sourceafReflux::Preferences.fan

using afIoc

** (Service) -
** Loads / saves and maintains a cache of preference objects.
** Instances are cached until the backing file is updated / modified.
**
** Because Reflux is application centric, preference files are not associated
** with pods, but with the application name supplied at startup:
**
**   %FAN_HOME%/etc/<app-name>/xxx.fog
**
** Preference instances must be serializable.
mixin Preferences {

    ** Returns an instance of the given preferences object.
    **
    **   syntax: fantom
    **   preferences.loadPrefs(MyPrefs#, "myPrefs.fog")
    abstract Obj loadPrefs(Type prefsType, Str? name := null)

    ** Saves the given preference instance.
    **
    **   syntax: fantom
    **   preferences.savePrefs(myPrefs, "myPrefs.fog")
    abstract Void savePrefs(Obj prefs, Str? name := null)

    ** Returns 'true' if the preferences file has been updated since it was last read.
    abstract Bool updated(Type prefsType, Str? name := null)

    ** Finds the named file in the applications 'etc' dir.
    ** If such a file does not exist, a file in the 'workDir' is returned.
    abstract File? findFile(Str name)

}

internal class PreferencesImpl : Preferences {
            private static const Log    log     := Preferences#.pod.log
            private Str:CachedPrefs     cache   := Str:CachedPrefs[:]
            private Str                 appName
    @Inject private Registry            registry

    private new make(RegistryMeta regMeta, |This| in) {
        in(this)
        this.appName = regMeta[RefluxConstants.meta_appName].toStr.fromDisplayName
    }

    override Obj loadPrefs(Type prefsType, Str? name := null) {
        name = name ?: "${prefsType.name}.fog"
        cached  := loadFromCache(name)

        if (cached != null) {
            log.debug("Returning cached $prefsType.name $cached")
            return cached
        }

        file    := findFile(name)
        prefs   := loadFromFile(file)

        if (prefs == null) {
            log.debug("Making preferences: $prefsType.name")
            prefs = registry.autobuild(prefsType)
        }

        cache[name] = CachedPrefs(file, prefs)

        return prefs
    }

    override Void savePrefs(Obj prefs, Str? name := null) {
        name = name ?: "${prefs.typeof.name}.fog"
        if (runtimeIsJs) {
            log.info("Cannot save $name in JS")
            return
        }
        file := findFile(name)
        file.writeObj(prefs, ["indent":2])
    }

    override Bool updated(Type prefsType, Str? name := null) {
        name = name ?: "${prefsType.name}.fog"
        return cache[name]?.modified ?: true
    }

    override File? findFile(Str name) {
        pathUri := `etc/${appName}/${name}`
        if (runtimeIsJs) {
            log.info("File $pathUri does not exist in JS")
            return null
        }

        envFile := Env.cur.findFile(pathUri, false) ?: Env.cur.workDir + pathUri
        return envFile.normalize    // normalize gives the full absolute path
    }

    // ---- Private -------------------------------------------------------------------------------

    private Obj? loadFromCache(Str name) {
        cached      := cache[name]
        modified    := cached?.modified ?: true
        return modified ? null : cached.prefs
    }

    private Obj? loadFromFile(File? file) {
        Obj? value := null
        try {
            if (file != null && file.exists) {
                log.debug("Loading preferences: $file")
                value = file.readObj
                registry.injectIntoFields(value)
            }
        } catch (Err e) {
            log.err("Cannot load options: $file", e)
        }
        return value
    }

    private static Bool runtimeIsJs() {
        Env.cur.runtime == "js"
    }
}

internal class CachedPrefs {
    private File?       file
    private DateTime?   modied
            Obj         prefs

    new make(File? f, Obj prefs) {
        this.file   = f
        this.modied = f?.modified
        this.prefs  = prefs
    }

    Bool modified() {
        if (file == null)
            return false
        return file.modified != modied
    }
}