package process

import (
	"fmt"
	"log"
	"os"
	"strings"
	"sync"
)

// FingerprintEnv is the environment value the node-engine starts each process with, a service and a container alike:
// the fingerprint of the want it applies (novox/hq ADR 0656; design 47 *The fingerprint handover*).
const FingerprintEnv = "MESH_FINGERPRINT"

// OwnBuildUnknown is what a process started with no fingerprint says of its own build, in its journal and to whoever
// reads it (the node-engine's process builds, the indexer acting on it as ADR 0639 §8 has it).
const OwnBuildUnknown = "own build unknown"

// Build is the build a process was started with: its fingerprint, or why it is unknown.
type Build struct {
	Fingerprint string `json:"fingerprint,omitempty"`
	// Unknown says why there is no fingerprint, starting with OwnBuildUnknown; empty when there is one.
	Unknown string `json:"unknown,omitempty"`
}

// String is the fingerprint, or why the build is unknown.
func (b Build) String() string {
	if b.Fingerprint != "" {
		return b.Fingerprint
	}
	return b.Unknown
}

// ReadOwnBuild is the build getenv's FingerprintEnv names: one word, or unknown with the reason.
func ReadOwnBuild(getenv func(string) string) Build {
	fp := strings.TrimSpace(getenv(FingerprintEnv))
	switch {
	case fp == "":
		return Build{Unknown: OwnBuildUnknown + ": started without " + FingerprintEnv}
	case strings.ContainsAny(fp, " \t\r\n"):
		return Build{Unknown: fmt.Sprintf("%s: %s %q is not one fingerprint", OwnBuildUnknown, FingerprintEnv, fp)}
	}
	return Build{Fingerprint: fp}
}

// sayOwnBuild writes the process's own build in its journal; a variable so a test reads what it says.
var sayOwnBuild = func(b Build) { log.Printf("own build: %s", b) }

// readAndSay reads the build from this process's environment and says it.
func readAndSay() Build {
	b := ReadOwnBuild(os.Getenv)
	sayOwnBuild(b)
	return b
}

// ownBuild is read once; a test that reads it makes it again (sync.OnceValue(readAndSay)) and puts it back.
var ownBuild = sync.OnceValue(readAndSay)

// OwnBuild is this process's own build, read once from its environment at the first ask and said in its journal then;
// every later ask answers the same, whatever the environment says since. Connect and Dial ask it, so every process
// that reaches the bus says it at its start.
func OwnBuild() Build { return ownBuild() }