package service

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"time"
)

const (
	codexOAuthClientID     = "app_EMoamEEZ73f0CkXaXp7hrann"
	codexOAuthAuthorizeURL = "https://auth.openai.com/oauth/authorize"
	codexOAuthTokenURL     = "https://auth.openai.com/oauth/token"
	codexOAuthRedirectURI  = "http://localhost:1455/auth/callback"
	codexOAuthScope        = "openid profile email offline_access"
	codexJWTClaimPath      = "https://api.openai.com/auth"
	defaultHTTPTimeout     = 20 * time.Second
)

type CodexOAuthTokenResult struct {
	AccessToken  string
	RefreshToken string
	ExpiresAt    time.Time
}

type CodexOAuthAuthorizationFlow struct {
	State        string
	Verifier     string
	Challenge    string
	AuthorizeURL string
}

func RefreshCodexOAuthToken(ctx context.Context, refreshToken string) (*CodexOAuthTokenResult, error) {
	client := &http.Client{Timeout: defaultHTTPTimeout}
	return refreshCodexOAuthToken(ctx, client, codexOAuthTokenURL, codexOAuthClientID, refreshToken)
}

func ExchangeCodexAuthorizationCode(ctx context.Context, code string, verifier string) (*CodexOAuthTokenResult, error) {
	client := &http.Client{Timeout: defaultHTTPTimeout}
	return exchangeCodexAuthorizationCode(ctx, client, codexOAuthTokenURL, codexOAuthClientID, code, verifier, codexOAuthRedirectURI)
}

func CreateCodexOAuthAuthorizationFlow() (*CodexOAuthAuthorizationFlow, error) {
	state, err := createStateHex(16)
	if err != nil {
		return nil, err
	}
	verifier, challenge, err := generatePKCEPair()
	if err != nil {
		return nil, err
	}
	u, err := buildCodexAuthorizeURL(state, challenge)
	if err != nil {
		return nil, err
	}
	return &CodexOAuthAuthorizationFlow{
		State:        state,
		Verifier:     verifier,
		Challenge:    challenge,
		AuthorizeURL: u,
	}, nil
}

func refreshCodexOAuthToken(
	ctx context.Context,
	client *http.Client,
	tokenURL string,
	clientID string,
	refreshToken string,
) (*CodexOAuthTokenResult, error) {
	rt := strings.TrimSpace(refreshToken)
	if rt == "" {
		return nil, errors.New("empty refresh_token")
	}

	form := url.Values{}
	form.Set("grant_type", "refresh_token")
	form.Set("refresh_token", rt)
	form.Set("client_id", clientID)

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, tokenURL, strings.NewReader(form.Encode()))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	req.Header.Set("Accept", "application/json")

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

	var payload struct {
		AccessToken  string `json:"access_token"`
		RefreshToken string `json:"refresh_token"`
		ExpiresIn    int    `json:"expires_in"`
	}

	if err := json.NewDecoder(resp.Body).Decode(&payload); err != nil {
		return nil, err
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, fmt.Errorf("codex oauth refresh failed: status=%d", resp.StatusCode)
	}

	if strings.TrimSpace(payload.AccessToken) == "" || strings.TrimSpace(payload.RefreshToken) == "" || payload.ExpiresIn <= 0 {
		return nil, errors.New("codex oauth refresh response missing fields")
	}

	return &CodexOAuthTokenResult{
		AccessToken:  strings.TrimSpace(payload.AccessToken),
		RefreshToken: strings.TrimSpace(payload.RefreshToken),
		ExpiresAt:    time.Now().Add(time.Duration(payload.ExpiresIn) * time.Second),
	}, nil
}

func exchangeCodexAuthorizationCode(
	ctx context.Context,
	client *http.Client,
	tokenURL string,
	clientID string,
	code string,
	verifier string,
	redirectURI string,
) (*CodexOAuthTokenResult, error) {
	c := strings.TrimSpace(code)
	v := strings.TrimSpace(verifier)
	if c == "" {
		return nil, errors.New("empty authorization code")
	}
	if v == "" {
		return nil, errors.New("empty code_verifier")
	}

	form := url.Values{}
	form.Set("grant_type", "authorization_code")
	form.Set("client_id", clientID)
	form.Set("code", c)
	form.Set("code_verifier", v)
	form.Set("redirect_uri", redirectURI)

