//go:build linux || freebsd
// +build linux freebsd

package auth

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

// OAuthConfig configuration for OAuth 2.0
type OAuthConfig struct {
	ClientID     string    `json:"client_id,omitempty" toml:"client_id,omitempty"`
	ClientSecret string    `json:"client_secret,omitempty" toml:"client_secret,omitempty"`
	TokenURL     string    `json:"token_url,omitempty" toml:"token_url,omitempty"`
	AuthURL      string    `json:"auth_url,omitempty" toml:"auth_url,omitempty"`
	RedirectURI  string    `json:"redirect_uri,omitempty" toml:"redirect_uri,omitempty"`
	Scopes       []string  `json:"scopes,omitempty" toml:"scopes,omitempty"`
	AccessToken  string    `json:"access_token,omitempty" toml:"access_token,omitempty"`
	RefreshToken string    `json:"refresh_token,omitempty" toml:"refresh_token,omitempty"`
	TokenType    string    `json:"token_type,omitempty" toml:"token_type,omitempty"`
	Expiry       time.Time `json:"expiry,omitempty" toml:"expiry,omitempty"`
	GrantType    string    `json:"grant_type,omitempty" toml:"grant_type,omitempty"` // authorization_code, client_credentials, password, refresh_token
}

// TokenResponse response from a token endpoint
type TokenResponse struct {
	AccessToken  string `json:"access_token"`
	TokenType    string `json:"token_type"`
	RefreshToken string `json:"refresh_token,omitempty"`
	ExpiresIn    int    `json:"expires_in,omitempty"`
	Scope        string `json:"scope,omitempty"`
	Error        string `json:"error,omitempty"`
	ErrorDesc    string `json:"error_description,omitempty"`
}

// OAuthClient client for OAuth 2.0 authentication
type OAuthClient struct {
	config *OAuthConfig
	client *http.Client
}

// NewOAuthClient creates a new OAuth client
func NewOAuthClient(cfg *OAuthConfig) *OAuthClient {
	if cfg.TokenType == "" {
		cfg.TokenType = "Bearer"
	}
	return &OAuthClient{
		config: cfg,
		client: &http.Client{Timeout: 30 * time.Second},
	}
}

// IsTokenValid checks whether the token is valid
func (c *OAuthClient) IsTokenValid() bool {
	if c.config.AccessToken == "" {
		return false
	}
	if c.config.Expiry.IsZero() {
		return true // No expiry, assume valid
	}
	// Token is valid if it expires in more than 30 seconds
	return time.Now().Add(30 * time.Second).Before(c.config.Expiry)
}

// RequestToken gets new access token
func (c *OAuthClient) RequestToken(ctx context.Context) (*TokenResponse, error) {
	if c.config.TokenURL != "" {
		u, err := url.Parse(c.config.TokenURL)
		if err != nil {
			return nil, fmt.Errorf("invalid oauth token URL: %w", err)
		}
		if u.Scheme != "https" && u.Hostname() != "localhost" && u.Hostname() != "127.0.0.1" && u.Hostname() != "::1" {
			return nil, fmt.Errorf("oauth token URL must use HTTPS for security")
		}
	}

	formData := url.Values{}

	grantType := c.config.GrantType
	if grantType == "" {
		grantType = "client_credentials"
	}

	formData.Set("grant_type", grantType)

	switch grantType {
	case "client_credentials":
		formData.Set("client_id", c.config.ClientID)
		formData.Set("client_secret", c.config.ClientSecret)
		if len(c.config.Scopes) > 0 {
			formData.Set("scope", strings.Join(c.config.Scopes, " "))
		}

	case "password":
		formData.Set("client_id", c.config.ClientID)
		formData.Set("client_secret", c.config.ClientSecret)
		// Username and password would need to be passed separately
		// This is handled by caller

	case "authorization_code":
		formData.Set("client_id", c.config.ClientID)
		formData.Set("client_secret", c.config.ClientSecret)
		// Code and redirect_uri would need to be passed separately

	case "refresh_token":
		formData.Set("client_id", c.config.ClientID)
		formData.Set("client_secret", c.config.ClientSecret)
		formData.Set("refresh_token", c.config.RefreshToken)
	}

	req, err := http.NewRequestWithContext(ctx, "POST", c.config.TokenURL, strings.NewReader(formData.Encode()))
	if err != nil {
		return nil, fmt.Errorf("failed to create token request: %w", err)
	}

	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	req.Header.Set("Accept", "application/json")

	resp, err := c.client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("token request failed: %w", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("failed to read token response: %w", err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, fmt.Errorf("token endpoint returned %s", formatOAuthError(resp.StatusCode, body))
	}

	var tokenResp TokenResponse
	if err := json.Unmarshal(body, &tokenResp); err != nil {
		return nil, fmt.Errorf("failed to parse token response: %w", err)
	}

	if tokenResp.Error != "" {
		return nil, fmt.Errorf("oauth error: %s - %s", tokenResp.Error, tokenResp.ErrorDesc)
	}

	return &tokenResp, nil
}

// ApplyToken applies the token to the HTTP request
func (c *OAuthClient) ApplyToken(req *http.Request) {
	if c.config.AccessToken == "" {
		return
	}
	tokenType := c.config.TokenType
	if tokenType == "" {
		tokenType = "Bearer"
	}
	req.Header.Set("Authorization", fmt.Sprintf("%s %s", tokenType, c.config.AccessToken))
}

