package phraser

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os/exec"
	"regexp"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/kami/maven/internal/delivery"
	"github.com/kami/maven/internal/loop"
)

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

type LLMPhraser struct {
	cfg    Config
	client *http.Client
	port   string
	cmd    *exec.Cmd
	cancel context.CancelFunc
	wg     sync.WaitGroup
}

type Config struct {
	ModelPath  string
	BinPath    string
	Listen     string
	NGpuLayers int
	NCtx       int
	Timeout    time.Duration
}

func DefaultConfig(modelPath string) Config {
	return Config{
		ModelPath:  modelPath,
		BinPath:    "llama-server",
		Listen:     "127.0.0.1:0",
		NGpuLayers: -1,
		NCtx:       2048,
		Timeout:    30 * time.Second,
	}
}

func NewLLMPhraser(ctx context.Context, cfg Config) (*LLMPhraser, error) {
	ctx, cancel := context.WithCancel(ctx)
	p := &LLMPhraser{
		cfg:    cfg,
		client: &http.Client{Timeout: cfg.Timeout},
		cancel: cancel,
	}
	if err := p.start(ctx); err != nil {
		cancel()
		return nil, err
	}
	return p, nil
}

func (p *LLMPhraser) start(ctx context.Context) error {
	args := []string{
		"-m", p.cfg.ModelPath,
		"--host", "127.0.0.1",
		"--port", extractPort(p.cfg.Listen),
		"-c", fmt.Sprintf("%d", p.cfg.NCtx),
		"-ngl", fmt.Sprintf("%d", p.cfg.NGpuLayers),
		"--no-webui",
	}
	cmd := exec.CommandContext(ctx, p.cfg.BinPath, args...)
	// Pdeathsig: the kernel SIGKILLs llama-server the moment mavend dies — by
	// ANY means, including SIGKILL/OOM/panic where our Close() never runs. Without
	// it a hard-killed mavend orphans its llama-server (reparented to init, keeps
	// eating GPU/RAM); repeated dev restarts pile up orphans until the box OOMs.
	// Setpgid isolates it in its own process group so a stray Ctrl-C on the
	// terminal group doesn't half-kill it out from under us. (Linux-only, like
	// the rest of the daemon.)
	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true, Pdeathsig: syscall.SIGKILL}
	p.cmd = cmd

	stderr, err := cmd.StderrPipe()
	if err != nil {
		return fmt.Errorf("llm: stderr pipe: %w", err)
	}

	if err := cmd.Start(); err != nil {
		return fmt.Errorf("llm: start: %w", err)
	}

	portCh := make(chan string, 1)
	errCh := make(chan error, 1)
	p.wg.Add(1)
	go func() {
		defer p.wg.Done()
		buf := make([]byte, 4096)
		var leftover []byte
		for {
			n, err := stderr.Read(buf)
			if n > 0 {
				data := append(leftover, buf[:n]...)
				lines := bytes.Split(data, []byte("\n"))
				for _, line := range lines[:len(lines)-1] {
					if m := listenRE.FindSubmatch(line); len(m) > 1 {
						addr := string(m[1])
						portCh <- addr
						close(portCh)
					}
				}
				leftover = lines[len(lines)-1]
			}
			if err != nil {
				errCh <- err
				return
			}
		}
	}()

	select {
	case addr := <-portCh:
		p.port = addr
		return nil
	case err := <-errCh:
		_ = cmd.Process.Kill()
		return fmt.Errorf("llm: server output: %w", err)
	case <-ctx.Done():
		_ = cmd.Process.Kill()
		return ctx.Err()
	case <-time.After(60 * time.Second):
		_ = cmd.Process.Kill()
		return fmt.Errorf("llm: server did not start within 60s")
	}
}

func (p *LLMPhraser) Close() error {
	p.cancel()
	if p.cmd != nil && p.cmd.Process != nil {
		_ = p.cmd.Process.Kill()
	}
	p.wg.Wait()
	return nil
}

func (p *LLMPhraser) PhraseNudge(ctx context.Context, c loop.Candidate) (delivery.PhrasedNudge, error) {
	prompt := buildNudgePrompt(c)
	resp, err := p.chat(ctx, prompt)
	if err != nil {
		return delivery.PhrasedNudge{}, err
	}
	body, summary := parsePhrase(resp)
	if body == "" {
		body = fmt.Sprintf("%s — %s", c.Rule.Name, sevLabel(c.Severity))
	}
	if summary == "" {
		summary = c.Rule.Name
	}
	return delivery.PhrasedNudge{Candidate: c, Body: body, Summary: summary}, nil
}

