/// OAuth 2.0 Service — Google & GitHub
///
/// Implements the standard Authorization Code flow:
///   1. `auth_url()` — build the redirect URL the browser goes to
///   2. `exchange_code()` — swap the code for an access token
///   3. `fetch_profile()` — get the user's email/name from the provider API
///   4. `find_or_create_merchant()` — upsert into `oauth_accounts`, auto-create
///      a merchant row if this is a brand-new user
///
/// No external OAuth crate needed — plain `reqwest` + `serde_json`.
use crate::core::session;
use crate::domain::error::{AppError, AppResult};
use crate::infrastructure::db::DbPool;
use rand::Rng;
use serde::{Deserialize, Serialize};
use uuid::Uuid;

// ─── Provider Configuration ───────────────────────────────────────────────────

#[derive(Clone)]
pub struct OAuthConfig {
    pub google_client_id: String,
    pub google_client_secret: String,
    pub github_client_id: String,
    pub github_client_secret: String,
    /// Base URL of this API server (used to build callback URLs)
    pub redirect_base: String,
    /// Frontend URL (used to redirect the user after successful auth)
    pub frontend_url: String,
}

impl OAuthConfig {
    pub fn from_env() -> Self {
        Self {
            google_client_id: std::env::var("GOOGLE_CLIENT_ID").unwrap_or_default(),
            google_client_secret: std::env::var("GOOGLE_CLIENT_SECRET").unwrap_or_default(),
            github_client_id: std::env::var("GITHUB_CLIENT_ID").unwrap_or_default(),
            github_client_secret: std::env::var("GITHUB_CLIENT_SECRET").unwrap_or_default(),
            redirect_base: std::env::var("OAUTH_REDIRECT_BASE")
                .unwrap_or_else(|_| "http://localhost:3000".to_string()),
            frontend_url: std::env::var("FRONTEND_URL")
                .unwrap_or_else(|_| "http://localhost:5173".to_string()),
        }
    }

    pub fn google_redirect_uri(&self) -> String {
        format!("{}/v1/auth/oauth/google/callback", self.redirect_base)
    }

    pub fn github_redirect_uri(&self) -> String {
        format!("{}/v1/auth/oauth/github/callback", self.redirect_base)
    }
}

// ─── Normalised User Profile (provider-agnostic) ─────────────────────────────

#[derive(Debug)]
pub struct OAuthProfile {
    pub provider: &'static str, // "google" | "github"
    pub provider_user_id: String,
    pub email: String,
    pub display_name: Option<String>,
    pub avatar_url: Option<String>,
}

// ─── Token Exchange Response (shared shape) ───────────────────────────────────

#[derive(Deserialize)]
struct TokenResponse {
    access_token: String,
}

// ─── Google Raw API Types ─────────────────────────────────────────────────────

#[derive(Deserialize)]
struct GoogleUserInfo {
    sub: String, // unique Google user ID
    email: String,
    name: Option<String>,
    picture: Option<String>,
}

// ─── GitHub Raw API Types ─────────────────────────────────────────────────────

#[derive(Deserialize)]
struct GithubUser {
    id: u64,
    login: String,
    name: Option<String>,
    avatar_url: Option<String>,
    email: Option<String>,
}

#[derive(Deserialize)]
struct GithubEmail {
    email: String,
    primary: bool,
    verified: bool,
}

// ─── State Nonce ─────────────────────────────────────────────────────────────

/// Generates a short cryptographically-random state string to prevent CSRF
/// on the OAuth callback. In production this should be stored in a signed
/// cookie or server-side cache; here we generate it and embed it in the URL
/// for stateless verification.
pub fn generate_state() -> String {
    let mut rng = rand::thread_rng();
    (0..32)
        .map(|_| rng.sample(rand::distributions::Alphanumeric) as char)
        .collect()
}

// ─── Google ───────────────────────────────────────────────────────────────────

