// Fengaldar provides a logger, or, 'one who cuts trees'.
//
// The result of NewLogger().Println("Some message") looks like:
//	INFO 2020-09-03T18:53:04-06:00 Some message
//
// The result of NewJSONLogger().Println("Some message") looks like:
//	{"timestamp":"2020-09-03T18:53:04-06:00", "severity":"INFO", "message":"Some message"}
//
// The result of NewJSONLogger().Notice("Some message", LogContext{"extra":"info"}) looks like:
//	{"timestamp": "2020-09-03T18:53:04-06:00", "severity": "INFO", "message": "Some message", "additionalContext": "{\"extra\":\"info\"}"}
//
// Of course you'll likely store the result of NewLogger() in a var so your code might look more like this:
//	import ( fen "git.ondollo.com/fengaldar" )
//	...
//	l := fen.NewLogger()
//	...
//	l.Log("Something happened")
//	...
//	l.Notice("Something interesting happened")
//
// You might also want to tweak the defaults with your own. That might look something like this:
//	import ( fen "git.ondollo.com/fengaldar" )
//	...
//	minSeverityToLog := fen.Warning
//	defaultLogSeverity := fen.Notice
//	customOptions := fen.Options{minSeverityToLog, defaultLogSeverity, time.RFC822}
//	l := fen.NewLoggerWithOptions(customOptions)
//	...
//	l.Log("Something happened") // This will be ignored due to having set 'minSeverityToLog' to a higher Severity than the default (which was provided in defaultLogSeverity)
//	...
//	l.Notice("Something interesting happened") // This will also be ignored due to having set 'minSeverityToLog' to a higher Severity than the default (which was provided in defaultLogSeverity)
//	...
//	l.Critical("Something caused a brief outage") // This will NOT be ignored
//
// You might also want to add some context to the log entry, and that might look something like this:
//	import ( fen "git.ondollo.com/fengaldar" )
//	...
//	l := fen.NewLogger()
//	...
//	l.Log("Something happened", fen.LogContext{"somethingWasSetTo": "someValue"})
package fengaldar

import (
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

// Severity represents the severity of the related log entry.
// Naming, ordering, and guidlines are based on severity consts found at https://pkg.go.dev/cloud.google.com/go/logging#pkg-constants
type Severity int

const (
	Debug     Severity = iota // Debug - debug or trace information.
	Info                      // Info - routine information, such as ongoing status or performance.
	Notice                    // Notice - normal but significant events, such as start up, shut down, or configuration.
	Warning                   // Warning - events that might cause problems.
	Error                     // Error - events that are likely to cause problems.
	Critical                  // Critical - events that cause more severe problems or brief outages.
	Alert                     // Alert - a person must take an action immediately.
	Emergency                 // Emergency - one or more systems are unusable.
	Panic                     // Panic - one or more systems are unusable and this package will throw a panic.
	Fatal                     // Fatal - one or more systems are unusable and this package will call os.Exit(1).
)

var sevStrings = []string{
	"DEBUG",
	"INFO",
	"NOTICE",
	"WARNING",
	"ERROR",
	"CRITICAL",
	"ALERT",
	"EMERGENCY",
	"PANIC",
	"FATAL",
}

func (s Severity) String() string {
	return sevStrings[s]
}

// LogContext provides a way to express additional context on a log entry.
type LogContext map[string]string

// LogContext.String will produce a unicode box-drawing prefix-wrapped output where each key in the LogContext is on it's own line
func (lc LogContext) String() string {
	var s strings.Builder
	s.WriteString(" \u250f\n")
	for k, v := range lc {
		s.WriteString(fmt.Sprintf(" \u2503 %q: %q\n", k, v))
	}
	s.WriteString(" \u2517")
	return s.String()
}

// LogContext.JSON will produce a JSON object, where each key and value remain
// keys and values and are converted with fmt.Sprintf("%q")
func (lc LogContext) JSON() string {
	var s strings.Builder
	s.WriteString("{")
	first := true
	for k, v := range lc {
		if !first {
			s.WriteString(",")
		}
		s.WriteString(fmt.Sprintf("%q:%q", k, v))
		first = false
	}
	s.WriteString("}")
	return s.String()
}

