package main

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"sync"
	"time"

	"gorm.io/gorm"

	logger "git.site.quack-lab.dev/dave/cylogger"
	"github.com/fasthttp/router"
	"github.com/valyala/fasthttp"
)

const (
	issuerAuthorizeURL = "https://login.eveonline.com/v2/oauth/authorize"
	issuerTokenURL     = "https://login.eveonline.com/v2/oauth/token"
)

type Token struct {
	ID            uint   `gorm:"primaryKey"`
	CharacterName string `gorm:"uniqueIndex"`
	AccessToken   string
	RefreshToken  string
	ExpiresAt     time.Time
	UpdatedAt     time.Time
	CreatedAt     time.Time
}

type SSO struct {
	clientID     string
	redirectURI  string
	scopes       []string
	db           DB
	mu           sync.Mutex
	router       *router.Router
	state        string
	callbackChan chan struct {
		code  string
		state string
		err   error
	}
}

// NewSSO creates a new SSO instance
func NewSSO(clientID, redirectURI string, scopes []string) (*SSO, error) {
	logger.Info("Creating new SSO instance for clientID %s with redirectURI %s and scopes %v", clientID, redirectURI, scopes)

	db, err := GetDB()
	if err != nil {
		logger.Error("Failed to get database connection %v", err)
		return nil, err
	}

	s := &SSO{
		clientID:    clientID,
		redirectURI: redirectURI,
		scopes:      scopes,
		db:          db,
	}

	if err := s.initDB(); err != nil {
		logger.Error("Failed to initialize SSO database %v", err)
		return nil, err
	}

	logger.Info("SSO instance created successfully")
	return s, nil
}

// SetRouter allows the SSO to use an existing fasthttp router
func (s *SSO) SetRouter(r *router.Router) {
	s.router = r
	logger.Debug("SSO configured to use existing fasthttp router")
	s.setupCallbackHandler()
}

func (s *SSO) initDB() error {
	logger.Debug("Initializing SSO database schema")
	err := s.db.AutoMigrate(&Token{})
	if err != nil {
		logger.Error("Failed to migrate Token table %v", err)
		return err
	}
	logger.Debug("SSO database schema initialized successfully")
	return nil
}

// GetToken returns a valid access token for the given character name
// If no token exists, it will start the OAuth flow
// If token is expired, it will refresh it automatically
func (s *SSO) GetToken(ctx context.Context, characterName string) (string, error) {
	logger.Debug("Getting token for character %s", characterName)
	s.mu.Lock()
	defer s.mu.Unlock()

	// Try to get existing token from DB
	token, err := s.db.GetTokenForCharacter(characterName)
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			logger.Info("No existing token found for character %s, starting authentication flow", characterName)
			// No token exists, need to authenticate
			if err := s.startAuthFlow(ctx, characterName); err != nil {
				return "", err
			}
			// After authentication, fetch the token from DB
			token, err = s.db.GetTokenForCharacter(characterName)
			if err != nil {
				return "", err
			}
			logger.Info("Successfully authenticated character %s", characterName)
		} else {
			return "", err
		}
	} else {
		logger.Debug("Found existing token for character %s, expires at %v", characterName, token.ExpiresAt)
	}

	// Check if token needs refresh
	if time.Now().After(token.ExpiresAt.Add(-60 * time.Second)) {
		logger.Info("Token for character %s is expired or expiring soon, refreshing", characterName)
		if err := s.refreshToken(ctx, token); err != nil {
			logger.Warning("Token refresh failed for character %s, re-authenticating: %v", characterName, err)
			// Refresh failed, need to re-authenticate
			if err := s.startAuthFlow(ctx, characterName); err != nil {
				return "", err
			}
			// After re-authentication, fetch the token from DB
			token, err = s.db.GetTokenForCharacter(characterName)
			if err != nil {
				return "", err
			}
			logger.Info("Successfully re-authenticated character %s", characterName)
		} else {
			logger.Debug("Token refreshed successfully for character %s", characterName)
		}
	} else {
		logger.Debug("Token for character %s is still valid", characterName)
	}

	logger.Debug("Returning valid token for character %s", characterName)
	return token.AccessToken, nil
}

func (s *SSO) startAuthFlow(ctx context.Context, characterName string) error {
	logger.Info("Starting authentication flow for character %s", characterName)

	// Generate PKCE
	logger.Debug("Generating PKCE parameters")
	verifier, challenge, err := generatePKCE()
	if err != nil {
		return err
	}

	s.state = randString(24)
	s.callbackChan = make(chan struct {
		code  string
		state string
		err   error
	}, 1)
	authURL := s.buildAuthURL(challenge, s.state)

	logger.Info("Generated authentication URL for character %s", characterName)
	logger.Info("Please visit this URL to authenticate: \n%s", authURL)
	logger.Info("Waiting for authentication...")

