package systemd

import (
	"fmt"
	"strings"
	"text/template"

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

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 service.BaseName(u, prefix, suffix) + ".service"
}

// Generate produces the .service file content for a unit.
func Generate(u config.Unit, prefix, suffix string) (string, error) {
	if err := service.Validate(u); err != nil {
		return "", err
	}

	spec := service.Resolve(u)
	data := templateData{
		ServiceName:    ServiceName(u, prefix, suffix),
		Unit:           u,
		ExecStart:      spec.Start,
		ExecStop:       spec.Stop,
		RuntimeService: runtimeService(u.Runtime),
		Label:          spec.Label,
		ServiceType:    spec.Type,
		WorkingDir:     spec.WorkingDir,
	}

	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 ""
}