package audit

import (
	"bufio"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"sync"

	"github.com/mathiasbq/hyperguild/ingestion/internal/capture"
)

// FileBuffer is a durable, restart-surviving audit buffer backed by a
// JSONL file: one {id, entry} record per line. It is the internal/public
// tier fallback when loki is unreachable. Confirm rewrites the file
// without the confirmed record, so a record is cleared only after its
// central write is confirmed.
//
// Access is serialised by a mutex; the buffer is low-throughput (only
// written during a loki outage), so a whole-file rewrite on Confirm is
// acceptable and keeps the on-disk format trivially correct.
type FileBuffer struct {
	path string
	mu   sync.Mutex
}

type bufferLine struct {
	ID    string              `json:"id"`
	Entry capture.AuditEntry  `json:"entry"`
}

// NewFileBuffer returns a buffer backed by path. The parent directory is
// created if needed. The file itself is created lazily on first Append.
func NewFileBuffer(path string) (*FileBuffer, error) {
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return nil, fmt.Errorf("create buffer dir: %w", err)
	}
	return &FileBuffer{path: path}, nil
}

// Writable reports whether the buffer file can be appended to. It probes
// by opening the file for append (creating it if absent) — the same
// operation Append performs — so Reserve's check matches Append's reality.
func (b *FileBuffer) Writable() error {
	b.mu.Lock()
	defer b.mu.Unlock()
	f, err := os.OpenFile(b.path, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o644)
	if err != nil {
		return err
	}
	return f.Close()
}

// Append durably writes one audit record. The ID is derived from the
// content + timestamp so it is stable and unique per record.
func (b *FileBuffer) Append(e capture.AuditEntry) error {
	b.mu.Lock()
	defer b.mu.Unlock()

	line := bufferLine{ID: recordID(e), Entry: e}
	data, err := json.Marshal(line)
	if err != nil {
		return fmt.Errorf("marshal buffer line: %w", err)
	}
	f, err := os.OpenFile(b.path, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o644)
	if err != nil {
		return err
	}
	defer func() { _ = f.Close() }()
	if _, err := f.Write(append(data, '\n')); err != nil {
		return err
	}
	return f.Sync()
}

// Pending reads all buffered records. A missing file means none.
func (b *FileBuffer) Pending() ([]Buffered, error) {
	b.mu.Lock()
	defer b.mu.Unlock()
	return b.readAllLocked()
}

func (b *FileBuffer) readAllLocked() ([]Buffered, error) {
	f, err := os.Open(b.path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, err
	}
	defer func() { _ = f.Close() }()

	var out []Buffered
	sc := bufio.NewScanner(f)
	sc.Buffer(make([]byte, 0, 64*1024), 1024*1024)
	for sc.Scan() {
		raw := sc.Bytes()
		if len(raw) == 0 {
			continue
		}
		var l bufferLine
		if err := json.Unmarshal(raw, &l); err != nil {
			return nil, fmt.Errorf("parse buffer line: %w", err)
		}
		out = append(out, Buffered(l))
	}
	return out, sc.Err()
}

// Confirm removes a single record after its central write is confirmed, by
// rewriting the file without it. Unknown IDs are a no-op.
func (b *FileBuffer) Confirm(id string) error {
	b.mu.Lock()
	defer b.mu.Unlock()

	all, err := b.readAllLocked()
	if err != nil {
		return err
	}
	tmp := b.path + ".tmp"
	f, err := os.OpenFile(tmp, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0o644)
	if err != nil {
		return err
	}
	w := bufio.NewWriter(f)
	kept := 0
	for _, rec := range all {
		if rec.ID == id {
			continue
		}
		data, _ := json.Marshal(bufferLine(rec))
		if _, err := w.Write(append(data, '\n')); err != nil {
			_ = f.Close()
			return err
		}
		kept++
	}
	if err := w.Flush(); err != nil {
		_ = f.Close()
		return err
	}
	if err := f.Sync(); err != nil {
		_ = f.Close()
		return err
	}
	if err := f.Close(); err != nil {
		return err
	}
	// Empty buffer → remove the file entirely so Pending sees nothing.
	if kept == 0 {
		_ = os.Remove(tmp)
		return os.Remove(b.path)
	}
	return os.Rename(tmp, b.path)
}

// recordID is a stable per-record identifier: sha256 of the principal,
// timestamp, and item list. Distinct captures never collide; the same
// buffered record always hashes the same.
func recordID(e capture.AuditEntry) string {
	h := sha256.New()
	_, _ = fmt.Fprintf(h, "%s|%s|%v|%s", e.Principal, e.Timestamp.UTC().Format("2006-01-02T15:04:05.000000000Z07:00"), e.Items, e.SessionRef)
	return hex.EncodeToString(h.Sum(nil))[:16]
}