package systemd

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"text/template"

	"github.com/warkanum/unitdore/config"
)

const systemUnitTemplate = `# /etc/systemd/system/{{.ServiceName}}
# Generated by unitdore — do not edit manually

[Unit]
Description=Unitdore: {{.Unit.Name}} ({{.Label}})
After=network.target{{with .RuntimeService}} {{.}}
Requires={{.}}{{end}}

[Service]
Type={{.ServiceType}}
{{- if eq .ServiceType "oneshot"}}
RemainAfterExit=yes
{{- end}}
{{- with .WorkingDir}}
WorkingDirectory={{.}}
{{- end}}
ExecStart={{.ExecStart}}
ExecStop={{if .ExecStop}}-{{.ExecStop}}{{end}}
{{- if .Unit.Restart}}
Restart=on-failure
RestartSec={{.Unit.RestartSec}}
{{- if gt .Unit.RestartRetries 0}}
StartLimitBurst={{.Unit.RestartRetries}}
{{- end}}
{{- end}}

[Install]
WantedBy=multi-user.target
`

const userUnitTemplate = `# ~/.config/systemd/user/{{.ServiceName}}
# Generated by unitdore — do not edit manually

[Unit]
Description=Unitdore: {{.Unit.Name}} ({{.Label}})
After=default.target

[Service]
Type={{.ServiceType}}
{{- if eq .ServiceType "oneshot"}}
RemainAfterExit=yes
{{- end}}
{{- with .WorkingDir}}
WorkingDirectory={{.}}
{{- end}}
ExecStart={{.ExecStart}}
ExecStop={{if .ExecStop}}-{{.ExecStop}}{{end}}
{{- if .Unit.Restart}}
Restart=on-failure
RestartSec={{.Unit.RestartSec}}
{{- if gt .Unit.RestartRetries 0}}
StartLimitBurst={{.Unit.RestartRetries}}
{{- end}}
{{- end}}

[Install]
WantedBy=default.target
`

type templateData struct {
	ServiceName    string
	Unit           config.Unit
	ExecStart      string
	ExecStop       string
	RuntimeService string
	Label          string // shown in Description
	ServiceType    string // simple | oneshot
	WorkingDir     string
}

// ServiceName returns the systemd service name for a unit, with optional prefix/suffix.
func ServiceName(u config.Unit, prefix, suffix string) string {
	return fmt.Sprintf("unitdore-%s%s%s.service", prefix, u.Name, suffix)
}

// Generate produces the .service file content for a unit.
func Generate(u config.Unit, prefix, suffix string) (string, error) {
	data := templateData{
		ServiceName:    ServiceName(u, prefix, suffix),
		Unit:           u,
		RuntimeService: runtimeService(u.Runtime),
		Label:          u.Runtime,
		ServiceType:    "simple",
	}

	switch {
	case u.IsStack() && u.Command == "" && StackMode(u) == StackModeCompose:
		data.ExecStart, data.ExecStop = buildComposeCommands(u)
		data.Label = "podman-compose stack"
		data.WorkingDir = u.WorkingDir
	case u.IsStack() && u.Command == "":
		data.ExecStart, data.ExecStop = buildPodCommands(u)
		data.Label = "podman pod"
		data.ServiceType = "oneshot"
	default:
		data.ExecStart, data.ExecStop = buildExecCommands(u)
	}

	tmplStr := systemUnitTemplate
	if u.User != "" {
		tmplStr = userUnitTemplate
	}

	tmpl, err := template.New("unit").Parse(tmplStr)
	if err != nil {
		return "", fmt.Errorf("parsing template: %w", err)
	}

	var buf strings.Builder
	if err := tmpl.Execute(&buf, data); err != nil {
		return "", fmt.Errorf("rendering template: %w", err)
	}
	return buf.String(), nil
}

// runtimeService returns the systemd service name that must be running for the
// given container runtime, or "" if none is required (e.g. daemonless podman).
func runtimeService(runtime string) string {
	if runtime == "docker" {
		return "docker.service"
	}
	return ""
}

func buildExecCommands(u config.Unit) (start, stop string) {
	// If a custom command is provided, use it directly
	if u.Command != "" {
		return u.Command, ""
	}

	switch u.Runtime {
	case "podman":
		start = fmt.Sprintf("/usr/bin/podman start -a %s", u.Name)
		stop = fmt.Sprintf("/usr/bin/podman stop %s", u.Name)
	case "docker":
		start = fmt.Sprintf("/usr/bin/docker start -a %s", u.Name)
		stop = fmt.Sprintf("/usr/bin/docker stop %s", u.Name)
	default:
		start = fmt.Sprintf("/usr/bin/%s start %s", u.Runtime, u.Name)
		stop = fmt.Sprintf("/usr/bin/%s stop %s", u.Runtime, u.Name)
	}
	return start, stop
}

// Stack modes: compose (podman-compose up/stop) with pod start/stop as fallback.
const (
	StackModeCompose = "compose"
	StackModePod     = "pod"
)

// StackMode picks how a stack unit is started: compose when the compose binary,
// working dir and compose files all exist; otherwise pod start/stop.
func StackMode(u config.Unit) string {
	if ComposeAvailable(u) {
		return StackModeCompose
	}
	return StackModePod
}

// ComposeAvailable reports whether the stack can be driven by podman-compose.
func ComposeAvailable(u config.Unit) bool {
	if u.ComposeBin == "" || u.WorkingDir == "" {
		return false
	}
	if !exists(u.ComposeBin) || !exists(u.WorkingDir) {
		return false
	}
	for _, f := range u.ComposeFiles {
		if !filepath.IsAbs(f) {
			f = filepath.Join(u.WorkingDir, f)
		}
		if !exists(f) {
			return false
		}
	}
	return true
}

func exists(path string) bool {
	_, err := os.Stat(path)
	return err == nil
}

func buildComposeCommands(u config.Unit) (start, stop string) {
	args := []string{quoteArg(u.ComposeBin), "-p", quoteArg(u.Project)}
	for _, f := range u.ComposeFiles {
		args = append(args, "-f", quoteArg(f))
	}
	base := strings.Join(args, " ")
	return base + " up", base + " stop"
}

func buildPodCommands(u config.Unit) (start, stop string) {
	pod := quoteArg("pod_" + u.Project)
	return "/usr/bin/podman pod start " + pod, "/usr/bin/podman pod stop " + pod
}

// quoteArg double-quotes an argument for systemd command lines if it
// contains whitespace or quotes.
func quoteArg(s string) string {
	if !strings.ContainsAny(s, " \t\"'\\") {
		return s
	}
	r := strings.NewReplacer(`\`, `\\`, `"`, `\"`)
	return `"` + r.Replace(s) + `"`
}