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

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

	"github.com/aritmolab/thothii/tools/tht/internal/config"
)

const defaultCaptureBytes = 4 * 1024 * 1024
const maximumCaptureBytes = 64 * 1024 * 1024

// ErrOutputLimit reports that a child exceeded one of its capture limits.
var ErrOutputLimit = errors.New("Docker command output limit exceeded")

// CaptureLimits bounds each captured stream while the child is running.
type CaptureLimits struct {
	StdoutBytes int
	StderrBytes int
}

// Result is the captured output and process exit code for one Docker invocation.
type Result struct {
	Stdout   string
	Stderr   string
	ExitCode int
}

// Runner is the shell-free Docker command boundary used by the host CLI.
type Runner interface {
	Run(context.Context, []string, io.Reader) (Result, error)
}

type boundedRunner interface {
	RunBounded(context.Context, []string, io.Reader, CaptureLimits) (Result, error)
}

// execRunner executes the Docker CLI. It never invokes a shell.
type execRunner 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 execRunner{binary: binary}
}

// Run invokes Docker with the supplied argument array and optional standard input.
func (r execRunner) Run(ctx context.Context, args []string, stdin io.Reader) (Result, error) {
	return r.RunBounded(ctx, args, stdin, CaptureLimits{
		StdoutBytes: defaultCaptureBytes,
		StderrBytes: defaultCaptureBytes,
	})
}

// RunBounded invokes Docker while enforcing both stream limits during capture.
func (r execRunner) RunBounded(ctx context.Context, args []string, stdin io.Reader, limits CaptureLimits) (Result, error) {
	if err := validCaptureLimits(limits); err != nil {
		return Result{}, err
	}
	if err := ctx.Err(); err != nil {
		return Result{}, err
	}
	command := exec.Command(r.binary, args...)
	configureProcess(command)
	command.Stdin = stdin
	overflow := make(chan struct{}, 1)
	stdout := newCappedBuffer(limits.StdoutBytes, overflow)
	stderr := newCappedBuffer(limits.StderrBytes, overflow)
	command.Stdout = stdout
	command.Stderr = stderr
	if err := command.Start(); err != nil {
		return startFailure(err)
	}
	done := make(chan error, 1)
	go func() { done <- command.Wait() }()
	var err error
	select {
	case err = <-done:
	case <-ctx.Done():
		_ = terminateProcess(command, done)
		err = ctx.Err()
	case <-overflow:
		_ = terminateProcess(command, done)
		err = ErrOutputLimit
	}
	result := Result{Stdout: stdout.String(), Stderr: stderr.String()}
	if command.ProcessState != nil {
		result.ExitCode = command.ProcessState.ExitCode()
	}
	if stdout.Overflowed() || stderr.Overflowed() {
		return result, ErrOutputLimit
	}
	if err == nil {
		return result, nil
	}
	if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) || errors.Is(err, ErrOutputLimit) {
		return result, err
	}
	var exitError *exec.ExitError
	if errors.As(err, &exitError) {
		result.ExitCode = exitError.ExitCode()
		return result, err
	}
	return result, err
}

// RunBounded uses the production runner's during-capture limits while retaining compatibility
// with injected runners, whose already-bounded test results are checked before use.
func RunBounded(runner Runner, ctx context.Context, args []string, stdin io.Reader, limits CaptureLimits) (Result, error) {
	if err := validCaptureLimits(limits); err != nil {
		return Result{}, err
	}
	if bounded, ok := runner.(boundedRunner); ok {
		return bounded.RunBounded(ctx, args, stdin, limits)
	}
	result, err := runner.Run(ctx, args, stdin)
	if len(result.Stdout) > limits.StdoutBytes || len(result.Stderr) > limits.StderrBytes {
		return Result{
			Stdout:   boundedString(result.Stdout, limits.StdoutBytes),
			Stderr:   boundedString(result.Stderr, limits.StderrBytes),
			ExitCode: result.ExitCode,
		}, ErrOutputLimit
	}
	return result, err
}

func validCaptureLimits(limits CaptureLimits) error {
	if limits.StdoutBytes < 1 || limits.StderrBytes < 1 ||
		limits.StdoutBytes > maximumCaptureBytes || limits.StderrBytes > maximumCaptureBytes {
		return errors.New("Docker command capture limits are invalid")
	}
	return nil
}

func boundedString(value string, maximum int) string {
	if len(value) <= maximum {
		return value
	}
	return value[:maximum]
}

func startFailure(err error) (Result, error) {
	result := Result{}
	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
}

type cappedBuffer struct {
	mu       sync.Mutex
	contents []byte
	maximum  int
	overflow chan<- struct{}
	exceeded bool
}

func newCappedBuffer(maximum int, overflow chan<- struct{}) *cappedBuffer {
	capacity := maximum
	if capacity > 4096 {
		capacity = 4096
	}
	return &cappedBuffer{contents: make([]byte, 0, capacity), maximum: maximum, overflow: overflow}
}

func (b *cappedBuffer) Write(value []byte) (int, error) {
	b.mu.Lock()
	defer b.mu.Unlock()
	remaining := b.maximum - len(b.contents)
	if remaining > 0 {
		kept := len(value)
		if kept > remaining {
			kept = remaining
		}
		b.contents = append(b.contents, value[:kept]...)
	}
	if len(value) > remaining && !b.exceeded {
		b.exceeded = true
		select {
		case b.overflow <- struct{}{}:
		default:
		}
	}
	return len(value), nil
}

func (b *cappedBuffer) String() string {
	b.mu.Lock()
	defer b.mu.Unlock()
	return string(b.contents)
}

func (b *cappedBuffer) Overflowed() bool {
	b.mu.Lock()
	defer b.mu.Unlock()
	return b.exceeded
}

// InstallationRunner applies an installation's validated Compose arguments to commands that
// explicitly start with compose. Direct Docker image commands remain host-side.
type InstallationRunner struct {
	Installation config.Installation
	Runner       Runner
}

// SessionInventoryScope supplies the installation's intended visibility to lifecycle callers.
func (r InstallationRunner) SessionInventoryScope() string {
	if r.Installation.Profile == "local" {
		return "mine"
	}
	return "all"
}

// Run transforms only Compose invocations. It never performs shell interpolation.
func (r InstallationRunner) Run(ctx context.Context, args []string, stdin io.Reader) (Result, error) {
	if len(args) > 0 && args[0] == "compose" {
		return r.Runner.Run(ctx, r.Installation.ComposeArgs(args[1:]...), stdin)
	}
	return r.Runner.Run(ctx, args, stdin)
}

// RunBounded preserves bounded capture when Compose argument injection is wrapped per installation.
func (r InstallationRunner) RunBounded(ctx context.Context, args []string, stdin io.Reader, limits CaptureLimits) (Result, error) {
	if len(args) > 0 && args[0] == "compose" {
		return RunBounded(r.Runner, ctx, r.Installation.ComposeArgs(args[1:]...), stdin, limits)
	}
	return RunBounded(r.Runner, ctx, args, stdin, limits)
}