// Package compose executes Docker Compose through a fixed executable and argument arrays.
package compose

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"sync"
	"os"
	"os/exec"
)

// Result is the captured output and process exit code for one Docker invocation.
var ErrOutputLimit = errors.New("compose output limit exceeded")

// CaptureLimits bounds each stream independently. Overflow is never retained.
type CaptureLimits struct { StdoutBytes int64; StderrBytes int64 }

type Result struct {
	Stdout   string
	Stderr   string
	ExitCode int
}

// Runner executes the Docker CLI. It never invokes a shell.
type Runner struct {
	binary string
}

// NewRunner returns a runner for binary. An empty binary selects docker from PATH.
func NewRunner(binary string) Runner {
	if binary == "" {
		binary = "docker"
	}
	return Runner{binary: binary}
}

// Run invokes Docker with the supplied argument array and optional standard input.
func (r Runner) Run(ctx context.Context, args []string, stdin io.Reader) (Result, error) {
	command := exec.CommandContext(ctx, r.binary, args...)
	command.Stdin = stdin
	var stdout, stderr bytes.Buffer
	command.Stdout = &stdout
	command.Stderr = &stderr
	err := command.Run()
	result := Result{Stdout: stdout.String(), Stderr: stderr.String()}
	if err == nil {
		return result, nil
	}
	var exitError *exec.ExitError
	if errors.As(err, &exitError) {
		result.ExitCode = exitError.ExitCode()
		return result, err
	}
	if errors.Is(err, exec.ErrNotFound) || errors.Is(err, os.ErrNotExist) {
		result.ExitCode = 127
		return result, fmt.Errorf("%w: %w", exec.ErrNotFound, err)
	}
	return result, err
}


// RunBounded executes one owned process while retaining at most the configured bytes per stream.
// The complete process group is terminated as soon as either stream exceeds its limit.
func (r Runner) RunBounded(ctx context.Context, args []string, stdin io.Reader, limits CaptureLimits) (Result, error) {
	if limits.StdoutBytes < 0 || limits.StderrBytes < 0 { return Result{}, ErrOutputLimit }
	command := exec.Command(r.binary, args...)
	command.Stdin = stdin
	stdoutPipe, err := command.StdoutPipe(); if err != nil { return Result{}, err }
	stderrPipe, err := command.StderrPipe(); if err != nil { return Result{}, err }
	configureOwnedProcess(command)
	if err := command.Start(); err != nil { return Result{ExitCode: 127}, err }
	type stream struct { b []byte; overflow bool }
	var out, er stream
	overflow := make(chan struct{}, 1)
	var wg sync.WaitGroup; wg.Add(2)
	read := func(rd io.Reader, max int64, target *stream) {
		defer wg.Done()
		buf := make([]byte, 32*1024)
		for {
			n, readErr := rd.Read(buf)
			if n > 0 {
				remain := max - int64(len(target.b))
				if remain > 0 { take := int64(n); if take > remain { take = remain }; target.b = append(target.b, buf[:take]...) }
				if int64(n) > remain {
					target.overflow = true
					select { case overflow <- struct{}{}: default: }
					return
				}
			}
			if readErr != nil { return }
		}
	}
	go read(stdoutPipe, limits.StdoutBytes, &out); go read(stderrPipe, limits.StderrBytes, &er)
	finished := make(chan error, 1); go func() { finished <- command.Wait() }()
	var waitErr error
	select {
	case waitErr = <-finished:
		// The parent may exit while a descendant inherited stdout/stderr; tear down the owned group.
		terminateOwnedProcess(command)
	case <-overflow:
		terminateOwnedProcess(command); waitErr = <-finished
	case <-ctx.Done():
		terminateOwnedProcess(command); waitErr = <-finished
	}
	wg.Wait()
	result := Result{Stdout: string(out.b), Stderr: string(er.b)}
	if out.overflow || er.overflow { return result, ErrOutputLimit }
	if waitErr == nil { return result, nil }
	var exitErr *exec.ExitError
	if errors.As(waitErr, &exitErr) { result.ExitCode = exitErr.ExitCode(); return result, waitErr }
	if errors.Is(waitErr, exec.ErrNotFound) || errors.Is(waitErr, os.ErrNotExist) { result.ExitCode = 127; return result, fmt.Errorf("%w: %w", exec.ErrNotFound, waitErr) }
	if ctx.Err() != nil { return result, ctx.Err() }
	return result, waitErr
}