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use anyhow::{anyhow, Result};
use pancake_engine_ssi::{ClientCommitDecision, Txn, DB};
use pancake_types::types::{Deser, PrimaryKey, Ser, SubValue, SubValueSpec, Value};
use std::sync::Arc;
use wit_bindgen_host_wasmtime_rust::wasmtime::{
    self,
    component::{Component, Linker},
    Config, Engine, Store,
};

wit_bindgen_host_wasmtime_rust::generate!({
    import: "./assets/db.wit",
    default: "./assets/udf.wit",
    name: "udf",
});
use db::{Pk, Pkpv, Pv, Sv, SvSpec};

pub struct WasmEngine {
    db: Arc<DB>,
    engine: Engine,
    linker: Linker<WasmState>,
}

impl WasmEngine {
    pub fn new(db: Arc<DB>) -> Result<Self> {
        let mut config = Config::new();
        config.wasm_component_model(true);
        let engine = Engine::new(&config)?;

        let mut linker = Linker::new(&engine);
        db::add_to_linker(&mut linker, |state: &mut WasmState| &mut state.db_provider)?;

        Ok(Self { db, engine, linker })
    }

    pub async fn serve(&self, compo_bytes: &[u8], retry_limit: usize) -> Result<String> {
        let state = WasmState {
            db_provider: DbProvider { txn_ptr: 0 },
        };
        let mut store = Store::new(&self.engine, state);

        let compo = Component::new(&self.engine, compo_bytes)?;
        let (udf, _inst) = Udf::instantiate(&mut store, &compo, &self.linker)?;

        let client_res = Txn::run(&self.db, retry_limit, |txn| {
            store.data_mut().db_provider = DbProvider {
                txn_ptr: txn as *mut _ as usize,
            };

            let res_commit_dec = udf.run_txn(&mut store)?;
            match res_commit_dec {
                Err(client_str) => Err(anyhow!(client_str)),
                Ok(CommitDecision::Abort(client_str)) => {
                    Ok(ClientCommitDecision::Abort(client_str))
                }
                Ok(CommitDecision::Commit(client_str)) => {
                    Ok(ClientCommitDecision::Commit(client_str))
                }
            }
        })
        .await;
        client_res
    }
}

struct WasmState {
    db_provider: DbProvider,
}

struct DbProvider {
    /// This field stands in for `*mut Txn<'one_try>`.
    /// We could use `SendPtr`.
    txn_ptr: usize,
}
impl DbProvider {
    /// 'db > 'txn > 'one_try
    /// `'one_try` refers to the lifetime of one (re)try run of the transaction.
    fn txn<'a, 'b, 'one_try>(&'a self) -> &'b mut Txn<'one_try> {
        let txn_ptr = self.txn_ptr as *mut Txn<'one_try>;
        unsafe { &mut *txn_ptr }
    }
}
impl db::Db for DbProvider {
    fn get_pk_one(&mut self, pk: Pk) -> anyhow::Result<Result<Option<Pkpv>, String>> {
        let pk = PrimaryKey::deser_solo(&pk.bytes)?;

        let opt_entry = self.txn().get_pk_one(&pk)?;
        let opt_res_pkpv = opt_entry.map(|(pk, pv)| -> Result<Pkpv> {
            let pk = pk.ser_solo()?;
            let pv = pv.ser_solo()?;
            let pk = Pk { bytes: pk };
            let pv = Pv { bytes: pv };
            Ok(Pkpv { pk, pv })
        });
        let res_opt_pkpv = opt_res_pkpv.transpose().map_err(|e| e.to_string());
        Ok(res_opt_pkpv)
    }

    fn get_pk_range(
        &mut self,
        pk_lo: Option<Pk>,
        pk_hi: Option<Pk>,
    ) -> anyhow::Result<Result<Vec<Pkpv>, String>> {
        let pk_lo = pk_lo
            .map(|pk| PrimaryKey::deser_solo(&pk.bytes))
            .transpose()?;
        let pk_hi = pk_hi
            .map(|pk| PrimaryKey::deser_solo(&pk.bytes))
            .transpose()?;

        let mut ret = vec![];
        for entry in self.txn().get_pk_range(pk_lo.as_ref(), pk_hi.as_ref()) {
            let (pk, pv) = entry.try_borrow()?;
            let pk = pk.ser_solo()?;
            let pv = pv.ser_solo()?;
            let pk = Pk { bytes: pk };
            let pv = Pv { bytes: pv };
            ret.push(Pkpv { pk, pv });
        }
        Ok(Ok(ret))
    }

    fn get_sv_range(
        &mut self,
        sv_spec: SvSpec,
        sv_lo: Option<Sv>,
        sv_hi: Option<Sv>,
    ) -> anyhow::Result<Result<Vec<Pkpv>, String>> {
        let sv_spec = SubValueSpec::deser_solo(&sv_spec.bytes)?;
        let sv_lo = sv_lo
            .map(|sv| SubValue::deser_solo(&sv.bytes))
            .transpose()?;
        let sv_hi = sv_hi
            .map(|sv| SubValue::deser_solo(&sv.bytes))
            .transpose()?;

        let mut ret = vec![];
        for entry in self
            .txn()
            .get_sv_range(&sv_spec, sv_lo.as_ref(), sv_hi.as_ref())?
        {
            let (pk, pv) = entry.try_borrow()?;
            let pk = pk.ser_solo()?;
            let pv = pv.ser_solo()?;
            let pk = Pk { bytes: pk };
            let pv = Pv { bytes: pv };
            ret.push(Pkpv { pk, pv });
        }
        Ok(Ok(ret))
    }

    fn put(&mut self, pk: Pk, opt_pv: Option<Pv>) -> anyhow::Result<Result<(), String>> {
        let pk = PrimaryKey::deser_solo(&pk.bytes)?;
        let opt_pv = opt_pv.map(|pv| Value::deser_solo(&pv.bytes)).transpose()?;

        let pk = Arc::new(pk);
        let opt_pv = opt_pv.map(Arc::new);

        self.txn().put(&pk, &opt_pv)?;

        Ok(Ok(()))
    }
}