package configread

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"mime"
	"net/http"
	"net/url"
	"strings"
)

const dispatcherIDHeader = "X-DISPATCHER-id"
const dispatcherSecretHeader = "X-DISPATCHER-SECRET-KEY"
const configReadPath = "/internal/v1/dispatcher"

type Client struct {
	baseURL      string
	dispatcherID string
	secret       string
	httpClient   *http.Client
}

type HTTPError struct {
	StatusCode int
	Code       string
}

func (e *HTTPError) Error() string {
	if e.Code == "" {
		return fmt.Sprintf("configuration service returned HTTP %d", e.StatusCode)
	}
	return fmt.Sprintf("configuration service returned HTTP %d (%s)", e.StatusCode, e.Code)
}

func NewClient(baseURL, dispatcherID, secret string, httpClient *http.Client) (*Client, error) {
	parsed, err := url.ParseRequestURI(baseURL)
	if err != nil || parsed.Host == "" || (parsed.Scheme != "http" && parsed.Scheme != "https") || parsed.User != nil || parsed.RawQuery != "" || parsed.Fragment != "" {
		return nil, errors.New("configuration service URL must be an absolute HTTP(S) URL without credentials, query, or fragment")
	}
	if strings.TrimSpace(dispatcherID) == "" || strings.TrimSpace(secret) == "" {
		return nil, errors.New("dispatcher ID and secret are required")
	}
	if strings.ContainsAny(dispatcherID+secret, "\r\n") {
		return nil, errors.New("dispatcher credentials contain invalid header characters")
	}
	if httpClient == nil {
		httpClient = http.DefaultClient
	}
	return &Client{baseURL: strings.TrimRight(baseURL, "/"), dispatcherID: dispatcherID, secret: secret, httpClient: httpClient}, nil
}

func (c *Client) DispatcherID() string { return c.dispatcherID }

func (c *Client) get(ctx context.Context, path string) (json.RawMessage, error) {
	relative, err := url.Parse(path)
	if err != nil {
		return nil, fmt.Errorf("parse configuration path: %w", err)
	}
	base, err := url.Parse(c.baseURL)
	if err != nil {
		return nil, fmt.Errorf("parse configuration base URL: %w", err)
	}
	base = base.JoinPath(relative.Path)
	base.RawQuery = relative.RawQuery
	request, err := http.NewRequestWithContext(ctx, http.MethodGet, base.String(), nil)
	if err != nil {
		return nil, fmt.Errorf("build configuration request: %w", err)
	}
	request.Header.Set("Accept", "application/json")
	request.Header.Set(dispatcherIDHeader, c.dispatcherID)
	request.Header.Set(dispatcherSecretHeader, c.secret)
	response, err := c.httpClient.Do(request)
	if err != nil {
		return nil, fmt.Errorf("request configuration service: %w", err)
	}
	defer response.Body.Close()
	body, err := io.ReadAll(response.Body)
	if err != nil {
		return nil, fmt.Errorf("read configuration response: %w", err)
	}
	if response.StatusCode != http.StatusOK {
		return nil, &HTTPError{StatusCode: response.StatusCode, Code: responseErrorCode(body)}
	}
	mediaType, _, err := mime.ParseMediaType(response.Header.Get("Content-Type"))
	if err != nil || mediaType != "application/json" {
		return nil, errors.New("configuration service response must use application/json")
	}
	if !json.Valid(body) {
		return nil, errors.New("configuration service returned invalid JSON")
	}
	return json.RawMessage(body), nil
}

func responseErrorCode(body []byte) string {
	var response struct {
		Error struct {
			Code string `json:"code"`
		} `json:"error"`
	}
	if err := json.Unmarshal(body, &response); err != nil {
		return ""
	}
	return response.Error.Code
}