//! Guest checkout: purchase items without an MNW account.
//!
//! These endpoints are public (no auth required) and CORS-enabled for use from
//! embedded widgets on external sites.

use axum::{
    extract::{Path, State},
    http::{header, HeaderValue, StatusCode},
    response::{IntoResponse, Redirect, Response},
    Json,
};
use serde::{Deserialize, Serialize};
use uuid::Uuid;

use crate::{
    db::{self, Cents, ItemId},
    error::{AppError, Result, ResultExt},
    AppState,
};

/// Request body for creating a guest checkout session.
#[derive(Debug, Deserialize)]
pub(super) struct GuestCheckoutRequest {
    /// Buyer-chosen amount in cents (only for PWYW items).
    pub amount_cents: Option<i32>,
    /// Optional promo/discount code.
    pub promo_code: Option<String>,
}

/// Response from creating a guest checkout session.
#[derive(Serialize)]
struct CheckoutResponse {
    checkout_url: String,
}

/// POST /api/checkout/guest/{item_id}
///
/// Creates a Stripe Checkout Session for a guest purchase (no account required).
/// Returns the Stripe checkout URL. The embed or item page opens this in a popup
/// or redirects to it.
#[tracing::instrument(skip_all, name = "guest_checkout::create")]
pub(super) async fn create_guest_checkout(
    State(state): State<AppState>,
    Path(item_id): Path<ItemId>,
    Json(body): Json<GuestCheckoutRequest>,
) -> Result<Response> {
    // Fetch item
    let item = db::items::get_item_by_id(&state.db, item_id)
        .await?
        .ok_or(AppError::NotFound)?;

    if !item.is_public || !item.listed {
        return Err(AppError::NotFound);
    }

    // Fetch seller via project
    let project = db::projects::get_project_by_id(&state.db, item.project_id)
        .await?
        .ok_or(AppError::NotFound)?;
    let seller = db::users::get_user_by_id(&state.db, project.user_id)
        .await?
        .ok_or(AppError::NotFound)?;

    if seller.is_suspended() || seller.is_deactivated() || seller.is_creator_paused() {
        return Err(AppError::NotFound);
    }

    let seller_id = seller.id;

    // Determine price — use the same pricing model as the authenticated checkout
    let pricing = crate::pricing::for_item(&item);
    let mut final_price_cents = if item.pwyw_enabled {
        let buyer_amount = body.amount_cents
            .unwrap_or(item.price_cents);
        pricing.validate_amount(buyer_amount)
            .map_err(AppError::BadRequest)?;
        buyer_amount
    } else {
        item.price_cents
    };

    // Free items: skip Stripe entirely, redirect to the free claim endpoint
    if final_price_cents == 0 {
        return Err(AppError::BadRequest(
            "Free items use /api/checkout/guest-free/{item_id} instead".to_string(),
        ));
    }

    // Resolve and validate promo code with the same checks as authenticated checkout
    let mut promo_code_id = None;
    if let Some(code_str) = body.promo_code.as_deref().map(str::trim).filter(|s| !s.is_empty()) {
        if item.pwyw_enabled {
            return Err(AppError::BadRequest("Promo codes cannot be applied to pay-what-you-want items".to_string()));
        }
        // Guests have no account, so no platform-wide Fan+ credit fallback (None).
        if let Some(validated) =
            db::promo_codes::lookup_and_validate_promo(&state.db, seller_id, None, code_str).await?
        {
            use db::promo_codes::{PromoApplication, PromoIneligible};
            match db::promo_codes::apply_promo_to_item(&validated, item_id, item.project_id, item.price_cents)? {
                PromoApplication::Apply(price) => final_price_cents = price,
                PromoApplication::Ineligible(PromoIneligible::ScopeMismatch) => {
                    return Err(AppError::BadRequest("This promo code is not valid for this item".to_string()));
                }
                PromoApplication::Ineligible(PromoIneligible::BelowMinPrice) => {
                    return Err(AppError::BadRequest("This item does not meet the minimum price for this code".to_string()));
                }
            }
            promo_code_id = Some(validated.id());
        }
    }

