// TODO(performance): implement ping message channel buffering
//
// Pingo defines a number of high level functions and data structures to
// interact with and represent a Ping via Go. Primarily, it defines the
// Ping() function and Address data structure.
//
// NOTE this project does not provide a Go implementation of the ping protocol.
// Instead, this project merely provides a wrapper to your system's existing
// ping.c binary.
//
// NOTE(os): this project may fail with non-unix compliant system ping binaries,
// predominantly Windows platforms. This relates to the way in which the project
// interacts with the ping binary. (read: the project uses `ping -c1 ADDRESS`
// and will break on systems that implement a different CLI)
//
// The project defines a simple top level binding for the system's ping.c:
// Ping(). It simply reports a delay time as reported by the system ping, and
// any errors encountered.
//
// Additionally, the project defines the "Address" data structure to represent
// a series of ping results relating to the given host. Its fields are simple:
//
//	Address (string): the host or IP address
//
//	Results ([]float64): a series of ping results
//
//	MaxResults (int): The maximum number of results to track, as enforced by
//		Address.Truncate()
//
// The Address data structure provides a series of higher level access functions
// to prevent code repetition:
//
//	Example:
//		...
//		a := Address{Address:"google.ca", MaxResults:20}
//		latency, err := a.Ping() 	// get a single result and return the value
//		... 											// handle error
//		a.Results, err = a.Poll()	// append a ping to the Results slice, then return the updated slice
//		... 											// handle error
//		a.Results = a.Truncate()	// return a modified slice of only the most n*a.MaxResults long
//
// For more, see each function's GoDoc.
package pingo

import (
	"errors"
	"os/exec"
	"strconv"
	"strings"
)

// runPing returns the byte array as returned by [exec.Command]
//
// NOTE(os): this function may fail on non-unix compliant implementations of the Ping spec.
func runPing(address string) (delay *[]byte, err error) {
	out, err := exec.Command("ping", address, "-c 1").Output()
	if err != nil {
		return nil, err
	}
	return &out, err
}

// splitBytesToLines splits bytes as returned by runPing into an
// array of strings by newline
func splitBytesToLines(bytes *[]byte) (lines []string) {
	return strings.Split(strings.ReplaceAll(string(*bytes), "\r\n", "\n"), "\n")
}

// Ping returns the delay of a single Ping as reported by the system Ping binary.
//
// If the function is unable to resolve the system binary output or fails to
// successfully resolve a Ping, it will always return -1.
//
// NOTE(os): this function may fail on non-unix compliant implementations of the Ping spec.
func Ping(address string) (delay float64, err error) {
	out, err := runPing(address)
	if err != nil {
		return -1, err
	}

	lines := splitBytesToLines(out)

	for i := range lines {
		if strings.Contains(lines[i], "bytes from") {
			position := strings.Index(lines[i], "time=")

			before, _, success := strings.Cut(lines[i][position:], " ")
			if !success {
				return -1, errors.New("line does not match pattern")
			}
			_, after, success := strings.Cut(before, "=")
			if !success {
				return -1, errors.New("line does not match pattern")
			}

			delay, _ := strconv.ParseFloat(after, 64)
			return delay, nil
		}
	}
	return -1, errors.New("could not resolve host: " + address)
}

type Address struct {
	Address    string
	Results    []float64
	MaxResults int
}

// Enforces a Address.Result maximum length by dropping the oldest result,
// then returns the modified slice.
func (a Address) Truncate() []float64 {
	if len(a.Results) > a.MaxResults {
		a.Results = a.Results[len(a.Results)-a.MaxResults : len(a.Results)] // return modified slice missing first index
	}

	return a.Results
}

// Wraps Ping, passing Address.Address as its argument.
func (a Address) Ping() (delay float64, err error) {
	return Ping(a.Address)
}

// Poll the affiliated Address, append it to a.Results, and report the modified
// slice and any errors.
func (a Address) Poll() (results []float64, err error) {
	delay, err := a.Ping()
	a.Results = append(a.Results, delay)
	a.Results = a.Truncate() // enforce max length
	return a.Results, err
}

// Last returns the last result in Address.Results. Returns -1 if no previous result
func (a Address) Last() (delay float64) {
	if len(a.Results) > 0 {
		return a.Results[len(a.Results)-1]
	} else {
		return -1
	}
}