// phraser/server.go — the llama-server this phraser talks to: the child
// process it may own, and the startup handshake that waits for the port.
//
// Nothing here knows what a prompt is. Split out of llmphraser.go so the
// phrasing paths and the process lifetime read as two subjects.
package phraser

import (
	"context"
	"os/exec"
	"regexp"
	"strings"
	"sync"
)

var listenRE = regexp.MustCompile(`listening on (https?://\S+)`)

// backend — one llama-server this phraser talks to. Two implementations: a
// llamaProc we spawned and must reap, and a borrowedBackend someone else owns.
type backend interface {
	BaseURL() string
	Close() error
}

// borrowedBackend — a server started and owned by someone else (the phrasing
// scorer's shared llama-server). Closing it is a no-op by construction.
type borrowedBackend string

func (b borrowedBackend) BaseURL() string { return string(b) }
func (b borrowedBackend) Close() error    { return nil }

// llamaProc — a llama-server child process plus the goroutine reading its
// stderr. Close kills and reaps it; see the Pdeathsig note in spawnLlamaServer.
type llamaProc struct {
	base   string
	cmd    *exec.Cmd
	cancel context.CancelFunc
	wg     sync.WaitGroup
}

func (l *llamaProc) BaseURL() string { return l.base }

func (l *llamaProc) Close() error {
	l.cancel()
	if l.cmd != nil && l.cmd.Process != nil {
		_ = l.cmd.Process.Kill()
		_ = l.cmd.Wait() // reap the process — without Wait, the child becomes a zombie
	}
	l.wg.Wait()
	return nil
}

// lineTail keeps the last few startup lines so a server that dies before it
// listens can say why in the error, not just "EOF". Written by the reader
// goroutine and read by whoever gives up on startup, so it takes a lock.
type lineTail struct {
	mu    sync.Mutex
	lines []string
}

const lineTailMax = 12

func (t *lineTail) add(line string) {
	t.mu.Lock()
	defer t.mu.Unlock()
	t.lines = append(t.lines, line)
	if len(t.lines) > lineTailMax {
		t.lines = t.lines[len(t.lines)-lineTailMax:]
	}
}

func (t *lineTail) String() string {
	t.mu.Lock()
	defer t.mu.Unlock()
	if len(t.lines) == 0 {
		return "(no output)"
	}
	return strings.Join(t.lines, " | ")
}

func extractPort(listen string) string {
	_, port, _ := strings.Cut(listen, ":")
	if port == "" {
		return "0"
	}
	return port
}