package client

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/http/cookiejar"
	"net/url"
	"strings"
	"time"
)

const (
	maxResponseSize          = 2 << 20 // 2 MiB
	defaultTimeout           = 15 * time.Second
	defaultSessionCookieName = "gardomatic_session"
)

// Client is safe for concurrent use. A client configured with WithSessions
// owns one cookie jar and must therefore only be shared by callers that are
// meant to share the same login session.
type Client struct {
	baseURL     *url.URL
	httpClient  *http.Client
	bearerToken string
	headers     http.Header
	cookieName  string
}

type config struct {
	httpClient     *http.Client
	bearerToken    string
	headers        http.Header
	sessions       bool
	initialCookies []*http.Cookie
	cookieName     string
}

// Option configures a Client.
type Option func(*config) error

// WithHTTPClient supplies the HTTP client used for requests. The client is
// shallow-copied, so Client never changes the caller's value.
func WithHTTPClient(httpClient *http.Client) Option {
	return func(cfg *config) error {
		if httpClient == nil {
			return errors.New("client: HTTP client must not be nil")
		}
		cfg.httpClient = httpClient
		return nil
	}
}

// WithBearerToken authenticates every request using a bearer token.
func WithBearerToken(token string) Option {
	return func(cfg *config) error {
		if strings.TrimSpace(token) == "" {
			return errors.New("client: bearer token must not be empty")
		}
		cfg.bearerToken = token
		return nil
	}
}

// WithHeader adds a header to every request. Authorization and Cookie should
// be configured using WithBearerToken and WithSessions instead.
func WithHeader(name, value string) Option {
	return func(cfg *config) error {
		if strings.TrimSpace(name) == "" {
			return errors.New("client: header name must not be empty")
		}
		if cfg.headers == nil {
			cfg.headers = make(http.Header)
		}
		cfg.headers.Add(name, value)
		return nil
	}
}

// WithSessions gives the client a private cookie jar. Use one such Client per
// independent user session; do not share it globally in a web server.
func WithSessions() Option {
	return func(cfg *config) error {
		cfg.sessions = true
		return nil
	}
}

// WithSessionCookieName selects the cookie copied by ForRequest. It should
// match api.Config.Session.CookieName.
func WithSessionCookieName(name string) Option {
	return func(cfg *config) error {
		if strings.TrimSpace(name) == "" {
			return errors.New("client: session cookie name must not be empty")
		}
		cfg.cookieName = name
		return nil
	}
}

// WithInitialCookies enables sessions and seeds the private cookie jar with
// the configured session cookie. Other frontend cookies are not forwarded.
func WithInitialCookies(cookies ...*http.Cookie) Option {
	return func(cfg *config) error {
		cfg.sessions = true
		cfg.initialCookies = append(cfg.initialCookies, cookies...)
		return nil
	}
}

// New constructs a Gardomatic API client. baseURL may contain a path prefix;
// API paths are resolved below that prefix.
func New(baseURL string, options ...Option) (*Client, error) {
	parsedURL, err := url.Parse(baseURL)
	if err != nil {
		return nil, fmt.Errorf("client: parse base URL: %w", err)
	}
	if parsedURL.Scheme != "http" && parsedURL.Scheme != "https" {
		return nil, errors.New("client: base URL must use http or https")
	}
	if parsedURL.Host == "" {
		return nil, errors.New("client: base URL must include a host")
	}
	if parsedURL.RawQuery != "" || parsedURL.Fragment != "" {
		return nil, errors.New("client: base URL must not contain a query or fragment")
	}
	parsedURL.Path = strings.TrimSuffix(parsedURL.Path, "/") + "/"

	cfg := config{
		httpClient: &http.Client{Timeout: defaultTimeout},
		headers:    make(http.Header),
		cookieName: defaultSessionCookieName,
	}
	for _, option := range options {
		if option == nil {
			return nil, errors.New("client: option must not be nil")
		}
		if err := option(&cfg); err != nil {
			return nil, err
		}
	}