// FOR ALL DECLARATIONS OF `...LogContext` ONLY THE FIRST LogContext WILL BE USED.
// This allows the LogContext to be optional.
//
// You might notice that Printf is not provided.
//
// In cases where you would use Printf you should explore constructing a LogContext to
// convey the additional data, or use fmt.Sprintf.
type Logger interface {
	Time() string                    // Time is the result of applying the time.Layout specified in Options.TF in a call to time.Now().Format
	Sev() Severity                   // Sev is the default severity used in Println and Log
	Println(...interface{})          // For NewLogger, each parameter will be on it's own line. For NewJSONLogger, they're combined with a strings.Join("\n").
	Log(string, ...LogContext)       // FOR ALL DECLARATIONS OF `...LogContext` ONLY THE FIRST LogContext WILL BE USED
	Debug(string, ...LogContext)     // Debug - debug or trace information.
	Info(string, ...LogContext)      // Info - routine information, such as ongoing status or performance.
	Notice(string, ...LogContext)    // Notice - normal but significant events, such as start up, shut down, or configuration.
	Warning(string, ...LogContext)   // Warning - events that might cause problems.
	Error(string, ...LogContext)     // Error - events that are likely to cause problems.
	Critical(string, ...LogContext)  // Critical - events that cause more severe problems or brief outages.
	Alert(string, ...LogContext)     // Alert - a person must take an action immediately.
	Emergency(string, ...LogContext) // Emergency - one or more systems are unusable.
	Panic(string, ...LogContext)     // Panic - one or more systems are unusable and this package will throw a panic.
	Fatal(string, ...LogContext)     // Fatal - one or more systems are unusable and this package will call os.Exit(1).
}

// Options allow you to specify different defaults for loggers
type Options struct {
	Min Severity // The minimum severity to actually produce output. Any log entry with an associated severity *below* this will be ignored.
	Sev Severity
	// TF is the TimeFormat that will be used when producing log entries.
	// This follows the time.Layout format seen here: https://pkg.go.dev/time#pkg-constants
	TF string
}

var DefaultOptions = Options{
	Min: Debug,
	Sev: Info,
	TF:  time.RFC3339,
}

// simple

func NewLogger() Logger { return NewLoggerWithOptions(DefaultOptions) }

func NewLoggerWithOptions(o Options) Logger {
	return &simpleLogger{
		o.Min,
		o.Sev,
		o.TF,
		strconv.Itoa(len(time.Now().Format(o.TF))),
	}
}

type simpleLogger struct {
	MS Severity
	DS Severity
	TF string
	TS string
}

func (sl simpleLogger) Time() string  { return time.Now().Format(sl.TF) }
func (sl simpleLogger) Sev() Severity { return sl.DS }
func (sl simpleLogger) line(sev Severity, s interface{}) string {
	return fmt.Sprintf("%10.10s %"+sl.TS+"."+sl.TS+"s %s\n", sev, sl.Time(), s)
}
func (sl simpleLogger) Println(ss ...interface{}) {
	if sl.Sev() < sl.MS {
		return
	}
	for _, s := range ss {
		fmt.Printf(sl.line(sl.Sev(), s))
	}
}
func (sl simpleLogger) internal(sev Severity, s string, lc ...LogContext) {
	if sev < sl.MS {
		return
	}
	fmt.Printf(sl.line(sev, s))
	if len(lc) > 0 {
		fmt.Println(lc[0])
	}
}
func (sl simpleLogger) Log(s string, lc ...LogContext)       { sl.internal(sl.Sev(), s, lc...) }
func (sl simpleLogger) Debug(s string, lc ...LogContext)     { sl.internal(Debug, s, lc...) }
func (sl simpleLogger) Info(s string, lc ...LogContext)      { sl.internal(Info, s, lc...) }
func (sl simpleLogger) Notice(s string, lc ...LogContext)    { sl.internal(Notice, s, lc...) }
func (sl simpleLogger) Warning(s string, lc ...LogContext)   { sl.internal(Warning, s, lc...) }
func (sl simpleLogger) Error(s string, lc ...LogContext)     { sl.internal(Error, s, lc...) }
func (sl simpleLogger) Critical(s string, lc ...LogContext)  { sl.internal(Critical, s, lc...) }
func (sl simpleLogger) Alert(s string, lc ...LogContext)     { sl.internal(Alert, s, lc...) }
func (sl simpleLogger) Emergency(s string, lc ...LogContext) { sl.internal(Emergency, s, lc...) }
func (sl simpleLogger) Panic(s string, lc ...LogContext)     { sl.internal(Panic, s, lc...); panic(s) }
func (sl simpleLogger) Fatal(s string, lc ...LogContext)     { sl.internal(Fatal, s, lc...); os.Exit(1) }