	// Setup callback handling
	if s.router == nil {
		logger.Error("No router configured for callback handling")
		return errors.New("no router configured for callback handling")
	}
	logger.Debug("Using fasthttp router for callback handling")

	// Wait for callback
	logger.Debug("Waiting for authentication callback")
	code, receivedState, err := s.waitForCallback()
	if err != nil {
		return err
	}

	if receivedState != s.state {
		logger.Error("Invalid state parameter received: %s, expected: %s", receivedState, s.state)
		return errors.New("invalid state parameter")
	}

	logger.Debug("Received valid callback, exchanging code for token")
	// Exchange code for token
	token, err := s.exchangeCodeForToken(ctx, code, verifier)
	if err != nil {
		return err
	}

	// Save token to DB
	token.CharacterName = characterName
	logger.Debug("Saving token to database for character %s", characterName)
	if err := s.db.SaveTokenForCharacter(token); err != nil {
		return err
	}

	logger.Info("Authentication flow completed successfully for character %s", characterName)
	return nil
}

func (s *SSO) buildAuthURL(challenge, state string) string {
	q := url.Values{}
	q.Set("response_type", "code")
	q.Set("client_id", s.clientID)
	q.Set("redirect_uri", s.redirectURI)
	if len(s.scopes) > 0 {
		q.Set("scope", strings.Join(s.scopes, " "))
	}
	q.Set("state", state)
	q.Set("code_challenge", challenge)
	q.Set("code_challenge_method", "S256")

	return issuerAuthorizeURL + "?" + q.Encode()
}

func (s *SSO) setupCallbackHandler() {
	u, err := url.Parse(s.redirectURI)
	if err != nil {
		logger.Error("Failed to parse redirect URI for callback handler: %v", err)
		return
	}

	logger.Debug("Setting up callback handler on path: %s", u.Path)
	s.router.GET(u.Path, s.handleCallback)
}

func (s *SSO) handleCallback(ctx *fasthttp.RequestCtx) {
	s.processCallback(
		ctx.IsGet(),
		string(ctx.QueryArgs().Peek("code")),
		string(ctx.QueryArgs().Peek("state")),
		func(status int, body string) {
			ctx.SetStatusCode(status)
			ctx.WriteString(body)
		},
		func(contentType string) {
			ctx.SetContentType(contentType)
		},
	)
}

func (s *SSO) processCallback(isGet bool, code, state string, writeResponse func(int, string), setContentType func(string)) {
	if !isGet {
		logger.Warning("Invalid callback method")
		writeResponse(http.StatusMethodNotAllowed, "Method not allowed")
		s.callbackChan <- struct {
			code  string
			state string
			err   error
		}{"", "", errors.New("method not allowed")}
		return
	}

	if code == "" || state == "" || state != s.state {
		logger.Error("Invalid SSO response: code=%s, state=%s, expected_state=%s", code, state, s.state)
		writeResponse(http.StatusBadRequest, "Invalid SSO response")
		s.callbackChan <- struct {
			code  string
			state string
			err   error
		}{"", "", errors.New("invalid state")}
		return
	}

	logger.Info("Received valid callback, exchanging token for code: %s", code)
	setContentType("text/html")
	writeResponse(http.StatusOK, "<html><body><h1>Login successful!</h1><p>You can close this window.</p></body></html>")
	s.callbackChan <- struct {
		code  string
		state string
		err   error
	}{code, state, nil}
}

func (s *SSO) waitForCallback() (code, state string, err error) {
	logger.Debug("Waiting for authentication callback (timeout: 30s)")
	// Wait for callback through channel
	select {
	case result := <-s.callbackChan:
		if result.err != nil {
			logger.Error("Callback received with error: %v", result.err)
			return "", "", result.err
		}
		logger.Debug("Callback received successfully")
		return result.code, result.state, result.err
	case <-time.After(30 * time.Second):
		logger.Error("Callback timeout after 30 seconds")
		return "", "", errors.New("callback timeout")
	}
}

func (s *SSO) exchangeCodeForToken(ctx context.Context, code, verifier string) (*Token, error) {
	logger.Debug("Exchanging authorization code for access token")
	form := url.Values{}
	form.Set("grant_type", "authorization_code")
	form.Set("code", code)
	form.Set("client_id", s.clientID)
	form.Set("code_verifier", verifier)

