package endpoints

import (
	"bytes"
	"compress/gzip"
	"encoding/base64"
	"fmt"
	"io"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/michaelquigley/df/dl"
	"github.com/pkg/errors"
)

// OAuthCookieConfig defines the interface that OAuth configurations must implement
// to work with the shared cookie utilities
type OAuthCookieConfig interface {
	GetCookieName() string
	GetCookieDomain() string
	GetMaxCookieSize() int
	GetMaxCookieChunks() int
	GetSessionLifetime() time.Duration
}

const (
	defaultMaxCookieChunks = 10
	hardMaxCookieChunks    = 32
)

func getEffectiveMaxCookieChunks(cfg OAuthCookieConfig) int {
	maxCookieChunks := cfg.GetMaxCookieChunks()
	if maxCookieChunks == 0 {
		return defaultMaxCookieChunks
	}
	return min(maxCookieChunks, hardMaxCookieChunks)
}

func getChunkCount(compressedToken string, maxCookieSize int) (int, int, error) {
	chunkCount := 1
	for {
		prefixLen := len(fmt.Sprintf("%d|", chunkCount))
		firstChunkSize := maxCookieSize - prefixLen
		if firstChunkSize <= 0 {
			return 0, 0, errors.New("max cookie size too small for striping")
		}

		requiredChunks := 1
		if len(compressedToken) > firstChunkSize {
			requiredChunks += (len(compressedToken) - firstChunkSize + maxCookieSize - 1) / maxCookieSize
		}
		if requiredChunks == chunkCount {
			return chunkCount, firstChunkSize, nil
		}
		chunkCount = requiredChunks
	}
}

// CompressToken compresses a JWT token string using gzip and returns a base64-encoded string
func CompressToken(token string) (string, error) {
	var buf bytes.Buffer
	gzWriter := gzip.NewWriter(&buf)

	if _, err := gzWriter.Write([]byte(token)); err != nil {
		return "", errors.Wrap(err, "failed to write to gzip writer")
	}

	if err := gzWriter.Close(); err != nil {
		return "", errors.Wrap(err, "failed to close gzip writer")
	}

	return base64.URLEncoding.EncodeToString(buf.Bytes()), nil
}

// DecompressToken decompresses a base64-encoded gzip string back to the original JWT token
func DecompressToken(compressed string) (string, error) {
	data, err := base64.URLEncoding.DecodeString(compressed)
	if err != nil {
		return "", errors.Wrap(err, "failed to decode base64")
	}

	gzReader, err := gzip.NewReader(bytes.NewReader(data))
	if err != nil {
		return "", errors.Wrap(err, "failed to create gzip reader")
	}
	defer gzReader.Close()

	decompressed, err := io.ReadAll(gzReader)
	if err != nil {
		return "", errors.Wrap(err, "failed to read decompressed data")
	}

	return string(decompressed), nil
}

// GetSessionCookie retrieves and reassembles a session cookie, handling both single and striped cookies
func GetSessionCookie(r *http.Request, cfg OAuthCookieConfig) (*http.Cookie, error) {
	cookieName := cfg.GetCookieName()

	// get the first cookie
	cookie, err := r.Cookie(cookieName)
	if err != nil {
		return nil, err
	}

	var compressedValue string

	// check if the cookie value has the stripe count prefix: {count}|{data}
	if strings.Contains(cookie.Value, "|") {
		parts := strings.SplitN(cookie.Value, "|", 2)
		if len(parts) == 2 {
			count, err := strconv.Atoi(parts[0])
			if err != nil || count <= 0 {
				return nil, errors.Errorf("invalid cookie chunk count '%s'", parts[0])
			}

			maxCookieChunks := getEffectiveMaxCookieChunks(cfg)
			if count > maxCookieChunks {
				return nil, errors.Errorf("cookie chunk count '%d' exceeds maximum '%d'", count, maxCookieChunks)
			}

			// this is a striped cookie
			chunks := make([]string, count)
			chunks[0] = parts[1]

			// fetch the remaining chunks
			for i := 1; i < count; i++ {
				chunkCookie, err := r.Cookie(fmt.Sprintf("%s_%d", cookieName, i))
				if err != nil {
					return nil, errors.Errorf("missing cookie chunk '%s_%d'", cookieName, i)
				}
				chunks[i] = chunkCookie.Value
			}

			// reassemble the compressed value
			compressedValue = strings.Join(chunks, "")
		} else {
			compressedValue = cookie.Value
		}
	} else {
		// single cookie, no striping
		compressedValue = cookie.Value
	}

	// decompress the value
	decompressedValue, err := DecompressToken(compressedValue)
	if err != nil {
		return nil, errors.Wrap(err, "failed to decompress cookie value")
	}

