use std::{borrow::Cow, sync::Arc};

use axum::{Router, http::StatusCode, routing::post};
use bank_core::{ApiError, Name, NameOrUuid, make_schemas, transaction::Transaction};
use deadpool_postgres::GenericClient;
use garde::Validate;
use schemars::JsonSchema;
use serde::Deserialize;
use tokio_postgres::Statement;
use tracing::{error, instrument};
use uuid::Uuid;

use crate::model::{Accounts, Transactions, Users};

use super::{
    AppState, EState, Error, InteropState, Json, State,
    auth::Auth,
    socket::{SocketEvent, SocketMessage},
};

pub(super) fn router() -> Router<Arc<AppState>> {
    Router::new().route("/", post(make_payment))
}

make_schemas!((MakePayment); ());

#[derive(Debug, Validate, PartialEq)]
#[cfg_attr(feature = "schemas", derive(schemars::JsonSchema))]
pub struct AccountSelector {
    #[garde(dive)]
    pub user: NameOrUuid,
    #[garde(dive)]
    pub account: Option<Name>,
}

impl AccountSelector {
    #[instrument(skip(client))]
    pub async fn account_id(
        &self,
        client: &impl GenericClient,
    ) -> Result<Option<(Uuid, Uuid)>, tokio_postgres::Error> {
        let user_id = match &self.user {
            NameOrUuid::Id(uuid) => *uuid,
            NameOrUuid::Name(name) => match Users::info_by_name(client, &*name).await? {
                Some(info) => info.id,
                None => return Ok(None),
            },
        };
        let account_id = match self.account.as_ref() {
            Some(name) => match Accounts::get_for_user(client, user_id, &*name).await? {
                Some(info) => info.id,
                None => return Ok(None),
            },
            None => user_id,
        };
        Ok(Some((user_id, account_id)))
    }
}

#[doc(hidden)]
#[derive(Debug, Deserialize, Validate, PartialEq)]
#[cfg_attr(feature = "schemas", derive(schemars::JsonSchema))]
#[serde(untagged)]
pub enum UnvalidatedAccountSelector {
    Username(#[garde(dive)] Name),
    Object {
        #[garde(dive)]
        user: NameOrUuid,
        #[garde(dive)]
        account: Option<Name>,
    },
}

impl<'de> Deserialize<'de> for AccountSelector {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        Ok(
            match UnvalidatedAccountSelector::deserialize(deserializer)? {
                UnvalidatedAccountSelector::Username(name) => Self {
                    user: NameOrUuid::Name(name),
                    account: None,
                },
                UnvalidatedAccountSelector::Object { user, account } => Self { user, account },
            },
        )
    }
}

pub trait ValidateTransform: Sized {
    type Src: Validate;
    fn schema_name() -> Cow<'static, str>;
    fn schema_id() -> Cow<'static, str> {
        Cow::Borrowed(std::any::type_name::<Self>())
    }
    fn validate_transform_into(
        src: Self::Src,
        ctx: &<Self::Src as Validate>::Context,
        parent: &mut dyn FnMut() -> garde::Path,
        report: &mut garde::Report,
    ) -> Option<Self>;
}

#[derive(Debug, PartialEq)]
pub struct UnvalidatedTransform<Dest: ValidateTransform> {
    src: Dest::Src,
}

impl<'de, Dest> Deserialize<'de> for UnvalidatedTransform<Dest>
where
    Dest: ValidateTransform,
    Dest::Src: Deserialize<'de>,
{
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        Ok(UnvalidatedTransform {
            src: <Dest::Src as Deserialize<'de>>::deserialize(deserializer)?,
        })
    }
}

#[derive(Debug, PartialEq)]
pub enum AccountTarget {
    Selector(AccountSelector),
    Interop(String),
}

#[derive(Debug, PartialEq, Validate)]
#[cfg_attr(feature = "schemas", derive(schemars::JsonSchema))]
#[cfg_attr(feature = "schemas", serde(untagged))]
pub enum UnvalidatedAccountTarget {
    /// Interop user
    Interop(#[garde(pattern("^.{2,}@[a-z0-9]{2,4}$"))] String),
    Selector(#[garde(dive)] UnvalidatedAccountSelector),
}

