use crate::application::ports::DictSource;
use crate::core::entities::{DictEntry, DictEntryId};
use serde::Deserialize;
use std::fs::File;
use std::io::BufReader;
use std::path::Path;

// The "Wire Format".
// It exists ONLY here to map external JSON names to internal Entity names.
#[derive(Deserialize)]
struct JsonEntry {
    id: u32,
    word: String, // "word" in JSON, "text" in Entity
                  // If JSON has extra fields we don't care about, Serde ignores them.
}

pub struct JsonFileDictSource {
    // Helper iterator from Serde
    iter:
        serde_json::StreamDeserializer<'static, serde_json::de::IoRead<BufReader<File>>, JsonEntry>,
}

impl JsonFileDictSource {
    pub fn new<P: AsRef<Path>>(path: P) -> anyhow::Result<Self> {
        let file = File::open(path)?;
        let reader = BufReader::new(file);
        let iter = serde_json::Deserializer::from_reader(reader).into_iter::<JsonEntry>();
        Ok(Self { iter })
    }
}

impl DictSource for JsonFileDictSource {
    fn next_entry(&mut self) -> Option<Result<DictEntry, anyhow::Error>> {
        self.iter.next().map(|res| {
            match res {
                Ok(json) => {
                    // MAPPING HAPPENS HERE.
                    // This is type-safe. If DictEntry::new signature changes, this breaks.
                    Ok(DictEntry::new(json.id as DictEntryId, json.word))
                }
                Err(e) => Err(anyhow::Error::new(e)),
            }
        })
    }
}