package internal

import (
	"encoding/json"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"strings"
	"time"
)

type checkState struct {
	Status        nagiosCode
	PrevStatus    nagiosCode
	Epoch         int64 `json:"Epoch,omitempty"`
	output        string
	federatedFrom string
}

func (cs checkState) federated() bool {
	return cs.federatedFrom != ""
}

func (cs checkState) changed() bool {
	return cs.Status != cs.PrevStatus
}

type state struct {
	stateFile  string
	checks     map[string]checkState
	staleEpoch int64
}

func newState(conf config) (state, error) {
	s := state{
		stateFile:  fmt.Sprintf("%s/state.json", conf.StateDir),
		checks:     make(map[string]checkState),
		staleEpoch: time.Now().Unix() - int64(conf.StaleThreshold),
	}

	if _, err := os.Stat(s.stateFile); err != nil {
		// OK, may be first run with no state yet.
		return s, nil
	}

	file, err := os.Open(s.stateFile)
	if err != nil {
		return s, err
	}
	defer file.Close()

	bytes, err := io.ReadAll(file)
	if err != nil {
		return s, err
	}

	if err := json.Unmarshal(bytes, &s.checks); err != nil {
		return s, err
	}

	var obsolete []string
	for name := range s.checks {
		if _, ok := conf.Checks[name]; !ok {
			obsolete = append(obsolete, name)
		}
	}

	for _, name := range obsolete {
		delete(s.checks, name)
		log.Printf("State of %s is obsolete (removed)", name)
	}

	return s, nil
}

func (s state) update(result checkResult) {
	prevStatus := nagiosUnknown
	prevState, ok := s.checks[result.name]
	if ok {
		prevStatus = prevState.Status
	}

	cs := checkState{result.status, prevStatus, result.epoch, result.output, result.federatedFrom}
	s.checks[result.name] = cs
	log.Println(result.name, cs)
}

func (s state) age(name string) time.Duration {
	if prevState, ok := s.checks[name]; ok {
		return time.Since(time.Unix(prevState.Epoch, 0))
	}

	return time.Duration(0)
}

// To be used to merge the state of another server running Gogios
func (s state) merge(other state) error {
	for name, cs := range other.checks {
		if _, ok := s.checks[name]; ok {
			return fmt.Errorf("can't merge state due to duplicate check name '%s'", name)
		}
		s.checks[name] = cs
	}
	return nil
}

func (s state) mergeFromBytes(bytes []byte) error {
	var other state
	if err := json.Unmarshal(bytes, &other.checks); err != nil {
		return err
	}
	return s.merge(other)
}

func (s state) persist() error {
	stateDir := filepath.Dir(s.stateFile)
	if _, err := os.Stat(stateDir); os.IsNotExist(err) {
		if err := os.MkdirAll(stateDir, 0o755); err != nil {
			return err
		}
	}

	jsonData, err := json.Marshal(s.checks)
	if err != nil {
		return err
	}

	return os.WriteFile(s.stateFile, jsonData, os.ModePerm)
}

func (s state) report(renotify, force bool) (string, string, bool) {
	var sb strings.Builder

	sb.WriteString("This is the recent Gogios report!\n\n")

	sb.WriteString("# Alerts with status changed:\n\n")
	changed := s.reportChanged(&sb)
	if !changed {
		sb.WriteString("There were no status changes...\n\n")
	}

	sb.WriteString("# Unhandled alerts:\n\n")
	numCriticals, numWarnings, numUnknown, numOK := s.reportUnhandled(&sb)
	hasUnhandled := (numCriticals + numWarnings + numUnknown) > 0
	if !hasUnhandled {
		sb.WriteString("There are no unhandled alerts...\n\n")
	}

	sb.WriteString("# Stale alerts:\n\n")
	numStale := s.reportStaleAlerts(&sb)
	if numStale == 0 {
		sb.WriteString("There are no stale alerts...\n\n")
	}

	sb.WriteString("Have a nice day!\n")

	subject := fmt.Sprintf("GOGIOS Report [C:%d W:%d U:%d S:%d OK:%d]",
		numCriticals, numWarnings, numUnknown, numStale, numOK)

	doNotify := force || (changed || (renotify && hasUnhandled))
	return subject, sb.String(), doNotify
}

func (s state) reportChanged(sb *strings.Builder) (changed bool) {
	if 0 < s.reportBy(sb, true, false, func(cs checkState) bool {
		return cs.Status == nagiosCritical && cs.changed()
	}) {
		changed = true
	}

	if 0 < s.reportBy(sb, true, false, func(cs checkState) bool {
		return cs.Status == nagiosWarning && cs.changed()
	}) {
		changed = true
	}

	if 0 < s.reportBy(sb, true, false, func(cs checkState) bool {
		return cs.Status == nagiosUnknown && cs.changed()
	}) {
		changed = true
	}

	if 0 < s.reportBy(sb, true, false, func(cs checkState) bool {
		return cs.Status == nagiosOk && cs.changed()
	}) {
		changed = true
	}

	return
}

func (s state) reportUnhandled(sb *strings.Builder) (numCriticals, numWarnings,
	numUnknown, numOK int,
) {
	numCriticals = s.reportBy(sb, false, false, func(cs checkState) bool {
		return cs.Status == nagiosCritical
	})

	numWarnings = s.reportBy(sb, false, false, func(cs checkState) bool {
		return cs.Status == nagiosWarning
	})

	numUnknown = s.reportBy(sb, false, false, func(cs checkState) bool {
		return cs.Status == nagiosUnknown
	})

	numOK = s.countBy(func(cs checkState) bool {
		return cs.Status == nagiosOk
	})

	return
}

func (s state) reportStaleAlerts(sb *strings.Builder) int {
	return s.reportBy(sb, false, true, func(cs checkState) bool {
		return cs.Epoch < s.staleEpoch
	})
}

func (s state) reportBy(sb *strings.Builder, showStatusChange, isStaleReport bool,
	filter func(cs checkState) bool,
) (count int) {
	for name, cs := range s.checks {
		if !filter(cs) {
			continue
		}
		if !isStaleReport && cs.Epoch < s.staleEpoch {
			continue // skip stale checks in non-stale report
		}
		count++

		if showStatusChange && cs.changed() {
			sb.WriteString(nagiosCode(cs.PrevStatus).Str())
			sb.WriteString("->")
		}

		sb.WriteString(nagiosCode(cs.Status).Str())
		sb.WriteString(": ")
		sb.WriteString(name)
		sb.WriteString(": ")
		sb.WriteString(cs.output)
		if cs.federated() {
			sb.WriteString(" [federated from ")
			sb.WriteString(cs.federatedFrom)
			sb.WriteString("]")
		}

		if isStaleReport {
			lastCheckedAgo := time.Since(time.Unix(cs.Epoch, 0))
			sb.WriteString(fmt.Sprintf(" (last checked %v ago)", lastCheckedAgo))
		}

		sb.WriteString("\n")
	}

	if count > 0 {
		sb.WriteString("\n")
	}
	return
}

func (s state) countBy(filter func(cs checkState) bool) (count int) {
	for _, cs := range s.checks {
		if filter(cs) {
			count++
		}
	}
	return
}