// Package research executes the embedded Python research engine with bounded inputs.
package research

import (
	"bytes"
	"context"
	_ "embed"
	"encoding/json"
	"errors"
	"os"
	"os/exec"
	"time"
)

//go:embed backtest.py
var script string

type Engine struct{ executable string }

func New(executable string) *Engine { return &Engine{executable} }
func (e *Engine) Execute(ctx context.Context, input json.RawMessage) (json.RawMessage, error) {
	ctx, cancel := context.WithTimeout(ctx, 20*time.Second)
	defer cancel()
	cmd := exec.CommandContext(ctx, e.executable, "-I", "-c", script)
	// No application credentials or Python startup configuration reach the child.
	cmd.Env = []string{"PATH=" + os.Getenv("PATH"), "LANG=en_US.UTF-8"}
	cmd.Stdin = bytes.NewReader(input)
	var output boundedBuffer
	cmd.Stdout = &output
	if err := cmd.Run(); err != nil {
		return nil, errors.New("Python research execution failed; check Python installation and input data")
	}
	if !json.Valid(output.Bytes()) {
		return nil, errors.New("invalid research result")
	}
	return json.RawMessage(output.Bytes()), nil
}

type boundedBuffer struct{ bytes.Buffer }

func (b *boundedBuffer) Write(p []byte) (int, error) {
	if b.Len()+len(p) > 2<<20 {
		return 0, errors.New("research output exceeds limit")
	}
	return b.Buffer.Write(p)
}