config.go

package cfg

import (
	"errors"
	"fmt"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/wiggin77/cfg/timeconv"
)

// ErrNotFound returned when an operation is attempted on a
// resource that doesn't exist, such as fetching a non-existing
// property name.
var ErrNotFound = errors.New("not found")

type sourceEntry struct {
	src   Source
	props map[string]string
}

// Config provides methods for retrieving property values from one or more
// configuration sources.
type Config struct {
	mutexSrc         sync.RWMutex
	mutexListeners   sync.RWMutex
	srcs             []*sourceEntry
	chgListeners     []ChangedListener
	shutdown         chan interface{}
	wantPanicOnError bool
}

// PrependSource inserts one or more `Sources` at the beginning of
// the list of sources such that the first source will be the
// source checked first when resolving a property value.
func (config *Config) PrependSource(srcs ...Source) {
	arr := config.wrapSources(srcs...)

	config.mutexSrc.Lock()
	if config.shutdown == nil {
		config.shutdown = make(chan interface{})
	}
	config.srcs = append(arr, config.srcs...)
	config.mutexSrc.Unlock()

	for _, se := range arr {
		if _, ok := se.src.(SourceMonitored); ok {
			config.monitor(se)
		}
	}
}

// AppendSource appends one or more `Sources` at the end of
// the list of sources such that the last source will be the
// source checked last when resolving a property value.
func (config *Config) AppendSource(srcs ...Source) {
	arr := config.wrapSources(srcs...)

	config.mutexSrc.Lock()
	if config.shutdown == nil {
		config.shutdown = make(chan interface{})
	}
	config.srcs = append(config.srcs, arr...)
	config.mutexSrc.Unlock()

	for _, se := range arr {
		if _, ok := se.src.(SourceMonitored); ok {
			config.monitor(se)
		}
	}
}

// wrapSources wraps one or more Source's and returns
// them as an array of `sourceEntry`.
func (config *Config) wrapSources(srcs ...Source) []*sourceEntry {
	arr := make([]*sourceEntry, 0, len(srcs))
	for _, src := range srcs {
		se := &sourceEntry{src: src}
		config.reloadProps(se)
		arr = append(arr, se)
	}
	return arr
}

// SetWantPanicOnError sets the flag determining if Config
// should panic when `GetProps` or `GetLastModified` errors
// for a `Source`.
func (config *Config) SetWantPanicOnError(b bool) {
	config.mutexSrc.Lock()
	config.wantPanicOnError = b
	config.mutexSrc.Unlock()
}

// ShouldPanicOnError gets the flag determining if Config
// should panic when `GetProps` or `GetLastModified` errors
// for a `Source`.
func (config *Config) ShouldPanicOnError() (b bool) {
	config.mutexSrc.RLock()
	b = config.wantPanicOnError
	config.mutexSrc.RUnlock()
	return b
}

// getProp returns the value of a named property.
// Each `Source` is checked, in the order created by adding via
// `AppendSource` and `PrependSource`, until a value for the
// property is found.
func (config *Config) getProp(name string) (val string, ok bool) {
	config.mutexSrc.RLock()
	defer config.mutexSrc.RUnlock()

	var s string
	for _, se := range config.srcs {
		if se.props != nil {
			if s, ok = se.props[name]; ok {
				val = strings.TrimSpace(s)
				return
			}
		}
	}
	return
}

// String returns the value of the named prop as a string.
// If the property is not found then the supplied default `def`
// and `ErrNotFound` are returned.
func (config *Config) String(name string, def string) (val string, err error) {
	if v, ok := config.getProp(name); ok {
		val = v
		err = nil
		return
	}

	err = ErrNotFound
	val = def
	return
}

// Int returns the value of the named prop as an `int`.
// If the property is not found then the supplied default `def`
// and `ErrNotFound` are returned.
//
// See config.String
func (config *Config) Int(name string, def int) (val int, err error) {
	var s string
	if s, err = config.String(name, ""); err == nil {
		var i int64
		if i, err = strconv.ParseInt(s, 10, 32); err == nil {
			val = int(i)
		}
	}
	if err != nil {
		val = def
	}
	return
}

// Int64 returns the value of the named prop as an `int64`.
// If the property is not found then the supplied default `def`
// and `ErrNotFound` are returned.
//
// See config.String
func (config *Config) Int64(name string, def int64) (val int64, err error) {
	var s string
	if s, err = config.String(name, ""); err == nil {
		val, err = strconv.ParseInt(s, 10, 64)
	}
	if err != nil {
		val = def
	}
	return
}

// Float64 returns the value of the named prop as a `float64`.
// If the property is not found then the supplied default `def`
// and `ErrNotFound` are returned.
//
// See config.String
func (config *Config) Float64(name string, def float64) (val float64, err error) {
	var s string
	if s, err = config.String(name, ""); err == nil {
		val, err = strconv.ParseFloat(s, 64)
	}
	if err != nil {
		val = def
	}
	return
}