impl<'de> Deserialize<'de> for UnvalidatedAccountTarget {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        #[derive(Deserialize)]
        #[serde(untagged)]
        enum AccountTargetHelper {
            Text(String),
            Selector(UnvalidatedAccountSelector),
        }
        Ok(match AccountTargetHelper::deserialize(deserializer)? {
            AccountTargetHelper::Text(text) => {
                // TODO: don't hardcode prefix
                if let Some(text) = text.strip_suffix("@thc") {
                    Self::Interop(text.into())
                } else {
                    Self::Selector(UnvalidatedAccountSelector::Username(Name(text)))
                }
            }
            AccountTargetHelper::Selector(selector) => Self::Selector(selector),
        })
    }
}

impl ValidateTransform for AccountTarget {
    type Src = UnvalidatedAccountTarget;

    fn schema_name() -> Cow<'static, str> {
        Cow::Borrowed("AccountTarget")
    }

    fn validate_transform_into(
        src: Self::Src,
        ctx: &<Self::Src as Validate>::Context,
        parent: &mut dyn FnMut() -> garde::Path,
        report: &mut garde::Report,
    ) -> Option<Self> {
        match src {
            UnvalidatedAccountTarget::Interop(user) => Some(AccountTarget::Interop(user)),
            UnvalidatedAccountTarget::Selector(selector) => {
                AccountSelector::validate_transform_into(selector, ctx, parent, report)
                    .map(Self::Selector)
            }
        }
    }
}

impl<Dest> schemars::JsonSchema for UnvalidatedTransform<Dest>
where
    Dest: ValidateTransform,
    Dest::Src: JsonSchema,
{
    fn schema_name() -> Cow<'static, str> {
        Dest::schema_name()
    }

    fn schema_id() -> Cow<'static, str> {
        Dest::schema_id()
    }

    fn json_schema(generator: &mut schemars::SchemaGenerator) -> schemars::Schema {
        <Dest::Src as schemars::JsonSchema>::json_schema(generator)
    }
    fn always_inline_schema() -> bool {
        <Dest::Src as schemars::JsonSchema>::always_inline_schema()
    }
}

impl<Dest: ValidateTransform> UnvalidatedTransform<Dest> {
    pub fn validate_transform_into(
        self,
        ctx: &<Dest::Src as Validate>::Context,
        parent: &mut dyn FnMut() -> garde::Path,
        report: &mut garde::Report,
    ) -> Option<Dest> {
        Dest::validate_transform_into(self.src, ctx, parent, report)
    }
    pub fn validate_with(
        self,
        ctx: &<Dest::Src as Validate>::Context,
    ) -> Result<Dest, garde::Report> {
        let mut report = garde::Report::new();
        let result =
            Dest::validate_transform_into(self.src, ctx, &mut garde::Path::empty, &mut report);
        match report.is_empty() {
            true => Ok(result.unwrap()),
            false => Err(report),
        }
    }
}

impl ValidateTransform for AccountSelector {
    type Src = UnvalidatedAccountSelector;

    fn schema_name() -> Cow<'static, str> {
        Cow::Borrowed("AccountSelector")
    }

    fn validate_transform_into(
        src: Self::Src,
        ctx: &<Self::Src as Validate>::Context,
        mut parent: &mut dyn FnMut() -> garde::Path,
        report: &mut garde::Report,
    ) -> Option<Self> {
        let count = report.iter().count();
        match src {
            UnvalidatedAccountSelector::Username(name) => {
                name.validate_into(ctx, parent, report);
                if count != report.iter().count() {
                    return None;
                }
                Some(AccountSelector {
                    user: NameOrUuid::Name(name),
                    account: None,
                })
            }
            UnvalidatedAccountSelector::Object { user, account } => {
                {
                    let mut path = garde::util::nested_path!(parent, "user");
                    user.validate_into(ctx, &mut path, report);
                }
                let mut path = garde::util::nested_path!(parent, "account");
                account.validate_into(ctx, &mut path, report);
                if count != report.iter().count() {
                    return None;
                }
                Some(AccountSelector { user, account })
            }
        }
    }
}