// JSON

func NewJSONLogger() Logger                     { return NewJSONLoggerWithOptions(DefaultOptions) }
func NewJSONLoggerWithOptions(o Options) Logger { return &jsonLogger{o.Min, o.Sev, o.TF} }

type jsonLogger struct {
	MS Severity
	DS Severity
	TF string
}

func (jl jsonLogger) Time() string  { return time.Now().Format(jl.TF) }
func (jl jsonLogger) Sev() Severity { return jl.DS }
func (jl jsonLogger) line(sev Severity, s interface{}) string {
	return fmt.Sprintf(`"timestamp":%q, "severity":%q, "message":%q`, jl.Time(), sev, s)
}
func (jl jsonLogger) lineWithContext(s interface{}, lc LogContext) string {
	return fmt.Sprintf(`%s, "additionalContext":%q`, jl.line(jl.Sev(), s), lc.JSON())
}
func (jl jsonLogger) Println(ss ...interface{}) {
	if jl.Sev() < jl.MS {
		return
	}
	var jss strings.Builder
	for i, s := range ss {
		if i > 0 {
			jss.WriteString("\n")
		}
		jss.WriteString(s.(string))
	}
	fmt.Printf("{%s}\n", jl.line(jl.Sev(), jss.String()))
}
func (jl jsonLogger) internal(sev Severity, s string, lc ...LogContext) {
	if sev < jl.MS {
		return
	}
	if len(lc) == 0 {
		fmt.Printf("{%s}\n", jl.line(sev, s))
	} else {
		fmt.Printf("{%s}\n", jl.lineWithContext(s, lc[0]))
	}
}
func (jl jsonLogger) Log(s string, lc ...LogContext)       { jl.internal(jl.Sev(), s, lc...) }
func (jl jsonLogger) Debug(s string, lc ...LogContext)     { jl.internal(Debug, s, lc...) }
func (jl jsonLogger) Info(s string, lc ...LogContext)      { jl.internal(Info, s, lc...) }
func (jl jsonLogger) Notice(s string, lc ...LogContext)    { jl.internal(Notice, s, lc...) }
func (jl jsonLogger) Warning(s string, lc ...LogContext)   { jl.internal(Warning, s, lc...) }
func (jl jsonLogger) Error(s string, lc ...LogContext)     { jl.internal(Error, s, lc...) }
func (jl jsonLogger) Critical(s string, lc ...LogContext)  { jl.internal(Critical, s, lc...) }
func (jl jsonLogger) Alert(s string, lc ...LogContext)     { jl.internal(Alert, s, lc...) }
func (jl jsonLogger) Emergency(s string, lc ...LogContext) { jl.internal(Emergency, s, lc...) }
func (jl jsonLogger) Panic(s string, lc ...LogContext)     { jl.internal(Panic, s, lc...); panic(s) }
func (jl jsonLogger) Fatal(s string, lc ...LogContext)     { jl.internal(Fatal, s, lc...); os.Exit(1) }