// Bool returns the value of the named prop as a `bool`.
// If the property is not found then the supplied default `def`
// and `ErrNotFound` are returned.
//
// Supports (t, true, 1, y, yes) for true, and (f, false, 0, n, no) for false,
// all case-insensitive.
//
// See config.String
func (config *Config) Bool(name string, def bool) (val bool, err error) {
	var s string
	if s, err = config.String(name, ""); err == nil {
		switch strings.ToLower(s) {
		case "t", "true", "1", "y", "yes":
			val = true
		case "f", "false", "0", "n", "no":
			val = false
		default:
			err = errors.New("invalid syntax")
		}
	}
	if err != nil {
		val = def
	}
	return
}

// Duration returns the value of the named prop as a `time.Duration`, representing
// a span of time.
//
// Units of measure are supported: ms, sec, min, hour, day, week, year.
// See config.UnitsToMillis for a complete list of units supported.
//
// If the property is not found then the supplied default `def`
// and `ErrNotFound` are returned.
//
// See config.String
func (config *Config) Duration(name string, def time.Duration) (val time.Duration, err error) {
	var s string
	if s, err = config.String(name, ""); err == nil {
		var ms int64
		ms, err = timeconv.ParseMilliseconds(s)
		val = time.Duration(ms) * time.Millisecond
	}
	if err != nil {
		val = def
	}
	return
}

// AddChangedListener adds a listener that will receive notifications
// whenever one or more property values change within the config.
func (config *Config) AddChangedListener(l ChangedListener) {
	config.mutexListeners.Lock()
	defer config.mutexListeners.Unlock()

	config.chgListeners = append(config.chgListeners, l)
}

// RemoveChangedListener removes all instances of a ChangedListener.
// Returns `ErrNotFound` if the listener was not present.
func (config *Config) RemoveChangedListener(l ChangedListener) error {
	config.mutexListeners.Lock()
	defer config.mutexListeners.Unlock()

	dest := make([]ChangedListener, 0, len(config.chgListeners))
	err := ErrNotFound

	// Remove all instances of the listener by
	// copying list while filtering.
	for _, s := range config.chgListeners {
		if s != l {
			dest = append(dest, s)
		} else {
			err = nil
		}
	}
	config.chgListeners = dest
	return err
}

// Shutdown can be called to stop monitoring of all config sources.
func (config *Config) Shutdown() {
	config.mutexSrc.RLock()
	defer config.mutexSrc.RUnlock()
	if config.shutdown != nil {
		close(config.shutdown)
	}
}

// onSourceChanged is called whenever one or more properties of a
// config source has changed.
func (config *Config) onSourceChanged(src SourceMonitored) {
	defer func() {
		if p := recover(); p != nil {
			fmt.Println(p)
		}
	}()
	config.mutexListeners.RLock()
	defer config.mutexListeners.RUnlock()
	for _, l := range config.chgListeners {
		l.ConfigChanged(config, src)
	}
}

// monitor periodically checks a config source for changes.
func (config *Config) monitor(se *sourceEntry) {
	go func(se *sourceEntry, shutdown <-chan interface{}) {
		var src SourceMonitored
		var ok bool
		if src, ok = se.src.(SourceMonitored); !ok {
			return
		}
		paused := false
		last := time.Time{}
		freq := src.GetMonitorFreq()
		if freq <= 0 {
			paused = true
			freq = 10
			last, _ = src.GetLastModified()
		}
		timer := time.NewTimer(freq)
		for {
			select {
			case <-timer.C:
				if !paused {
					if latest, err := src.GetLastModified(); err != nil {
						if config.ShouldPanicOnError() {
							panic(fmt.Sprintf("error <%v> getting last modified for %v", err, src))
						}
					} else {
						if last.Before(latest) {
							last = latest
							config.reloadProps(se)
							// TODO: calc diff and provide detailed changes
							config.onSourceChanged(src)
						}
					}
				}
				freq = src.GetMonitorFreq()
				if freq <= 0 {
					paused = true
					freq = 10
				} else {
					paused = false
				}
				timer.Reset(freq)
			case <-shutdown:
				// stop the timer and exit
				if !timer.Stop() {
					<-timer.C
				}
				return
			}
		}
	}(se, config.shutdown)
}

// reloadProps causes a Source to reload its properties.
func (config *Config) reloadProps(se *sourceEntry) {
	config.mutexSrc.Lock()
	defer config.mutexSrc.Unlock()

	m, err := se.src.GetProps()
	if err != nil {
		if config.wantPanicOnError {
			panic(fmt.Sprintf("GetProps error for %v", se.src))
		}
		return
	}

	se.props = make(map[string]string)
	for k, v := range m {
		se.props[k] = v
	}
}