// RefreshToken refreshes access token using a refresh token
func (c *OAuthClient) RefreshToken(ctx context.Context) error {
	if c.config.RefreshToken == "" {
		return fmt.Errorf("no refresh token available")
	}

	oldGrantType := c.config.GrantType
	c.config.GrantType = "refresh_token"
	defer func() { c.config.GrantType = oldGrantType }()

	tokenResp, err := c.RequestToken(ctx)
	if err != nil {
		return err
	}

	c.UpdateToken(tokenResp)
	return nil
}

// UpdateToken updates internal token from response
func (c *OAuthClient) UpdateToken(tokenResp *TokenResponse) {
	c.config.AccessToken = tokenResp.AccessToken
	c.config.TokenType = tokenResp.TokenType
	if tokenResp.RefreshToken != "" {
		c.config.RefreshToken = tokenResp.RefreshToken
	}
	if tokenResp.ExpiresIn > 0 {
		c.config.Expiry = time.Now().Add(time.Duration(tokenResp.ExpiresIn) * time.Second)
	}
}

// GetAuthorizationURL returns the authorization URL (for authorization_code flow)
func (c *OAuthClient) GetAuthorizationURL(state string) string {
	if c.config.AuthURL == "" {
		return ""
	}

	params := url.Values{}
	params.Set("client_id", c.config.ClientID)
	params.Set("redirect_uri", c.config.RedirectURI)
	params.Set("response_type", "code")
	params.Set("state", state)
	if len(c.config.Scopes) > 0 {
		params.Set("scope", strings.Join(c.config.Scopes, " "))
	}

	baseURL := c.config.AuthURL
	if strings.Contains(baseURL, "?") {
		return baseURL + "&" + params.Encode()
	}
	return baseURL + "?" + params.Encode()
}

// ExchangeCode exchanges an authorization code for an access token
func (c *OAuthClient) ExchangeCode(ctx context.Context, code string) (*TokenResponse, error) {
	formData := url.Values{}
	formData.Set("grant_type", "authorization_code")
	formData.Set("code", code)
	formData.Set("redirect_uri", c.config.RedirectURI)
	formData.Set("client_id", c.config.ClientID)
	formData.Set("client_secret", c.config.ClientSecret)

	req, err := http.NewRequestWithContext(ctx, "POST", c.config.TokenURL, strings.NewReader(formData.Encode()))
	if err != nil {
		return nil, fmt.Errorf("failed to create code exchange request: %w", err)
	}

	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	req.Header.Set("Accept", "application/json")

	resp, err := c.client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("code exchange request failed: %w", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("failed to read code exchange response: %w", err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, fmt.Errorf("code exchange endpoint returned %s", formatOAuthError(resp.StatusCode, body))
	}

	var tokenResp TokenResponse
	if err := json.Unmarshal(body, &tokenResp); err != nil {
		return nil, fmt.Errorf("failed to parse code exchange response: %w", err)
	}

	if tokenResp.Error != "" {
		return nil, fmt.Errorf("oauth error: %s - %s", tokenResp.Error, tokenResp.ErrorDesc)
	}

	return &tokenResp, nil
}

// formatOAuthError converts a non-2xx OAuth response into a human-readable
// error string while avoiding leaking sensitive data. The OAuth provider's
// raw response body is never returned verbatim: we first try to extract
// the structured `error` and `error_description` fields defined in RFC
// 6749 §5.2 (which is what well-behaved providers return), and only fall
// back to a 512-byte truncated snippet of the raw body if the body is
// not structured. This prevents upstream providers that echo back
// secrets, stack traces, or other sensitive payloads in their error
// bodies from leaking those payloads into our logs and error displays.
func formatOAuthError(statusCode int, body []byte) string {
	if len(body) == 0 {
		return fmt.Sprintf("status %d with empty body", statusCode)
	}

	var structured struct {
		Error            string `json:"error"`
		ErrorDescription string `json:"error_description"`
	}
	if err := json.Unmarshal(body, &structured); err == nil && structured.Error != "" {
		if structured.ErrorDescription != "" {
			return fmt.Sprintf("status %d: %s - %s", statusCode, structured.Error, structured.ErrorDescription)
		}
		return fmt.Sprintf("status %d: %s", statusCode, structured.Error)
	}

	const maxSnippet = 512
	snippet := string(body)
	if len(snippet) > maxSnippet {
		snippet = snippet[:maxSnippet] + "... (truncated)"
	}
	return fmt.Sprintf("status %d: %s", statusCode, snippet)
}