/// Build the Google OAuth authorization URL that the browser redirects to.
pub fn google_auth_url(config: &OAuthConfig, state: &str) -> String {
    let params = [
        ("client_id", config.google_client_id.as_str()),
        ("redirect_uri", &config.google_redirect_uri()),
        ("response_type", "code"),
        ("scope", "openid email profile"),
        ("state", state),
        ("access_type", "online"),
        ("prompt", "select_account"),
    ];

    let query = params
        .iter()
        .map(|(k, v)| format!("{}={}", k, urlencoding::encode(v)))
        .collect::<Vec<_>>()
        .join("&");

    format!("https://accounts.google.com/o/oauth2/v2/auth?{}", query)
}

/// Exchange a Google authorization code for a user profile.
pub async fn exchange_google_code(config: &OAuthConfig, code: &str) -> AppResult<OAuthProfile> {
    let client = reqwest::Client::new();

    // 1. Exchange code → access token
    let token_res: TokenResponse = client
        .post("https://oauth2.googleapis.com/token")
        .form(&[
            ("code", code),
            ("client_id", &config.google_client_id),
            ("client_secret", &config.google_client_secret),
            ("redirect_uri", &config.google_redirect_uri()),
            ("grant_type", "authorization_code"),
        ])
        .send()
        .await
        .map_err(|e| AppError::Internal(format!("Google token exchange failed: {}", e)))?
        .json::<serde_json::Value>()
        .await
        .map_err(|e| AppError::Internal(format!("Google token parse failed: {}", e)))
        .and_then(|v| {
            serde_json::from_value::<TokenResponse>(v.clone()).map_err(|_| {
                let err = v
                    .get("error_description")
                    .and_then(|e| e.as_str())
                    .unwrap_or("unknown error");
                AppError::Auth(format!("Google OAuth error: {}", err))
            })
        })?;

    // 2. Fetch user profile
    let user: GoogleUserInfo = client
        .get("https://www.googleapis.com/oauth2/v3/userinfo")
        .bearer_auth(&token_res.access_token)
        .send()
        .await
        .map_err(|e| AppError::Internal(format!("Google userinfo fetch failed: {}", e)))?
        .json()
        .await
        .map_err(|e| AppError::Internal(format!("Google userinfo parse failed: {}", e)))?;

    Ok(OAuthProfile {
        provider: "google",
        provider_user_id: user.sub,
        email: user.email,
        display_name: user.name,
        avatar_url: user.picture,
    })
}

// ─── GitHub ───────────────────────────────────────────────────────────────────

/// Build the GitHub OAuth authorization URL.
pub fn github_auth_url(config: &OAuthConfig, state: &str) -> String {
    let params = [
        ("client_id", config.github_client_id.as_str()),
        ("redirect_uri", &config.github_redirect_uri()),
        ("scope", "user:email read:user"),
        ("state", state),
    ];

    let query = params
        .iter()
        .map(|(k, v)| format!("{}={}", k, urlencoding::encode(v)))
        .collect::<Vec<_>>()
        .join("&");

    format!("https://github.com/login/oauth/authorize?{}", query)
}

/// Exchange a GitHub authorization code for a user profile.
pub async fn exchange_github_code(config: &OAuthConfig, code: &str) -> AppResult<OAuthProfile> {
    let client = reqwest::Client::new();

    // 1. Exchange code → access token (GitHub returns form-encoded)
    let token_body = client
        .post("https://github.com/login/oauth/access_token")
        .header("Accept", "application/json")
        .form(&[
            ("code", code),
            ("client_id", &config.github_client_id),
            ("client_secret", &config.github_client_secret),
            ("redirect_uri", &config.github_redirect_uri()),
        ])
        .send()
        .await
        .map_err(|e| AppError::Internal(format!("GitHub token exchange failed: {}", e)))?
        .json::<serde_json::Value>()
        .await
        .map_err(|e| AppError::Internal(format!("GitHub token parse failed: {}", e)))?;

    let access_token = token_body
        .get("access_token")
        .and_then(|v| v.as_str())
        .ok_or_else(|| {
            let err = token_body
                .get("error_description")
                .and_then(|v| v.as_str())
                .unwrap_or("access_token missing");
            AppError::Auth(format!("GitHub OAuth error: {}", err))
        })?
        .to_string();

