// Package chatapi provides a client for the chat server HTTP API.
package chatapi

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strconv"
	"time"
)

const (
	httpTimeout      = 30 * time.Second
	pollExtraDelay   = 5
	httpErrThreshold = 400
)

// ErrHTTP is returned for non-2xx responses.
var ErrHTTP = errors.New("http error")

// ErrUnexpectedFormat is returned when the response format is
// not recognised.
var ErrUnexpectedFormat = errors.New("unexpected format")

// Client wraps HTTP calls to the chat server API.
type Client struct {
	BaseURL    string
	Token      string
	HTTPClient *http.Client
}

// NewClient creates a new API client.
func NewClient(baseURL string) *Client {
	return &Client{
		BaseURL: baseURL,
		HTTPClient: &http.Client{
			Timeout: httpTimeout,
		},
	}
}

// CreateSession creates a new session on the server.
func (c *Client) CreateSession(
	nick string,
) (*SessionResponse, error) {
	data, err := c.do(
		"POST", "/api/v1/session",
		&SessionRequest{Nick: nick},
	)
	if err != nil {
		return nil, err
	}

	var resp SessionResponse

	err = json.Unmarshal(data, &resp)
	if err != nil {
		return nil, fmt.Errorf("decode session: %w", err)
	}

	c.Token = resp.Token

	return &resp, nil
}

// GetState returns the current user state.
func (c *Client) GetState() (*StateResponse, error) {
	data, err := c.do("GET", "/api/v1/state", nil)
	if err != nil {
		return nil, err
	}

	var resp StateResponse

	err = json.Unmarshal(data, &resp)
	if err != nil {
		return nil, fmt.Errorf("decode state: %w", err)
	}

	return &resp, nil
}

// SendMessage sends a message (any IRC command).
func (c *Client) SendMessage(msg *Message) error {
	_, err := c.do("POST", "/api/v1/messages", msg)

	return err
}

// PollMessages long-polls for new messages.
func (c *Client) PollMessages(
	afterID string,
	timeout int,
) ([]Message, error) {
	pollTimeout := time.Duration(
		timeout+pollExtraDelay,
	) * time.Second

	client := &http.Client{Timeout: pollTimeout}

	params := url.Values{}
	if afterID != "" {
		params.Set("after", afterID)
	}

	params.Set("timeout", strconv.Itoa(timeout))

	path := "/api/v1/messages"
	if len(params) > 0 {
		path += "?" + params.Encode()
	}

	req, err := http.NewRequest( //nolint:noctx // CLI tool
		http.MethodGet, c.BaseURL+path, nil,
	)
	if err != nil {
		return nil, err
	}

	req.Header.Set("Authorization", "Bearer "+c.Token)

	resp, err := client.Do(req) //nolint:gosec // URL from user config
	if err != nil {
		return nil, err
	}

	defer func() { _ = resp.Body.Close() }()

	data, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, err
	}

	if resp.StatusCode >= httpErrThreshold {
		return nil, fmt.Errorf(
			"%w: %d: %s",
			ErrHTTP, resp.StatusCode, string(data),
		)
	}

	return decodeMessages(data)
}

func decodeMessages(data []byte) ([]Message, error) {
	var msgs []Message

	err := json.Unmarshal(data, &msgs)
	if err == nil {
		return msgs, nil
	}

	var wrapped MessagesResponse

	err2 := json.Unmarshal(data, &wrapped)
	if err2 != nil {
		return nil, fmt.Errorf(
			"decode messages: %w (raw: %s)",
			err, string(data),
		)
	}

	return wrapped.Messages, nil
}

// JoinChannel joins a channel via the unified command
// endpoint.
func (c *Client) JoinChannel(channel string) error {
	return c.SendMessage(
		&Message{Command: "JOIN", To: channel},
	)
}

// PartChannel leaves a channel via the unified command
// endpoint.
func (c *Client) PartChannel(channel string) error {
	return c.SendMessage(
		&Message{Command: "PART", To: channel},
	)
}

// ListChannels returns all channels on the server.
func (c *Client) ListChannels() ([]Channel, error) {
	data, err := c.do("GET", "/api/v1/channels", nil)
	if err != nil {
		return nil, err
	}

	var channels []Channel

	err = json.Unmarshal(data, &channels)
	if err != nil {
		return nil, err
	}

	return channels, nil
}

// GetMembers returns members of a channel.
func (c *Client) GetMembers(
	channel string,
) ([]string, error) {
	path := "/api/v1/channels/" +
		url.PathEscape(channel) + "/members"

	data, err := c.do("GET", path, nil)
	if err != nil {
		return nil, err
	}

	var members []string

	err = json.Unmarshal(data, &members)
	if err != nil {
		return nil, fmt.Errorf(
			"%w: members: %s",
			ErrUnexpectedFormat, string(data),
		)
	}

	return members, nil
}

// GetServerInfo returns server info.
func (c *Client) GetServerInfo() (*ServerInfo, error) {
	data, err := c.do("GET", "/api/v1/server", nil)
	if err != nil {
		return nil, err
	}

	var info ServerInfo

	err = json.Unmarshal(data, &info)
	if err != nil {
		return nil, err
	}

	return &info, nil
}

func (c *Client) do(
	method, path string,
	body any,
) ([]byte, error) {
	var bodyReader io.Reader

	if body != nil {
		data, err := json.Marshal(body)
		if err != nil {
			return nil, fmt.Errorf("marshal: %w", err)
		}

		bodyReader = bytes.NewReader(data)
	}

	req, err := http.NewRequest( //nolint:noctx // CLI tool
		method, c.BaseURL+path, bodyReader,
	)
	if err != nil {
		return nil, fmt.Errorf("request: %w", err)
	}

	req.Header.Set("Content-Type", "application/json")

	if c.Token != "" {
		req.Header.Set("Authorization", "Bearer "+c.Token)
	}

	resp, err := c.HTTPClient.Do(req) //nolint:gosec // URL from user config
	if err != nil {
		return nil, fmt.Errorf("http: %w", err)
	}

	defer func() { _ = resp.Body.Close() }()

	data, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("read body: %w", err)
	}

	if resp.StatusCode >= httpErrThreshold {
		return data, fmt.Errorf(
			"%w: %d: %s",
			ErrHTTP, resp.StatusCode, string(data),
		)
	}

	return data, nil
}