package puppet

import (
	"bufio"
	"os"
	"strings"
)

// StdinReader returns a buffered reader over f and true only when f actually
// carries piped/redirected data. Terminals and character devices such as
// /dev/null return false, and an empty pipe or empty file (immediate EOF on
// peek) also returns false. This mirrors node-lookup's no-TTY behaviour: when
// invoked without a real pipe the caller can fall back to arguments instead of
// blocking on or silently consuming empty input.
func StdinReader(f *os.File) (*bufio.Reader, bool) {
	fi, err := f.Stat()
	if err != nil {
		return nil, false
	}
	if (fi.Mode() & os.ModeCharDevice) != 0 {
		return nil, false // terminal or /dev/null
	}
	r := bufio.NewReader(f)
	if _, err := r.Peek(1); err != nil {
		return nil, false // empty pipe / empty file (EOF)
	}
	return r, true
}

// ReadHosts resolves the list of hostnames to act on. Explicit args win; failing
// that it reads the first whitespace-separated field of each non-empty line from
// stdin (so `node-lookup -R | pburl` and `node-lookup -1 | pburl` both work).
// Order is preserved and duplicates are removed. Returns nil when neither args
// nor piped stdin data are present.
func ReadHosts(stdin *os.File, args []string) []string {
	if len(args) > 0 {
		return dedupe(args)
	}
	r, ok := StdinReader(stdin)
	if !ok {
		return nil
	}
	var hosts []string
	sc := bufio.NewScanner(r)
	for sc.Scan() {
		fields := strings.Fields(sc.Text())
		if len(fields) == 0 {
			continue
		}
		hosts = append(hosts, fields[0])
	}
	return dedupe(hosts)
}

func dedupe(in []string) []string {
	seen := make(map[string]struct{}, len(in))
	out := make([]string, 0, len(in))
	for _, s := range in {
		if _, ok := seen[s]; ok {
			continue
		}
		seen[s] = struct{}{}
		out = append(out, s)
	}
	return out
}