package gitea

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"html"
	"io"
	"net/http"
	"net/url"
	"regexp"
	"strconv"
	"strings"
	"time"
)

var ErrTokenNotConfigured = errors.New("gitea API token is not configured")

var (
	signedUserIDMeta    = regexp.MustCompile(`(?is)<meta\s+name=["']hop-signed-user-id["']\s+content=["']([0-9]+)["']\s*/?>`)
	signedUserLoginMeta = regexp.MustCompile(`(?is)<meta\s+name=["']hop-signed-user-login["']\s+content=(?:"([^"]*)"|'([^']*)')\s*/?>`)
)

type Repository struct {
	ID            int64  `json:"id"`
	Owner         Owner  `json:"owner"`
	Name          string `json:"name"`
	FullName      string `json:"full_name"`
	CloneURL      string `json:"clone_url"`
	DefaultBranch string `json:"default_branch"`
}

type Owner struct {
	Login    string `json:"login"`
	Username string `json:"username"`
}

type User struct {
	ID       int64  `json:"id"`
	Login    string `json:"login"`
	Username string `json:"username"`
}

func (u User) LoginName() string {
	if u.Login != "" {
		return u.Login
	}
	return u.Username
}

func (r Repository) OwnerName() string {
	if r.Owner.Login != "" {
		return r.Owner.Login
	}
	return r.Owner.Username
}

type Client struct {
	baseURL *url.URL
	token   string
	http    *http.Client
}

func NewClient(baseURL, token string) (*Client, error) {
	u, err := url.Parse(strings.TrimRight(baseURL, "/"))
	if err != nil || u.Scheme == "" || u.Host == "" {
		return nil, fmt.Errorf("invalid GITEA_BASE_URL %q", baseURL)
	}
	return &Client{baseURL: u, token: token, http: &http.Client{Timeout: 10 * time.Second}}, nil
}

func (c *Client) Repository(ctx context.Context, owner, name string) (Repository, error) {
	if c.token == "" {
		return Repository{}, ErrTokenNotConfigured
	}
	u := c.baseURL.JoinPath("api", "v1", "repos", owner, name)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return Repository{}, err
	}
	req.Header.Set("Authorization", "token "+c.token)
	req.Header.Set("Accept", "application/json")

	resp, err := c.http.Do(req)
	if err != nil {
		return Repository{}, fmt.Errorf("request repository: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return Repository{}, fmt.Errorf("gitea repository lookup returned %s", resp.Status)
	}

	var repo Repository
	if err := json.NewDecoder(resp.Body).Decode(&repo); err != nil {
		return Repository{}, fmt.Errorf("decode repository: %w", err)
	}
	if repo.ID <= 0 || repo.OwnerName() == "" || repo.Name == "" {
		return Repository{}, errors.New("gitea returned an incomplete repository")
	}
	return repo, nil
}

func (c *Client) User(ctx context.Context, login string) (User, error) {
	if c.token == "" {
		return User{}, ErrTokenNotConfigured
	}
	u := c.baseURL.JoinPath("api", "v1", "users", login)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return User{}, err
	}
	req.Header.Set("Authorization", "token "+c.token)
	req.Header.Set("Accept", "application/json")

	resp, err := c.http.Do(req)
	if err != nil {
		return User{}, fmt.Errorf("request user: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return User{}, fmt.Errorf("gitea user lookup returned %s", resp.Status)
	}
	var user User
	if err := json.NewDecoder(resp.Body).Decode(&user); err != nil {
		return User{}, fmt.Errorf("decode user: %w", err)
	}
	if user.ID <= 0 || user.LoginName() == "" {
		return User{}, errors.New("gitea returned an incomplete user")
	}
	return user, nil
}

func (c *Client) AuthenticatedUser(ctx context.Context, cookie string) (User, bool, error) {
	if strings.TrimSpace(cookie) == "" {
		return User{}, false, nil
	}
	// Gitea's API user endpoint requires an API token and intentionally rejects
	// browser sessions. The protected profile settings page includes Hop's custom
	// server-rendered user identity metadata for the active Gitea session.
	u := c.baseURL.JoinPath("user", "settings")
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return User{}, false, err
	}
	req.Header.Set("Cookie", cookie)
	req.Header.Set("Accept", "text/html")

	resp, err := c.doWithoutRedirect(req)
	if err != nil {
		return User{}, false, fmt.Errorf("load authenticated user: %w", err)
	}
	defer resp.Body.Close()
	switch resp.StatusCode {
	case http.StatusFound, http.StatusSeeOther, http.StatusTemporaryRedirect, http.StatusPermanentRedirect,
		http.StatusUnauthorized, http.StatusForbidden:
		return User{}, false, nil
	case http.StatusOK:
		// Continue below.
	default:
		return User{}, false, fmt.Errorf("gitea authenticated user lookup returned %s", resp.Status)
	}
	body, err := io.ReadAll(io.LimitReader(resp.Body, 2<<20))
	if err != nil {
		return User{}, false, fmt.Errorf("read authenticated user settings: %w", err)
	}
	idMatch := signedUserIDMeta.FindSubmatch(body)
	loginMatch := signedUserLoginMeta.FindSubmatch(body)
	if len(idMatch) != 2 || len(loginMatch) != 3 {
		return User{}, false, errors.New("gitea settings page did not identify the signed-in user")
	}
	id, err := strconv.ParseInt(string(idMatch[1]), 10, 64)
	if err != nil || id <= 0 {
		return User{}, false, errors.New("gitea settings page returned an invalid user ID")
	}
	login := string(loginMatch[1])
	if login == "" {
		login = string(loginMatch[2])
	}
	login = strings.TrimSpace(html.UnescapeString(login))
	if login == "" {
		return User{}, false, errors.New("gitea settings page returned an empty username")
	}
	return User{ID: id, Login: login}, true, nil
}

// ViewerCanReadRepository checks a browser's existing Gitea session against
// the repository web route. Gitea API routes require API tokens and do not
// recognize browser sessions.
func (c *Client) ViewerCanReadRepository(ctx context.Context, cookie, owner, name string) (bool, error) {
	if strings.TrimSpace(cookie) == "" {
		return false, nil
	}
	u := c.baseURL.JoinPath(owner, name)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return false, err
	}
	req.Header.Set("Cookie", cookie)
	req.Header.Set("Accept", "text/html")

	resp, err := c.doWithoutRedirect(req)
	if err != nil {
		return false, fmt.Errorf("check viewer repository access: %w", err)
	}
	defer resp.Body.Close()
	switch resp.StatusCode {
	case http.StatusOK:
		return true, nil
	case http.StatusFound, http.StatusSeeOther, http.StatusTemporaryRedirect, http.StatusPermanentRedirect,
		http.StatusUnauthorized, http.StatusForbidden, http.StatusNotFound:
		return false, nil
	default:
		return false, fmt.Errorf("gitea viewer repository check returned %s", resp.Status)
	}
}

func (c *Client) doWithoutRedirect(req *http.Request) (*http.Response, error) {
	client := *c.http
	client.CheckRedirect = func(*http.Request, []*http.Request) error {
		return http.ErrUseLastResponse
	}
	return client.Do(req)
}