package builder

import (
	"context"
	"fmt"
	"log/slog"
	"regexp"
	"sort"
	"strings"
	"sync"
	"time"

	"code.t-juice.club/torjus/homelab-deploy/internal/messages"
	"code.t-juice.club/torjus/homelab-deploy/internal/metrics"
	"code.t-juice.club/torjus/homelab-deploy/internal/nats"
)

// hostnameRegex validates hostnames from flake output.
// Allows: alphanumeric, dashes, underscores, dots.
var hostnameRegex = regexp.MustCompile(`^[a-zA-Z0-9._-]+$`)

// truncateOutputLines truncates output to the first and last N lines if it exceeds 2*N lines,
// returning the result as a slice of strings.
func truncateOutputLines(output string, keepLines int) []string {
	lines := strings.Split(output, "\n")
	if len(lines) <= keepLines*2 {
		return lines
	}
	head := lines[:keepLines]
	tail := lines[len(lines)-keepLines:]
	omitted := len(lines) - keepLines*2
	result := make([]string, 0, keepLines*2+1)
	result = append(result, head...)
	result = append(result, fmt.Sprintf("... (%d lines omitted) ...", omitted))
	result = append(result, tail...)
	return result
}

// truncateOutput truncates output to the first and last N lines if it exceeds 2*N lines.
func truncateOutput(output string, keepLines int) string {
	lines := strings.Split(output, "\n")
	if len(lines) <= keepLines*2 {
		return output
	}
	head := lines[:keepLines]
	tail := lines[len(lines)-keepLines:]
	omitted := len(lines) - keepLines*2
	return strings.Join(head, "\n") + fmt.Sprintf("\n\n... (%d lines omitted) ...\n\n", omitted) + strings.Join(tail, "\n")
}

// BuilderConfig holds the configuration for the builder.
type BuilderConfig struct {
	NATSUrl        string
	NKeyFile       string
	ConfigFile     string
	Timeout        time.Duration
	MetricsEnabled bool
	MetricsAddr    string
}

// Builder handles build requests from NATS.
type Builder struct {
	cfg      BuilderConfig
	repoCfg  *Config
	client   *nats.Client
	executor *Executor
	lock     sync.Mutex
	busy     bool
	logger   *slog.Logger

	// metrics server and collector (nil if metrics disabled)
	metricsServer *metrics.Server
	metrics       *metrics.BuildCollector
}

// New creates a new builder with the given configuration.
func New(cfg BuilderConfig, repoCfg *Config, logger *slog.Logger) *Builder {
	if logger == nil {
		logger = slog.Default()
	}

	b := &Builder{
		cfg:      cfg,
		repoCfg:  repoCfg,
		executor: NewExecutor(cfg.Timeout),
		logger:   logger,
	}

	if cfg.MetricsEnabled {
		b.metricsServer = metrics.NewServer(metrics.ServerConfig{
			Addr:   cfg.MetricsAddr,
			Logger: logger,
		})
		b.metrics = metrics.NewBuildCollector(b.metricsServer.Registry())
	}

	return b
}

// Run starts the builder and blocks until the context is cancelled.
func (b *Builder) Run(ctx context.Context) error {
	// Start metrics server if enabled
	if b.metricsServer != nil {
		if err := b.metricsServer.Start(); err != nil {
			return fmt.Errorf("failed to start metrics server: %w", err)
		}
		defer func() {
			shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
			defer cancel()
			_ = b.metricsServer.Shutdown(shutdownCtx)
		}()
	}

	// Connect to NATS
	b.logger.Info("connecting to NATS", "url", b.cfg.NATSUrl)

	client, err := nats.Connect(nats.Config{
		URL:      b.cfg.NATSUrl,
		NKeyFile: b.cfg.NKeyFile,
		Name:     "homelab-deploy-builder",
	})
	if err != nil {
		return fmt.Errorf("failed to connect to NATS: %w", err)
	}
	b.client = client
	defer b.client.Close()

	b.logger.Info("connected to NATS")