	httpClient := *cfg.httpClient
	if cfg.sessions {
		jar, err := cookiejar.New(nil)
		if err != nil {
			return nil, fmt.Errorf("client: create cookie jar: %w", err)
		}
		jar.SetCookies(parsedURL, sessionCookies(cfg.initialCookies, cfg.cookieName))
		httpClient.Jar = jar
	}

	return &Client{
		baseURL:     parsedURL,
		httpClient:  &httpClient,
		bearerToken: cfg.bearerToken,
		headers:     cfg.headers.Clone(),
		cookieName:  cfg.cookieName,
	}, nil
}

func sessionCookies(cookies []*http.Cookie, name string) []*http.Cookie {
	for _, cookie := range cookies {
		if cookie != nil && cookie.Name == name {
			return []*http.Cookie{cookie}
		}
	}
	return nil
}

// ForRequest returns a client with a private cookie jar seeded from r. This is
// the safe way to use a shared base client in an HTTP frontend.
func (c *Client) ForRequest(r *http.Request) (*Client, error) {
	if r == nil {
		return nil, errors.New("client: request must not be nil")
	}

	httpClient := *c.httpClient
	jar, err := cookiejar.New(nil)
	if err != nil {
		return nil, fmt.Errorf("client: create cookie jar: %w", err)
	}
	jar.SetCookies(c.baseURL, sessionCookies(r.Cookies(), c.cookieName))
	httpClient.Jar = jar

	return &Client{
		baseURL:     c.baseURL,
		httpClient:  &httpClient,
		bearerToken: c.bearerToken,
		headers:     c.headers.Clone(),
		cookieName:  c.cookieName,
	}, nil
}

// Response contains the HTTP response metadata. The body has already been
// read and closed. Cookies remains useful for forwarding Set-Cookie headers.
type Response struct {
	*http.Response
}

func (c *Client) do(ctx context.Context, method, path string, input, output any) (*Response, error) {
	if ctx == nil {
		return nil, errors.New("client: context must not be nil")
	}

	var body io.Reader
	if input != nil {
		encoded, err := json.Marshal(input)
		if err != nil {
			return nil, fmt.Errorf("client: encode request: %w", err)
		}
		body = bytes.NewReader(encoded)
	}

	relativeURL, err := url.Parse(strings.TrimPrefix(path, "/"))
	if err != nil {
		return nil, fmt.Errorf("client: parse request path: %w", err)
	}
	request, err := http.NewRequestWithContext(ctx, method, c.baseURL.ResolveReference(relativeURL).String(), body)
	if err != nil {
		return nil, fmt.Errorf("client: create request: %w", err)
	}
	request.Header = c.headers.Clone()
	request.Header.Set("Accept", "application/json")
	if input != nil {
		request.Header.Set("Content-Type", "application/json")
	}
	if c.bearerToken != "" {
		request.Header.Set("Authorization", "Bearer "+c.bearerToken)
	}

	httpResponse, err := c.httpClient.Do(request)
	if err != nil {
		return nil, fmt.Errorf("client: execute request: %w", err)
	}
	response := &Response{httpResponse}
	defer httpResponse.Body.Close()

	responseBody, err := io.ReadAll(io.LimitReader(httpResponse.Body, maxResponseSize+1))
	if err != nil {
		return response, fmt.Errorf("client: read response: %w", err)
	}
	if len(responseBody) > maxResponseSize {
		return response, errors.New("client: response exceeds 2 MiB")
	}

	if httpResponse.StatusCode < http.StatusOK || httpResponse.StatusCode >= http.StatusMultipleChoices {
		return response, newAPIError(httpResponse, responseBody)
	}
	if output == nil || httpResponse.StatusCode == http.StatusNoContent || len(bytes.TrimSpace(responseBody)) == 0 {
		return response, nil
	}
	if err := json.Unmarshal(responseBody, output); err != nil {
		return response, fmt.Errorf("client: decode response: %w", err)
	}

	return response, nil
}