package main

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	neturl "net/url"
	"os"
	"strings"
	"time"

	oauth "github.com/haileyok/atproto-oauth-golang"
	"github.com/haileyok/atproto-oauth-golang/helpers"
	"github.com/lestrrat-go/jwx/v2/jwk"
)

// OAuthManager handles OAuth 2.0 authentication for the dashboard
type OAuthManager struct {
	client       *oauth.Client
	clientID     string
	redirectURI  string
	privateJWK   jwk.Key
	publicJWK    jwk.Key
	sessions     *SessionStore
	cookieSecret []byte
	allowedScope string
}

// OAuthConfig holds configuration for the OAuth manager
type OAuthConfig struct {
	ClientID     string // URL to client metadata (e.g., https://app.1440.news/.well-known/oauth-client-metadata)
	RedirectURI  string // OAuth callback URL (e.g., https://app.1440.news/auth/callback)
	CookieSecret string // 32-byte hex string for AES-256-GCM encryption
	PrivateJWK   string // ES256 private key as JSON
}

// NewOAuthManager creates a new OAuth manager
func NewOAuthManager(cfg OAuthConfig) (*OAuthManager, error) {
	// Parse cookie secret (must be 32 bytes for AES-256)
	cookieSecret, err := parseHexSecret(cfg.CookieSecret)
	if err != nil {
		return nil, fmt.Errorf("invalid cookie secret: %v", err)
	}
	if len(cookieSecret) != 32 {
		return nil, fmt.Errorf("cookie secret must be 32 bytes, got %d", len(cookieSecret))
	}

	// Parse private JWK
	privateJWK, err := helpers.ParseJWKFromBytes([]byte(cfg.PrivateJWK))
	if err != nil {
		return nil, fmt.Errorf("invalid private JWK: %v", err)
	}

	// Extract public key
	publicJWK, err := privateJWK.PublicKey()
	if err != nil {
		return nil, fmt.Errorf("failed to extract public key: %v", err)
	}

	// Create HTTP client with longer timeout
	httpClient := &http.Client{
		Timeout: 30 * time.Second,
	}

	// Create OAuth client
	client, err := oauth.NewClient(oauth.ClientArgs{
		Http:        httpClient,
		ClientJwk:   privateJWK,
		ClientId:    cfg.ClientID,
		RedirectUri: cfg.RedirectURI,
	})
	if err != nil {
		return nil, fmt.Errorf("failed to create OAuth client: %v", err)
	}

	return &OAuthManager{
		client:       client,
		clientID:     cfg.ClientID,
		redirectURI:  cfg.RedirectURI,
		privateJWK:   privateJWK,
		publicJWK:    publicJWK,
		sessions:     NewSessionStore(),
		cookieSecret: cookieSecret,
		allowedScope: "atproto",
	}, nil
}

// LoadOAuthConfig loads OAuth configuration from environment or oauth.env file
func LoadOAuthConfig(baseURL string) (*OAuthConfig, error) {
	cfg := &OAuthConfig{
		ClientID:    baseURL + "/.well-known/oauth-client-metadata",
		RedirectURI: baseURL + "/auth/callback",
	}

	// Try environment variables first
	cfg.CookieSecret = os.Getenv("OAUTH_COOKIE_SECRET")
	cfg.PrivateJWK = os.Getenv("OAUTH_PRIVATE_JWK")

	// Fall back to oauth.env file
	if cfg.CookieSecret == "" || cfg.PrivateJWK == "" {
		if data, err := os.ReadFile("oauth.env"); err == nil {
			for _, line := range strings.Split(string(data), "\n") {
				line = strings.TrimSpace(line)
				if strings.HasPrefix(line, "#") || line == "" {
					continue
				}
				parts := strings.SplitN(line, "=", 2)
				if len(parts) == 2 {
					key := strings.TrimSpace(parts[0])
					value := strings.TrimSpace(parts[1])
					switch key {
					case "OAUTH_COOKIE_SECRET":
						cfg.CookieSecret = value
					case "OAUTH_PRIVATE_JWK":
						cfg.PrivateJWK = value
					}
				}
			}
		}
	}