	// Subscribe to build subjects for each repo
	for repoName := range b.repoCfg.Repos {
		// Subscribe to build.<repo>.all and build.<repo>.<hostname>
		allSubject := fmt.Sprintf("build.%s.*", repoName)
		b.logger.Info("subscribing to build subject", "subject", allSubject)
		if _, err := b.client.Subscribe(allSubject, b.handleBuildRequest); err != nil {
			return fmt.Errorf("failed to subscribe to %s: %w", allSubject, err)
		}
	}

	b.logger.Info("builder started", "repos", len(b.repoCfg.Repos))

	// Wait for context cancellation
	<-ctx.Done()
	b.logger.Info("shutting down builder")

	return nil
}

func (b *Builder) handleBuildRequest(subject string, data []byte) {
	req, err := messages.UnmarshalBuildRequest(data)
	if err != nil {
		b.logger.Error("failed to unmarshal build request",
			"subject", subject,
			"error", err,
		)
		return
	}

	b.logger.Info("received build request",
		"subject", subject,
		"repo", req.Repo,
		"target", req.Target,
		"branch", req.Branch,
		"reply_to", req.ReplyTo,
	)

	// Validate request
	if err := req.Validate(); err != nil {
		b.logger.Warn("invalid build request", "error", err)
		b.sendResponse(req.ReplyTo, messages.NewBuildResponse(
			messages.BuildStatusRejected,
			err.Error(),
		))
		return
	}

	// Get repo config
	repo, err := b.repoCfg.GetRepo(req.Repo)
	if err != nil {
		b.logger.Warn("unknown repo", "repo", req.Repo)
		b.sendResponse(req.ReplyTo, messages.NewBuildResponse(
			messages.BuildStatusRejected,
			fmt.Sprintf("unknown repo: %s", req.Repo),
		))
		return
	}

	// Try to acquire lock
	b.lock.Lock()
	if b.busy {
		b.lock.Unlock()
		b.logger.Warn("build already in progress")
		b.sendResponse(req.ReplyTo, messages.NewBuildResponse(
			messages.BuildStatusRejected,
			"another build is already in progress",
		))
		return
	}
	b.busy = true
	b.lock.Unlock()

	defer func() {
		b.lock.Lock()
		b.busy = false
		b.lock.Unlock()
	}()

	// Use default branch if not specified
	branch := req.Branch
	if branch == "" {
		branch = repo.DefaultBranch
	}

	// Determine hosts to build
	var hosts []string
	if req.Target == "all" {
		// List hosts from flake
		b.sendResponse(req.ReplyTo, messages.NewBuildResponse(
			messages.BuildStatusStarted,
			"discovering hosts...",
		))

		hosts, err = b.executor.ListHosts(context.Background(), repo.URL, branch)
		if err != nil {
			b.logger.Error("failed to list hosts", "error", err)
			b.sendResponse(req.ReplyTo, messages.NewBuildResponse(
				messages.BuildStatusFailed,
				fmt.Sprintf("failed to list hosts: %v", err),
			).WithError(err.Error()))
			if b.metrics != nil {
				b.metrics.RecordBuildFailure(req.Repo, "")
			}
			return
		}
		// Filter out hostnames with invalid characters (security: prevent injection)
		validHosts := make([]string, 0, len(hosts))
		for _, host := range hosts {
			if hostnameRegex.MatchString(host) {
				validHosts = append(validHosts, host)
			} else {
				b.logger.Warn("skipping hostname with invalid characters", "hostname", host)
			}
		}
		hosts = validHosts
		// Sort hosts for consistent ordering
		sort.Strings(hosts)
	} else {
		hosts = []string{req.Target}
	}

	if len(hosts) == 0 {
		b.sendResponse(req.ReplyTo, messages.NewBuildResponse(
			messages.BuildStatusFailed,
			"no hosts to build",
		))
		return
	}

