package haproxy

import (
	"bufio"
	"fmt"
	"log/slog"
	"net"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"time"
)

// InstanceRoute represents a Wild Cloud instance's ingress routing configuration
// InstanceRoute represents an L4 TCP passthrough route (k8s instance).
type InstanceRoute struct {
	Name       string `json:"name"`       // identifier for backend naming
	Domain     string `json:"domain"`     // e.g. "cloud.payne.io"
	BackendIP  string `json:"backendIP"`  // k8s load balancer IP
	Subdomains bool   `json:"subdomains"` // if true, also match *.domain
}

// CustomRoute represents a custom TCP proxy rule for non-Wild Cloud services
type CustomRoute struct {
	Name    string // e.g. "civil_ssh"
	Port    int    // external listen port
	Backend string // e.g. "192.168.8.10:22"
}

// HTTPRoute represents an L7 HTTP reverse proxy route (for Wild Works services).
// Central terminates TLS using a wildcard certificate and proxies by Host header.
type HTTPRoute struct {
	Name       string // e.g. "my-api"
	Domain     string // e.g. "my-api.payne.io"
	Backend    string // e.g. "192.168.8.60:9001"
	HealthPath string // e.g. "/health" (optional, for active health checks)
}

const defaultConfigPath = "/etc/haproxy/haproxy.cfg"
const defaultSocketPath = "/var/run/haproxy/admin.sock"

// Manager handles HAProxy configuration generation and service management
type Manager struct {
	configPath string
	socketPath string
}

// NewManager creates a new HAProxy manager
func NewManager(configPath string) *Manager {
	if configPath == "" {
		configPath = defaultConfigPath
	}
	return &Manager{configPath: configPath, socketPath: defaultSocketPath}
}

// SetSocketPath overrides the HAProxy stats socket path (useful for testing)
func (m *Manager) SetSocketPath(path string) {
	m.socketPath = path
}

// GetConfigPath returns the HAProxy config file path
func (m *Manager) GetConfigPath() string {
	return m.configPath
}

// GenerateOpts holds optional parameters for HAProxy config generation.
type GenerateOpts struct {
	HTTPRoutes []HTTPRoute // L7 HTTP reverse proxy routes (TLS terminated by Central)
	CertsDir   string      // directory containing per-domain PEM files for L7 TLS
}

// Generate creates a complete HAProxy configuration from instance routes, custom routes,
// and optional config. Uses L4 TCP mode with SNI inspection for HTTPS —
// TLS terminates at each k8s cluster's traefik. HTTP routes add an L7 frontend
// where Central terminates TLS with a wildcard cert and reverse-proxies by Host header.
func (m *Manager) Generate(instances []InstanceRoute, custom []CustomRoute, centralDomain ...string) string {
	return m.GenerateWithOpts(instances, custom, GenerateOpts{})
}

// GenerateWithOpts creates a complete HAProxy configuration with full options.
func (m *Manager) GenerateWithOpts(instances []InstanceRoute, custom []CustomRoute, opts GenerateOpts) string {
	var sb strings.Builder

	sb.WriteString(`# Wild Cloud HAProxy Configuration
# Managed by Wild Cloud Central API — do not edit manually

global
    log /dev/log local0 info
    stats socket /var/run/haproxy/admin.sock mode 666 level admin expose-fd listeners
    stats timeout 30s
    maxconn 50000
    daemon

defaults
    log global
    mode tcp
    option tcplog
    option dontlognull
    timeout connect 5s
    timeout client 50s
    timeout server 50s

# Stats page (LAN access only — not proxied externally)
frontend stats
    bind *:8404
    mode http
    stats enable
    stats uri /stats
    stats refresh 10s

# HTTP: redirect all to HTTPS
frontend http_in
    bind *:80
    mode http
    redirect scheme https code 301

`)

	hasL4Routes := len(instances) > 0 || len(opts.HTTPRoutes) > 0

	if hasL4Routes {
		sb.WriteString("# HTTPS: SNI-based L4 routing (TLS passes through to k8s traefik)\n")
		sb.WriteString("frontend https_in\n")
		sb.WriteString("    bind *:443\n")
		sb.WriteString("    mode tcp\n")
		sb.WriteString("    tcp-request inspect-delay 5s\n")
		sb.WriteString("    tcp-request content accept if { req_ssl_hello_type 1 }\n")
		sb.WriteString("\n")

