package github

import (
	"context"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/github/github-mcp-server/pkg/scopes"
)

type apiHost struct {
	baseRESTURL *url.URL
	graphqlURL  *url.URL
	uploadURL   *url.URL
	rawURL      *url.URL
}

func newDotcomHost() (apiHost, error) {
	baseRestURL, err := url.Parse("https://api.github.com/")
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse dotcom REST URL: %w", err)
	}

	gqlURL, err := url.Parse("https://api.github.com/graphql")
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse dotcom GraphQL URL: %w", err)
	}

	uploadURL, err := url.Parse("https://uploads.github.com")
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse dotcom Upload URL: %w", err)
	}

	rawURL, err := url.Parse("https://raw.githubusercontent.com/")
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse dotcom Raw URL: %w", err)
	}

	return apiHost{
		baseRESTURL: baseRestURL,
		graphqlURL:  gqlURL,
		uploadURL:   uploadURL,
		rawURL:      rawURL,
	}, nil
}

func newGHECHost(hostname string) (apiHost, error) {
	u, err := url.Parse(hostname)
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse GHEC URL: %w", err)
	}

	// Unsecured GHEC would be an error
	if u.Scheme == "http" {
		return apiHost{}, fmt.Errorf("GHEC URL must be HTTPS")
	}

	restURL, err := url.Parse(fmt.Sprintf("https://api.%s/", u.Hostname()))
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse GHEC REST URL: %w", err)
	}

	gqlURL, err := url.Parse(fmt.Sprintf("https://api.%s/graphql", u.Hostname()))
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse GHEC GraphQL URL: %w", err)
	}

	uploadURL, err := url.Parse(fmt.Sprintf("https://uploads.%s", u.Hostname()))
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse GHEC Upload URL: %w", err)
	}

	rawURL, err := url.Parse(fmt.Sprintf("https://raw.%s/", u.Hostname()))
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse GHEC Raw URL: %w", err)
	}

	return apiHost{
		baseRESTURL: restURL,
		graphqlURL:  gqlURL,
		uploadURL:   uploadURL,
		rawURL:      rawURL,
	}, nil
}

func newGHESHost(hostname string) (apiHost, error) {
	u, err := url.Parse(hostname)
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse GHES URL: %w", err)
	}

	restURL, err := url.Parse(fmt.Sprintf("%s://%s/api/v3/", u.Scheme, u.Hostname()))
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse GHES REST URL: %w", err)
	}

	gqlURL, err := url.Parse(fmt.Sprintf("%s://%s/api/graphql", u.Scheme, u.Hostname()))
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse GHES GraphQL URL: %w", err)
	}

	// Check if subdomain isolation is enabled
	// See https://docs.github.com/en/enterprise-server@3.17/admin/configuring-settings/hardening-security-for-your-enterprise/enabling-subdomain-isolation#about-subdomain-isolation
	hasSubdomainIsolation := checkSubdomainIsolation(u.Scheme, u.Hostname())

	var uploadURL *url.URL
	if hasSubdomainIsolation {
		// With subdomain isolation: https://uploads.hostname/
		uploadURL, err = url.Parse(fmt.Sprintf("%s://uploads.%s/", u.Scheme, u.Hostname()))
	} else {
		// Without subdomain isolation: https://hostname/api/uploads/
		uploadURL, err = url.Parse(fmt.Sprintf("%s://%s/api/uploads/", u.Scheme, u.Hostname()))
	}
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse GHES Upload URL: %w", err)
	}

	var rawURL *url.URL
	if hasSubdomainIsolation {
		// With subdomain isolation: https://raw.hostname/
		rawURL, err = url.Parse(fmt.Sprintf("%s://raw.%s/", u.Scheme, u.Hostname()))
	} else {
		// Without subdomain isolation: https://hostname/raw/
		rawURL, err = url.Parse(fmt.Sprintf("%s://%s/raw/", u.Scheme, u.Hostname()))
	}
	if err != nil {
		return apiHost{}, fmt.Errorf("failed to parse GHES Raw URL: %w", err)
	}

	return apiHost{
		baseRESTURL: restURL,
		graphqlURL:  gqlURL,
		uploadURL:   uploadURL,
		rawURL:      rawURL,
	}, nil
}

// checkSubdomainIsolation detects if GitHub Enterprise Server has subdomain isolation enabled
// by attempting to ping the raw.<host>/_ping endpoint on the subdomain. The raw subdomain must always exist for subdomain isolation.
func checkSubdomainIsolation(scheme, hostname string) bool {
	subdomainURL := fmt.Sprintf("%s://raw.%s/_ping", scheme, hostname)

	client := &http.Client{
		Timeout: 5 * time.Second,
		// Don't follow redirects - we just want to check if the endpoint exists
		//nolint:revive // parameters are required by http.Client.CheckRedirect signature
		CheckRedirect: func(req *http.Request, via []*http.Request) error {
			return http.ErrUseLastResponse
		},
	}

	resp, err := client.Get(subdomainURL)
	if err != nil {
		return false
	}
	defer resp.Body.Close()

	return resp.StatusCode == http.StatusOK
}

// ParseAPIHost parses the given host string and returns the appropriate apiHost configuration.
func ParseAPIHost(s string) (apiHost, error) {
	if s == "" {
		return newDotcomHost()
	}

	u, err := url.Parse(s)
	if err != nil {
		return apiHost{}, fmt.Errorf("could not parse host as URL: %s", s)
	}

	if u.Scheme == "" {
		return apiHost{}, fmt.Errorf("host must have a scheme (http or https): %s", s)
	}

	if strings.HasSuffix(u.Hostname(), "github.com") {
		return newDotcomHost()
	}

	if strings.HasSuffix(u.Hostname(), "ghe.com") {
		return newGHECHost(s)
	}

	return newGHESHost(s)
}

// FetchTokenScopesForHost fetches the OAuth scopes for a token from the GitHub API.
// It constructs the appropriate API host URL based on the configured host.
func FetchTokenScopesForHost(ctx context.Context, token, host string) ([]string, error) {
	apiHost, err := ParseAPIHost(host)
	if err != nil {
		return nil, fmt.Errorf("failed to parse API host: %w", err)
	}

	fetcher := scopes.NewFetcher(scopes.FetcherOptions{
		APIHost: apiHost.baseRESTURL.String(),
	})

	return fetcher.FetchTokenScopes(ctx, token)
}