package providerapi

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"

	"proxy-pool/internal/config"
	controllerProvider "proxy-pool/internal/controller/provider"
)

const defaultRetryAfterMax = 30 * time.Second

type HTTPDoer interface {
	Do(*http.Request) (*http.Response, error)
}

type HTTPAdapter struct {
	doer          HTTPDoer
	method        string
	url           string
	headers       http.Header
	body          []byte
	basicUser     string
	basicPass     string
	bearerToken   string
	maxBytes      int64
	retryAfterMax time.Duration
	now           func() time.Time
}

type HTTPStatusError struct {
	StatusCode int
	retryable  bool
}

func (a *HTTPAdapter) String() string {
	if a == nil {
		return "providerapi.HTTPAdapter<nil>"
	}
	return fmt.Sprintf("providerapi.HTTPAdapter{method:%s,maxBytes:%d}", a.method, a.maxBytes)
}

func (a *HTTPAdapter) GoString() string { return a.String() }

func (e *HTTPStatusError) Error() string {
	return fmt.Sprintf("provider API returned HTTP status %d", e.StatusCode)
}

func (e *HTTPStatusError) Retryable() bool { return e.retryable }

type operationError struct {
	operation string
	cause     error
}

func (e *operationError) Error() string { return e.operation + " failed" }
func (e *operationError) Unwrap() error { return e.cause }

func NewHTTPAdapter(api config.ProviderAPI, fetch config.Fetch, doer HTTPDoer) (*HTTPAdapter, error) {
	parsedURL, err := url.Parse(api.URL)
	if err != nil || parsedURL.Host == "" || (parsedURL.Scheme != "http" && parsedURL.Scheme != "https") {
		return nil, fmt.Errorf("new provider HTTP adapter: invalid API URL")
	}
	method := strings.ToUpper(strings.TrimSpace(api.Method))
	if method == "" {
		method = http.MethodGet
	}
	if !validHTTPToken(method) {
		return nil, fmt.Errorf("new provider HTTP adapter: invalid method %q", api.Method)
	}

	query := parsedURL.Query()
	for key, value := range api.Query {
		query.Set(key, value)
	}
	headers := make(http.Header, len(api.Headers)+2)
	for key, value := range api.Headers {
		if !validHTTPToken(key) || !validHTTPHeaderValue(value) {
			return nil, fmt.Errorf("new provider HTTP adapter: invalid header")
		}
		headers.Set(key, value)
	}

	adapter := &HTTPAdapter{
		doer:          doer,
		method:        method,
		headers:       headers,
		maxBytes:      fetch.MaxResponseBytes,
		retryAfterMax: time.Duration(fetch.Retry.Max),
		now:           time.Now,
	}
	if adapter.doer == nil {
		adapter.doer = defaultHTTPClient()
	}
	if adapter.maxBytes <= 0 {
		adapter.maxBytes = defaultTemplateMaxBytes
	}
	if adapter.retryAfterMax <= 0 {
		adapter.retryAfterMax = defaultRetryAfterMax
	}

	switch api.Auth.Type {
	case "", "none":
	case "basic":
		if api.Auth.Username == "" || api.Auth.Password == "" {
			return nil, fmt.Errorf("new provider HTTP adapter: resolved basic credentials are required")
		}
		if headerHas(headers, "Authorization") {
			return nil, fmt.Errorf("new provider HTTP adapter: conflicting authorization header")
		}
		adapter.basicUser, adapter.basicPass = api.Auth.Username, api.Auth.Password
	case "bearer":
		if api.Auth.Token == "" {
			return nil, fmt.Errorf("new provider HTTP adapter: resolved bearer token is required")
		}
		if headerHas(headers, "Authorization") {
			return nil, fmt.Errorf("new provider HTTP adapter: conflicting authorization header")
		}
		adapter.bearerToken = api.Auth.Token
	case "apiKey":
		if api.Auth.Name == "" || api.Auth.Value == "" {
			return nil, fmt.Errorf("new provider HTTP adapter: resolved API key is required")
		}
		switch api.Auth.Location {
		case "header":
			if !validHTTPToken(api.Auth.Name) || !validHTTPHeaderValue(api.Auth.Value) {
				return nil, fmt.Errorf("new provider HTTP adapter: invalid API key header")
			}
			if headerHas(headers, api.Auth.Name) {
				return nil, fmt.Errorf("new provider HTTP adapter: conflicting API key header")
			}
			adapter.headers.Set(api.Auth.Name, api.Auth.Value)
		case "query":
			if query.Has(api.Auth.Name) {
				return nil, fmt.Errorf("new provider HTTP adapter: conflicting API key query parameter")
			}
			query.Set(api.Auth.Name, api.Auth.Value)
		default:
			return nil, fmt.Errorf("new provider HTTP adapter: invalid API key location %q", api.Auth.Location)
		}
	default:
		return nil, fmt.Errorf("new provider HTTP adapter: unsupported auth type %q", api.Auth.Type)
	}
	parsedURL.RawQuery = query.Encode()
	adapter.url = parsedURL.String()