    // 2. Fetch user profile
    let user: GithubUser = client
        .get("https://api.github.com/user")
        .bearer_auth(&access_token)
        .header("User-Agent", "Rtix-OAuth/1.0")
        .send()
        .await
        .map_err(|e| AppError::Internal(format!("GitHub user fetch failed: {}", e)))?
        .json()
        .await
        .map_err(|e| AppError::Internal(format!("GitHub user parse failed: {}", e)))?;

    // 3. Fetch primary verified email (may not be in the user object if private)
    let email = if let Some(e) = user.email.filter(|e| !e.is_empty()) {
        e
    } else {
        let emails: Vec<GithubEmail> = client
            .get("https://api.github.com/user/emails")
            .bearer_auth(&access_token)
            .header("User-Agent", "Rtix-OAuth/1.0")
            .send()
            .await
            .map_err(|e| AppError::Internal(format!("GitHub emails fetch failed: {}", e)))?
            .json()
            .await
            .map_err(|e| AppError::Internal(format!("GitHub emails parse failed: {}", e)))?;

        emails
            .into_iter()
            .find(|e| e.primary && e.verified)
            .map(|e| e.email)
            .ok_or_else(|| AppError::Auth(
                "GitHub account has no verified primary email. Please add one in GitHub settings.".to_string()
            ))?
    };

    Ok(OAuthProfile {
        provider: "github",
        provider_user_id: user.id.to_string(),
        email,
        display_name: user.name.or(Some(user.login)),
        avatar_url: user.avatar_url,
    })
}

// ─── Find or Create Merchant ──────────────────────────────────────────────────

/// OAuth result returned to the route handler after successful authentication.
#[derive(Serialize)]
pub struct OAuthResult {
    pub merchant_id: String,
    pub brand_name: String,
    pub slug: String,
    pub role: String,
    pub jwt_token: String,
    pub is_new_user: bool,
}

/// Core OAuth business logic: given a verified `OAuthProfile`, either:
///  - Find the existing `oauth_accounts` row → load merchant → issue JWT, or
///  - Find merchant by email → link OAuth account → issue JWT, or
///  - Create a brand-new merchant from OAuth profile → issue JWT
pub async fn find_or_create_merchant(
    pool: &DbPool,
    profile: OAuthProfile,
    jwt_secret: &[u8],
) -> AppResult<OAuthResult> {
    use sqlx::Row;

    // ── Step 1: Check if this OAuth identity already exists ────────────────
    let existing_link = sqlx::query(
        "SELECT merchant_id FROM oauth_accounts WHERE provider = $1 AND provider_user_id = $2",
    )
    .bind(profile.provider)
    .bind(&profile.provider_user_id)
    .fetch_optional(pool)
    .await
    .map_err(AppError::Database)?;

    let (merchant_id, is_new_user) = if let Some(row) = existing_link {
        // Known OAuth user — just load merchant_id
        (row.get::<String, _>("merchant_id"), false)
    } else {
        // ── Step 2: Check if a merchant with this email already exists ─────
        let existing_merchant = sqlx::query("SELECT merchant_id FROM merchants WHERE email = $1")
            .bind(&profile.email)
            .fetch_optional(pool)
            .await
            .map_err(AppError::Database)?;

        let mid = if let Some(row) = existing_merchant {
            // Existing email-password account — link the OAuth provider to it
            row.get::<String, _>("merchant_id")
        } else {
            // ── Step 3: Brand-new user — create merchant ───────────────────
            let new_id = Uuid::new_v4().to_string();
            let display = profile.display_name.as_deref().unwrap_or("My Store");
            let brand_name = display.to_string();

            // Build a URL-safe slug from display name
            let base_slug = display
                .to_lowercase()
                .split_whitespace()
                .collect::<Vec<_>>()
                .join("-")
                .chars()
                .filter(|c| c.is_alphanumeric() || *c == '-')
                .collect::<String>();

