/// Audio transcoding bridge for smartrust.
///
/// Thin CLI wrapper around `codec-lib`. Handles Opus ↔ G.722 ↔ PCMU transcoding.
///
/// Protocol:
///   -> {"id":"1","method":"init","params":{}}
///   <- {"id":"1","success":true,"result":{}}
///   -> {"id":"2","method":"create_session","params":{"session_id":"call-abc"}}
///   <- {"id":"2","success":true,"result":{}}
///   -> {"id":"3","method":"transcode","params":{"session_id":"call-abc","data_b64":"...","from_pt":111,"to_pt":9}}
///   <- {"id":"3","success":true,"result":{"data_b64":"..."}}
///   -> {"id":"4","method":"destroy_session","params":{"session_id":"call-abc"}}
///   <- {"id":"4","success":true,"result":{}}

use base64::engine::general_purpose::STANDARD as B64;
use base64::Engine as _;
use codec_lib::{codec_sample_rate, TranscodeState};
use serde::Deserialize;
use std::collections::HashMap;
use std::io::{self, BufRead, Write};

#[derive(Deserialize)]
struct Request {
    id: String,
    method: String,
    #[serde(default)]
    params: serde_json::Value,
}

fn respond(
    out: &mut impl Write,
    id: &str,
    success: bool,
    result: Option<serde_json::Value>,
    error: Option<&str>,
) {
    let mut resp = serde_json::json!({ "id": id, "success": success });
    if let Some(r) = result {
        resp["result"] = r;
    }
    if let Some(e) = error {
        resp["error"] = serde_json::Value::String(e.to_string());
    }
    let _ = writeln!(out, "{}", resp);
    let _ = out.flush();
}

/// Resolve a session: if session_id is provided, look it up in the sessions map;
/// otherwise fall back to the default state (backward compat with `init`).
fn get_session<'a>(
    sessions: &'a mut HashMap<String, TranscodeState>,
    default: &'a mut Option<TranscodeState>,
    params: &serde_json::Value,
) -> Option<&'a mut TranscodeState> {
    if let Some(sid) = params.get("session_id").and_then(|v| v.as_str()) {
        sessions.get_mut(sid)
    } else {
        default.as_mut()
    }
}

fn main() {
    let stdin = io::stdin();
    let stdout = io::stdout();
    let mut out = io::BufWriter::new(stdout.lock());

    let _ = writeln!(out, r#"{{"event":"ready","data":{{}}}}"#);
    let _ = out.flush();

    let mut default_state: Option<TranscodeState> = None;
    let mut sessions: HashMap<String, TranscodeState> = HashMap::new();

    for line in stdin.lock().lines() {
        let line = match line {
            Ok(l) if !l.trim().is_empty() => l,
            Ok(_) => continue,
            Err(_) => break,
        };

        let req: Request = match serde_json::from_str(&line) {
            Ok(r) => r,
            Err(e) => {
                respond(&mut out, "", false, None, Some(&format!("parse: {e}")));
                continue;
            }
        };

        match req.method.as_str() {
            "init" => match TranscodeState::new() {
                Ok(s) => {
                    default_state = Some(s);
                    respond(&mut out, &req.id, true, Some(serde_json::json!({})), None);
                }
                Err(e) => respond(&mut out, &req.id, false, None, Some(&e)),
            },

            "create_session" => {
                let session_id = match req.params.get("session_id").and_then(|v| v.as_str()) {
                    Some(s) => s.to_string(),
                    None => {
                        respond(&mut out, &req.id, false, None, Some("missing session_id"));
                        continue;
                    }
                };
                if sessions.contains_key(&session_id) {
                    respond(&mut out, &req.id, true, Some(serde_json::json!({})), None);
                    continue;
                }
                match TranscodeState::new() {
                    Ok(s) => {
                        sessions.insert(session_id, s);
                        respond(&mut out, &req.id, true, Some(serde_json::json!({})), None);
                    }
                    Err(e) => respond(&mut out, &req.id, false, None, Some(&e)),
                }
            }

            "destroy_session" => {
                let session_id = match req.params.get("session_id").and_then(|v| v.as_str()) {
                    Some(s) => s,
                    None => {
                        respond(&mut out, &req.id, false, None, Some("missing session_id"));
                        continue;
                    }
                };
                sessions.remove(session_id);
                respond(&mut out, &req.id, true, Some(serde_json::json!({})), None);
            }