    // If a promo code brought the price to zero, redirect to the free claim flow
    if final_price_cents == 0 {
        return Err(AppError::BadRequest(
            "Free items use /api/checkout/guest-free/{item_id} instead".to_string(),
        ));
    }

    // Reject sub-Stripe-minimum charges (a Discount promo can land a fixed item
    // at 1–49¢) using the shared `check_min_charge` the Stripe session call
    // enforces internally. Gating here, before the promo reservation, means a
    // rejection doesn't burn a use of the code.
    crate::payments::check_min_charge(final_price_cents as i64)?;

    // Verify seller has Stripe configured
    let stripe_account_id = seller.stripe_account_id.as_ref()
        .ok_or_else(|| AppError::BadRequest("Creator hasn't set up payments yet".to_string()))?;
    if !seller.stripe_charges_enabled {
        return Err(AppError::BadRequest("Creator's payment account is not ready".to_string()));
    }

    let stripe = state.stripe.as_ref()
        .ok_or_else(|| AppError::BadRequest("Stripe is not configured".to_string()))?;

    // Reserve the promo code BEFORE creating the Stripe session or pending row,
    // mirroring the authenticated item-checkout path. The old order (reserve
    // last) meant a swallowed 23505 returned a live checkout URL with NO pending
    // row for the webhook to complete — the buyer paid and the sale vanished —
    // and a failed reservation could orphan the pending row's promo. Every
    // failure path below now releases this reservation.
    if let Some(pc_id) = promo_code_id {
        let reserved = db::promo_codes::try_increment_use_count(&state.db, pc_id)
            .await
            .context("reserve promo code use at guest checkout")?;
        if !reserved {
            return Err(AppError::BadRequest("This promo code has reached its usage limit".to_string()));
        }
    }

    // Release the reservation above on any failure path below (no-op if no promo).
    let release_promo = || async {
        if let Some(pc_id) = promo_code_id {
            db::promo_codes::release_use_count(&state.db, pc_id).await.ok();
        }
    };

    // Build URLs
    let success_url = format!("{}/stripe/success?session_id={{CHECKOUT_SESSION_ID}}", state.config.host_url);
    let cancel_url = format!("{}/i/{}", state.config.host_url, item_id);

    // Create guest checkout session
    let checkout_params = crate::payments::GuestCheckoutParams {
        connected_account_id: stripe_account_id,
        item_title: &item.title,
        amount_cents: Cents::new(final_price_cents as i64),
        seller_id,
        item_id,
        success_url: &success_url,
        cancel_url: &cancel_url,
        promo_code_id,
        enable_stripe_tax: seller.stripe_tax_enabled,
    };
    let result = match stripe.create_guest_checkout_session(&checkout_params).await {
        Ok(r) => r,
        Err(e) => {
            release_promo().await;
            return Err(e).with_context(|| format!("create guest Stripe checkout for item {item_id}"));
        }
    };

    // Create pending transaction (buyer_id = None for guest). On a unique
    // violation (a checkout for this item is already in progress) we must NOT
    // return the live Stripe URL: there'd be no pending row for the webhook to
    // complete, so the buyer would be charged and the sale silently lost.
    // Release the promo and return an error (guests have no purchase page to
    // redirect to, unlike the authenticated path).
    match db::transactions::create_transaction(
        &state.db,
        &db::transactions::CreateTransactionParams {
            buyer_id: None,
            seller_id,
            item_id: Some(item_id),
            amount_cents: final_price_cents.into(),
            platform_fee_cents: Cents::ZERO,
            stripe_checkout_session_id: &result.id,
            item_title: &item.title,
            seller_username: &seller.username,
            share_contact: false,
            project_id: Some(item.project_id),
            promo_code_id,
            guest_email: None, // Set by webhook when Stripe provides it
        },
    ).await {
        Ok(_) => {}
        Err(AppError::Database(sqlx::Error::Database(ref db_err)))
            if db_err.code().as_deref() == Some("23505") =>
        {
            release_promo().await;
            tracing::info!(item_id = %item_id, "duplicate pending guest checkout blocked");
            return Err(AppError::BadRequest(
                "A checkout for this item is already in progress. Please complete or cancel it before starting another.".to_string(),
            ));
        }
        Err(e) => {
            release_promo().await;
            return Err(e).context("create pending guest transaction");
        }
    }