            // Collision-safe slug
            let mut final_slug = base_slug.clone();
            let mut attempts = 0u8;
            loop {
                let taken: Option<String> =
                    sqlx::query_scalar("SELECT merchant_id FROM merchants WHERE slug = $1")
                        .bind(&final_slug)
                        .fetch_optional(pool)
                        .await
                        .map_err(AppError::Database)?;

                if taken.is_none() {
                    break;
                }

                attempts += 1;
                if attempts > 5 {
                    return Err(AppError::Internal("Could not generate unique slug".into()));
                }
                final_slug = format!("{}-{}", base_slug, &Uuid::new_v4().to_string()[..4]);
            }

            sqlx::query(
                r#"INSERT INTO merchants
                   (merchant_id, email, password_hash, brand_name, slug,
                    session_version, delivery_rate_per_km, delivery_base_fee,
                    base_pincode, auto_settle_threshold, trust_score,
                    verification_level, max_order_value_inr, plan, role,
                    logistics_config)
                   VALUES ($1,$2,'oauth_no_password',$3,$4,
                           1,10.0,20.0,'560001',0.5,100.0,
                           'UNVERIFIED',10000.0,'FREE','MERCHANT',
                           '{"complexity_bias":1.0,"weight_coefficient":0.02,"distance_coefficient":1.0}')"#,
            )
            .bind(&new_id)
            .bind(&profile.email)
            .bind(&brand_name)
            .bind(&final_slug)
            .execute(pool)
            .await
            .map_err(AppError::Database)?;

            new_id
        };

        // ── Step 4: Link the OAuth account ────────────────────────────────
        sqlx::query(
            r#"INSERT INTO oauth_accounts
               (id, merchant_id, provider, provider_user_id, email, display_name, avatar_url)
               VALUES ($1,$2,$3,$4,$5,$6,$7)
               ON CONFLICT (provider, provider_user_id) DO NOTHING"#,
        )
        .bind(Uuid::new_v4().to_string())
        .bind(&mid)
        .bind(profile.provider)
        .bind(&profile.provider_user_id)
        .bind(&profile.email)
        .bind(&profile.display_name)
        .bind(&profile.avatar_url)
        .execute(pool)
        .await
        .map_err(AppError::Database)?;

        (mid, existing_merchant_was_none(&profile.email, pool).await)
    };

    // ── Step 5: Load merchant & issue JWT ─────────────────────────────────
    let merchant = sqlx::query(
        "SELECT merchant_id, brand_name, slug, role, session_version FROM merchants WHERE merchant_id = $1"
    )
    .bind(&merchant_id)
    .fetch_one(pool)
    .await
    .map_err(AppError::Database)?;

    let brand_name: String = merchant.get("brand_name");
    let slug: String = merchant.get("slug");
    let role: String = merchant.get("role");
    let session_version: i64 = merchant.get("session_version");

    // Issue a JWT identical in structure to the password-auth JWT
    let claims = crate::interfaces::http::routes::auth::Claims {
        sub: merchant_id.clone(),
        email: profile.email,
        brand_name: brand_name.clone(),
        slug: slug.clone(),
        role: Some(role.clone()),
        version: session_version,
        exp: session::access_token_expiry(),
    };

    let jwt_token = jsonwebtoken::encode(
        &jsonwebtoken::Header::default(),
        &claims,
        &jsonwebtoken::EncodingKey::from_secret(jwt_secret),
    )
    .map_err(|e| AppError::Internal(format!("JWT encoding failed: {}", e)))?;

    Ok(OAuthResult {
        merchant_id,
        brand_name,
        slug,
        role,
        jwt_token,
        is_new_user,
    })
}

// Helper: was the email absent from merchants before we created it?
// We call this after insert so we read from the row we just made.
async fn existing_merchant_was_none(email: &str, pool: &DbPool) -> bool {
    sqlx::query_scalar::<_, i64>("SELECT COUNT(*) FROM oauth_accounts WHERE email = $1")
        .bind(email)
        .fetch_one(pool)
        .await
        .unwrap_or(0)
        <= 1 // If only 1 row exists, this is a brand-new user
}