	switch api.Body.Type {
	case "":
	case "json":
		adapter.body, err = json.Marshal(api.Body.Value)
		if err != nil {
			return nil, fmt.Errorf("new provider HTTP adapter: encode JSON body: %w", err)
		}
		if adapter.headers.Get("Content-Type") == "" {
			adapter.headers.Set("Content-Type", "application/json")
		}
	case "form":
		values := make(url.Values, len(api.Body.Value))
		for key, value := range api.Body.Value {
			values.Set(key, value)
		}
		adapter.body = []byte(values.Encode())
		if adapter.headers.Get("Content-Type") == "" {
			adapter.headers.Set("Content-Type", "application/x-www-form-urlencoded")
		}
	default:
		return nil, fmt.Errorf("new provider HTTP adapter: unsupported body type %q", api.Body.Type)
	}
	return adapter, nil
}

func (a *HTTPAdapter) Fetch(ctx context.Context) (controllerProvider.FetchResponse, error) {
	request, err := http.NewRequestWithContext(ctx, a.method, a.url, bytes.NewReader(a.body))
	if err != nil {
		return controllerProvider.FetchResponse{}, &operationError{operation: "build provider request", cause: err}
	}
	request.Header = a.headers.Clone()
	if a.basicUser != "" {
		request.SetBasicAuth(a.basicUser, a.basicPass)
	}
	if a.bearerToken != "" {
		request.Header.Set("Authorization", "Bearer "+a.bearerToken)
	}

	response, err := a.doer.Do(request)
	if err != nil {
		if response != nil && response.Body != nil {
			_ = response.Body.Close()
		}
		return controllerProvider.FetchResponse{}, &operationError{operation: "call provider API", cause: err}
	}
	if response == nil || response.Body == nil {
		return controllerProvider.FetchResponse{}, ErrInvalidHTTPResponse
	}
	defer response.Body.Close()
	body, readErr := readAllLimited(response.Body, a.maxBytes, ErrResponseTooLarge)
	if response.StatusCode < http.StatusOK || response.StatusCode >= http.StatusMultipleChoices {
		statusErr := &HTTPStatusError{
			StatusCode: response.StatusCode,
			retryable:  retryableHTTPStatus(response.StatusCode),
		}
		result := controllerProvider.FetchResponse{}
		if statusErr.retryable {
			result.RetryAfter = parseRetryAfter(response.Header.Get("Retry-After"), a.now(), a.retryAfterMax)
		}
		if readErr != nil {
			if !errors.Is(readErr, ErrResponseTooLarge) {
				readErr = &operationError{operation: "read provider response", cause: readErr}
			}
			return result, errors.Join(statusErr, readErr)
		}
		return result, statusErr
	}
	if readErr != nil {
		if errors.Is(readErr, ErrResponseTooLarge) {
			return controllerProvider.FetchResponse{}, readErr
		}
		return controllerProvider.FetchResponse{}, &operationError{operation: "read provider response", cause: readErr}
	}
	return controllerProvider.FetchResponse{Body: body}, nil
}

func retryableHTTPStatus(status int) bool {
	return status == http.StatusRequestTimeout || status == http.StatusTooEarly ||
		status == http.StatusTooManyRequests ||
		(status >= http.StatusInternalServerError && status <= 599)
}

func parseRetryAfter(value string, now time.Time, maximum time.Duration) time.Duration {
	value = strings.TrimSpace(value)
	if value == "" {
		return 0
	}
	if seconds, err := strconv.ParseInt(value, 10, 64); err == nil {
		if seconds <= 0 {
			return 0
		}
		if seconds > int64(maximum/time.Second) {
			return maximum
		}
		return time.Duration(seconds) * time.Second
	}
	when, err := http.ParseTime(value)
	if err != nil {
		return 0
	}
	delay := when.Sub(now)
	if delay <= 0 {
		return 0
	}
	if delay > maximum {
		return maximum
	}
	return delay
}

func defaultHTTPClient() *http.Client {
	return &http.Client{
		CheckRedirect: func(*http.Request, []*http.Request) error {
			return http.ErrUseLastResponse
		},
	}
}

func validHTTPToken(value string) bool {
	if value == "" {
		return false
	}
	for _, character := range value {
		if character <= 0x20 || character >= 0x7f || strings.ContainsRune("()<>@,;:\\\"/[]?={}", character) {
			return false
		}
	}
	return true
}

func validHTTPHeaderValue(value string) bool {
	for _, character := range value {
		if character == '\t' {
			continue
		}
		if character < 0x20 || character == 0x7f {
			return false
		}
	}
	return true
}

func headerHas(headers http.Header, key string) bool {
	_, exists := headers[http.CanonicalHeaderKey(key)]
	return exists
}