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, issuerTokenURL, strings.NewReader(form.Encode()))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

	logger.Debug("Sending token exchange request to %s", issuerTokenURL)
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		b, _ := io.ReadAll(resp.Body)
		logger.Error("Token exchange failed with status %d: %s", resp.StatusCode, string(b))
		return nil, fmt.Errorf("token exchange failed: %s: %s", resp.Status, string(b))
	}

	var tr tokenResponse
	if err := json.NewDecoder(resp.Body).Decode(&tr); err != nil {
		return nil, err
	}

	// Parse character info from token
	name, _ := parseTokenCharacter(tr.AccessToken)
	logger.Info("Successfully exchanged code for token, character: %s", name)

	return &Token{
		CharacterName: name,
		AccessToken:   tr.AccessToken,
		RefreshToken:  tr.RefreshToken,
		ExpiresAt:     time.Now().Add(time.Duration(tr.ExpiresIn-30) * time.Second),
	}, nil
}

func (s *SSO) refreshToken(ctx context.Context, token *Token) error {
	logger.Debug("Refreshing token for character %s", token.CharacterName)
	form := url.Values{}
	form.Set("grant_type", "refresh_token")
	form.Set("refresh_token", token.RefreshToken)
	form.Set("client_id", s.clientID)

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, issuerTokenURL, strings.NewReader(form.Encode()))
	if err != nil {
		return err
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

	logger.Debug("Sending token refresh request to %s", issuerTokenURL)
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		b, _ := io.ReadAll(resp.Body)
		logger.Error("Token refresh failed with status %d: %s", resp.StatusCode, string(b))
		return fmt.Errorf("token refresh failed: %s: %s", resp.Status, string(b))
	}

	var tr tokenResponse
	if err := json.NewDecoder(resp.Body).Decode(&tr); err != nil {
		return err
	}

	// Update token
	token.AccessToken = tr.AccessToken
	if tr.RefreshToken != "" {
		token.RefreshToken = tr.RefreshToken
	}
	if tr.ExpiresIn > 0 {
		token.ExpiresAt = time.Now().Add(time.Duration(tr.ExpiresIn-30) * time.Second)
	}

	logger.Debug("Saving refreshed token to database for character %s", token.CharacterName)
	if err := s.db.SaveTokenForCharacter(token); err != nil {
		return err
	}

	logger.Info("Token refreshed successfully for character %s", token.CharacterName)
	return nil
}

// Utility functions
func generatePKCE() (verifier string, challenge string, err error) {
	buf := make([]byte, 32)
	if _, err = rand.Read(buf); err != nil {
		return
	}
	v := base64.RawURLEncoding.EncodeToString(buf)
	h := sha256.Sum256([]byte(v))
	c := base64.RawURLEncoding.EncodeToString(h[:])
	return v, c, nil
}

func randString(n int) string {
	buf := make([]byte, n)
	_, _ = rand.Read(buf)
	return base64.RawURLEncoding.EncodeToString(buf)
}

func parseTokenCharacter(jwt string) (name string, id int64) {
	parts := strings.Split(jwt, ".")
	if len(parts) != 3 {
		return "", 0
	}
	payload, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return "", 0
	}
	var m map[string]any
	if err := json.Unmarshal(payload, &m); err != nil {
		return "", 0
	}
	if v, ok := m["name"].(string); ok {
		name = v
	}
	if v, ok := m["sub"].(string); ok {
		if idx := strings.LastIndexByte(v, ':'); idx > -1 {
			if idv, err := strconv.ParseInt(v[idx+1:], 10, 64); err == nil {
				id = idv
			}
		}
	}
	return
}

type tokenResponse struct {
	AccessToken  string `json:"access_token"`
	RefreshToken string `json:"refresh_token"`
	TokenType    string `json:"token_type"`
	ExpiresIn    int    `json:"expires_in"`
}