// Fengaldar provides a logger, or, 'one who cuts trees'.
//
// The result of NewLogger().Println("Some message") looks like:
//	INFO 2020-09-03T18:53:04-06:00 Some message
//
// The result of NewJSONLogger().Println("Some message") looks like:
//	{"timestamp":"2020-09-03T18:53:04-06:00", "severity":"INFO", "message":"Some message"}
//
// The result of NewJSONLogger().Notice("Some message", LogContext{"extra":"info"}) looks like:
//	{"timestamp": "2020-09-03T18:53:04-06:00", "severity": "INFO", "message": "Some message", "additionalContext": "{\"extra\":\"info\"}"}
//
// Of course you'll likely store the result of NewLogger() in a var so your code might look more like this:
//	import ( fen "git.ondollo.com/fengaldar" )
//	...
//	l := fen.NewLogger()
//	...
//	l.Log("Something happened")
//	...
//	l.Notice("Something interesting happened")
//
// You might also want to tweak the defaults with your own. That might look something like this:
//	import ( fen "git.ondollo.com/fengaldar" )
//	...
//	minSeverityToLog := fen.Warning
//	defaultLogSeverity := fen.Notice
//	customOptions := fen.Options{minSeverityToLog, defaultLogSeverity, time.RFC822}
//	l := fen.NewLoggerWithOptions(customOptions)
//	...
//	l.Log("Something happened") // This will be ignored due to having set 'minSeverityToLog' to a higher Severity than the default (which was provided in defaultLogSeverity)
//	...
//	l.Notice("Something interesting happened") // This will also be ignored due to having set 'minSeverityToLog' to a higher Severity than the default (which was provided in defaultLogSeverity)
//	...
//	l.Critical("Something caused a brief outage") // This will NOT be ignored
//
// You might also want to add some context to the log entry, and that might look something like this:
//	import ( fen "git.ondollo.com/fengaldar" )
//	...
//	l := fen.NewLogger()
//	...
//	l.Log("Something happened", fen.LogContext{"somethingWasSetTo": "someValue"})
package fengaldar

import (
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

// Severity represents the severity of the related log entry.
// Naming, ordering, and guidlines are based on severity consts found at https://pkg.go.dev/cloud.google.com/go/logging#pkg-constants
type Severity int

const (
	Debug     Severity = iota // Debug - debug or trace information.
	Info                      // Info - routine information, such as ongoing status or performance.
	Notice                    // Notice - normal but significant events, such as start up, shut down, or configuration.
	Warning                   // Warning - events that might cause problems.
	Error                     // Error - events that are likely to cause problems.
	Critical                  // Critical - events that cause more severe problems or brief outages.
	Alert                     // Alert - a person must take an action immediately.
	Emergency                 // Emergency - one or more systems are unusable.
	Panic                     // Panic - one or more systems are unusable and this package will throw a panic.
	Fatal                     // Fatal - one or more systems are unusable and this package will call os.Exit(1).
)

var sevStrings = []string{
	"DEBUG",
	"INFO",
	"NOTICE",
	"WARNING",
	"ERROR",
	"CRITICAL",
	"ALERT",
	"EMERGENCY",
	"PANIC",
	"FATAL",
}

func (s Severity) String() string {
	return sevStrings[s]
}

// LogContext provides a way to express additional context on a log entry.
type LogContext map[string]string

// LogContext.String will produce a unicode box-drawing prefix-wrapped output where each key in the LogContext is on it's own line
func (lc LogContext) String() string {
	var s strings.Builder
	s.WriteString(" \u250f\n")
	for k, v := range lc {
		s.WriteString(fmt.Sprintf(" \u2503 %q: %q\n", k, v))
	}
	s.WriteString(" \u2517")
	return s.String()
}

// LogContext.JSON will produce a JSON object, where each key and value remain
// keys and values and are converted with fmt.Sprintf("%q")
func (lc LogContext) JSON() string {
	var s strings.Builder
	s.WriteString("{")
	first := true
	for k, v := range lc {
		if !first {
			s.WriteString(",")
		}
		s.WriteString(fmt.Sprintf("%q:%q", k, v))
		first = false
	}
	s.WriteString("}")
	return s.String()
}