    let checkout_url = result.url
        .ok_or_else(|| AppError::BadRequest("No checkout URL returned".to_string()))?;

    let mut response = Json(CheckoutResponse { checkout_url }).into_response();

    // CORS headers for cross-origin embed usage
    let headers = response.headers_mut();
    headers.insert(header::ACCESS_CONTROL_ALLOW_ORIGIN, HeaderValue::from_static("*"));
    headers.insert(header::ACCESS_CONTROL_ALLOW_METHODS, HeaderValue::from_static("POST, OPTIONS"));
    headers.insert(header::ACCESS_CONTROL_ALLOW_HEADERS, HeaderValue::from_static("content-type"));

    Ok(response)
}

/// OPTIONS /api/checkout/guest/{item_id}: CORS preflight
pub(super) async fn guest_checkout_preflight() -> Response {
    let mut response = StatusCode::NO_CONTENT.into_response();
    let headers = response.headers_mut();
    headers.insert(header::ACCESS_CONTROL_ALLOW_ORIGIN, HeaderValue::from_static("*"));
    headers.insert(header::ACCESS_CONTROL_ALLOW_METHODS, HeaderValue::from_static("POST, OPTIONS"));
    headers.insert(header::ACCESS_CONTROL_ALLOW_HEADERS, HeaderValue::from_static("content-type"));
    headers.insert(header::ACCESS_CONTROL_MAX_AGE, HeaderValue::from_static("86400"));
    response
}

/// GET /download/{download_token}
///
/// Download a purchased item using a token from the guest purchase email.
/// No authentication required; the token is the proof of purchase.
#[tracing::instrument(skip_all, name = "guest_checkout::download")]
pub(super) async fn guest_download(
    State(state): State<AppState>,
    Path(token): Path<db::DownloadToken>,
) -> Result<Response> {
    let tx = db::transactions::get_transaction_by_download_token(&state.db, token)
        .await?
        .ok_or(AppError::NotFound)?;

    let item_id = tx.item_id.ok_or(AppError::NotFound)?;
    let item = db::items::get_item_by_id(&state.db, item_id)
        .await?
        .ok_or(AppError::NotFound)?;

    // Get the S3 key for the content
    let s3_key = item.audio_s3_key.as_deref()
        .or(item.video_s3_key.as_deref())
        .ok_or_else(|| AppError::NotFound)?;

    let s3 = state.s3.as_ref()
        .ok_or_else(|| AppError::ServiceUnavailable("File storage is not configured".to_string()))?;

    let download_url = s3.presign_download(s3_key, Some(3600)).await?;

    Ok(Redirect::temporary(&download_url).into_response())
}

/// POST /api/purchases/claim
///
/// Attach a guest purchase to the authenticated user's account using a claim token.
#[tracing::instrument(skip_all, name = "guest_checkout::claim")]
pub(super) async fn claim_purchase(
    State(state): State<AppState>,
    crate::auth::AuthUser(user): crate::auth::AuthUser,
    Json(body): Json<ClaimRequest>,
) -> Result<Response> {
    user.check_not_sandbox()?;
    let tx = db::transactions::claim_guest_purchase(&state.db, body.claim_token, user.id)
        .await?
        .ok_or_else(|| AppError::BadRequest(
            "Invalid or already-claimed token".to_string()
        ))?;

    tracing::info!(
        user_id = %user.id,
        transaction_id = %tx.id,
        "guest purchase claimed"
    );