		// ACL ordering is critical. Process in this order:
		// 1. L7 HTTP exact matches (central, wild-cloud app) → L7 termination
		// 2. L4 exact matches (payne.io, civilsociety.dev) → instance backends
		// 3. L4 wildcard matches (*.cloud.payne.io) → instance backends
		// 4. Default → L7 termination (if any HTTP routes exist)

		// 1. L7 HTTP services — exact match, route to L7 TLS termination frontend
		if len(opts.HTTPRoutes) > 0 {
			sb.WriteString("    # L7 HTTP services (exact match → TLS termination)\n")
			for _, route := range opts.HTTPRoutes {
				aclName := "is_l7_" + sanitizeName(route.Name)
				fmt.Fprintf(&sb, "    acl %s req_ssl_sni -m str %s\n", aclName, route.Domain)
				fmt.Fprintf(&sb, "    use_backend be_l7_termination if %s\n", aclName)
			}
			sb.WriteString("\n")
		}

		// 2. L4 exact matches — instances with subdomains:false
		hasExact := false
		for _, inst := range instances {
			if inst.Subdomains {
				continue // handled in step 3
			}
			hasExact = true
			aclName := "is_" + sanitizeName(inst.Name)
			fmt.Fprintf(&sb, "    acl %s req_ssl_sni -m str %s\n", aclName, inst.Domain)
			fmt.Fprintf(&sb, "    use_backend be_https_%s if %s\n", sanitizeName(inst.Name), aclName)
		}
		if hasExact {
			sb.WriteString("\n")
		}

		// 3. L4 wildcard matches — instances with subdomains:true
		sb.WriteString("    # L4 instance routes (wildcard subdomain matching)\n")
		for _, inst := range instances {
			if !inst.Subdomains {
				continue // already handled in step 2
			}
			aclName := "is_" + sanitizeName(inst.Name)
			fmt.Fprintf(&sb, "    acl %s req_ssl_sni -m end .%s\n", aclName, inst.Domain)
			fmt.Fprintf(&sb, "    acl %s req_ssl_sni -m str %s\n", aclName, inst.Domain)
			fmt.Fprintf(&sb, "    use_backend be_https_%s if %s\n", sanitizeName(inst.Name), aclName)
		}
		sb.WriteString("\n")

		// 4. Default → L7 termination fallback
		if len(opts.HTTPRoutes) > 0 {
			sb.WriteString("    default_backend be_l7_termination\n")
		}

		sb.WriteString("\n")

		// Instance L4 backends
		for _, inst := range instances {
			fmt.Fprintf(&sb, "backend be_https_%s\n", sanitizeName(inst.Name))
			sb.WriteString("    mode tcp\n")
			sb.WriteString("    option tcp-check\n")
			fmt.Fprintf(&sb, "    server s0 %s:443 check\n", inst.BackendIP)
			sb.WriteString("\n")
		}

		// L7 TLS termination backend + frontend (for HTTP routes)
		if len(opts.HTTPRoutes) > 0 {
			// Load all PEM files from the certs directory — HAProxy serves
			// the right cert per-SNI. Each service gets its own <domain>.pem.
			certPath := opts.CertsDir
			if certPath == "" {
				certPath = "/etc/haproxy/certs/"
			}

			sb.WriteString("backend be_l7_termination\n")
			sb.WriteString("    mode tcp\n")
			sb.WriteString("    server s0 127.0.0.1:8443\n")
			sb.WriteString("\n")

			sb.WriteString("# L7 HTTP frontend: TLS termination + Host-based routing\n")
			sb.WriteString("frontend l7_https\n")
			fmt.Fprintf(&sb, "    bind 127.0.0.1:8443 ssl crt %s\n", certPath)
			sb.WriteString("    mode http\n")
			sb.WriteString("\n")

			for _, route := range opts.HTTPRoutes {
				aclName := "host_" + sanitizeName(route.Name)
				fmt.Fprintf(&sb, "    acl %s hdr(host) -i %s\n", aclName, route.Domain)
				fmt.Fprintf(&sb, "    use_backend be_l7_%s if %s\n", sanitizeName(route.Name), aclName)
			}
			sb.WriteString("\n")