// FOR ALL DECLARATIONS OF `...LogContext` ONLY THE FIRST LogContext WILL BE USED.
// This allows the LogContext to be optional.
//
// You might notice that Printf is not provided.
//
// In cases where you would use Printf you should explore constructing a LogContext to
// convey the additional data, or use fmt.Sprintf.
type Logger interface {
	Time() string                    // Time is the result of applying the time.Layout specified in Options.TF in a call to time.Now().Format
	Sev() Severity                   // Sev is the default severity used in Println and Log
	Println(...interface{})          // For NewLogger, each parameter will be on it's own line. For NewJSONLogger, they're combined with a strings.Join("\n").
	Log(string, ...LogContext)       // FOR ALL DECLARATIONS OF `...LogContext` ONLY THE FIRST LogContext WILL BE USED
	Debug(string, ...LogContext)     // Debug - debug or trace information.
	Info(string, ...LogContext)      // Info - routine information, such as ongoing status or performance.
	Notice(string, ...LogContext)    // Notice - normal but significant events, such as start up, shut down, or configuration.
	Warning(string, ...LogContext)   // Warning - events that might cause problems.
	Error(string, ...LogContext)     // Error - events that are likely to cause problems.
	Critical(string, ...LogContext)  // Critical - events that cause more severe problems or brief outages.
	Alert(string, ...LogContext)     // Alert - a person must take an action immediately.
	Emergency(string, ...LogContext) // Emergency - one or more systems are unusable.
	Panic(string, ...LogContext)     // Panic - one or more systems are unusable and this package will throw a panic.
	Fatal(string, ...LogContext)     // Fatal - one or more systems are unusable and this package will call os.Exit(1).
}

// Options allow you to specify different defaults for loggers
type Options struct {
	Min Severity // The minimum severity to actually produce output. Any log entry with an associated severity *below* this will be ignored.
	Sev Severity
	// TF is the TimeFormat that will be used when producing log entries.
	// This follows the time.Layout format seen here: https://pkg.go.dev/time#pkg-constants
	TF string
}

var DefaultOptions = Options{
	Min: Debug,
	Sev: Info,
	TF:  time.RFC3339,
}

// simple

func NewLogger() Logger { return NewLoggerWithOptions(DefaultOptions) }

func NewLoggerWithOptions(o Options) Logger {
	return &simpleLogger{
		o.Min,
		o.Sev,
		o.TF,
		strconv.Itoa(len(time.Now().Format(o.TF))),
	}
}

type simpleLogger struct {
	MS Severity
	DS Severity
	TF string
	TS string
}

func (sl simpleLogger) Time() string  { return time.Now().Format(sl.TF) }
func (sl simpleLogger) Sev() Severity { return sl.DS }
func (sl simpleLogger) line(sev Severity, s interface{}) string {
	return fmt.Sprintf("%10.10s %"+sl.TS+"."+sl.TS+"s %s\n", sev, sl.Time(), s)
}
func (sl simpleLogger) Println(ss ...interface{}) {
	if sl.Sev() < sl.MS {
		return
	}
	for _, s := range ss {
		fmt.Printf(sl.line(sl.Sev(), s))
	}
}
func (sl simpleLogger) internal(sev Severity, s string, lc ...LogContext) {
	if sev < sl.MS {
		return
	}
	fmt.Printf(sl.line(sev, s))
	if len(lc) > 0 {
		fmt.Println(lc[0])
	}
}
func (sl simpleLogger) Log(s string, lc ...LogContext)       { sl.internal(sl.Sev(), s, lc...) }
func (sl simpleLogger) Debug(s string, lc ...LogContext)     { sl.internal(Debug, s, lc...) }
func (sl simpleLogger) Info(s string, lc ...LogContext)      { sl.internal(Info, s, lc...) }
func (sl simpleLogger) Notice(s string, lc ...LogContext)    { sl.internal(Notice, s, lc...) }
func (sl simpleLogger) Warning(s string, lc ...LogContext)   { sl.internal(Warning, s, lc...) }
func (sl simpleLogger) Error(s string, lc ...LogContext)     { sl.internal(Error, s, lc...) }
func (sl simpleLogger) Critical(s string, lc ...LogContext)  { sl.internal(Critical, s, lc...) }
func (sl simpleLogger) Alert(s string, lc ...LogContext)     { sl.internal(Alert, s, lc...) }
func (sl simpleLogger) Emergency(s string, lc ...LogContext) { sl.internal(Emergency, s, lc...) }
func (sl simpleLogger) Panic(s string, lc ...LogContext)     { sl.internal(Panic, s, lc...); panic(s) }
func (sl simpleLogger) Fatal(s string, lc ...LogContext)     { sl.internal(Fatal, s, lc...); os.Exit(1) }

