package auth

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

type GitHubOIDCProvider struct {
	registryURL string
}

// NewGitHubOIDCProvider creates a new GitHub OIDC provider
func NewGitHubOIDCProvider(registryURL string) Provider {
	return &GitHubOIDCProvider{
		registryURL: registryURL,
	}
}

// GetToken retrieves the registry JWT token using GitHub Actions OIDC token
func (o *GitHubOIDCProvider) GetToken(ctx context.Context) (string, error) {
	audience, err := audienceFromRegistryURL(o.registryURL)
	if err != nil {
		return "", fmt.Errorf("invalid --registry URL: %w", err)
	}

	// Get OIDC token from GitHub Actions endpoint
	oidcToken, err := o.getOIDCTokenFromGitHub(ctx, audience)
	if err != nil {
		return "", fmt.Errorf("failed to get OIDC token from GitHub: %w", err)
	}

	// Exchange OIDC token for registry token
	registryToken, err := o.exchangeOIDCTokenForRegistry(ctx, oidcToken)
	if err != nil {
		return "", fmt.Errorf("failed to exchange OIDC token: %w", err)
	}

	return registryToken, nil
}

// Login is not needed for OIDC since tokens are provided by GitHub Actions
func (o *GitHubOIDCProvider) Login(_ context.Context) error {
	// No interactive login needed for OIDC
	return nil
}

// Name returns the name of this auth provider
func (o *GitHubOIDCProvider) Name() string {
	return "github-oidc"
}

// exchangeOIDCTokenForRegistry exchanges a GitHub OIDC token for a registry JWT token
func (o *GitHubOIDCProvider) exchangeOIDCTokenForRegistry(ctx context.Context, oidcToken string) (string, error) {
	if o.registryURL == "" {
		return "", fmt.Errorf("registry URL is required for token exchange")
	}

	// Prepare the request body
	payload := map[string]string{
		"oidc_token": oidcToken,
	}

	jsonData, err := json.Marshal(payload)
	if err != nil {
		return "", fmt.Errorf("failed to marshal request: %w", err)
	}

	// Make the token exchange request
	exchangeURL := o.registryURL + "/v0/auth/github-oidc"
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, exchangeURL, bytes.NewBuffer(jsonData))
	if err != nil {
		return "", fmt.Errorf("failed to create request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "application/json")

	client := &http.Client{}
	resp, err := client.Do(req)
	if err != nil {
		return "", fmt.Errorf("failed to send request: %w", err)
	}
	defer resp.Body.Close()

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

	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("token exchange failed with status %d: %s", resp.StatusCode, body)
	}

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

	return tokenResp.RegistryToken, nil
}

// getOIDCTokenFromGitHub fetches the OIDC token from GitHub Actions endpoint.
func (o *GitHubOIDCProvider) getOIDCTokenFromGitHub(ctx context.Context, audience string) (string, error) {
	// Check for required environment variables
	requestToken := os.Getenv("ACTIONS_ID_TOKEN_REQUEST_TOKEN")
	if requestToken == "" {
		return "", fmt.Errorf("ACTIONS_ID_TOKEN_REQUEST_TOKEN environment variable not found - are you running in GitHub Actions with id-token: write permissions?")
	}

	requestURL := os.Getenv("ACTIONS_ID_TOKEN_REQUEST_URL")
	if requestURL == "" {
		return "", fmt.Errorf("ACTIONS_ID_TOKEN_REQUEST_URL environment variable not found - are you running in GitHub Actions with id-token: write permissions?")
	}

	// Build the full URL with audience parameter
	fullURL := requestURL + "&audience=" + url.QueryEscape(audience)

	// Create the request
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, fullURL, nil) //nolint:gosec // G704: URL is from GitHub Actions ACTIONS_ID_TOKEN_REQUEST_URL env var
	if err != nil {
		return "", fmt.Errorf("failed to create request: %w", err)
	}

	// Set the authorization header
	req.Header.Set("Authorization", "Bearer "+requestToken)
	req.Header.Set("Accept", "application/json")

	// Make the request
	client := &http.Client{}
	resp, err := client.Do(req) //nolint:gosec // G704: URL is from GitHub Actions env var
	if err != nil {
		return "", fmt.Errorf("failed to send request: %w", err)
	}
	defer resp.Body.Close()

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

	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("GitHub OIDC token request failed with status %d: %s", resp.StatusCode, body)
	}

	// Parse the response to extract the token value
	var tokenResp struct {
		Value string `json:"value"`
	}
	err = json.Unmarshal(body, &tokenResp)
	if err != nil {
		return "", fmt.Errorf("failed to unmarshal OIDC token response: %w", err)
	}

	if tokenResp.Value == "" {
		return "", fmt.Errorf("OIDC token value is empty in response")
	}

	return tokenResp.Value, nil
}

// audienceFromRegistryURL returns scheme + lowercased host for the given URL.
func audienceFromRegistryURL(registryURL string) (string, error) {
	registryURL = strings.TrimSpace(registryURL)
	if registryURL == "" {
		return "", fmt.Errorf("registry URL is empty")
	}
	u, err := url.Parse(registryURL)
	if err != nil {
		return "", fmt.Errorf("parse %q: %w", registryURL, err)
	}
	if u.Scheme == "" || u.Host == "" {
		return "", fmt.Errorf("registry URL must include scheme and host: %q", registryURL)
	}
	return u.Scheme + "://" + strings.ToLower(u.Host), nil
}