package perfdata // import nocternity.net/gomonop/pkg/perfdata

import (
	"fmt"
	"strings"
)

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

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

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

// Generates the range's string representation so it can be sent to the
// monitoring system.
func (r *Range) 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
}

// A state of the range parser.
type rangeParserState int

const (
	rpsInit        = iota // Initial state
	rpsExpectStart        // Expect the start of the range
	rpsInStart            // Reading the start of the range
	rpsExpectColon        // Expect the colon that separates the start and end
	rpsExpectEnd          // Expect the end of the range
	rpsInEnd              // Reading the end of the range
)

// An error emitted by the range parser.
type rangeParserError struct {
	input    string
	position int
	message  string
}

// parseError creates a new range parser error.
func parseError(input string, position int, message string) *rangeParserError {
	return &rangeParserError{
		input:    input,
		position: position,
		message:  message,
	}
}

// Error implements the error interface for the range parser error type.
func (rpe *rangeParserError) Error() string {
	return fmt.Sprintf("in `%s' at position %d: %s", rpe.input, rpe.position, rpe.message)
}

// Try to parse a string into a performance data range.
func ParseRange(input string) (*Range, error) {
	runes := []rune(input)
	index := 0
	state := rpsInit
	parsed := Range{}
	startOfStart := 0
	startOfEnd := 0
	strBuilder := strings.Builder{}

	for index < len(runes) {
		curRune := runes[index]

		switch state {
		case rpsInit:
			if curRune == '@' {
				parsed.inside = true
				index += 1
			}
			state = rpsExpectStart

		case rpsExpectStart:
			switch curRune {
			case ':':
				parsed.start = "0"
				state = rpsExpectEnd
			case '~':
				state = rpsExpectColon
			default:
				strBuilder.WriteRune(curRune)
				startOfStart = index
				state = rpsInStart
			}
			index += 1

		case rpsInStart:
			switch curRune {
			case ':':
				parsed.start = strBuilder.String()
				if !valueCheck.MatchString(parsed.start) {
					return nil, parseError(input, startOfStart, "invalid start value")
				}
				strBuilder.Reset()
				state = rpsExpectEnd
			default:
				strBuilder.WriteRune(curRune)
			}
			index += 1

		case rpsExpectColon:
			switch curRune {
			case ':':
				state = rpsExpectEnd
				index += 1
			default:
				return nil, parseError(input, index, "expected ':'")
			}

		case rpsExpectEnd:
			startOfEnd = index
			state = rpsInEnd

		case rpsInEnd:
			strBuilder.WriteRune(curRune)
			index += 1
		}
	}

	if state != rpsInEnd {
		return nil, parseError(input, index, "unexpected end of input")
	}

	parsed.end = strBuilder.String()
	if !valueCheck.MatchString(parsed.end) {
		return nil, parseError(input, startOfEnd, "invalid end value")
	}

	return &parsed, nil
}