			// L7 backends
			for _, route := range opts.HTTPRoutes {
				fmt.Fprintf(&sb, "backend be_l7_%s\n", sanitizeName(route.Name))
				sb.WriteString("    mode http\n")
				if route.HealthPath != "" {
					fmt.Fprintf(&sb, "    option httpchk GET %s\n", route.HealthPath)
					fmt.Fprintf(&sb, "    server s0 %s check\n", route.Backend)
				} else {
					fmt.Fprintf(&sb, "    server s0 %s\n", route.Backend)
				}
				sb.WriteString("\n")
			}
		}
	}

	for _, route := range custom {
		fmt.Fprintf(&sb, "# Custom route: %s\n", route.Name)
		fmt.Fprintf(&sb, "frontend fe_%s\n", sanitizeName(route.Name))
		fmt.Fprintf(&sb, "    bind *:%d\n", route.Port)
		sb.WriteString("    mode tcp\n")
		fmt.Fprintf(&sb, "    default_backend be_%s\n", sanitizeName(route.Name))
		sb.WriteString("\n")
		fmt.Fprintf(&sb, "backend be_%s\n", sanitizeName(route.Name))
		sb.WriteString("    mode tcp\n")
		fmt.Fprintf(&sb, "    server s0 %s\n", route.Backend)
		sb.WriteString("\n")
	}

	return sb.String()
}

// sanitizeName converts a name to a valid HAProxy identifier (alphanumeric + underscore)
func sanitizeName(name string) string {
	return strings.Map(func(r rune) rune {
		if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9') || r == '_' {
			return r
		}
		return '_'
	}, name)
}

// GetListenPorts returns all TCP/HTTP ports HAProxy is configured to listen on.
// Used to keep nftables rules in sync.
func (m *Manager) GetListenPorts(instances []InstanceRoute, custom []CustomRoute) []int {
	ports := []int{80, 443, 8404}
	for _, route := range custom {
		ports = append(ports, route.Port)
	}
	return ports
}

// ValidateConfig tests an HAProxy configuration file for syntax errors
func (m *Manager) ValidateConfig(configPath string) error {
	cmd := exec.Command("haproxy", "-c", "-f", configPath)
	output, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("haproxy config validation failed: %w (output: %s)", err, string(output))
	}
	return nil
}

// WriteConfig validates and atomically writes the HAProxy configuration
func (m *Manager) WriteConfig(content string) error {
	tempFile := m.configPath + ".tmp"

	if err := os.WriteFile(tempFile, []byte(content), 0644); err != nil {
		return fmt.Errorf("writing temp config: %w", err)
	}

	if err := m.ValidateConfig(tempFile); err != nil {
		os.Remove(tempFile)
		return err
	}

	if err := os.Rename(tempFile, m.configPath); err != nil {
		os.Remove(tempFile)
		return fmt.Errorf("installing config: %w", err)
	}

	slog.Info("haproxy config written", "component", "haproxy", "path", m.configPath)
	return nil
}

// ReloadService gracefully reloads HAProxy (starts it if not running)
func (m *Manager) ReloadService() error {
	cmd := exec.Command("systemctl", "reload-or-restart", "haproxy.service")
	output, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("failed to reload haproxy: %w (output: %s)", err, string(output))
	}
	slog.Info("haproxy service reloaded", "component", "haproxy")
	return nil
}

// RestartService performs a full restart of HAProxy
func (m *Manager) RestartService() error {
	cmd := exec.Command("systemctl", "restart", "haproxy.service")
	output, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("failed to restart haproxy: %w (output: %s)", err, string(output))
	}
	slog.Info("haproxy service restarted", "component", "haproxy")
	return nil
}

// ServiceStatus represents the status of the HAProxy service
type ServiceStatus struct {
	Status      string    `json:"status"`
	PID         int       `json:"pid"`
	ConfigFile  string    `json:"configFile"`
	LastRestart time.Time `json:"lastRestart"`
}

