// Copyright 2023 Greptime Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::collections::HashMap;
use std::sync::Arc;

use futures::stream;
use once_cell::sync::Lazy;
use pgwire::api::results::{DataRowEncoder, FieldFormat, FieldInfo, QueryResponse, Response, Tag};
use pgwire::api::Type;
use pgwire::error::PgWireResult;
use pgwire::messages::data::DataRow;
use regex::Regex;
use session::context::QueryContextRef;

fn build_string_data_rows(
    schema: Arc<Vec<FieldInfo>>,
    rows: Vec<Vec<String>>,
) -> Vec<PgWireResult<DataRow>> {
    rows.iter()
        .map(|row| {
            let mut encoder = DataRowEncoder::new(schema.clone());
            for value in row {
                encoder.encode_field(&Some(value))?;
            }
            encoder.finish()
        })
        .collect()
}

static VAR_VALUES: Lazy<HashMap<&str, &str>> = Lazy::new(|| {
    HashMap::from([
        ("default_transaction_isolation", "read committed"),
        ("transaction isolation level", "read committed"),
        ("standard_conforming_strings", "on"),
        ("client_encoding", "UTF8"),
    ])
});

static SHOW_PATTERN: Lazy<Regex> = Lazy::new(|| Regex::new("(?i)^SHOW (.*?);?$").unwrap());
static SET_TRANSACTION_PATTERN: Lazy<Regex> =
    Lazy::new(|| Regex::new("(?i)^SET TRANSACTION (.*?);?$").unwrap());
static TRANSACTION_PATTERN: Lazy<Regex> =
    Lazy::new(|| Regex::new("(?i)^(BEGIN|ROLLBACK|COMMIT);?").unwrap());

/// Test if given query statement matches the patterns
pub(crate) fn matches(query: &str) -> bool {
    TRANSACTION_PATTERN.captures(query).is_some()
        || SHOW_PATTERN.captures(query).is_some()
        || SET_TRANSACTION_PATTERN.is_match(query)
}

/// Process unsupported SQL and return fixed result as a compatibility solution
pub(crate) fn process<'a>(query: &str, _query_ctx: QueryContextRef) -> Option<Vec<Response<'a>>> {
    // Transaction directives:
    if let Some(tx) = TRANSACTION_PATTERN.captures(query) {
        let tx_tag = &tx[1];
        Some(vec![Response::Execution(Tag::new(&tx_tag.to_uppercase()))])
    } else if let Some(show_var) = SHOW_PATTERN.captures(query) {
        let show_var = show_var[1].to_lowercase();
        if let Some(value) = VAR_VALUES.get(&show_var.as_ref()) {
            let f1 = FieldInfo::new(
                show_var.clone(),
                None,
                None,
                Type::VARCHAR,
                FieldFormat::Text,
            );
            let schema = Arc::new(vec![f1]);
            let data = stream::iter(build_string_data_rows(
                schema.clone(),
                vec![vec![value.to_string()]],
            ));

            Some(vec![Response::Query(QueryResponse::new(schema, data))])
        } else {
            None
        }
    } else if SET_TRANSACTION_PATTERN.is_match(query) {
        Some(vec![Response::Execution(Tag::new("SET"))])
    } else {
        None
    }
}

#[cfg(test)]
mod test {
    use session::context::{QueryContext, QueryContextRef};

    use super::*;

    fn assert_tag(q: &str, t: &str, query_context: QueryContextRef) {
        if let Response::Execution(tag) = process(q, query_context.clone())
            .unwrap_or_else(|| panic!("fail to match {}", q))
            .remove(0)
        {
            assert_eq!(Tag::new(t), tag);
        } else {
            panic!("Invalid response");
        }
    }

    fn get_data<'a>(q: &str, query_context: QueryContextRef) -> QueryResponse<'a> {
        if let Response::Query(resp) = process(q, query_context.clone())
            .unwrap_or_else(|| panic!("fail to match {}", q))
            .remove(0)
        {
            resp
        } else {
            panic!("Invalid response");
        }
    }

    #[test]
    fn test_process() {
        let query_context = QueryContext::arc();

        assert_tag("BEGIN", "BEGIN", query_context.clone());
        assert_tag("BEGIN;", "BEGIN", query_context.clone());
        assert_tag("begin;", "BEGIN", query_context.clone());
        assert_tag("ROLLBACK", "ROLLBACK", query_context.clone());
        assert_tag("ROLLBACK;", "ROLLBACK", query_context.clone());
        assert_tag("rollback;", "ROLLBACK", query_context.clone());
        assert_tag("COMMIT", "COMMIT", query_context.clone());
        assert_tag("COMMIT;", "COMMIT", query_context.clone());
        assert_tag("commit;", "COMMIT", query_context.clone());
        assert_tag(
            "SET TRANSACTION ISOLATION LEVEL READ COMMITTED",
            "SET",
            query_context.clone(),
        );
        assert_tag(
            "SET TRANSACTION ISOLATION LEVEL READ COMMITTED;",
            "SET",
            query_context.clone(),
        );
        assert_tag(
            "SET transaction isolation level READ COMMITTED;",
            "SET",
            query_context.clone(),
        );

        let resp = get_data("SHOW transaction isolation level", query_context.clone());
        assert_eq!(1, resp.row_schema().len());
        let resp = get_data("show client_encoding;", query_context.clone());
        assert_eq!(1, resp.row_schema().len());
        let resp = get_data("show standard_conforming_strings;", query_context.clone());
        assert_eq!(1, resp.row_schema().len());
        let resp = get_data("show default_transaction_isolation", query_context.clone());
        assert_eq!(1, resp.row_schema().len());

        assert!(process("SELECT 1", query_context.clone()).is_none());
        assert!(process("SHOW TABLES ", query_context.clone()).is_none());
        assert!(process("SET TIME_ZONE=utc ", query_context.clone()).is_none());
    }
}