package twitter

//go:generate mockery --recursive --name Getter --output ../generated/mocks

import (
	"encoding/json"
	"fmt"
	"net/http"
	"time"
)

// ElonID is the Twitter ID of @elonmusk.
const ElonID = "44196397"

// User represents a Twitter user.
type User struct {
	ID       string
	Name     string
	Username string
}

// Tweet represents a tweet.
type Tweet struct {
	ID   string
	Text string
}

// bearerTokenTransport implements http.RoundTripper.
type bearerTokenTransport struct {
	bearerToken string
}

// RoundTrip sets the Authorization header with the provided bearerToken, and
// forwards the request. It will panic if the request includes a body (which
// requires special handling).
func (t *bearerTokenTransport) RoundTrip(req *http.Request) (*http.Response, error) {
	if req.Body != nil {
		panic("bearerTokenTransport does not handle requests with non-nil body")
	}
	req2 := cloneRequest(req)
	req2.Header.Set("Authorization", "Bearer "+t.bearerToken)
	return http.DefaultTransport.RoundTrip(req2)
}

// https://go.googlesource.com/oauth2/+/f95fa95eaa936d9d87489b15d1d18b97c1ba9c28/transport.go#96
func cloneRequest(r *http.Request) *http.Request {
	// shallow copy of the struct
	r2 := new(http.Request)
	*r2 = *r
	// deep copy of the Header
	r2.Header = make(http.Header, len(r.Header))
	for k, s := range r.Header {
		r2.Header[k] = append([]string(nil), s...)
	}
	return r2
}

type Getter interface {
	Get(string) (*http.Response, error)
}

// NewAPIClient returns a new APIClient.
func NewAPIClient(httpclient Getter) *APIClient {
	return &APIClient{httpclient}
}

// NewAPIClient returns a new APIClient which will authenticate with the
// provided bearer token.
func NewAPIClientWithBearerToken(bearerToken string) *APIClient {
	return &APIClient{&http.Client{
		Timeout:   time.Second * 5,
		Transport: &bearerTokenTransport{bearerToken: bearerToken},
	}}
}

// APIClient interacts with the Twitter API V2.
type APIClient struct {
	Getter
}

// GetMe returns the currently authenticated user.
func (c *APIClient) GetMe() (*User, error) {
	type oauthResponse struct {
		Data *User `json:"data"`
	}

	resp, err := c.Get("https://api.twitter.com/2/users/me")
	if err != nil {
		return nil, fmt.Errorf("error fetching resource: %v", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("error fetching resource: status code %d", resp.StatusCode)
	}

	var oauthResp oauthResponse
	if err = json.NewDecoder(resp.Body).Decode(&oauthResp); err != nil {
		return nil, fmt.Errorf("error decoding resource: %v", err)
	}

	return oauthResp.Data, nil
}

// GetElonTweets returns the latest tweets for a given user.
func (c *APIClient) GetTweets(userID string, sinceID string) ([]*Tweet, error) {
	type oauthResponse struct {
		Data []*Tweet `json:"data"`
	}

	resp, err := c.Get(fmt.Sprintf("https://api.twitter.com/2/users/%s/tweets?since_id=%s", userID, sinceID))
	if err != nil {
		return nil, fmt.Errorf("error fetching resource: %v", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("error fetching resource: status code %d", resp.StatusCode)
	}

	var oauthResp oauthResponse
	if err = json.NewDecoder(resp.Body).Decode(&oauthResp); err != nil {
		return nil, fmt.Errorf("error decoding resource: %v", err)
	}

	return oauthResp.Data, nil
}