// JSON

func NewJSONLogger() Logger                     { return NewJSONLoggerWithOptions(DefaultOptions) }
func NewJSONLoggerWithOptions(o Options) Logger { return &jsonLogger{o.Min, o.Sev, o.TF} }

type jsonLogger struct {
	MS Severity
	DS Severity
	TF string
}

func (jl jsonLogger) Time() string  { return time.Now().Format(jl.TF) }
func (jl jsonLogger) Sev() Severity { return jl.DS }
func (jl jsonLogger) line(sev Severity, s interface{}) string {
	return fmt.Sprintf(`"timestamp":%q, "severity":%q, "message":%q`, jl.Time(), sev, s)
}
func (jl jsonLogger) lineWithContext(s interface{}, lc LogContext) string {
	return fmt.Sprintf(`%s, "additionalContext":%q`, jl.line(jl.Sev(), s), lc.JSON())
}
func (jl jsonLogger) Println(ss ...interface{}) {
	if jl.Sev() < jl.MS {
		return
	}
	var jss strings.Builder
	for i, s := range ss {
		if i > 0 {
			jss.WriteString("\n")
		}
		jss.WriteString(s.(string))
	}
	fmt.Printf("{%s}\n", jl.line(jl.Sev(), jss.String()))
}
func (jl jsonLogger) internal(sev Severity, s string, lc ...LogContext) {
	if sev < jl.MS {
		return
	}
	if len(lc) == 0 {
		fmt.Printf("{%s}\n", jl.line(sev, s))
	} else {
		fmt.Printf("{%s}\n", jl.lineWithContext(s, lc[0]))
	}
}
func (jl jsonLogger) Log(s string, lc ...LogContext)       { jl.internal(jl.Sev(), s, lc...) }
func (jl jsonLogger) Debug(s string, lc ...LogContext)     { jl.internal(Debug, s, lc...) }
func (jl jsonLogger) Info(s string, lc ...LogContext)      { jl.internal(Info, s, lc...) }
func (jl jsonLogger) Notice(s string, lc ...LogContext)    { jl.internal(Notice, s, lc...) }
func (jl jsonLogger) Warning(s string, lc ...LogContext)   { jl.internal(Warning, s, lc...) }
func (jl jsonLogger) Error(s string, lc ...LogContext)     { jl.internal(Error, s, lc...) }
func (jl jsonLogger) Critical(s string, lc ...LogContext)  { jl.internal(Critical, s, lc...) }
func (jl jsonLogger) Alert(s string, lc ...LogContext)     { jl.internal(Alert, s, lc...) }
func (jl jsonLogger) Emergency(s string, lc ...LogContext) { jl.internal(Emergency, s, lc...) }
func (jl jsonLogger) Panic(s string, lc ...LogContext)     { jl.internal(Panic, s, lc...); panic(s) }
func (jl jsonLogger) Fatal(s string, lc ...LogContext)     { jl.internal(Fatal, s, lc...); os.Exit(1) }