// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

//! A dead simple runtime variable db, backed by a single JSON file.

use anyhow::Context;
use fs_err::File;
use serde::Deserialize;
use serde::Serialize;
use serde_json::value::RawValue;
use std::borrow::Cow;
use std::collections::BTreeMap;
use std::io::Seek;
use std::io::Write;
use std::path::Path;

/// On-disk format for the var db
#[derive(Serialize, Deserialize)]
#[serde(transparent)]
struct VarDb<'a> {
    vars: BTreeMap<String, (bool, Cow<'a, RawValue>)>,
}

/// Implements [`flowey_core::node::RuntimeVarDb`] backed by a JSON file.
pub struct SingleJsonFileVarDb {
    file: File,
}

impl SingleJsonFileVarDb {
    pub fn new(backing_file: impl AsRef<Path>) -> anyhow::Result<Self> {
        let backing_file = backing_file.as_ref();
        let exists = backing_file.exists();
        let mut file = fs_err::OpenOptions::new()
            .read(true)
            .write(true)
            .create(true)
            .open(backing_file)
            .context("failed to open/create database file")?;

        // seed the database file with an empty json map
        if !exists {
            eprintln!(
                "seeding new empty database file: {}",
                backing_file.display()
            );
            file.write_all(b"{}")?;
        }

        Ok(Self { file })
    }

    fn load_db(&mut self) -> VarDb<'static> {
        self.file.rewind().unwrap();
        serde_json::from_reader(&self.file).expect("corrupt runtime variable db")
    }
}

impl flowey_core::node::RuntimeVarDb for SingleJsonFileVarDb {
    fn try_get_var(&mut self, var_name: &str) -> Option<(Vec<u8>, bool)> {
        let db = self.load_db();
        let (is_secret, ref val) = *db.vars.get(var_name)?;
        if is_secret {
            log::debug!("[db] read var: {} = <secret>", var_name);
        } else {
            log::debug!("[db] read var: {} = {}", var_name, val);
        }
        Some((val.get().into(), is_secret))
    }

    fn set_var(&mut self, var_name: &str, is_secret: bool, value: Vec<u8>) {
        let value: &RawValue = serde_json::from_slice(&value)
            .unwrap_or_else(|err| panic!("invalid JSON for var {}: {}", var_name, err));
        if is_secret {
            log::debug!("[db] set var: {} = <secret>", var_name)
        } else {
            log::debug!("[db] set var: {} = {}", var_name, value)
        };
        let mut db = self.load_db();
        let existing = db
            .vars
            .insert(var_name.into(), (is_secret, Cow::Borrowed(value)));
        assert!(existing.is_none()); // all vars are one-time-write
        self.file.set_len(0).unwrap();
        self.file.rewind().unwrap();
        serde_json::to_writer(&self.file, &db).expect("failed to write to db JSON");
    }
}