	// return a cookie with the decompressed JWT value
	return &http.Cookie{
		Name:  cookieName,
		Value: decompressedValue,
	}, nil
}

// SetSessionCookie sets a session cookie, compressing and striping it if necessary
func SetSessionCookie(w http.ResponseWriter, cookieName string, tokenValue string, cfg OAuthCookieConfig) error {
	// compress the JWT token
	compressedToken, err := CompressToken(tokenValue)
	if err != nil {
		return errors.Wrap(err, "failed to compress token")
	}

	// use default max cookie size if not configured
	maxCookieSize := cfg.GetMaxCookieSize()
	if maxCookieSize == 0 {
		maxCookieSize = 2048
	}

	// common cookie attributes
	cookieAttrs := &http.Cookie{
		MaxAge:  int(cfg.GetSessionLifetime().Seconds()),
		Domain:  cfg.GetCookieDomain(),
		Path:    "/",
		Expires: time.Now().Add(cfg.GetSessionLifetime()),
		// Secure:  true, // pending server tls feature https://github.com/openziti/zrok/issues/24
		HttpOnly: true,                 // enabled because zrok frontend is the only intended consumer of this cookie, not client-side scripts
		SameSite: http.SameSiteLaxMode, // explicitly set to the default Lax mode which allows the zrok share to be navigated to from another site and receive the cookie
	}

	// check if we need to stripe the cookie
	if len(compressedToken) > maxCookieSize {
		// calculate number of chunks needed, accounting for the count prefix in the first chunk
		chunkCount, firstChunkSize, err := getChunkCount(compressedToken, maxCookieSize)
		if err != nil {
			return err
		}

		maxCookieChunks := getEffectiveMaxCookieChunks(cfg)
		if chunkCount > maxCookieChunks {
			return errors.Errorf("compressed token requires '%d' cookie chunks; maximum is '%d'", chunkCount, maxCookieChunks)
		}

		// set first cookie with count prefix
		firstChunk := compressedToken[:min(firstChunkSize, len(compressedToken))]
		firstCookie := *cookieAttrs
		firstCookie.Name = cookieName
		firstCookie.Value = fmt.Sprintf("%d|%s", chunkCount, firstChunk)
		http.SetCookie(w, &firstCookie)

		// set remaining chunks
		offset := firstChunkSize
		for i := 1; i < chunkCount; i++ {
			end := min(offset+maxCookieSize, len(compressedToken))
			chunk := compressedToken[offset:end]

			chunkCookie := *cookieAttrs
			chunkCookie.Name = fmt.Sprintf("%s_%d", cookieName, i)
			chunkCookie.Value = chunk
			http.SetCookie(w, &chunkCookie)

			offset = end
		}

		dl.Debugf("striped session cookie into '%d' chunks", chunkCount)
	} else {
		// single cookie is sufficient
		cookie := *cookieAttrs
		cookie.Name = cookieName
		cookie.Value = compressedToken
		http.SetCookie(w, &cookie)
	}

	return nil
}

// ClearSessionCookies clears all session cookies including striped cookie chunks
func ClearSessionCookies(w http.ResponseWriter, r *http.Request, cookieName string, cfg OAuthCookieConfig) {
	// iterate through all cookies and clear any that match the session cookie pattern
	for _, cookie := range r.Cookies() {
		// clear base cookie or any numbered chunks (cookieName_1, cookieName_2, etc.)
		if cookie.Name == cookieName || strings.HasPrefix(cookie.Name, cookieName+"_") {
			http.SetCookie(w, &http.Cookie{
				Name:     cookie.Name,
				Value:    "",
				MaxAge:   -1,
				Domain:   cfg.GetCookieDomain(),
				Path:     "/",
				HttpOnly: true,
			})
		}
	}
}

// FilterSessionCookies filters out session cookies and their striped chunks from a cookie list
func FilterSessionCookies(cookies []*http.Cookie, cookieName string) []*http.Cookie {
	filtered := make([]*http.Cookie, 0, len(cookies))
	for _, cookie := range cookies {
		// filter out the base session cookie
		if cookie.Name == cookieName {
			continue
		}
		// filter out striped session cookie chunks (e.g., cookieName_1, cookieName_2)
		if strings.HasPrefix(cookie.Name, cookieName+"_") {
			// check if the suffix is a number
			suffix := strings.TrimPrefix(cookie.Name, cookieName+"_")
			if _, err := strconv.Atoi(suffix); err == nil {
				continue
			}
		}
		// filter out pkce cookie
		if cookie.Name == "pkce" {
			continue
		}
		filtered = append(filtered, cookie)
	}
	return filtered
}