package main

import (
	"context"
	"errors"
	"log"
	"net/url"
	"strconv"
	"sync"
	"time"
)

// Schedule says when a saved search runs, in the server time zone (TZ).
type Schedule struct {
	Every   string `json:"every"`             // "hours", "day" or "week"
	Hours   int    `json:"hours,omitempty"`   // every: hours (1..168)
	Weekday int    `json:"weekday,omitempty"` // every: week, 0 = Sunday
	Hour    int    `json:"hour"`              // every: day / week
	Minute  int    `json:"minute"`
}

func (sc Schedule) Valid() bool {
	switch sc.Every {
	case "hours":
		return sc.Hours >= 1 && sc.Hours <= 168
	case "day", "week":
		return sc.Hour >= 0 && sc.Hour < 24 && sc.Minute >= 0 && sc.Minute < 60 &&
			sc.Weekday >= 0 && sc.Weekday < 7
	}
	return false
}

// Next returns the first run time strictly after "after". last is the time of
// the last run, used by the "hours" schedule.
func (sc Schedule) Next(after, last time.Time) time.Time {
	switch sc.Every {
	case "hours":
		every := time.Duration(sc.Hours) * time.Hour
		if last.IsZero() || last.Add(every).Before(after) {
			return after.Add(time.Minute)
		}
		return last.Add(every)
	case "day", "week":
		t := time.Date(after.Year(), after.Month(), after.Day(), sc.Hour, sc.Minute, 0, 0, after.Location())
		for !t.After(after) || (sc.Every == "week" && int(t.Weekday()) != sc.Weekday) {
			t = t.AddDate(0, 0, 1)
		}
		return t
	}
	return time.Time{}
}

// Scheduler runs the saved searches when they are due.
type Scheduler struct {
	store *Store
	gh    *GitHub
	runMu sync.Mutex // one run at a time, to spare the GitHub quota
}

func NewScheduler(store *Store, gh *GitHub) *Scheduler {
	return &Scheduler{store: store, gh: gh}
}

// Start checks every 30 seconds for due searches until ctx is done.
func (s *Scheduler) Start(ctx context.Context) {
	now := time.Now()
	for _, x := range s.store.List() { // plan searches that have no next run yet
		if x.Enabled && x.NextRunAt.IsZero() {
			_, _ = s.store.Update(x.ID, func(v *SavedSearch) { v.NextRunAt = v.Schedule.Next(now, v.LastRunAt) })
		}
	}
	go func() {
		tick := time.NewTicker(30 * time.Second)
		defer tick.Stop()
		for {
			s.runDue(ctx)
			select {
			case <-ctx.Done():
				return
			case <-tick.C:
			}
		}
	}()
}

func (s *Scheduler) runDue(ctx context.Context) {
	for _, x := range s.store.List() {
		if ctx.Err() != nil {
			return
		}
		if x.Enabled && !x.NextRunAt.IsZero() && !time.Now().Before(x.NextRunAt) {
			if _, err := s.Run(ctx, x.ID, "schedule"); err != nil {
				log.Printf("saved search %q: %v", x.Name, err)
			}
		}
	}
}

// Run executes a saved search now and stores the snapshot.
func (s *Scheduler) Run(ctx context.Context, id, trigger string) (Run, error) {
	s.runMu.Lock()
	defer s.runMu.Unlock()
	x, err := s.store.Get(id)
	if err != nil {
		return Run{}, err
	}
	start := time.Now()
	info := RunInfo{ID: start.UTC().Format("20060102T150405Z"), At: start, Trigger: trigger}

	var repos []Repo
	c, err := criteriaFor(x)
	if err == nil {
		info.Query = c.Query(start)
		var res SearchResult
		if res, err = s.gh.Search(ctx, c); err == nil {
			info.Total = res.Total
			repos = res.Items
		}
	}
	info.TookMs = time.Since(start).Milliseconds()
	if err != nil {
		info.Error = err.Error()
	}
	run, serr := s.store.AddRun(id, info, repos)
	if serr != nil {
		return Run{}, serr
	}

	_, uerr := s.store.Update(id, func(v *SavedSearch) {
		v.LastRunAt = start
		v.LastError = info.Error
		ri := run.RunInfo
		v.LastRun = &ri
		next := v.Schedule.Next(time.Now(), start)
		if err != nil {
			var ce *codedError
			if errors.As(err, &ce) && ce.code == "rate_limited" {
				// Quota exhausted: try again in a few minutes rather than next week.
				next = time.Now().Add(3 * time.Minute)
			}
		}
		v.NextRunAt = next
	})
	if uerr != nil {
		return run, uerr
	}
	if err != nil {
		return run, err
	}
	return run, nil
}

// criteriaFor parses the stored parameters; a saved search always reads the
// first page, sorted as saved.
func criteriaFor(x SavedSearch) (Criteria, error) {
	v, err := url.ParseQuery(x.Params)
	if err != nil {
		return Criteria{}, &codedError{code: "bad_param", msg: "invalid parameters", detail: err.Error()}
	}
	v.Del("page")
	v.Set("per_page", strconv.Itoa(x.MaxResults))
	return ParseCriteria(v)
}