	// Validate required fields
	if cfg.CookieSecret == "" {
		return nil, fmt.Errorf("OAUTH_COOKIE_SECRET not configured")
	}
	if cfg.PrivateJWK == "" {
		return nil, fmt.Errorf("OAUTH_PRIVATE_JWK not configured")
	}

	return cfg, nil
}

// parseHexSecret converts a hex string to bytes
func parseHexSecret(hex string) ([]byte, error) {
	if len(hex)%2 != 0 {
		return nil, fmt.Errorf("hex string must have even length")
	}
	b := make([]byte, len(hex)/2)
	for i := 0; i < len(hex); i += 2 {
		var val byte
		for j := 0; j < 2; j++ {
			c := hex[i+j]
			switch {
			case c >= '0' && c <= '9':
				val = val*16 + (c - '0')
			case c >= 'a' && c <= 'f':
				val = val*16 + (c - 'a' + 10)
			case c >= 'A' && c <= 'F':
				val = val*16 + (c - 'A' + 10)
			default:
				return nil, fmt.Errorf("invalid hex character: %c", c)
			}
		}
		b[i/2] = val
	}
	return b, nil
}

// resolveHandle resolves a Bluesky handle to a DID
func resolveHandle(ctx context.Context, handle string) (string, error) {
	// Normalize handle (remove @ prefix and whitespace)
	handle = strings.TrimSpace(handle)
	handle = strings.TrimPrefix(handle, "@")
	handle = strings.ToLower(handle)

	// Try DNS-based resolution first
	url := fmt.Sprintf("https://bsky.social/xrpc/com.atproto.identity.resolveHandle?handle=%s", neturl.QueryEscape(handle))
	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
	if err != nil {
		return "", err
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return "", fmt.Errorf("resolve handle failed: %s", string(body))
	}

	var result struct {
		DID string `json:"did"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
		return "", err
	}

	return result.DID, nil
}

// resolveDIDToHandle resolves a DID to the current handle
func resolveDIDToHandle(ctx context.Context, did string) (string, error) {
	// Fetch DID document
	var docURL string
	if strings.HasPrefix(did, "did:plc:") {
		docURL = fmt.Sprintf("https://plc.directory/%s", did)
	} else if strings.HasPrefix(did, "did:web:") {
		domain := strings.TrimPrefix(did, "did:web:")
		docURL = fmt.Sprintf("https://%s/.well-known/did.json", domain)
	} else {
		return "", fmt.Errorf("unsupported DID method: %s", did)
	}

	req, err := http.NewRequestWithContext(ctx, "GET", docURL, nil)
	if err != nil {
		return "", err
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("failed to fetch DID document: %d", resp.StatusCode)
	}

	var doc struct {
		AlsoKnownAs []string `json:"alsoKnownAs"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&doc); err != nil {
		return "", err
	}

	// Find the at:// handle
	for _, aka := range doc.AlsoKnownAs {
		if strings.HasPrefix(aka, "at://") {
			return strings.TrimPrefix(aka, "at://"), nil
		}
	}

	return "", fmt.Errorf("no handle found for DID %s", did)
}

// resolveDIDToService gets the PDS service URL from a DID
func resolveDIDToService(ctx context.Context, did string) (string, error) {
	var docURL string
	if strings.HasPrefix(did, "did:plc:") {
		docURL = fmt.Sprintf("https://plc.directory/%s", did)
	} else if strings.HasPrefix(did, "did:web:") {
		domain := strings.TrimPrefix(did, "did:web:")
		docURL = fmt.Sprintf("https://%s/.well-known/did.json", domain)
	} else {
		return "", fmt.Errorf("unsupported DID method: %s", did)
	}

	req, err := http.NewRequestWithContext(ctx, "GET", docURL, nil)
	if err != nil {
		return "", err
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("failed to fetch DID document: %d", resp.StatusCode)
	}

	var doc struct {
		Service []struct {
			ID              string `json:"id"`
			Type            string `json:"type"`
			ServiceEndpoint string `json:"serviceEndpoint"`
		} `json:"service"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&doc); err != nil {
		return "", err
	}

	// Find the atproto_pds service
	for _, svc := range doc.Service {
		if svc.Type == "AtprotoPersonalDataServer" || svc.ID == "#atproto_pds" {
			return svc.ServiceEndpoint, nil
		}
	}

	return "", fmt.Errorf("no PDS service found for DID %s", did)
}