package nix

import (
	"context"
	"io"
	"iter"
)

// Cmd represents an external command or container being prepared to run.
type Cmd interface {
	Start() error
	Wait() error
	StdinPipe() (io.WriteCloser, error)
	StdoutPipe() (io.ReadCloser, error)
	StderrPipe() (io.ReadCloser, error)

	Stdin(io.Reader)
	Stdout(io.Writer)
	Stderr(io.Writer)
	AppendArgs(a ...string)
	ReplaceEnv(env []string)
}

// Context holds configuration and environment information for interacting with nix.
type Context interface {
	// Streams returns the stdout and stderr writers held by this [Context].
	Streams() (stdout, stderr io.Writer)
	// Extra returns a copy of extra arguments held by this [Context].
	Extra() []string
	// StoreEnv returns extra [Store] environment variables.
	StoreEnv() []string

	// Nix returns an implementation of [Cmd] for running a nix command.
	Nix(ctx context.Context, arg ...string) Cmd
	// WriteStdin calls [WriteStdin] for [Cmd]. The function f points to is called if [WriteStdin] succeeds.
	WriteStdin(cmd Cmd, installables iter.Seq[string], f func() error) (int, error)

	// Unwrap returns the stored [context.Context]
	Unwrap() context.Context
}

// setStreams sets the stdout and stderr streams of [Cmd] according to [Context].
func setStreams(ctx Context, cmd Cmd) {
	stdout, stderr := ctx.Streams()
	cmd.Stdout(stdout)
	cmd.Stderr(stderr)
}