c.emit(Event{
		Kind: EventMessage,
		Message: Message{
			Content:    content,
			Metadata:   in.Metadata,
			SeqNum:     in.SeqNum,
			IsResponse: in.IsResponse,
			CreatedAt:  in.CreatedAt,
		},
	})
}

func (c *Client) emit(ev Event) {
	select {
	case c.events_ch <- ev:
	default:
		// Drop if user isn't consuming.
	}
}

type outgoing_frame struct {
	Content     string `json:"content"`
	Metadata    string `json:"metadata"`
	SeqNum      uint64 `json:"seq_num"`
	IsEncrypted bool   `json:"is_encrypted"`
	Salt        string `json:"salt"`
}

type incoming_frame struct {
	Content     string `json:"content"`
	Metadata    string `json:"metadata"`
	SeqNum      uint64 `json:"seq_num"`
	IsEncrypted bool   `json:"is_encrypted"`
	IsResponse  bool   `json:"is_response"`
	Salt        string `json:"salt"`
	CreatedAt   int64  `json:"created_at"`
}