func (p *LLMPhraser) PhraseReminder(ctx context.Context, d loop.ReminderDecision) (delivery.PhrasedReminder, error) {
	text := extractReminderText(d.Reminder.Payload)
	if text == "" {
		text = "reminder"
	}

	prompt := fmt.Sprintf(
		`The user set a reminder: "%s". Rephrase it briefly as a gentle nudge. Respond as JSON: {"body": "...", "summary": "..."}`,
		text,
	)
	resp, err := p.chat(ctx, prompt)
	if err != nil {
		return delivery.PhrasedReminder{}, err
	}
	body, summary := parsePhrase(resp)
	if body == "" {
		body = text
	}
	if summary == "" {
		summary = text
		if len(summary) > 60 {
			summary = summary[:57] + "..."
		}
	}
	return delivery.PhrasedReminder{Decision: d, Body: body, Summary: summary}, nil
}

type chatMsg struct {
	Role    string `json:"role"`
	Content string `json:"content"`
}

type chatReq struct {
	Model       string    `json:"model"`
	Messages    []chatMsg `json:"messages"`
	Temperature float64   `json:"temperature"`
	MaxTokens   int       `json:"max_tokens"`
}

type chatResp struct {
	Choices []struct {
		Message struct {
			Content string `json:"content"`
		} `json:"message"`
	} `json:"choices"`
}

func (p *LLMPhraser) chat(ctx context.Context, userPrompt string) (string, error) {
	req := chatReq{
		Messages: []chatMsg{
			{Role: "system", Content: systemPrompt()},
			{Role: "user", Content: userPrompt},
		},
		Temperature: 0.7,
		MaxTokens:   256,
	}
	body, err := json.Marshal(req)
	if err != nil {
		return "", fmt.Errorf("llm: marshal: %w", err)
	}

	httpReq, err := http.NewRequestWithContext(ctx, "POST", p.port+"/v1/chat/completions", bytes.NewReader(body))
	if err != nil {
		return "", fmt.Errorf("llm: request: %w", err)
	}
	httpReq.Header.Set("Content-Type", "application/json")

	resp, err := p.client.Do(httpReq)
	if err != nil {
		return "", fmt.Errorf("llm: post: %w", err)
	}
	defer resp.Body.Close()

	raw, err := io.ReadAll(resp.Body)
	if err != nil {
		return "", fmt.Errorf("llm: read: %w", err)
	}
	if resp.StatusCode != 200 {
		return "", fmt.Errorf("llm: status %d: %s", resp.StatusCode, strings.TrimSpace(string(raw)))
	}

	var cr chatResp
	if err := json.Unmarshal(raw, &cr); err != nil {
		return "", fmt.Errorf("llm: parse: %w", err)
	}
	if len(cr.Choices) == 0 {
		return "", fmt.Errorf("llm: no choices in response")
	}
	return cr.Choices[0].Message.Content, nil
}

func systemPrompt() string {
	return `You are maven, a self-hosted personal assistant. Generate brief, natural nudge messages in the user's language (Russian or English). Respond ONLY with valid JSON: {"body": "full voice message", "summary": "brief away-channel version (<60 chars)"}. body is what the user hears on voice; summary is for push notifications (ntfy/telegram) — minimal, no exfil detail.`
}

func buildNudgePrompt(c loop.Candidate) string {
	var ctxParts []string
	ctxParts = append(ctxParts, fmt.Sprintf("Rule: %s", c.Rule.Name))
	ctxParts = append(ctxParts, fmt.Sprintf("Severity: %s", sevLabel(c.Severity)))

	if d, ok := c.State.Since(c.Rule.Name); ok {
		ctxParts = append(ctxParts, fmt.Sprintf("Duration since last event: %s", humanDur(d)))
	}

	return fmt.Sprintf(
		`Generate a nudge message. Context:
%s

Respond as JSON: {"body": "...", "summary": "..."}`,
		strings.Join(ctxParts, "\n"),
	)
}

func parsePhrase(raw string) (body, summary string) {
	cleaned := strings.TrimSpace(raw)
	start := strings.Index(cleaned, "{")
	end := strings.LastIndex(cleaned, "}")
	if start < 0 || end < 0 || end <= start {
		return "", ""
	}
	var parsed struct {
		Body    string `json:"body"`
		Summary string `json:"summary"`
	}
	if err := json.Unmarshal([]byte(cleaned[start:end+1]), &parsed); err != nil {
		return "", ""
	}
	return parsed.Body, parsed.Summary
}

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