// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package envknob provides access to environment-variable tweakable
// debug settings.
//
// These are primarily knobs used by Tailscale developers during
// development or by users when instructed to by Tailscale developers
// when debugging something. They are not a stable interface and may
// be removed or any time.
//
// A related package, control/controlknobs, are knobs that can be
// changed at runtime by the control plane. Sometimes both are used:
// an envknob for the default/explicit value, else falling back
// to the controlknob value.
package envknob

import (
	"log"
	"os"
	"strconv"

	"tailscale.com/types/opt"
)

// String returns the named environment variable, using os.Getenv.
//
// In the future it will also track usage for reporting on debug pages.
func String(envVar string) string {
	return os.Getenv(envVar)
}

// Bool returns the boolean value of the named environment variable.
// If the variable is not set, it returns false.
// An invalid value exits the binary with a failure.
func Bool(envVar string) bool {
	return boolOr(envVar, false)
}

// BoolDefaultTrue is like Bool, but returns true by default if the
// environment variable isn't present.
func BoolDefaultTrue(envVar string) bool {
	return boolOr(envVar, true)
}

func boolOr(envVar string, implicitValue bool) bool {
	val := os.Getenv(envVar)
	if val == "" {
		return implicitValue
	}
	b, err := strconv.ParseBool(val)
	if err == nil {
		return b
	}
	log.Fatalf("invalid environment variable %s value %q: %v", envVar, val, err)
	panic("unreachable")
}

// LookupBool returns the boolean value of the named environment value.
// The ok result is whether a value was set.
// If the value isn't a valid int, it exits the program with a failure.
func LookupBool(envVar string) (v bool, ok bool) {
	val := os.Getenv(envVar)
	if val == "" {
		return false, false
	}
	b, err := strconv.ParseBool(val)
	if err == nil {
		return b, true
	}
	log.Fatalf("invalid environment variable %s value %q: %v", envVar, val, err)
	panic("unreachable")
}

// OptBool is like Bool, but returns an opt.Bool, so the caller can
// distinguish between implicitly and explicitly false.
func OptBool(envVar string) opt.Bool {
	b, ok := LookupBool(envVar)
	if !ok {
		return ""
	}
	var ret opt.Bool
	ret.Set(b)
	return ret
}

// LookupInt returns the integer value of the named environment value.
// The ok result is whether a value was set.
// If the value isn't a valid int, it exits the program with a failure.
func LookupInt(envVar string) (v int, ok bool) {
	val := os.Getenv(envVar)
	if val == "" {
		return 0, false
	}
	v, err := strconv.Atoi(val)
	if err == nil {
		return v, true
	}
	log.Fatalf("invalid environment variable %s value %q: %v", envVar, val, err)
	panic("unreachable")
}