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, tokenURL, strings.NewReader(form.Encode()))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	req.Header.Set("Accept", "application/json")

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

	var payload struct {
		AccessToken  string `json:"access_token"`
		RefreshToken string `json:"refresh_token"`
		ExpiresIn    int    `json:"expires_in"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&payload); err != nil {
		return nil, err
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, fmt.Errorf("codex oauth code exchange failed: status=%d", resp.StatusCode)
	}
	if strings.TrimSpace(payload.AccessToken) == "" || strings.TrimSpace(payload.RefreshToken) == "" || payload.ExpiresIn <= 0 {
		return nil, errors.New("codex oauth token response missing fields")
	}
	return &CodexOAuthTokenResult{
		AccessToken:  strings.TrimSpace(payload.AccessToken),
		RefreshToken: strings.TrimSpace(payload.RefreshToken),
		ExpiresAt:    time.Now().Add(time.Duration(payload.ExpiresIn) * time.Second),
	}, nil
}

func buildCodexAuthorizeURL(state string, challenge string) (string, error) {
	u, err := url.Parse(codexOAuthAuthorizeURL)
	if err != nil {
		return "", err
	}
	q := u.Query()
	q.Set("response_type", "code")
	q.Set("client_id", codexOAuthClientID)
	q.Set("redirect_uri", codexOAuthRedirectURI)
	q.Set("scope", codexOAuthScope)
	q.Set("code_challenge", challenge)
	q.Set("code_challenge_method", "S256")
	q.Set("state", state)
	q.Set("id_token_add_organizations", "true")
	q.Set("codex_cli_simplified_flow", "true")
	q.Set("originator", "codex_cli_rs")
	u.RawQuery = q.Encode()
	return u.String(), nil
}

func createStateHex(nBytes int) (string, error) {
	if nBytes <= 0 {
		return "", errors.New("invalid state bytes length")
	}
	b := make([]byte, nBytes)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return fmt.Sprintf("%x", b), nil
}

func generatePKCEPair() (verifier string, challenge string, err error) {
	b := make([]byte, 32)
	if _, err := rand.Read(b); err != nil {
		return "", "", err
	}
	verifier = base64.RawURLEncoding.EncodeToString(b)
	sum := sha256.Sum256([]byte(verifier))
	challenge = base64.RawURLEncoding.EncodeToString(sum[:])
	return verifier, challenge, nil
}

func ExtractCodexAccountIDFromJWT(token string) (string, bool) {
	claims, ok := decodeJWTClaims(token)
	if !ok {
		return "", false
	}
	raw, ok := claims[codexJWTClaimPath]
	if !ok {
		return "", false
	}
	obj, ok := raw.(map[string]any)
	if !ok {
		return "", false
	}
	v, ok := obj["chatgpt_account_id"]
	if !ok {
		return "", false
	}
	s, ok := v.(string)
	if !ok {
		return "", false
	}
	s = strings.TrimSpace(s)
	if s == "" {
		return "", false
	}
	return s, true
}

func ExtractEmailFromJWT(token string) (string, bool) {
	claims, ok := decodeJWTClaims(token)
	if !ok {
		return "", false
	}
	v, ok := claims["email"]
	if !ok {
		return "", false
	}
	s, ok := v.(string)
	if !ok {
		return "", false
	}
	s = strings.TrimSpace(s)
	if s == "" {
		return "", false
	}
	return s, true
}

func decodeJWTClaims(token string) (map[string]any, bool) {
	parts := strings.Split(token, ".")
	if len(parts) != 3 {
		return nil, false
	}
	payloadRaw, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return nil, false
	}
	var claims map[string]any
	if err := json.Unmarshal(payloadRaw, &claims); err != nil {
		return nil, false
	}
	return claims, true
}