// SPDX-License-Identifier: AGPL-3.0-only

package provenance

import (
	"context"
	"errors"
	"fmt"
	"path/filepath"
	"strconv"
	"strings"

	"gamertan.com/tend/internal/process"
)

type Source struct {
	Commit string
	Epoch  int64
}

func Inspect(ctx context.Context, runner process.Runner, dir, branch string) (Source, error) {
	gitDir, err := gitPath(ctx, runner, dir, "--git-dir")
	if err != nil {
		return Source{}, fmt.Errorf("inspect Git directory: %w", err)
	}
	commonDir, err := gitPath(ctx, runner, dir, "--git-common-dir")
	if err != nil {
		return Source{}, fmt.Errorf("inspect Git common directory: %w", err)
	}
	if gitDir != commonDir {
		return Source{}, errors.New("release packaging does not yet support linked Git worktrees; use a clean standalone clone of the exact pushed commit")
	}
	status, err := runner.Run(ctx, dir, nil, "git", "status", "--porcelain=v1", "--untracked-files=all")
	if err != nil {
		return Source{}, err
	}
	if len(status) != 0 {
		return Source{}, errors.New("source checkout is not clean")
	}
	commitOut, err := runner.Run(ctx, dir, nil, "git", "rev-parse", "HEAD")
	if err != nil {
		return Source{}, err
	}
	commit := strings.TrimSpace(string(commitOut))
	if len(commit) != 40 {
		return Source{}, errors.New("source commit is not a full SHA-1 object id")
	}
	remoteOut, err := runner.Run(ctx, dir, nil, "git", "ls-remote", "--exit-code", "origin", "refs/heads/"+branch)
	if err != nil {
		return Source{}, fmt.Errorf("verify pushed commit: %w", err)
	}
	fields := strings.Fields(string(remoteOut))
	if len(fields) != 2 || fields[0] != commit || fields[1] != "refs/heads/"+branch {
		return Source{}, errors.New("HEAD is not the exact pushed branch commit")
	}
	epochOut, err := runner.Run(ctx, dir, nil, "git", "show", "-s", "--format=%ct", commit)
	if err != nil {
		return Source{}, err
	}
	epoch, err := strconv.ParseInt(strings.TrimSpace(string(epochOut)), 10, 64)
	if err != nil || epoch <= 0 {
		return Source{}, errors.New("commit timestamp is invalid")
	}
	return Source{Commit: commit, Epoch: epoch}, nil
}

func gitPath(ctx context.Context, runner process.Runner, dir, argument string) (string, error) {
	out, err := runner.Run(ctx, dir, nil, "git", "rev-parse", argument)
	if err != nil {
		return "", err
	}
	path := strings.TrimSpace(string(out))
	if path == "" {
		return "", errors.New("Git returned an empty path")
	}
	if !filepath.IsAbs(path) {
		path = filepath.Join(dir, path)
	}
	return filepath.Clean(path), nil
}