package client

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net"
	"net/http"
	"net/url"
	"os"
	"reflect"
	"strings"

	"github.com/moby/moby/api/types/common"
)

// head sends an http request to the docker API using the method HEAD.
func (cli *Client) head(ctx context.Context, path string, query url.Values, headers http.Header) (*http.Response, error) {
	return cli.sendRequest(ctx, http.MethodHead, path, query, nil, headers)
}

// get sends an http request to the docker API using the method GET with a specific Go context.
func (cli *Client) get(ctx context.Context, path string, query url.Values, headers http.Header) (*http.Response, error) {
	return cli.sendRequest(ctx, http.MethodGet, path, query, nil, headers)
}

// post sends an http POST request to the API.
func (cli *Client) post(ctx context.Context, path string, query url.Values, body any, headers http.Header) (*http.Response, error) {
	jsonBody, headers, err := prepareJSONRequest(body, headers)
	if err != nil {
		return nil, err
	}
	return cli.sendRequest(ctx, http.MethodPost, path, query, jsonBody, headers)
}

func (cli *Client) postRaw(ctx context.Context, path string, query url.Values, body io.Reader, headers http.Header) (*http.Response, error) {
	return cli.sendRequest(ctx, http.MethodPost, path, query, body, headers)
}

func (cli *Client) put(ctx context.Context, path string, query url.Values, body any, headers http.Header) (*http.Response, error) {
	jsonBody, headers, err := prepareJSONRequest(body, headers)
	if err != nil {
		return nil, err
	}
	return cli.putRaw(ctx, path, query, jsonBody, headers)
}

// putRaw sends an http request to the docker API using the method PUT.
func (cli *Client) putRaw(ctx context.Context, path string, query url.Values, body io.Reader, headers http.Header) (*http.Response, error) {
	// PUT requests are expected to always have a body (apparently)
	// so explicitly pass an empty body to sendRequest to signal that
	// it should set the Content-Type header if not already present.
	if body == nil {
		body = http.NoBody
	}
	return cli.sendRequest(ctx, http.MethodPut, path, query, body, headers)
}

// delete sends an http request to the docker API using the method DELETE.
func (cli *Client) delete(ctx context.Context, path string, query url.Values, headers http.Header) (*http.Response, error) {
	return cli.sendRequest(ctx, http.MethodDelete, path, query, nil, headers)
}

// prepareJSONRequest encodes the given body to JSON and returns it as an [io.Reader], and sets the Content-Type
// header. If body is nil, or a nil-interface, a "nil" body is returned without
// error.
//
// TODO(thaJeztah): should this return an error if a different Content-Type is already set?
// TODO(thaJeztah): is "nil" the appropriate approach for an empty body, or should we use [http.NoBody] (or similar)?
func prepareJSONRequest(body any, headers http.Header) (io.Reader, http.Header, error) {
	if body == nil {
		return nil, headers, nil
	}
	// encoding/json encodes a nil pointer as the JSON document `null`,
	// irrespective of whether the type implements json.Marshaler or encoding.TextMarshaler.
	// That is almost certainly not what the caller intended as the request body.
	//
	// TODO(thaJeztah): consider moving this to jsonEncode, which would also allow returning an (empty) reader instead of nil.
	if reflect.TypeOf(body).Kind() == reflect.Ptr && reflect.ValueOf(body).IsNil() {
		return nil, headers, nil
	}

	jsonBody, err := jsonEncode(body)
	if err != nil {
		return nil, headers, err
	}
	hdr := http.Header{}
	if headers != nil {
		hdr = headers.Clone()
	}

	hdr.Set("Content-Type", "application/json")
	return jsonBody, hdr, nil
}

func (cli *Client) buildRequest(ctx context.Context, method, path string, body io.Reader, headers http.Header) (*http.Request, error) {
	req, err := http.NewRequestWithContext(ctx, method, path, body)
	if err != nil {
		return nil, err
	}
	req = cli.addHeaders(req, headers)
	req.URL.Scheme = cli.scheme
	req.URL.Host = cli.addr

	if cli.proto == "unix" || cli.proto == "npipe" {
		// Override host header for non-tcp connections.
		req.Host = DummyHost
	}

	if body != nil && req.Header.Get("Content-Type") == "" {
		req.Header.Set("Content-Type", "text/plain")
	}
	return req, nil
}

func (cli *Client) sendRequest(ctx context.Context, method, path string, query url.Values, body io.Reader, headers http.Header) (*http.Response, error) {
	req, err := cli.buildRequest(ctx, method, cli.getAPIPath(ctx, path, query), body, headers)
	if err != nil {
		return nil, err
	}

	resp, err := cli.doRequest(req)
	if err != nil {
		// Failed to connect or context error.
		return resp, err
	}

	// Successfully made a request; return the response and handle any
	// API HTTP response errors.
	return resp, checkResponseErr(resp)
}