// GetStatus returns the current HAProxy service status
func (m *Manager) GetStatus() (*ServiceStatus, error) {
	status := &ServiceStatus{
		ConfigFile: m.configPath,
	}

	cmd := exec.Command("systemctl", "is-active", "haproxy.service")
	output, err := cmd.Output()
	if err != nil {
		status.Status = "inactive"
		return status, nil
	}

	status.Status = strings.TrimSpace(string(output))

	if status.Status == "active" {
		cmd = exec.Command("systemctl", "show", "haproxy.service", "--property=MainPID")
		if output, err := cmd.Output(); err == nil {
			parts := strings.Split(strings.TrimSpace(string(output)), "=")
			if len(parts) == 2 {
				if pid, err := strconv.Atoi(parts[1]); err == nil {
					status.PID = pid
				}
			}
		}

		cmd = exec.Command("systemctl", "show", "haproxy.service", "--property=ActiveEnterTimestamp")
		if output, err := cmd.Output(); err == nil {
			parts := strings.Split(strings.TrimSpace(string(output)), "=")
			if len(parts) == 2 {
				if t, err := time.Parse("Mon 2006-01-02 15:04:05 MST", parts[1]); err == nil {
					status.LastRestart = t
				}
			}
		}
	}

	return status, nil
}

// ReadConfig reads the current HAProxy configuration file
func (m *Manager) ReadConfig() (string, error) {
	data, err := os.ReadFile(m.configPath)
	if err != nil {
		return "", fmt.Errorf("reading haproxy config: %w", err)
	}
	return string(data), nil
}

// BackendStat holds per-backend connection counts from the HAProxy stats socket
type BackendStat struct {
	Name        string `json:"name"`
	Status      string `json:"status"`
	ActiveConns int    `json:"activeConns"`
	Rate        int    `json:"rate"`
	PeakRate    int    `json:"peakRate"`
	TotalConns  int64  `json:"totalConns"`
	Errors      int64  `json:"errors"`
}

// GetStats reads live connection stats from the HAProxy stats socket.
// Returns an empty slice (not an error) when HAProxy is not running.
func (m *Manager) GetStats() ([]BackendStat, error) {
	conn, err := net.Dial("unix", m.socketPath)
	if err != nil {
		// HAProxy not running or socket not yet created — not a hard error
		return []BackendStat{}, nil
	}
	defer conn.Close()

	if _, err := fmt.Fprintf(conn, "show stat\n"); err != nil {
		return nil, fmt.Errorf("sending stats command: %w", err)
	}

	// CSV format: # pxname,svname,...,status,...,scur,...,stot,...,eresp,...
	var stats []BackendStat
	scanner := bufio.NewScanner(conn)
	var headers []string
	for scanner.Scan() {
		line := scanner.Text()
		if strings.HasPrefix(line, "#") {
			// Header line: "# pxname,svname,..."
			headers = strings.Split(strings.TrimPrefix(line, "# "), ",")
			continue
		}
		if line == "" || len(headers) == 0 {
			continue
		}
		fields := strings.Split(line, ",")
		if len(fields) < len(headers) {
			continue
		}
		idx := func(name string) int {
			for i, h := range headers {
				if h == name {
					return i
				}
			}
			return -1
		}
		// Only report backends (svname == "BACKEND")
		svIdx := idx("svname")
		if svIdx < 0 || fields[svIdx] != "BACKEND" {
			continue
		}
		stat := BackendStat{
			Name:   fields[idx("pxname")],
			Status: fields[idx("status")],
		}
		if i := idx("scur"); i >= 0 {
			fmt.Sscanf(fields[i], "%d", &stat.ActiveConns)
		}
		if i := idx("rate"); i >= 0 {
			fmt.Sscanf(fields[i], "%d", &stat.Rate)
		}
		if i := idx("rate_max"); i >= 0 {
			fmt.Sscanf(fields[i], "%d", &stat.PeakRate)
		}
		if i := idx("stot"); i >= 0 {
			fmt.Sscanf(fields[i], "%d", &stat.TotalConns)
		}
		if i := idx("eresp"); i >= 0 {
			fmt.Sscanf(fields[i], "%d", &stat.Errors)
		}
		stats = append(stats, stat)
	}
	if err := scanner.Err(); err != nil {
		return nil, fmt.Errorf("reading stats: %w", err)
	}
	return stats, nil
}