// Package inspect reports local prerequisite observations without executing
// commands, connecting to Docker or altering configuration.
package inspect

import (
	"errors"
	"io/fs"
	"os"
	"runtime"
)

type Report struct {
	ProtocolVersion   int      `json:"protocolVersion"`
	OS                string   `json:"os"`
	Architecture      string   `json:"architecture"`
	SupportedPlatform bool     `json:"supportedPlatform"`
	SystemdRuntime    string   `json:"systemdRuntime"`
	DockerClient      string   `json:"dockerClient"`
	DockerDaemon      string   `json:"dockerDaemon"`
	Compose           string   `json:"compose"`
	Unchecked         []string `json:"unchecked"`
	DeploymentReady   bool     `json:"deploymentReady"`
}

func Collect() Report { return Probe(runtime.GOOS, runtime.GOARCH, os.DirFS("/")) }

// Probe observes filesystem metadata only. "present" is not an assertion that
// systemd is responsive or the Docker executable is authentic or operational.
func Probe(goos, arch string, files fs.FS) Report {
	r := Report{ProtocolVersion: 1, OS: goos, Architecture: arch, SupportedPlatform: goos == "linux" && (arch == "amd64" || arch == "arm64"), SystemdRuntime: "not_checked", DockerClient: "not_checked", DockerDaemon: "not_checked", Compose: "not_checked", Unchecked: []string{"docker_daemon", "compose_version", "host_identity", "distribution_support", "permissions", "disk_space", "ports", "dns", "firewall", "gateway"}}
	if goos != "linux" {
		return r
	}
	r.SystemdRuntime = observe(files, "run/systemd/system", true)
	r.DockerClient = observe(files, "usr/bin/docker", false)
	if r.DockerClient != "present" {
		alternate := observe(files, "usr/local/bin/docker", false)
		// Either known executable establishes presence. Otherwise retain any
		// uncertainty instead of reporting absence from an incomplete check.
		switch {
		case alternate == "present":
			r.DockerClient = "present"
		case r.DockerClient == "unknown" || alternate == "unknown":
			r.DockerClient = "unknown"
		case r.DockerClient == "invalid" || alternate == "invalid":
			r.DockerClient = "invalid"
		}
	}
	return r
}

func observe(files fs.FS, path string, directory bool) string {
	info, err := fs.Stat(files, path)
	if errors.Is(err, fs.ErrNotExist) {
		return "missing"
	}
	if err != nil {
		return "unknown"
	}
	if directory {
		if info.IsDir() {
			return "present"
		}
		return "invalid"
	}
	if !info.Mode().IsRegular() || info.Mode().Perm()&0111 == 0 {
		return "invalid"
	}
	return "present"
}