// doRequest sends an HTTP request and returns an HTTP response. It is a
// wrapper around [http.Client.Do] with extra handling to decorate errors.
//
// Otherwise, it behaves identical to [http.Client.Do]; an error is returned
// when failing to make a connection, On error, any Response can be ignored.
// A non-2xx status code doesn't cause an error.
func (cli *Client) doRequest(req *http.Request) (*http.Response, error) {
	resp, err := cli.client.Do(req)
	if err == nil {
		return resp, nil
	}

	if cli.scheme != "https" && strings.Contains(err.Error(), "malformed HTTP response") {
		return nil, errConnectionFailed{fmt.Errorf("%w.\n* Are you trying to connect to a TLS-enabled daemon without TLS?", err)}
	}

	const (
		// Go 1.25 /  TLS 1.3 may produce a generic "handshake failure"
		// whereas TLS 1.2 may produce a "bad certificate" TLS alert.
		// See https://github.com/golang/go/issues/56371
		//
		// > https://tip.golang.org/doc/go1.12#tls_1_3
		// >
		// > In TLS 1.3 the client is the last one to speak in the handshake, so if
		// > it causes an error to occur on the server, it will be returned on the
		// > client by the first Read, not by Handshake. For example, that will be
		// > the case if the server rejects the client certificate.
		//
		// https://github.com/golang/go/blob/go1.25.1/src/crypto/tls/alert.go#L71-L72
		alertBadCertificate   = "bad certificate"   // go1.24 / TLS 1.2
		alertHandshakeFailure = "handshake failure" // go1.25 / TLS 1.3
	)

	// TODO(thaJeztah): see if we can use errors.As for a [crypto/tls.AlertError] instead of bare string matching.
	if cli.scheme == "https" && (strings.Contains(err.Error(), alertHandshakeFailure) || strings.Contains(err.Error(), alertBadCertificate)) {
		return nil, errConnectionFailed{fmt.Errorf("the server probably has client authentication (--tlsverify) enabled; check your TLS client certification settings: %w", err)}
	}

	// Don't decorate context sentinel errors; users may be comparing to
	// them directly.
	if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
		return nil, err
	}

	if errors.Is(err, os.ErrPermission) {
		// Don't include request errors ("Get "http://%2Fvar%2Frun%2Fdocker.sock/v1.51/version"),
		// which are irrelevant if we weren't able to connect.
		return nil, errConnectionFailed{fmt.Errorf("permission denied while trying to connect to the docker API at %v", cli.host)}
	}
	if errors.Is(err, os.ErrNotExist) {
		// Unwrap the error to remove request errors ("Get "http://%2Fvar%2Frun%2Fdocker.sock/v1.51/version"),
		// which are irrelevant if we weren't able to connect.
		err = errors.Unwrap(err)
		return nil, errConnectionFailed{fmt.Errorf("failed to connect to the docker API at %v; check if the path is correct and if the daemon is running: %w", cli.host, err)}
	}
	var dnsErr *net.DNSError
	if errors.As(err, &dnsErr) {
		return nil, errConnectionFailed{fmt.Errorf("failed to connect to the docker API at %v: %w", cli.host, dnsErr)}
	}

	var nErr net.Error
	if errors.As(err, &nErr) {
		// FIXME(thaJeztah): any net.Error should be considered a connection error (but we should include the original error)?
		if nErr.Timeout() {
			return nil, connectionFailed(cli.host)
		}
		if strings.Contains(nErr.Error(), "connection refused") || strings.Contains(nErr.Error(), "dial unix") {
			return nil, connectionFailed(cli.host)
		}
	}

	// Although there's not a strongly typed error for this in go-winio,
	// lots of people are using the default configuration for the docker
	// daemon on Windows where the daemon is listening on a named pipe
	// `//./pipe/docker_engine, and the client must be running elevated.
	// Give users a clue rather than the not-overly useful message
	// such as `error during connect: Get http://%2F%2F.%2Fpipe%2Fdocker_engine/v1.26/info:
	// open //./pipe/docker_engine: The system cannot find the file specified.`.
	// Note we can't string compare "The system cannot find the file specified" as
	// this is localised - for example in French the error would be
	// `open //./pipe/docker_engine: Le fichier spécifié est introuvable.`
	if strings.Contains(err.Error(), `open //./pipe/docker_engine`) {
		// Checks if client is running with elevated privileges
		if f, elevatedErr := os.Open(`\\.\PHYSICALDRIVE0`); elevatedErr != nil {
			err = fmt.Errorf("in the default daemon configuration on Windows, the docker client must be run with elevated privileges to connect: %w", err)
		} else {
			_ = f.Close()
			err = fmt.Errorf("this error may indicate that the docker daemon is not running: %w", err)
		}
	}

