package subprocess

import (
	"context"
	"fmt"
	"os"
	"os/exec"
	"strings"
	"time"

	"gitea.maximumdirect.net/eric/narratio/internal/fileops"
	"gopkg.in/yaml.v3"
)

// RunRequest defines a subprocess invocation.
type RunRequest struct {
	Executable        string
	Args              []string
	WorkingDir        string
	EnvOverrides      map[string]string
	SensitiveEnvNames []string
	DiagnosticOwner   string
	Timeout           time.Duration
	StdoutLogPath     string
	StderrLogPath     string
}

// RunResult captures subprocess execution details.
type RunResult struct {
	ExitCode      int
	StartedAt     time.Time
	CompletedAt   time.Time
	Duration      time.Duration
	StdoutLogPath string
	StderrLogPath string
	TimedOut      bool
	Canceled      bool
}

// Run executes a subprocess with context cancellation and optional timeout.
func Run(ctx context.Context, req RunRequest) (RunResult, error) {
	if strings.TrimSpace(req.Executable) == "" {
		return RunResult{}, fmt.Errorf("subprocess executable is required")
	}
	if ctx == nil {
		ctx = context.Background()
	}

	runCtx := ctx
	cancel := func() {}
	if req.Timeout > 0 {
		runCtx, cancel = context.WithTimeout(ctx, req.Timeout)
	}
	defer cancel()

	childEnv := buildChildEnvironment(os.Environ(), req.EnvOverrides)
	logs, err := openLogWriters(req.StdoutLogPath, req.StderrLogPath, req.diagnosticOwner(), sensitiveEnvironmentValues(childEnv, req.SensitiveEnvNames))
	if err != nil {
		return RunResult{}, err
	}
	defer logs.Close()

	tree, err := newOwnedProcessTree()
	if err != nil {
		return RunResult{}, fmt.Errorf("prepare owned subprocess tree: %w", err)
	}

	cmd := exec.Command(req.Executable, req.Args...)
	cmd.Dir = req.WorkingDir
	cmd.Env = childEnv
	cmd.Stdout = logs.Stdout
	cmd.Stderr = logs.Stderr
	// Streaming capture uses pipes. Bound their lifetime when a leader exits
	// while a descendant still holds a stream descriptor.
	cmd.WaitDelay = forcefulTerminationWait

	started := time.Now().UTC()
	result := RunResult{
		ExitCode:      -1,
		StartedAt:     started,
		StdoutLogPath: req.StdoutLogPath,
		StderrLogPath: req.StderrLogPath,
	}

	if err := runCtx.Err(); err != nil {
		result.CompletedAt = time.Now().UTC()
		result.Duration = result.CompletedAt.Sub(result.StartedAt)
		return result, fmt.Errorf("command was not started: %w", err)
	}

	if err := tree.Start(cmd); err != nil {
		result.CompletedAt = time.Now().UTC()
		result.Duration = result.CompletedAt.Sub(result.StartedAt)
		return result, fmt.Errorf("start command %q with args %v: %w", req.Executable, req.Args, err)
	}

	waitCh := make(chan error, 1)
	go func() { waitCh <- cmd.Wait() }()

	waitErr, ctxErr, captureLimit, cleanupErr := waitForOwnedCommand(runCtx, tree, waitCh, logs.Limits())
	cleanupErr = joinErrors(cleanupErr, tree.Dispose())
	cleanupErr = joinErrors(cleanupErr, logs.Flush())
	if captureLimit == nil {
		captureLimit = logs.Limit()
	}
	result.CompletedAt = time.Now().UTC()
	result.Duration = result.CompletedAt.Sub(result.StartedAt)
	if cmd.ProcessState != nil {
		result.ExitCode = cmd.ProcessState.ExitCode()
	}

	if ctxErr == context.DeadlineExceeded {
		result.TimedOut = true
	}
	if ctxErr == context.Canceled && !result.TimedOut {
		result.Canceled = true
	}