#[derive(Debug, Deserialize, PartialEq)]
#[cfg_attr(feature = "schemas", derive(schemars::JsonSchema))]
pub struct MakePayment {
    from: NameOrUuid,
    to: UnvalidatedTransform<AccountTarget>,
    amount: u64,
}
impl MakePayment {
    pub fn validate(self) -> Result<(NameOrUuid, AccountTarget, u64), garde::Report> {
        let mut report = garde::Report::new();
        self.from
            .validate_into(&(), &mut || garde::Path::new("from"), &mut report);
        let to = self
            .to
            .validate_transform_into(&(), &mut || garde::Path::new("to"), &mut report);
        if let Err(error) = garde::rules::range::apply(&self.amount, (Some(1), None)) {
            report.append(garde::Path::new("amount"), error);
        }
        if !report.is_empty() {
            return Err(report);
        }
        Ok((self.from, to.unwrap(), self.amount))
    }
}

const TARGET_NOT_FOUND: ApiError<'static> = ApiError::const_new(
    StatusCode::NOT_FOUND,
    "transaction.target.not_found",
    "Not Found",
);

pub async fn make_payment(
    EState(state): State,
    auth: Auth,
    Json(body): Json<MakePayment>,
) -> Result<Json<Transaction>, Error> {
    let (from, to, amount) = body.validate()?;
    let user_id = auth.user_id();

    let mut client = state.conn().await?;
    let mut client = client.transaction().await?;

    let Some(from) = (match from {
        NameOrUuid::Id(uuid) => Accounts::by_id(&client, uuid).await?,
        NameOrUuid::Name(name) => Accounts::get_for_user(&client, user_id, &*name).await?,
    }) else {
        return Err(ApiError::const_new(
            StatusCode::NOT_FOUND,
            "transaction.from.not_found",
            "Not Found",
        )
        .into());
    };
    let transaction = match to {
        AccountTarget::Interop(user) => {
            let Some(interop) = &state.interop else {
                return Err(TARGET_NOT_FOUND.into());
            };
            let builder = TransactionBuilder::new(&mut client, amount).await?;
            let transaction = builder.interop_pay(from.id, user.clone(), None).await?;
            if amount % 100 != 0 {
                todo!()
            }
            if let Err(err) =
                send_interop_payment(&interop, &from.name, &user, (amount / 100) as u32).await
            {
                return Err(match err {
                    InteropError::NotFound => TARGET_NOT_FOUND.into(),
                    InteropError::Http(err) => {
                        error!("{err}");
                        ApiError::INTERNAL_SERVER_ERROR.into()
                    }
                    InteropError::Other(response) => {
                        error!("{response:?}");
                        ApiError::INTERNAL_SERVER_ERROR.into()
                    }
                });
            }
            transaction
        }
        AccountTarget::Selector(selector) => {
            let Some((to_user, to)) = selector.account_id(&client).await? else {
                return Err(TARGET_NOT_FOUND.into());
            };
            if from.balance < amount {
                return Err(ApiError::const_new(
                    StatusCode::BAD_REQUEST,
                    "transaction.insufficient_funds",
                    "Insufficient funds",
                )
                .into());
            }
            let builder = TransactionBuilder::new(&mut client, amount).await?;
            let (transaction, notification) = builder.normal(from.id, to, None).await?;
            client.commit().await?;
            state.sockets.send(to_user, notification).await;
            transaction
        }
    };
    Ok(Json(transaction))
}

pub struct TransactionBuilder<'a, T> {
    client: &'a mut T,
    update_balance: Statement,
    amount: u64,
}

impl<'a, T: GenericClient> TransactionBuilder<'a, T> {
    pub async fn new(client: &'a mut T, amount: u64) -> Result<Self, tokio_postgres::Error> {
        let update_balance = client
            .prepare_cached("update accounts set balance = balance + $2 where id = $1")
            .await?;
        Ok(Self {
            client,
            update_balance,
            amount,
        })
    }

    async fn update_balance(
        &mut self,
        account: Uuid,
        is_to: bool,
    ) -> Result<(), tokio_postgres::Error> {
        let amount = if is_to {
            self.amount as i64
        } else {
            -(self.amount as i64)
        };
        self.client
            .execute(&self.update_balance, &[&account, &amount])
            .await?;
        Ok(())
    }

    pub async fn system(
        mut self,
        to: Uuid,
        message: Option<String>,
    ) -> Result<(Transaction, SocketMessage), tokio_postgres::Error> {
        self.update_balance(to, true).await?;
        let transaction =
            Transactions::create(self.client, None, Some(to), None, self.amount, message).await?;
        Ok((
            transaction,
            SocketMessage::Event(SocketEvent::PaymentReceived {
                from: None,
                to,
                amount: self.amount,
            }),
        ))
    }

