// Copyright (C) 2024  Umorpha Systems
// SPDX-License-Identifier: AGPL-3.0-or-later

package main

import (
	"cmp"
	"context"
	"encoding"
	"fmt"
	"io"
	"os"
	"slices"
	"sync"
	"time"

	"github.com/datawire/ocibuild/pkg/cliutil"
	"github.com/spf13/cobra"
	"sigs.k8s.io/yaml"

	"git.mothstuff.lol/lukeshu/eclipse/lib/gitcache"
)

type Duration struct {
	time.Duration
}

var _ encoding.TextUnmarshaler = (*Duration)(nil)

func (d *Duration) UnmarshalText(text []byte) error {
	var err error
	d.Duration, err = time.ParseDuration(string(text))
	return err
}

type Config struct {
	Daemon struct {
		GitCacheDir       string   `json:"cache_git_dir"`
		GitCacheFor       Duration `json:"cache_git_for"`
		ParallelDownloads int      `json:"parallel_downloads"`
	} `json:"daemon"`

	Actions []Action `json:"actions"`
}

type Action struct {
	Triggers []GitTrigger `json:"triggers"`
	Run      string       `json:"run"`
}

type GitTrigger struct {
	RepoURL string `json:"repo_url"`
	Rev     string `json:"rev"`
}

func min[T cmp.Ordered](a, b T) T {
	if a < b {
		return a
	}
	return b
}

func max[T cmp.Ordered](a, b T) T {
	if a > b {
		return a
	}
	return b
}

func keys[K comparable, V any](m map[K]V) []K {
	ret := make([]K, 0, len(m))
	for k := range m {
		ret = append(ret, k)
	}
	return ret
}

func sortedKeys[K cmp.Ordered, V any](m map[K]V) []K {
	ret := keys(m)
	slices.Sort(ret)
	return ret
}

type Set[T comparable] map[T]struct{}

func (s Set[T]) Has(v T) bool {
	_, ok := s[v]
	return ok
}

func parallel[T any](
	nWorkers int,
	generator func(yield func(T)),
	consumer func(T),
) {
	ch := make(chan T)
	go func() {
		defer close(ch)
		generator(func(v T) { ch <- v })
	}()

	var wg sync.WaitGroup
	wg.Add(nWorkers)
	for i := 0; i < nWorkers; i++ {
		go func() {
			defer wg.Done()
			for v := range ch {
				consumer(v)
			}
		}()
	}
	wg.Wait()
}

func Trigger(allowedRepos Set[string]) error {
	cfgBytes, err := io.ReadAll(os.Stdin)
	if err != nil {
		return err
	}
	var cfg Config
	if err := yaml.UnmarshalStrict(cfgBytes, &cfg); err != nil {
		return err
	}

	repos := map[string]map[string]string{}
	for _, action := range cfg.Actions {
		for _, trigger := range action.Triggers {
			if len(allowedRepos) > 0 && !allowedRepos.Has(trigger.RepoURL) {
				continue
			}
			if repos[trigger.RepoURL] == nil {
				repos[trigger.RepoURL] = make(map[string]string, 1)
			}
			repos[trigger.RepoURL][trigger.Rev] = ""
		}
	}

	cache := &gitcache.Cache{
		Dir:       cfg.Daemon.GitCacheDir,
		MinPeriod: cfg.Daemon.GitCacheFor.Duration,
	}

	// Fetch.
	parallel[string](min(cfg.Daemon.ParallelDownloads, len(repos)),
		func(yield func(string)) {
			for repo := range repos {
				yield(repo)
			}
		},
		func(repo string) {
			if err := cache.Fetch(os.Stderr, repo); err != nil {
				fmt.Fprintf(os.Stderr, "error: updating %q: %v\n", repo, err)
			}
		},
	)

	// Resolve revs.
	parallel[string](len(repos),
		func(yield func(string)) {
			for repo := range repos {
				yield(repo)
			}
		},
		func(repo string) {
			exprs := keys(repos[repo])
			hashs, err := cache.RevParse(os.Stderr, repo, exprs...)
			if err != nil {
				fmt.Fprintf(os.Stderr, "error: resolving in %q: %v\n", repo, err)
				return
			}
			for i := range hashs {
				repos[repo][exprs[i]] = hashs[i]
			}
		},
	)

	// TODO.  Just print them for now.
	for _, repo := range keys(repos) {
		for _, expr := range keys(repos[repo]) {
			hash := repos[repo][expr]
			fmt.Printf("%q %q : %s\n", repo, expr, hash)
		}
	}
	return nil
}

func main() {
	argparser := &cobra.Command{
		Use:   os.Args[0] + " [flags] <config.yml",
		Short: "Trigger actions",

		RunE: func(_ *cobra.Command, args []string) error {
			allowedRepos := make(Set[string], len(args))
			for _, repo := range args {
				allowedRepos[repo] = struct{}{}
			}
			return Trigger(allowedRepos)
		},

		SilenceErrors: true, // we'll handle this ourselves after .ExecuteContext()
		SilenceUsage:  true, // FlagErrorFunc will handle this

		CompletionOptions: cobra.CompletionOptions{
			DisableDefaultCmd: true,
		},
	}
	argparser.SetFlagErrorFunc(cliutil.FlagErrorFunc)
	argparser.SetHelpTemplate(cliutil.HelpTemplate)

	ctx := context.Background()

	if err := argparser.ExecuteContext(ctx); err != nil {
		fmt.Fprintf(os.Stderr, "%v: error: %v\n", argparser.CommandPath(), err)
		os.Exit(1)
	}
}