	if waitErr == nil && ctxErr == nil && cleanupErr == nil {
		return result, nil
	}

	stderrTail := logs.stderr.Tail()
	diagnostics := buildDiagnostics(req, result, stderrTail)

	if captureLimit != nil {
		if cause := joinErrors(waitErr, cleanupErr); cause != nil {
			return result, fmt.Errorf("%w (%s): %w", captureLimit, diagnostics, cause)
		}
		return result, fmt.Errorf("%w (%s)", captureLimit, diagnostics)
	}
	if result.TimedOut {
		return result, fmt.Errorf("command timed out after %s (%s): %w", req.Timeout, diagnostics, joinErrors(ctxErr, waitErr, cleanupErr))
	}
	if result.Canceled {
		return result, fmt.Errorf("command canceled (%s): %w", diagnostics, joinErrors(ctxErr, waitErr, cleanupErr))
	}
	if exitErr, ok := waitErr.(*exec.ExitError); ok {
		return result, fmt.Errorf("command failed with exit code %d (%s): %w", exitErr.ExitCode(), diagnostics, joinErrors(waitErr, cleanupErr))
	}
	if cleanupErr != nil {
		return result, fmt.Errorf("command cleanup failed (%s): %w", diagnostics, joinErrors(waitErr, cleanupErr))
	}

	return result, fmt.Errorf("command failed to run (%s): %w", diagnostics, joinErrors(waitErr, cleanupErr))
}

// WriteYAMLAtomic marshals value as YAML and atomically writes it to path.
func WriteYAMLAtomic(path string, value any, perm os.FileMode) error {
	data, err := yaml.Marshal(value)
	if err != nil {
		return fmt.Errorf("marshal yaml for %q: %w", path, err)
	}
	if err := WriteFileAtomic(path, data, perm); err != nil {
		return fmt.Errorf("write yaml %q: %w", path, err)
	}
	return nil
}

// WriteFileAtomic writes bytes through the shared durable replacement primitive.
func WriteFileAtomic(path string, data []byte, perm os.FileMode) error {
	if strings.TrimSpace(path) == "" {
		return fmt.Errorf("write file: path is required")
	}
	if err := fileops.WriteFileAtomic(path, data, perm); err != nil {
		return fmt.Errorf("write file %q: %w", path, err)
	}
	return nil
}

func buildDiagnostics(req RunRequest, result RunResult, stderrTail string) string {
	details := fmt.Sprintf(
		"executable=%q args=%v cwd=%q timeout=%s exit_code=%d timed_out=%t canceled=%t stdout_log=%q stderr_log=%q",
		req.Executable,
		req.Args,
		req.WorkingDir,
		req.Timeout,
		result.ExitCode,
		result.TimedOut,
		result.Canceled,
		req.StdoutLogPath,
		req.StderrLogPath,
	)
	if strings.TrimSpace(stderrTail) == "" {
		if hint := fdDiagnosticsHint(result.ExitCode, ""); hint != "" {
			return details + fmt.Sprintf(" hint=%q", hint)
		}
		return details
	}
	details = details + fmt.Sprintf(" stderr_tail=%q", stderrTail)
	if hint := fdDiagnosticsHint(result.ExitCode, stderrTail); hint != "" {
		details = details + fmt.Sprintf(" hint=%q", hint)
	}
	return details
}

func fdDiagnosticsHint(exitCode int, stderrTail string) string {
	lowerTail := strings.ToLower(stderrTail)
	if strings.Contains(lowerTail, "bad file descriptor") || strings.Contains(lowerTail, "errno 9") {
		return "stderr stream appears invalid in child process (fd 2); check wrapper/subprocess environment differences versus direct shell execution"
	}
	if exitCode == 120 {
		return "exit code 120 may indicate interpreter shutdown stream-flush failures (commonly invalid stdout/stderr descriptors in Python processes)"
	}
	return ""
}