package obs

import (
	"errors"
	"sync"
	"time"

	"github.com/prometheus/client_golang/prometheus"
)

var errCommit = errors.New("obs: a commit is 40 or 64 lowercase hexadecimal digits")

var (
	commitInfoDesc = prometheus.NewDesc("tug_config_commit_info",
		"The configuration in force: its source, and for a git source the applied commit.", []string{"source", "commit"}, nil)
	lastFetchDesc = prometheus.NewDesc("tug_config_last_fetch_success_timestamp_seconds",
		"When the git source last fetched its remote successfully, in Unix seconds.", nil, nil)
	rollbackDesc = prometheus.NewDesc("tug_config_rollback_refused_total",
		"Fetched commits refused because the applied commit is not their ancestor.", nil, nil)
)

type ConfigSource struct {
	mu      sync.Mutex
	source  string
	commit  string
	fetched time.Time
	refused uint64
}

func (r *Registry) ConfigSource(source string) *ConfigSource {
	if r == nil {
		return nil
	}
	if source != "file" && source != "git" {
		source = "unknown"
	}
	c := &ConfigSource{source: source}
	r.reg.MustRegister(c)
	return c
}

func (c *ConfigSource) Applied(commit string) error {
	if c == nil {
		return nil
	}
	if !validCommit(commit) {
		return errCommit
	}
	c.mu.Lock()
	defer c.mu.Unlock()
	c.commit = commit
	return nil
}

func validCommit(s string) bool {
	if len(s) != 40 && len(s) != 64 {
		return false
	}
	for i := 0; i < len(s); i++ {
		if !('0' <= s[i] && s[i] <= '9' || 'a' <= s[i] && s[i] <= 'f') {
			return false
		}
	}
	return true
}

func (c *ConfigSource) Fetched(at time.Time) {
	if c == nil {
		return
	}
	c.mu.Lock()
	defer c.mu.Unlock()
	c.fetched = at
}

func (c *ConfigSource) RollbackRefused() {
	if c == nil {
		return
	}
	c.mu.Lock()
	defer c.mu.Unlock()
	c.refused++
}

func (c *ConfigSource) Describe(ch chan<- *prometheus.Desc) {
	ch <- commitInfoDesc
	ch <- lastFetchDesc
	ch <- rollbackDesc
}

func (c *ConfigSource) Collect(ch chan<- prometheus.Metric) {
	c.mu.Lock()
	source, commit, fetched, refused := c.source, c.commit, c.fetched, c.refused
	c.mu.Unlock()
	ch <- prometheus.MustNewConstMetric(commitInfoDesc, prometheus.GaugeValue, 1, source, commit)
	if !fetched.IsZero() {
		ch <- prometheus.MustNewConstMetric(lastFetchDesc, prometheus.GaugeValue, float64(fetched.UnixNano())/1e9)
	}
	ch <- prometheus.MustNewConstMetric(rollbackDesc, prometheus.CounterValue, float64(refused))
}