	return nil, errConnectionFailed{fmt.Errorf("error during connect: %w", err)}
}

func checkResponseErr(serverResp *http.Response) (retErr error) {
	if serverResp == nil {
		return nil
	}
	if serverResp.StatusCode >= http.StatusOK && serverResp.StatusCode < http.StatusBadRequest {
		return nil
	}
	defer func() {
		retErr = httpErrorFromStatusCode(retErr, serverResp.StatusCode)
	}()

	var body []byte
	var err error
	var reqURL string
	if serverResp.Request != nil {
		reqURL = serverResp.Request.URL.String()
	}
	statusMsg := serverResp.Status
	if statusMsg == "" {
		statusMsg = http.StatusText(serverResp.StatusCode)
	}
	if serverResp.Body != nil {
		bodyMax := 1 * 1024 * 1024 // 1 MiB
		bodyR := &io.LimitedReader{
			R: serverResp.Body,
			N: int64(bodyMax),
		}
		body, err = io.ReadAll(bodyR)
		if err != nil {
			return err
		}
		if bodyR.N == 0 {
			if reqURL != "" {
				return fmt.Errorf("request returned %s with a message (> %d bytes) for API route and version %s, check if the server supports the requested API version", statusMsg, bodyMax, reqURL)
			}
			return fmt.Errorf("request returned %s with a message (> %d bytes); check if the server supports the requested API version", statusMsg, bodyMax)
		}
	}
	if len(body) == 0 {
		if reqURL != "" {
			return fmt.Errorf("request returned %s for API route and version %s, check if the server supports the requested API version", statusMsg, reqURL)
		}
		return fmt.Errorf("request returned %s; check if the server supports the requested API version", statusMsg)
	}

	var daemonErr error
	if serverResp.Header.Get("Content-Type") == "application/json" {
		var errorResponse common.ErrorResponse
		if err := json.Unmarshal(body, &errorResponse); err != nil {
			return fmt.Errorf("error reading JSON: %w", err)
		}
		if errorResponse.Message == "" {
			// Error-message is empty, which means that we successfully parsed the
			// JSON-response (no error produced), but it didn't contain an error
			// message. This could either be because the response was empty, or
			// the response was valid JSON, but not with the expected schema
			// ([common.ErrorResponse]).
			//
			// We cannot use "strict" JSON handling (json.NewDecoder with DisallowUnknownFields)
			// due to the API using an open schema (we must anticipate fields
			// being added to [common.ErrorResponse] in the future, and not
			// reject those responses.
			//
			// For these cases, we construct an error with the status-code
			// returned, but we could consider returning (a truncated version
			// of) the actual response as-is.
			//
			// TODO(thaJeztah): consider adding a log.Debug to allow clients to debug the actual response when enabling debug logging.
			daemonErr = fmt.Errorf(`API returned a %d (%s) but provided no error-message`,
				serverResp.StatusCode,
				http.StatusText(serverResp.StatusCode),
			)
		} else {
			daemonErr = errors.New(strings.TrimSpace(errorResponse.Message))
		}
	} else {
		// Fall back to returning the response as-is for situations where a
		// plain text error is returned. This branch may also catch
		// situations where a proxy is involved, returning a HTML response.
		daemonErr = errors.New(strings.TrimSpace(string(body)))
	}
	return fmt.Errorf("Error response from daemon: %w", daemonErr)
}

func (cli *Client) addHeaders(req *http.Request, headers http.Header) *http.Request {
	// Add CLI Config's HTTP Headers BEFORE we set the Docker headers
	// then the user can't change OUR headers
	for k, v := range cli.customHTTPHeaders {
		req.Header.Set(k, v)
	}

	for k, v := range headers {
		req.Header[http.CanonicalHeaderKey(k)] = v
	}

	if cli.userAgent != nil {
		if *cli.userAgent == "" {
			req.Header.Del("User-Agent")
		} else {
			req.Header.Set("User-Agent", *cli.userAgent)
		}
	}
	return req
}

func jsonEncode(data any) (io.Reader, error) {
	var params bytes.Buffer
	if data != nil {
		if err := json.NewEncoder(&params).Encode(data); err != nil {
			return nil, err
		}
	}
	return &params, nil
}

func ensureReaderClosed(response *http.Response) {
	if response != nil && response.Body != nil {
		// Drain up to 512 bytes and close the body to let the Transport reuse the connection
		// see https://github.com/google/go-github/pull/317/files#r57536827
		//
		// TODO(thaJeztah): see if this optimization is still needed, or already implemented in stdlib,
		//   and check if context-cancellation should handle this as well. If still needed, consider
		//   wrapping response.Body, or returning a "closer()" from [Client.sendRequest] and related
		//   methods.
		_, _ = io.CopyN(io.Discard, response.Body, 512)
		_ = response.Body.Close()
	}
}