    pub async fn normal(
        mut self,
        from: Uuid,
        to: Uuid,
        message: Option<String>,
    ) -> Result<(Transaction, SocketMessage), tokio_postgres::Error> {
        self.update_balance(from, false).await?;
        self.update_balance(to, true).await?;
        let transaction = Transactions::create(
            self.client,
            Some(from),
            Some(to),
            None,
            self.amount,
            message,
        )
        .await?;
        Ok((
            transaction,
            SocketMessage::Event(SocketEvent::PaymentReceived {
                from: Some(NameOrUuid::Id(from)),
                to,
                amount: self.amount,
            }),
        ))
    }

    pub async fn interop_pay(
        mut self,
        from: Uuid,
        name: String,
        message: Option<String>,
    ) -> Result<Transaction, tokio_postgres::Error> {
        self.update_balance(from, false).await?;
        let transaction = Transactions::create(
            self.client,
            Some(from),
            None,
            Some(name),
            self.amount,
            message,
        )
        .await?;
        Ok(transaction)
    }

    pub async fn interop_receive(
        mut self,
        to: Uuid,
        name: String,
        message: Option<String>,
    ) -> Result<(Transaction, SocketMessage), tokio_postgres::Error> {
        self.update_balance(to, true).await?;
        let transaction = Transactions::create(
            self.client,
            None,
            Some(to),
            Some(name.clone()),
            self.amount,
            message,
        )
        .await?;
        Ok((
            transaction,
            SocketMessage::Event(SocketEvent::PaymentReceived {
                from: Some(NameOrUuid::Name(Name(name))),
                to,
                amount: self.amount,
            }),
        ))
    }
}

enum InteropError {
    NotFound,
    Http(reqwest::Error),
    Other(reqwest::Response),
}

async fn send_interop_payment(
    interop: &InteropState,
    from: &str,
    to: &str,
    amount: u32,
) -> Result<(), InteropError> {
    let response = interop
        .client
        .post(interop.pay_url.clone())
        .json(&serde_json::json!({
            "from": from,
            "to": to,
            "amount": amount
        }))
        .send()
        .await
        .map_err(InteropError::Http)?;
    if response.status() == StatusCode::OK {
        return Ok(());
    }
    if response.status() == StatusCode::NOT_FOUND {
        return Err(InteropError::NotFound);
    }
    Err(InteropError::Other(response))
}

#[cfg(test)]
mod tests {
    use bank_core::Name;

    use crate::api::transactions::{
        AccountSelector, AccountTarget, NameOrUuid, UnvalidatedAccountSelector,
        UnvalidatedAccountTarget, UnvalidatedTransform,
    };

    use super::MakePayment;

    #[test]
    fn payment_body() {
        let uuid = uuid::uuid!("6fd8b7ab-7278-45b5-9916-2b09b4224a38");
        let payment = serde_json::from_str::<MakePayment>(
            r#"{"from":"personal", "to": { "user": "6fd8b7ab-7278-45b5-9916-2b09b4224a38" }, "amount": 100}"#,
        )
        .unwrap();
        assert_eq!(
            MakePayment {
                from: NameOrUuid::Name(Name("personal".into())),
                to: UnvalidatedTransform {
                    src: UnvalidatedAccountTarget::Selector(UnvalidatedAccountSelector::Object {
                        user: NameOrUuid::Id(uuid),
                        account: None
                    })
                },
                amount: 100
            },
            payment
        );
        assert_eq!(
            payment.validate().unwrap(),
            (
                NameOrUuid::Name(Name("personal".into())),
                AccountTarget::Selector(AccountSelector {
                    user: NameOrUuid::Id(uuid),
                    account: None
                }),
                100
            )
        );
        let payment = serde_json::from_str::<MakePayment>(
            r#"{"from":"personal", "to": { "user": "test", "account": "abc" }, "amount": 100}"#,
        )
        .unwrap();
        assert_eq!(
            MakePayment {
                from: NameOrUuid::Name(Name("personal".into())),
                to: UnvalidatedTransform {
                    src: UnvalidatedAccountTarget::Selector(UnvalidatedAccountSelector::Object {
                        user: NameOrUuid::Name(Name("test".into())),
                        account: Some(Name("abc".into()))
                    })
                },
                amount: 100
            },
            payment
        );
        assert_eq!(
            payment.validate().unwrap(),
            (
                NameOrUuid::Name(Name("personal".into())),
                AccountTarget::Selector(AccountSelector {
                    user: NameOrUuid::Name(Name("test".into())),
                    account: Some(Name("abc".into()))
                }),
                100
            )
        );
    }
}