	// Send started response
	b.sendResponse(req.ReplyTo, &messages.BuildResponse{
		Status:     messages.BuildStatusStarted,
		Message:    fmt.Sprintf("building %d host(s)", len(hosts)),
		HostsTotal: len(hosts),
	})

	// Build each host sequentially
	startTime := time.Now()
	results := make([]messages.BuildHostResult, 0, len(hosts))
	succeeded := 0
	failed := 0

	for i, host := range hosts {
		hostStart := time.Now()
		b.logger.Info("building host",
			"host", host,
			"repo", req.Repo,
			"rev", branch,
			"progress", fmt.Sprintf("%d/%d", i+1, len(hosts)),
			"command", b.executor.BuildCommand(repo.URL, branch, host),
		)

		result := b.executor.Build(context.Background(), repo.URL, branch, host)
		hostDuration := time.Since(hostStart).Seconds()

		hostResult := messages.BuildHostResult{
			Host:            host,
			Success:         result.Success,
			DurationSeconds: hostDuration,
		}
		if !result.Success {
			if result.Error != nil {
				hostResult.Error = result.Error.Error()
			}
			if result.Stderr != "" {
				hostResult.Output = truncateOutput(result.Stderr, 50)
			}
		}
		results = append(results, hostResult)

		if result.Success {
			succeeded++
			b.logger.Info("host build succeeded", "host", host, "repo", req.Repo, "rev", branch, "duration", hostDuration)
			if b.metrics != nil {
				b.metrics.RecordHostBuildSuccess(req.Repo, host, hostDuration)
			}
		} else {
			failed++
			b.logger.Error("host build failed", "host", host, "repo", req.Repo, "rev", branch, "error", hostResult.Error)
			if result.Stderr != "" {
				for _, line := range truncateOutputLines(result.Stderr, 50) {
					b.logger.Warn("build output", "host", host, "repo", req.Repo, "line", line)
				}
			}
			if b.metrics != nil {
				b.metrics.RecordHostBuildFailure(req.Repo, host, hostDuration)
			}
		}

		// Send progress update
		success := result.Success
		b.sendResponse(req.ReplyTo, &messages.BuildResponse{
			Status:         messages.BuildStatusProgress,
			Host:           host,
			HostSuccess:    &success,
			HostsCompleted: i + 1,
			HostsTotal:     len(hosts),
		})
	}

	totalDuration := time.Since(startTime).Seconds()

	// Send final response
	status := messages.BuildStatusCompleted
	message := fmt.Sprintf("built %d/%d hosts successfully", succeeded, len(hosts))
	if failed > 0 {
		status = messages.BuildStatusFailed
		message = fmt.Sprintf("build failed: %d/%d hosts failed", failed, len(hosts))
	}

	b.sendResponse(req.ReplyTo, &messages.BuildResponse{
		Status:               status,
		Message:              message,
		Results:              results,
		TotalDurationSeconds: totalDuration,
		Succeeded:            succeeded,
		Failed:               failed,
	})

	// Record overall build metrics
	if b.metrics != nil {
		if failed == 0 {
			b.metrics.RecordBuildSuccess(req.Repo)
		} else {
			b.metrics.RecordBuildFailure(req.Repo, "")
		}
	}
}

func (b *Builder) sendResponse(replyTo string, resp *messages.BuildResponse) {
	data, err := resp.Marshal()
	if err != nil {
		b.logger.Error("failed to marshal build response", "error", err)
		return
	}

	if err := b.client.Publish(replyTo, data); err != nil {
		b.logger.Error("failed to publish build response",
			"reply_to", replyTo,
			"error", err,
		)
	}

	// Flush to ensure response is sent immediately
	if err := b.client.Flush(); err != nil {
		b.logger.Error("failed to flush", "error", err)
	}
}