            "transcode" => {
                let st = match get_session(&mut sessions, &mut default_state, &req.params) {
                    Some(s) => s,
                    None => {
                        respond(
                            &mut out,
                            &req.id,
                            false,
                            None,
                            Some("not initialized (no session or default state)"),
                        );
                        continue;
                    }
                };
                let data_b64 = match req.params.get("data_b64").and_then(|v| v.as_str()) {
                    Some(s) => s,
                    None => {
                        respond(&mut out, &req.id, false, None, Some("missing data_b64"));
                        continue;
                    }
                };
                let from_pt =
                    req.params.get("from_pt").and_then(|v| v.as_u64()).unwrap_or(0) as u8;
                let to_pt = req.params.get("to_pt").and_then(|v| v.as_u64()).unwrap_or(0) as u8;
                let direction = req.params.get("direction").and_then(|v| v.as_str());

                let data = match B64.decode(data_b64) {
                    Ok(b) => b,
                    Err(e) => {
                        respond(
                            &mut out,
                            &req.id,
                            false,
                            None,
                            Some(&format!("b64: {e}")),
                        );
                        continue;
                    }
                };

                match st.transcode(&data, from_pt, to_pt, direction) {
                    Ok(result) => {
                        respond(
                            &mut out,
                            &req.id,
                            true,
                            Some(serde_json::json!({ "data_b64": B64.encode(&result) })),
                            None,
                        );
                    }
                    Err(e) => respond(&mut out, &req.id, false, None, Some(&e)),
                }
            }

            "encode_pcm" => {
                let st = match get_session(&mut sessions, &mut default_state, &req.params) {
                    Some(s) => s,
                    None => {
                        respond(
                            &mut out,
                            &req.id,
                            false,
                            None,
                            Some("not initialized (no session or default state)"),
                        );
                        continue;
                    }
                };
                let data_b64 = match req.params.get("data_b64").and_then(|v| v.as_str()) {
                    Some(s) => s,
                    None => {
                        respond(&mut out, &req.id, false, None, Some("missing data_b64"));
                        continue;
                    }
                };
                let sample_rate = req
                    .params
                    .get("sample_rate")
                    .and_then(|v| v.as_u64())
                    .unwrap_or(22050) as u32;
                let to_pt = req.params.get("to_pt").and_then(|v| v.as_u64()).unwrap_or(9) as u8;

                let data = match B64.decode(data_b64) {
                    Ok(b) => b,
                    Err(e) => {
                        respond(
                            &mut out,
                            &req.id,
                            false,
                            None,
                            Some(&format!("b64: {e}")),
                        );
                        continue;
                    }
                };

                if data.len() % 2 != 0 {
                    respond(
                        &mut out,
                        &req.id,
                        false,
                        None,
                        Some("PCM data has odd byte count (expected 16-bit LE samples)"),
                    );
                    continue;
                }

                let pcm: Vec<i16> = data
                    .chunks_exact(2)
                    .map(|c| i16::from_le_bytes([c[0], c[1]]))
                    .collect();

                let target_rate = codec_sample_rate(to_pt);
                let resampled = match st.resample(&pcm, sample_rate, target_rate) {
                    Ok(r) => r,
                    Err(e) => {
                        respond(&mut out, &req.id, false, None, Some(&e));
                        continue;
                    }
                };

                match st.encode_from_pcm(&resampled, to_pt) {
                    Ok(encoded) => {
                        respond(
                            &mut out,
                            &req.id,
                            true,
                            Some(serde_json::json!({ "data_b64": B64.encode(&encoded) })),
                            None,
                        );
                    }
                    Err(e) => {
                        respond(&mut out, &req.id, false, None, Some(&e));
                    }
                }
            }

            "encode" | "decode" => {
                respond(
                    &mut out,
                    &req.id,
                    false,
                    None,
                    Some("use 'transcode' command instead"),
                );
            }

            _ => respond(
                &mut out,
                &req.id,
                false,
                None,
                Some(&format!("unknown: {}", req.method)),
            ),
        }
    }
}