package main

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"time"

	"github.com/go-git/go-git/v5"
	"github.com/go-git/go-git/v5/config"
	"github.com/go-git/go-git/v5/plumbing"
	"github.com/go-git/go-git/v5/plumbing/object"
	"github.com/go-git/go-git/v5/plumbing/storer"
	"github.com/go-git/go-git/v5/storage/memory"
)

type UnixTimestamp struct {
	time.Time
}

func (ut *UnixTimestamp) UnmarshalJSON(bytes []byte) error {
	var raw int64
	err := json.Unmarshal(bytes, &raw)
	if err != nil {
		fmt.Printf("error decoding timestamp: %s\n", err)
		return err
	}

	ut.Time = time.Unix(raw, 0)
	return nil
}

type Config struct {
	FlakePath string
	Interval  time.Duration
}

type FlakeMetadata struct {
	Description  string        `json:"description"`
	LastModified UnixTimestamp `json:"lastModified"`
	Locks        struct {
		Nodes map[string]struct {
			Locked struct {
				LastModified UnixTimestamp `json:"lastModified"`
				NARHash      string        `json:"narHash"`
				Owner        string        `json:"owner"`
				Repo         string        `json:"repo"`
				Rev          string        `json:"rev"`
				Ref          string        `json:"ref"`
				Type         string        `json:"type"`
				URL          string        `json:"url"`
			} `json:"locked"`
			Original struct {
				Owner string `json:"owner"`
				Repo  string `json:"repo"`
				Type  string `json:"type"`
				Ref   string `json:"ref"`
			} `json:"original"`
		} `json:"nodes"`
	} `json:"locks"`
}

func LoadConfig() (*Config, error) {
	var c Config
	if path := os.Getenv("GFLAKESTAT_PATH"); path != "" {
		c.FlakePath = path
	} else {
		return nil, fmt.Errorf("GFLAKESTAT_PATH not set or empty")
	}

	if interval := os.Getenv("GFLAKESTAT_INTERVAL"); interval != "" {
		if dur, err := time.ParseDuration(interval); err != nil {
			return nil, fmt.Errorf("failed parsing duration: %w", err)
		} else {
			c.Interval = dur
		}
	} else {
		c.Interval = 30 * time.Minute
	}

	return &c, nil
}

func ReadFlakeMetadata(cfg *Config) (*FlakeMetadata, error) {
	args := []string{
		"flake",
		"metadata",
		"--json",
		cfg.FlakePath,
	}
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	cmd := exec.CommandContext(ctx, "nix", args...)

	output, err := cmd.Output()
	if err != nil {
		return nil, err
	}

	var metadata FlakeMetadata

	if err := json.Unmarshal(output, &metadata); err != nil {
		return nil, err
	}

	return &metadata, nil
}

func main() {
	cfg, err := LoadConfig()
	if err != nil {
		fmt.Printf("Error loading config from env: %s\n", err)
		os.Exit(1)
	}

	metadata, err := ReadFlakeMetadata(cfg)
	if err != nil {
		fmt.Printf("Error reading flake metadata: %s\n", err)
		os.Exit(1)
	}

	for key, val := range metadata.Locks.Nodes {
		if key != "nixpkgs" {
			continue
		}
		var url string
		switch val.Locked.Type {
		case "github":
			url = fmt.Sprintf("https://github.com/%s/%s.git", val.Locked.Owner, val.Locked.Repo)
		case "git":
			url = val.Locked.URL
		}

		branchName := "refs/heads/nixos-unstable"

		repo, err := git.Init(memory.NewStorage(), nil)
		if err != nil {
			panic(err)
		}

		if _, err := repo.CreateRemote(&config.RemoteConfig{
			Name: "origin",
			URLs: []string{url},
		}); err != nil {
			panic(err)
		}
		fmt.Println("Starting fetch")

		err = repo.Fetch(&git.FetchOptions{
			RemoteName: "origin",
			RefSpecs:   []config.RefSpec{config.RefSpec(branchName + ":" + branchName)},
			Depth:      1, // Shallow fetch to minimize data transfer
		})
		if err != nil {
			panic(err)
		}
		fmt.Println("Fetch done")

		ref, err := repo.Reference(plumbing.ReferenceName(branchName), true)
		if err != nil {
			panic(err)
		}
		latestCommit, err := repo.CommitObject(ref.Hash())
		if err != nil {
			panic(err)
		}
		startCommit, err := repo.CommitObject(plumbing.NewHash(val.Locked.Ref))
		if err != nil {
			panic(err)
		}
		count := 0
		commitIter := latestCommit.Parents()
		err = commitIter.ForEach(func(commit *object.Commit) error {
			count++
			if commit.Hash == startCommit.Hash {
				return storer.ErrStop
			}
			return nil
		})
		if err != nil {
			panic(err)
		}

		fmt.Printf("%s: %s: %d\n", key, url, count)
	}
}