    Ok(StatusCode::OK.into_response())
}

#[derive(Debug, Deserialize)]
pub(super) struct ClaimRequest {
    pub claim_token: db::ClaimToken,
}

/// Request body for free guest claim.
#[derive(Debug, Deserialize)]
pub(super) struct FreeGuestClaimRequest {
    pub email: String,
}

/// POST /api/checkout/guest-free/{item_id}
///
/// Claim a free item as a guest. Collects email, creates a completed transaction,
/// and sends download + claim links via email. No Stripe involved.
#[tracing::instrument(skip_all, name = "guest_checkout::claim_free")]
pub(super) async fn claim_free_guest(
    State(state): State<AppState>,
    Path(item_id): Path<ItemId>,
    Json(body): Json<FreeGuestClaimRequest>,
) -> Result<Response> {
    let email = db::Email::new(&body.email)
        .map_err(|_| AppError::BadRequest("Invalid email address".to_string()))?;

    let item = db::items::get_item_by_id(&state.db, item_id)
        .await?
        .ok_or(AppError::NotFound)?;

    if !item.is_public || !item.listed || item.price_cents != 0 {
        return Err(AppError::NotFound);
    }

    // Fetch seller
    let project = db::projects::get_project_by_id(&state.db, item.project_id)
        .await?
        .ok_or(AppError::NotFound)?;
    let seller = db::users::get_user_by_id(&state.db, project.user_id)
        .await?
        .ok_or(AppError::NotFound)?;

    if seller.is_suspended() || seller.is_deactivated() || seller.is_creator_paused() {
        return Err(AppError::NotFound);
    }

    // Check if email matches an existing user — auto-attach
    let existing_user_id = db::users::get_verified_user_id_by_email(&state.db, &email).await?;

    let claim_token = if existing_user_id.is_some() { None } else { Some(db::ClaimToken::new()) };
    let download_token = db::DownloadToken::new();
    let checkout_session_id = format!("free-guest-{}-{}", email, item_id);

    // Create completed transaction
    let result = db::transactions::create_free_guest_transaction(
        &state.db,
        existing_user_id,
        seller.id,
        item_id,
        &checkout_session_id,
        &item.title,
        &seller.username,
        email.as_str(),
        claim_token,
        download_token,
    )
    .await;

    match result {
        Ok(0) => {
            // Already claimed — still send the email with download link
        }
        Ok(_) => {
            // Increment sales count
            let _ = db::items::increment_sales_count(&state.db, item_id).await;
        }
        Err(e) => {
            // Unique violation (already in library for existing user)
            if let sqlx::Error::Database(ref db_err) = e {
                if db_err.code().as_deref() == Some("23505") {
                    // Already claimed, continue to send email
                } else {
                    return Err(AppError::Database(e));
                }
            } else {
                return Err(AppError::Database(e));
            }
        }
    }

    // Send download email
    let host_url = &state.config.host_url;
    let download_url = format!("{}/download/{}", host_url, download_token);
    let claim_url = format!("{}/claim?token={}", host_url, claim_token.unwrap_or(db::ClaimToken::from_uuid(Uuid::nil())));

    if existing_user_id.is_none() {
        let email_client = state.email.clone();
        let email_addr = email.clone().into_inner();
        let item_title = item.title.clone();
        let dl_url = download_url.clone();
        let cl_url = claim_url.clone();
        state.bg.spawn("free guest claim email", async move {
            if let Err(e) = email_client.send_guest_purchase_confirmation(
                &email_addr, &item_title, "Free", &dl_url, &cl_url,
            ).await {
                tracing::error!(error = ?e, "failed to send free guest claim email");
            }
        });
    }

    let mut response = Json(serde_json::json!({
        "status": "claimed",
        "download_url": download_url,
    })).into_response();

    // CORS headers
    let headers = response.headers_mut();
    headers.insert(header::ACCESS_CONTROL_ALLOW_ORIGIN, HeaderValue::from_static("*"));

    Ok(response)
}