package emitter

import (
	"errors"
	"fmt"
	"strings"

	"git.cloudinit.dev/coreci/orca/internal/jobspec"
)

// SystemdEmitter is the Emitter implementation for the "process"
// runtime. It renders the systemd unit file for the workload,
// including the lifecycle hooks (P04) and the R-007 socket plumbing
// (P08).
//
// Lifecycle hooks map to systemd semantics (PRD §10.1):
//
//   - lifecycle.pre_stop → ExecStop= (the command run on stop; systemd
//     runs ExecStop, then kills the main process after the deadline).
//   - lifecycle.post_start → ExecStartPost= (runs after the main
//     process starts).
//
// systemd has no ExecStartPre equivalent for a "pre_start" hook; the
// spec does not define pre_start (only pre_stop and post_start per
// PRD §10.1), so no mapping is needed.
//
// The unit name carries the `orca-v1-` prefix per the dual-write
// window (REQ-090) so the v0.9 SSH-push path does not collide with the
// v0.8 daemon's `orca-<job>.service` units during the migration
// window.
//
// Later phases extend this emitter:
//
//   - v0.10-P03: secrets via EnvironmentFile= + LoadCredential=
type SystemdEmitter struct{}

// unitNamePrefix is the v0.9 SSH-push unit-name prefix. The v0.8
// daemon uses `orca-<job>.service`; the v0.9 path uses
// `orca-v1-<spec.Name>.service` so the two never overlap (REQ-090,
// I-C-006). The prefix is load-bearing — do not change it without
// updating the dual-write window contract.
const unitNamePrefix = "orca-v1-"

// Render renders the systemd unit file for a process-runtime workload.
// The unit name is /etc/systemd/system/<unitNamePrefix><spec.Name>.service
// and the content is a [Service] block with ExecStart, optional
// ExecStartPost (lifecycle.post_start), optional ExecStop
// (lifecycle.pre_stop), and the R-007 socket-plumbing lines
// (RuntimeDirectory=, optional TCP-bind ExecStartPre). Mode is 0644.
//
// The rendered shape is:
//
//	[Service]
//	ExecStart=<runtime command>
//	ExecStartPost=<post_start command 1>
//	ExecStartPost=<post_start command 2>
//	ExecStop=<pre_stop command 1>
//	ExecStop=<pre_stop command 2>
//	RuntimeDirectory=orca/alloc-<alloc-id>
//	# socket: /run/orca/alloc-<alloc-id>/port-<name>.sock
//	ExecStartPre=/bin/echo orca: bind 127.0.0.1 port <name> (tcp, R-007 opt-in)
//
// Returns an error if the spec is nil, the spec is missing its name,
// the runtime block is nil, or the runtime command is empty (a
// workload with no command has nothing to ExecStart).
func (SystemdEmitter) Render(spec *jobspec.WorkloadSpec, node *Node) ([]File, error) {
	if spec == nil {
		return nil, errors.New("emitter/systemd: spec is nil")
	}
	if strings.TrimSpace(spec.Name) == "" {
		return nil, errors.New("emitter/systemd: spec name is empty")
	}
	if spec.Runtime == nil {
		return nil, errors.New("emitter/systemd: runtime block is nil")
	}
	if strings.TrimSpace(spec.Runtime.Command) == "" {
		return nil, errors.New("emitter/systemd: runtime command is empty")
	}
	path := fmt.Sprintf("/etc/systemd/system/%s%s.service", unitNamePrefix, spec.Name)
	content := renderSystemdUnit(spec)
	return []File{{Path: path, Content: content, Mode: "0644"}}, nil
}

// renderSystemdUnit renders the full [Service] block for the spec,
// including ExecStart, lifecycle hooks (ExecStartPost, ExecStop), and
// the R-007 socket-plumbing lines (RuntimeDirectory=, optional
// TCP-bind ExecStartPre). The output is a single string with a
// trailing newline per line.
func renderSystemdUnit(spec *jobspec.WorkloadSpec) string {
	var b strings.Builder
	b.WriteString("[Service]\n")
	b.WriteString(fmt.Sprintf("ExecStart=%s\n", spec.Runtime.Command))
	// Lifecycle: post_start → ExecStartPost (runs after start).
	for _, cmd := range lifecyclePostStart(spec) {
		b.WriteString(fmt.Sprintf("ExecStartPost=%s\n", cmd))
	}
	// Lifecycle: pre_stop → ExecStop (runs before the process is killed).
	for _, cmd := range lifecyclePreStop(spec) {
		b.WriteString(fmt.Sprintf("ExecStop=%s\n", cmd))
	}
	// R-007 socket plumbing: RuntimeDirectory= per port + optional
	// TCP-bind ExecStartPre.
	for _, line := range (SocketEmitter{}).RenderSocketLines(spec) {
		b.WriteString(line)
		b.WriteString("\n")
	}
	return b.String()
}

// lifecyclePostStart returns the post_start lifecycle commands for
// the spec, or nil when the spec has no lifecycle block or no
// post_start commands.
func lifecyclePostStart(spec *jobspec.WorkloadSpec) []string {
	if spec.Lifecycle == nil {
		return nil
	}
	return spec.Lifecycle.PostStart
}

// lifecyclePreStop returns the pre_stop lifecycle commands for the
// spec, or nil when the spec has no lifecycle block or no pre_stop
// commands.
func lifecyclePreStop(spec *jobspec.WorkloadSpec) []string {
	if spec.Lifecycle == nil {
		return nil
	}
	return spec.Lifecycle.PreStop
}