package upstream

import (
	"context"
	"encoding/json"
	"fmt"
	"gitea-mail-templates/tools/logging"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"time"
)

var tagPattern = regexp.MustCompile(`^v([0-9]+)\.[0-9]+\.[0-9]+$`)

func validTag(tag string) bool {
	m := tagPattern.FindStringSubmatch(tag)
	if m == nil {
		return false
	}
	major, err := strconv.Atoi(m[1])
	return err == nil && major >= 28
}

// Sync downloads by resolved commit, validates in memory, then swaps the whole
// snapshot. Network/adapter failures leave the existing snapshot untouched.
func Sync(ctx context.Context, tag, dir string) error {
	return syncFrom(ctx, tag, dir, "https://api.github.com/repos/go-gitea/gitea/", "https://raw.githubusercontent.com/go-gitea/gitea/")
}

func syncFrom(ctx context.Context, tag, dir, api, raw string) error {
	if !validTag(tag) {
		return fmt.Errorf("expected a stable Gitea 28+ tag, e.g. v28.0.0")
	}
	client := &http.Client{Timeout: 45 * time.Second}
	get := func(url string) ([]byte, error) {
		req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
		if err != nil {
			return nil, err
		}
		req.Header.Set("User-Agent", "GiteaMailTemplates-snapshot")
		resp, err := client.Do(req)
		if err != nil {
			return nil, err
		}
		defer resp.Body.Close()
		if resp.StatusCode != 200 {
			return nil, fmt.Errorf("%s: HTTP %d", url, resp.StatusCode)
		}
		b, err := io.ReadAll(io.LimitReader(resp.Body, 16<<20))
		return b, err
	}
	b, err := get(api + "commits/" + tag)
	if err != nil {
		return err
	}
	var commit struct {
		SHA    string `json:"sha"`
		Commit struct {
			Tree struct {
				SHA string `json:"sha"`
			} `json:"tree"`
		} `json:"commit"`
	}
	if err := json.Unmarshal(b, &commit); err != nil {
		return err
	}
	b, err = get(api + "git/trees/" + commit.Commit.Tree.SHA + "?recursive=1")
	if err != nil {
		return err
	}
	var tree struct {
		Truncated bool `json:"truncated"`
		Tree      []struct {
			Path string `json:"path"`
			Type string `json:"type"`
		} `json:"tree"`
	}
	if err := json.Unmarshal(b, &tree); err != nil {
		return err
	}
	if tree.Truncated {
		return fmt.Errorf("upstream tree is truncated")
	}
	s := &Snapshot{Lock: Lock{Schema: 1, Repository: "https://github.com/go-gitea/gitea", Tag: tag, Commit: commit.SHA, Files: map[string]string{}}, Files: map[string][]byte{}}
	for _, item := range tree.Tree {
		p := item.Path
		_, adapter := AdapterSources[p]
		selected := adapter || p == "LICENSE" || p == "public/assets/img/favicon.png" || (strings.HasPrefix(p, "templates/mail/") && strings.HasSuffix(p, ".tmpl")) || (strings.HasPrefix(p, "options/locale/locale_") && strings.HasSuffix(p, ".json"))
		if !selected || item.Type != "blob" {
			continue
		}
		b, err := get(raw + commit.SHA + "/" + p)
		if err != nil {
			return err
		}
		s.Files[p] = b
		s.Lock.Files[p] = Digest(b)
	}
	if err := s.validate(); err != nil {
		return err
	}
	abs, err := filepath.Abs(dir)
	if err != nil {
		return err
	}
	// Never replace a checkout or arbitrary non-snapshot directory.
	if filepath.Base(abs) != "upstream" {
		return fmt.Errorf("snapshot destination must be named upstream")
	}
	if entries, err := os.ReadDir(abs); err == nil && len(entries) > 0 {
		if _, err := loadFiles(abs); err != nil {
			return fmt.Errorf("refusing to replace invalid existing snapshot: %w", err)
		}
	}
	stage, err := os.MkdirTemp(filepath.Dir(abs), ".upstream-stage-")
	if err != nil {
		return err
	}
	defer os.RemoveAll(stage)
	for p, data := range s.Files {
		filename := filepath.Join(stage, filepath.FromSlash(p))
		if err := os.MkdirAll(filepath.Dir(filename), 0755); err != nil {
			return err
		}
		if err := os.WriteFile(filename, data, 0644); err != nil {
			return err
		}
	}
	b, err = json.MarshalIndent(s.Lock, "", "  ")
	if err != nil {
		return err
	}
	b = append(b, '\n')
	if err := os.WriteFile(filepath.Join(stage, "lock.json"), b, 0644); err != nil {
		return err
	}
	if _, err := os.Stat(abs); err == nil {
		backup, err := os.MkdirTemp(filepath.Dir(abs), ".upstream-backup-")
		if err != nil {
			return err
		}
		if err := os.Remove(backup); err != nil {
			return err
		}
		if err := os.Rename(abs, backup); err != nil {
			return err
		}
		if err := os.Rename(stage, abs); err != nil {
			_ = os.Rename(backup, abs)
			return err
		}
		if err := os.RemoveAll(backup); err != nil {
			return err
		}
	} else if err := os.Rename(stage, abs); err != nil {
		return err
	}
	logging.Info("Upstream", "Locked %s (%s): %d templates, %d languages", tag, commit.SHA, len(s.Templates), len(s.Locales))
	return nil
}