/*
 * Licensed to Elasticsearch B.V. under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch B.V. licenses this file to you 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.
 */

/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 *
 * Modifications Copyright OpenSearch Contributors. See
 * GitHub history for details.
 */

use super::Step;
use crate::step::Expr;
use anyhow::anyhow;
use inflector::Inflector;
use proc_macro2::{Span, TokenStream};
use quote::{quote, ToTokens, TokenStreamExt};
use serde_yaml::Value;
use syn::parse_quote;

pub struct Transformation {
    #[allow(dead_code)]
    raw: String,
    function: String,
    exprs: Vec<Expr>,
}

impl Transformation {
    pub fn transform(&self) -> syn::Expr {
        let func = syn::Ident::new(&self.function, Span::call_site());
        let exprs = self.exprs.iter().map(|e| e.expression());

        parse_quote!(#func ( #(json #exprs .as_str().unwrap()),* ))
    }
}

impl From<&str> for Transformation {
    fn from(t: &str) -> Self {
        let raw = t.to_string();
        let mut function = None;
        let mut exprs = Vec::new();
        let mut value = String::new();
        for ch in t.chars() {
            match ch {
                '#' => {
                    continue;
                }
                '(' => {
                    let name = format!("transform::{}", value.as_str().to_snake_case());
                    function = Some(name);
                    value = String::new();
                }
                ',' | ')' => {
                    let expr = value.trim();
                    exprs.push(Expr::new(expr));
                    value = String::new();
                }
                _ => {
                    value.push(ch);
                }
            }
        }

        Self {
            raw,
            function: function.unwrap(),
            exprs,
        }
    }
}

pub struct TransformAndSet {
    ident: syn::Ident,
    transformation: Transformation,
}

impl From<TransformAndSet> for Step {
    fn from(transform_and_set: TransformAndSet) -> Self {
        Step::TransformAndSet(transform_and_set)
    }
}

impl TransformAndSet {
    pub fn try_parse(yaml: &Value) -> anyhow::Result<TransformAndSet> {
        let hash = yaml
            .as_mapping()
            .ok_or_else(|| anyhow!("expected hash but found {:?}", yaml))?;

        let (k, v) = hash.iter().next().unwrap();
        let ident = k
            .as_str()
            .ok_or_else(|| anyhow!("expected string key but found {:?}", k))?;

        let transformation = v
            .as_str()
            .ok_or_else(|| anyhow!("expected string value but found {:?}", v))?;

        Ok(TransformAndSet {
            ident: syn::Ident::new(ident, Span::call_site()),
            transformation: transformation.into(),
        })
    }
}

impl ToTokens for TransformAndSet {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        let ident = &self.ident;
        let transform = &self.transformation.transform();
        tokens.append_all(quote! {
            let #ident = {
                let transform = #transform;
                json!(transform)
            };
        });
    }
}