// Package `perfdata` provides representations for a monitoring plugin's
// performance data.
package perfdata // import nocternity.net/gomonop/pkg/perfdata

import (
	"fmt"
	"regexp"
	"strings"
)

// Units of measurement, which may be used to qualify the performance data.
type UnitOfMeasurement int

const (
	UomNone UnitOfMeasurement = iota
	UomSeconds
	UomPercent
	UomBytes
	UomKilobytes
	UomMegabytes
	UomGigabytes
	UomTerabytes
	UomCounter
)

func (u UnitOfMeasurement) String() string {
	return [...]string{"", "s", "%", "B", "KB", "MB", "GB", "TB", "c"}[u]
}

// Flags indicating which elements of performance data have been set.
type perfDataBits int

const (
	PDatWarn perfDataBits = 1 << iota
	PDatCrit
	PDatMin
	PDatMax
)

// Regexps used to check values and ranges in performance data records.
var (
	// Common value check regexp.
	vcRegexp = `^-?(0(\.\d*)?|[1-9]\d*(\.\d*)?|\.\d+)$`
	// Compiled value check regexp.
	valueCheck = regexp.MustCompile(vcRegexp)
	// Compiled range min value check.
	rangeMinCheck = regexp.MustCompile(vcRegexp + `|^~$`)
)

// Performance data range.
type PDRange struct {
	start  string
	end    string
	inside bool
}

// Creates a performance data range from -inf to 0 and from the specified
// value to +inf.
func PDRMax(max string) *PDRange {
	if !valueCheck.MatchString(max) {
		panic("invalid performance data range maximum value")
	}
	pdRange := &PDRange{}
	pdRange.start = "0"
	pdRange.end = max
	return pdRange
}

// Creates a performance data range from -inf to the specified minimal value
// and from the specified maximal value to +inf.
func PDRMinMax(min, max string) *PDRange {
	if !valueCheck.MatchString(max) {
		panic("invalid performance data range maximum value")
	}
	if !rangeMinCheck.MatchString(min) {
		panic("invalid performance data range minimum value")
	}
	pdRange := &PDRange{}
	pdRange.start = min
	pdRange.end = max
	return pdRange
}

// Inverts the range.
func (r *PDRange) Inside() *PDRange {
	r.inside = true
	return r
}

// Generates the range's string representation so it can be sent to the
// monitoring system.
func (r *PDRange) String() string {
	var start, inside string

	switch r.start {
	case "":
		start = "~"
	case "0":
		start = ""
	default:
		start = r.start
	}

	if r.inside {
		inside = "@"
	}

	return inside + start + ":" + r.end
}

// Performance data, including a label, units, a value, warning/critical
// ranges and min/max boundaries.
type PerfData struct {
	Label      string
	units      UnitOfMeasurement
	bits       perfDataBits
	value      string
	warn, crit PDRange
	min, max   string
}

// Create performance data using the specified label and units.
func New(label string, units UnitOfMeasurement, value string) *PerfData {
	if value != "" && !valueCheck.MatchString(value) {
		panic("invalid value")
	}
	pdRange := &PerfData{}
	pdRange.Label = label
	pdRange.units = units
	if value == "" {
		pdRange.value = "U"
	} else {
		pdRange.value = value
	}
	return pdRange
}

// Set the warning range for the performance data record.
func (d *PerfData) SetWarn(r *PDRange) {
	d.warn = *r
	d.bits |= PDatWarn
}

// Set the critical range for the performance data record.
func (d *PerfData) SetCrit(r *PDRange) {
	d.crit = *r
	d.bits |= PDatCrit
}

// Set the performance data's minimal value.
func (d *PerfData) SetMin(min string) {
	if !valueCheck.MatchString(min) {
		panic("invalid value")
	}
	d.min = min
	d.bits |= PDatMin
}

// Set the performance data's maximal value.
func (d *PerfData) SetMax(max string) {
	if !valueCheck.MatchString(max) {
		panic("invalid value")
	}
	d.max = max
	d.bits |= PDatMax
}

// Converts performance data to a string which may be read by the monitoring
// system.
func (d *PerfData) String() string {
	var strBuilder strings.Builder
	needsQuotes := strings.ContainsAny(d.Label, " '=\"")
	if needsQuotes {
		strBuilder.WriteString("'")
	}
	strBuilder.WriteString(strings.ReplaceAll(d.Label, "'", "''"))
	if needsQuotes {
		strBuilder.WriteString("'")
	}
	strBuilder.WriteString("=")
	strBuilder.WriteString(fmt.Sprintf("%s%s;", d.value, d.units.String()))
	if d.bits&PDatWarn != 0 {
		strBuilder.WriteString(d.warn.String())
	}
	strBuilder.WriteString(";")
	if d.bits&PDatCrit != 0 {
		strBuilder.WriteString(d.crit.String())
	}
	strBuilder.WriteString(";")
	if d.bits&PDatMin != 0 {
		strBuilder.WriteString(d.min)
	}
	strBuilder.WriteString(";")
	if d.bits&PDatMax != 0 {
		strBuilder.WriteString(d.max)
	}

	return strBuilder.String()
}