// Package process runs child commands for ReleaseKit's internal adapters.
package process

import (
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"sort"
	"strings"
)

// Invocation describes one child process. UnsetEnv removes inherited values
// before Env overlays values for this child only.
type Invocation struct {
	Args     []string
	Dir      string
	Env      map[string]string
	UnsetEnv []string
	Stdin    io.Reader
	Stdout   io.Writer
	Stderr   io.Writer
}

// Run starts the command in the requested directory and waits for it to exit.
// Errors preserve the underlying exec error, including *exec.ExitError.
func Run(ctx context.Context, invocation Invocation) error {
	if len(invocation.Args) == 0 || invocation.Args[0] == "" {
		return errors.New("process invocation requires a command")
	}

	command := exec.CommandContext(ctx, invocation.Args[0], invocation.Args[1:]...)
	command.Dir = invocation.Dir
	command.Stdin = invocation.Stdin
	if len(invocation.Env) != 0 || len(invocation.UnsetEnv) != 0 {
		command.Env = environmentEntries(invocation.Env, invocation.UnsetEnv)
	}
	command.Stdout = invocation.Stdout
	command.Stderr = invocation.Stderr

	if err := command.Run(); err != nil {
		if contextErr := ctx.Err(); contextErr != nil {
			return fmt.Errorf("run %q: %w", invocation.Args[0], contextErr)
		}
		return fmt.Errorf("run %q: %w", invocation.Args[0], err)
	}
	return nil
}

func environmentEntries(overlay map[string]string, unset []string) []string {
	environment := make(map[string]string, len(os.Environ())+len(overlay))
	for _, entry := range os.Environ() {
		key, value, ok := strings.Cut(entry, "=")
		if ok {
			environment[key] = value
		}
	}
	for _, key := range unset {
		delete(environment, key)
	}
	for key, value := range overlay {
		environment[key] = value
	}

	keys := make([]string, 0, len(environment))
	for key := range environment {
		keys = append(keys, key)
	}
	sort.Strings(keys)

	entries := make([]string, 0, len(keys))
	for _, key := range keys {
		entries = append(entries, key+"="+environment[key])
	}
	return entries
}