//! JSON Transform — WASM guest module for ZCLAW skill system.
//!
//! Reads JSON from stdin, applies transforms, writes result to stdout.
//! Target: `wasm32-wasi`

use serde::{Deserialize, Serialize};
use serde_json::Value;
use std::io::{self, Read, Write};

#[derive(Deserialize)]
#[serde(tag = "type", rename_all = "lowercase")]
enum Transform {
    Pick { fields: Vec<String> },
    Rename { from: String, to: String },
    Filter { field: String, op: String, value: Value },
    Sort { field: String, order: String },
}

#[derive(Deserialize)]
struct Input {
    data: Value,
    #[serde(default)]
    transforms: Vec<Transform>,
}

#[derive(Serialize)]
struct Output {
    success: bool,
    #[serde(skip_serializing_if = "Option::is_none")]
    data: Option<Value>,
    #[serde(skip_serializing_if = "Option::is_none")]
    error: Option<String>,
}

impl Output {
    fn ok(data: Value) -> Self {
        Self {
            success: true,
            data: Some(data),
            error: None,
        }
    }

    fn err(msg: impl Into<String>) -> Self {
        Self {
            success: false,
            data: None,
            error: Some(msg.into()),
        }
    }
}

#[no_mangle]
pub extern "C" fn _start() {
    let mut input_str = String::new();
    if let Err(e) = io::stdin().read_to_string(&mut input_str) {
        write_output(&Output::err(format!("Failed to read stdin: {}", e)));
        return;
    }

    let input: Input = match serde_json::from_str(&input_str) {
        Ok(v) => v,
        Err(e) => {
            write_output(&Output::err(format!("Invalid JSON input: {}", e)));
            return;
        }
    };

    let mut data = input.data;
    for transform in input.transforms {
        data = match apply_transform(data, &transform) {
            Ok(v) => v,
            Err(e) => {
                write_output(&Output::err(e));
                return;
            }
        }
    }

    write_output(&Output::ok(data));
}

fn apply_transform(data: Value, transform: &Transform) -> Result<Value, String> {
    match transform {
        Transform::Pick { fields } => {
            let obj = data.as_object().ok_or("Pick requires object input")?;
            let mut result = serde_json::Map::new();
            for field in fields {
                if let Some(v) = obj.get(field) {
                    result.insert(field.clone(), v.clone());
                }
            }
            Ok(Value::Object(result))
        }
        Transform::Rename { from, to } => {
            let mut obj = data.as_object().ok_or("Rename requires object input")?.clone();
            if let Some(v) = obj.remove(from) {
                obj.insert(to.clone(), v);
            }
            Ok(Value::Object(obj))
        }
        Transform::Filter { field, op, value } => {
            let arr = data.as_array().ok_or("Filter requires array input")?;
            let filtered: Vec<Value> = arr
                .iter()
                .filter(|item| {
                    let item_val = item.get(field);
                    match op.as_str() {
                        "eq" => item_val == Some(value),
                        "ne" => item_val != Some(value),
                        "gt" => compare_values(item_val, value).map(|c| c.is_gt()).unwrap_or(false),
                        "lt" => compare_values(item_val, value).map(|c| c.is_lt()).unwrap_or(false),
                        _ => false,
                    }
                })
                .cloned()
                .collect();
            Ok(Value::Array(filtered))
        }
        Transform::Sort { field, order } => {
            let mut arr = data.as_array().ok_or("Sort requires array input")?.clone();
            let field = field.clone();
            let ascending = order != "desc";
            arr.sort_by(|a, b| {
                let va = a.get(&field).unwrap_or(&Value::Null);
                let vb = b.get(&field).unwrap_or(&Value::Null);
                let cmp = compare_values(Some(va), vb).unwrap_or(std::cmp::Ordering::Equal);
                if ascending { cmp } else { cmp.reverse() }
            });
            Ok(Value::Array(arr))
        }
    }
}

fn compare_values(a: Option<&Value>, b: &Value) -> Option<std::cmp::Ordering> {
    let a = a?;
    match (a, b) {
        (Value::Number(an), Value::Number(bn)) => {
            if let (Some(af), Some(bf)) = (an.as_f64(), bn.as_f64()) {
                Some(af.partial_cmp(&bf).unwrap_or(std::cmp::Ordering::Equal))
            } else {
                None
            }
        }
        (Value::String(as_), Value::String(bs)) => Some(as_.cmp(bs)),
        _ => None,
    }
}

fn write_output(output: &Output) {
    let json = serde_json::to_string(output).unwrap_or_else(|_| r#"{"success":false}"#.to_string());
    let _ = io::stdout().write_all(json.as_bytes());
    let _ = io::stdout().flush();
}