package publish

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"time"

	"go.maximumdirect.net/releasekit/internal/git"
)

const recordFormatVersion = 1

type recordEnvelope struct {
	FormatVersion int             `json:"format_version"`
	Evidence      json.RawMessage `json:"evidence"`
}

// LoadEvidence reads one complete supported private publication record.
func LoadEvidence(path string) (Evidence, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return Evidence{}, &RecoveryError{Kind: "record_read", RecordPath: path, cause: fmt.Errorf("read record %q: %w", path, err)}
	}
	decoder := json.NewDecoder(strings.NewReader(string(data)))
	var envelope recordEnvelope
	if err := decoder.Decode(&envelope); err != nil {
		return Evidence{}, &RecoveryError{Kind: "record_format", RecordPath: path, cause: fmt.Errorf("decode record %q: %w", path, err)}
	}
	var trailing any
	if err := decoder.Decode(&trailing); err != io.EOF {
		return Evidence{}, &RecoveryError{Kind: "record_format", RecordPath: path, cause: fmt.Errorf("record %q contains trailing JSON", path)}
	}
	if envelope.FormatVersion != recordFormatVersion {
		return Evidence{}, &RecoveryError{Kind: "record_format", RecordPath: path, cause: fmt.Errorf("record %q has unsupported format version %d", path, envelope.FormatVersion)}
	}
	if len(envelope.Evidence) == 0 || string(envelope.Evidence) == "null" {
		return Evidence{}, &RecoveryError{Kind: "record_format", RecordPath: path, cause: fmt.Errorf("record %q has no evidence object", path)}
	}
	var evidence Evidence
	if err := json.Unmarshal(envelope.Evidence, &evidence); err != nil {
		return Evidence{}, &RecoveryError{Kind: "record_format", RecordPath: path, cause: fmt.Errorf("decode record evidence %q: %w", path, err)}
	}
	return evidence, nil
}

// SaveEvidence writes one private attempt record and returns its absolute path.
func SaveEvidence(ctx context.Context, repositoryDir, override string, evidence Evidence) (string, error) {
	recordDir, root, err := resolveRecordDir(ctx, repositoryDir, override)
	if err != nil {
		return "", &RecoveryError{Kind: "record_write", cause: err}
	}
	return saveEvidenceInDir(ctx, repositoryDir, root, override, recordDir, evidence)
}

func saveEvidenceInDir(ctx context.Context, repositoryDir, root, override, recordDir string, evidence Evidence) (string, error) {
	return saveEvidenceNamed(ctx, repositoryDir, root, override, recordDir, evidence, proposedRecordPath)
}

func saveEvidenceNamed(ctx context.Context, repositoryDir, root, override, recordDir string, evidence Evidence, nextPath func(string) (string, error)) (string, error) {
	if evidence.RecordedAt == "" {
		evidence.RecordedAt = time.Now().UTC().Format(time.RFC3339Nano)
	}
	if err := os.MkdirAll(recordDir, 0o700); err != nil {
		return "", &RecoveryError{Kind: "record_write", cause: fmt.Errorf("create record directory %q: %w", recordDir, err)}
	}
	evidenceJSON, err := json.Marshal(evidence)
	if err != nil {
		return "", &RecoveryError{Kind: "record_write", cause: fmt.Errorf("encode publication evidence: %w", err)}
	}
	data, err := json.Marshal(recordEnvelope{FormatVersion: recordFormatVersion, Evidence: evidenceJSON})
	if err != nil {
		return "", &RecoveryError{Kind: "record_write", cause: fmt.Errorf("encode publication evidence: %w", err)}
	}
	for attempt := 0; attempt < 5; attempt++ {
		path, err := nextPath(recordDir)
		if err != nil {
			return "", &RecoveryError{Kind: "record_write", cause: fmt.Errorf("name publication record: %w", err)}
		}
		if override != "" && root != "" {
			if err := rejectUnignoredWorktreePath(ctx, repositoryDir, root, path); err != nil {
				return "", &RecoveryError{Kind: "record_write", cause: err}
			}
		}
		file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o600)
		if errors.Is(err, os.ErrExist) {
			continue
		}
		if err != nil {
			return "", &RecoveryError{Kind: "record_write", cause: fmt.Errorf("create record %q: %w", path, err)}
		}
		if _, err = file.Write(data); err != nil {
			_ = file.Close()
			_ = os.Remove(path)
			return "", &RecoveryError{Kind: "record_write", cause: fmt.Errorf("write record %q: %w", path, err)}
		}
		if err = file.Close(); err != nil {
			_ = os.Remove(path)
			return "", &RecoveryError{Kind: "record_write", cause: fmt.Errorf("close record %q: %w", path, err)}
		}
		return path, nil
	}
	return "", &RecoveryError{Kind: "record_write", cause: fmt.Errorf("could not allocate a unique record name in %q", recordDir)}
}

func resolveRecordDir(ctx context.Context, repositoryDir, override string) (string, string, error) {
	root, err := git.RepositoryRoot(ctx, repositoryDir)
	if err != nil {
		return "", "", err
	}
	if override != "" {
		if filepath.IsAbs(override) {
			return filepath.Clean(override), root, nil
		}
		return filepath.Join(root, override), root, nil
	}
	common, err := git.CommonDirectory(ctx, repositoryDir)
	if err != nil {
		return "", "", err
	}
	return filepath.Join(common, "releasekit", "publication-attempts"), root, nil
}

func proposedRecordPath(directory string) (string, error) {
	var nonce [16]byte
	if _, err := rand.Read(nonce[:]); err != nil {
		return "", err
	}
	return filepath.Join(directory, "attempt-"+hex.EncodeToString(nonce[:])+".json"), nil
}

func rejectUnignoredWorktreePath(ctx context.Context, repositoryDir, root, proposed string) error {
	parent, err := filepath.EvalSymlinks(filepath.Dir(proposed))
	if err != nil {
		return fmt.Errorf("resolve record directory %q: %w", filepath.Dir(proposed), err)
	}
	actual := filepath.Join(parent, filepath.Base(proposed))
	rel, err := filepath.Rel(root, actual)
	if err != nil || rel == ".." || strings.HasPrefix(rel, ".."+string(filepath.Separator)) {
		return nil
	}
	metadata, err := git.MetadataDirectories(ctx, repositoryDir)
	if err != nil {
		return err
	}
	for _, directory := range metadata {
		rel, err := filepath.Rel(directory, actual)
		if err == nil && rel != ".." && !strings.HasPrefix(rel, ".."+string(filepath.Separator)) {
			return nil
		}
	}
	ignored, err := git.IsIgnored(ctx, repositoryDir, actual)
	if err != nil {
		return fmt.Errorf("check Git ignore rules for record path %q: %w", actual, err)
	}
	if !ignored {
		return fmt.Errorf("record path %q is inside the worktree and is not ignored", actual)
	}
	return nil
}