package main

import (
	"context"
	"fmt"
	"sync"
	"time"

	"go.skia.org/infra/go/git/repograph"
	"go.skia.org/infra/go/sklog"
	"go.skia.org/infra/go/util"
	"go.skia.org/infra/task_scheduler/go/task_cfg_cache"
	"go.skia.org/infra/task_scheduler/go/types"
	"golang.org/x/oauth2"
)

// tasksPerCommitCache is a struct used for caching the number of task specs
// for various commits.
type tasksPerCommitCache struct {
	cached map[types.RepoState]int
	mtx    sync.Mutex
	period time.Duration
	repos  repograph.Map
	tcc    *task_cfg_cache.TaskCfgCacheImpl
}

// newTasksPerCommitCache returns a tasksPerCommitCache instance.
func newTasksPerCommitCache(ctx context.Context, repos repograph.Map, period time.Duration, btProject, btInstance string, ts oauth2.TokenSource) (*tasksPerCommitCache, error) {
	tcc, err := task_cfg_cache.NewTaskCfgCache(ctx, repos, btProject, btInstance, ts)
	if err != nil {
		return nil, err
	}
	c := &tasksPerCommitCache{
		cached: map[types.RepoState]int{},
		period: period,
		repos:  repos,
		tcc:    tcc,
	}
	go util.RepeatCtx(ctx, time.Minute, func(ctx context.Context) {
		if err := c.update(ctx); err != nil {
			sklog.Errorf("Failed to update tasksPerCommitCache: %s", err)
		}
	})
	return c, nil
}

// Get returns the number of tasks expected to run at the given commit.
func (c *tasksPerCommitCache) Get(ctx context.Context, rs types.RepoState) (int, error) {
	c.mtx.Lock()
	defer c.mtx.Unlock()

	if _, ok := c.cached[rs]; !ok {
		// Find the number of TaskSpecs expected to run at this commit.
		cfg, cachedErr, err := c.tcc.Get(ctx, rs)
		if err == task_cfg_cache.ErrNoSuchEntry {
			// The TasksCfg for this RepoState hasn't been cached
			// yet. Return 0 with no error for now.
			sklog.Warningf("No cache entry for %s@%s; returning 0.", rs.Repo, rs.Revision)
			return 0, nil
		} else if err != nil {
			return 0, err
		} else if cachedErr != nil {
			return 0, nil
		}
		tasksForCommit := make(map[string]bool, len(cfg.Tasks))
		var recurse func(string)
		recurse = func(taskSpec string) {
			if tasksForCommit[taskSpec] {
				return
			}
			tasksForCommit[taskSpec] = true
			for _, d := range cfg.Tasks[taskSpec].Dependencies {
				recurse(d)
			}
		}
		for _, job := range cfg.Jobs {
			if job.Trigger == "" {
				for _, taskSpec := range job.TaskSpecs {
					recurse(taskSpec)
				}
			}
		}
		c.cached[rs] = len(tasksForCommit)
	}
	return c.cached[rs], nil
}

// update pulls down new commits and evicts old entries from the cache.
func (c *tasksPerCommitCache) update(ctx context.Context) error {
	c.mtx.Lock()
	defer c.mtx.Unlock()
	start := time.Now().Add(-c.period)
	for rs := range c.cached {
		repo, ok := c.repos[rs.Repo]
		if !ok {
			return fmt.Errorf("No such repo: %s", rs.Repo)
		}
		commit := repo.Get(rs.Revision)
		if commit == nil {
			return fmt.Errorf("No such commit: %s in repo %s", rs.Revision, rs.Repo)
		}
		if commit.Timestamp.Before(start) {
			delete(c.cached, rs)
		}
	}
	return c.tcc.Cleanup(ctx, c.period)
}