package main

import (
	"context"
	"log"
	"net/http"
	"os/exec"
	"sync"
	"syscall"
	"time"
)

// runner owns one llama-server process. Owning it is the point of the daemon:
// the workstation cannot keep a 7-14B resident, because that holds 16GB against
// the owner's CPT runs, Correx and the manga-recap pipeline. So the thing that
// stays up is this, which costs no VRAM, and the model comes and goes under it.
type runner struct {
	bin  string
	args []string
	// ready is llama-server's own /health, which answers "is a model loaded".
	// Loading a 7-14B takes tens of seconds, so started is not ready.
	readyURL string

	mu    sync.Mutex
	cmd   *exec.Cmd
	ready bool
	// yielding — stop() has sent the signal and the exit that follows is ours.
	// llama-server aborts on SIGTERM (its static teardown throws, upstream
	// ggml-org/llama.cpp), so a routine yield and a real crash produce the same
	// "signal: aborted" and used to log identically (Vikunja #491).
	yielding bool
	http     *http.Client
}

func newRunner(bin string, args []string, readyURL string) *runner {
	return &runner{
		bin: bin, args: args, readyURL: readyURL,
		http: &http.Client{Timeout: 2 * time.Second},
	}
}

// pid is the child's, or 0. The GPU probe needs it to tell our own model apart
// from a contender.
func (r *runner) pid() int {
	r.mu.Lock()
	defer r.mu.Unlock()
	if r.cmd == nil || r.cmd.Process == nil {
		return 0
	}
	return r.cmd.Process.Pid
}

func (r *runner) running() bool { return r.pid() != 0 }

// isReady reports the cached readiness. The supervisor loop refreshes it; the
// health handler only reads, so answering /health never costs a round trip.
func (r *runner) isReady() bool {
	r.mu.Lock()
	defer r.mu.Unlock()
	return r.ready
}

// start launches llama-server. It returns as soon as the process exists, not
// when the model is loaded.
func (r *runner) start() error {
	r.mu.Lock()
	defer r.mu.Unlock()
	if r.cmd != nil {
		return nil
	}
	cmd := exec.Command(r.bin, r.args...)
	// Own process group, so stop kills anything llama-server spawned rather
	// than leaving it holding VRAM after we have declared the card yielded.
	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
	if err := cmd.Start(); err != nil {
		return err
	}
	r.cmd, r.ready, r.yielding = cmd, false, false
	log.Printf("mavgpud: started llama-server pid=%d", cmd.Process.Pid)
	go func() {
		err := cmd.Wait()
		r.mu.Lock()
		yielded := r.yielding
		r.cmd, r.ready, r.yielding = nil, false, false
		r.mu.Unlock()
		if yielded {
			log.Printf("mavgpud: llama-server stopped, card yielded (%v)", err)
			return
		}
		log.Printf("mavgpud: llama-server exited: %v", err)
	}()
	return nil
}

// stop ends llama-server and waits for the VRAM to come back. SIGTERM first so
// it unmaps cleanly, SIGKILL after the grace window. Returning before the
// process is gone would let the supervisor report a free card while 14GB is
// still mapped, which is the one lie that would make yielding useless.
func (r *runner) stop(grace time.Duration) {
	r.mu.Lock()
	cmd := r.cmd
	r.ready = false
	if cmd != nil && cmd.Process != nil {
		// The exit that follows is ours, not a crash.
		r.yielding = true
	}
	r.mu.Unlock()
	if cmd == nil || cmd.Process == nil {
		return
	}
	pgid := -cmd.Process.Pid
	_ = syscall.Kill(pgid, syscall.SIGTERM)
	deadline := time.Now().Add(grace)
	for time.Now().Before(deadline) {
		if !r.running() {
			return
		}
		time.Sleep(100 * time.Millisecond)
	}
	log.Printf("mavgpud: llama-server did not exit in %s, killing", grace)
	_ = syscall.Kill(pgid, syscall.SIGKILL)
}

// refreshReady asks llama-server whether the model is loaded. Called once per
// supervisor tick, never per request.
func (r *runner) refreshReady(ctx context.Context) {
	if !r.running() {
		return
	}
	ok := false
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, r.readyURL, nil)
	if err == nil {
		resp, err := r.http.Do(req)
		if err == nil {
			ok = resp.StatusCode == http.StatusOK
			resp.Body.Close()
		}
	}
	r.mu.Lock()
	was := r.ready
	r.ready = ok
	r.mu.Unlock()
	if ok && !was {
		log.Printf("mavgpud: model ready")
	}
}