package jsonlog

import (
	"bufio"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
)

// AppendLine appends a single JSON-encoded line and returns the resulting file size.
func AppendLine(path string, value interface{}) (int64, error) {
	data, err := json.Marshal(value)
	if err != nil {
		return 0, err
	}
	return AppendRawLine(path, data)
}

// AppendRawLine appends a raw JSON line and returns the resulting file size.
func AppendRawLine(path string, line []byte) (int64, error) {
	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
		return 0, err
	}
	f, err := os.OpenFile(path, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
	if err != nil {
		return 0, err
	}
	defer f.Close()
	if _, err := f.Write(append(line, '\n')); err != nil {
		return 0, err
	}
	st, err := f.Stat()
	if err != nil {
		return 0, err
	}
	return st.Size(), nil
}

// Scan walks each non-empty JSONL line in order.
func Scan(path string, fn func(line []byte) error) error {
	f, err := os.Open(path)
	if err != nil {
		return err
	}
	defer f.Close()

	scanner := bufio.NewScanner(f)
	scanner.Buffer(make([]byte, 0, 64*1024), 8*1024*1024)
	for scanner.Scan() {
		line := append([]byte(nil), scanner.Bytes()...)
		if len(line) == 0 {
			continue
		}
		if err := fn(line); err != nil {
			return err
		}
	}
	if err := scanner.Err(); err != nil {
		return fmt.Errorf("scan %s: %w", path, err)
	}
	return nil
}

// FileSize returns 0 when the file does not exist.
func FileSize(path string) (int64, error) {
	st, err := os.Stat(path)
	if err != nil {
		if os.IsNotExist(err) {
			return 0, nil
		}
		return 0, err
	}
	return st.Size(), nil
}

// ReadJSON reads a JSON sidecar file into dst.
func ReadJSON(path string, dst interface{}) error {
	data, err := os.ReadFile(path)
	if err != nil {
		return err
	}
	return json.Unmarshal(data, dst)
}

// WriteJSON writes a JSON sidecar file atomically enough for local runtime use.
func WriteJSON(path string, value interface{}) error {
	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
		return err
	}
	data, err := json.MarshalIndent(value, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(path, data, 0644)
}