package file

import (
	"context"
	"fmt"
	"os"
	"path/filepath"

	"github.com/enmanuel/agents/internal/config"
	"github.com/enmanuel/agents/tools"
)

// maxAppendTotal is the maximum total file size after appending (10 MB).
const maxAppendTotal = 10 * 1024 * 1024

// NewAppendFile creates an append_file tool that appends content to a local file.
// Deny-by-default: if AllowedPaths is empty, all operations are rejected.
// Rejects if ReadOnly is true. Creates the file (and parent directories) if it does not exist.
func NewAppendFile(cfg config.FileOpsCfg) tools.Tool {
	return tools.Tool{
		Def: tools.Def{
			Name:        "append_file",
			Description: "Append content to the end of a local file. Creates the file if it does not exist.",
			Parameters: []tools.Param{
				{Name: "path", Type: "string", Description: "Absolute path to the file to append to", Required: true},
				{Name: "content", Type: "string", Description: "Content to append to the file", Required: true},
			},
		},
		Exec: func(ctx context.Context, args map[string]any) tools.Result {
			path := tools.GetString(args, "path")
			if path == "" {
				return tools.Result{Err: fmt.Errorf("append_file: path is required")}
			}

			content := tools.GetString(args, "content")
			if content == "" {
				return tools.Result{Err: fmt.Errorf("append_file: content is required")}
			}

			absPath, err := filepath.Abs(path)
			if err != nil {
				return tools.Result{Err: fmt.Errorf("append_file: %w", err)}
			}

			if err := validateWritePath(absPath, cfg.AllowedPaths, cfg.ReadOnly); err != nil {
				return tools.Result{Err: err}
			}

			// Check existing file size to enforce the total limit.
			var existingSize int64
			info, err := os.Stat(absPath)
			if err == nil {
				existingSize = info.Size()
			}
			// err != nil means file doesn't exist, which is fine (will be created).

			newTotal := existingSize + int64(len(content))
			if newTotal > maxAppendTotal {
				return tools.Result{Err: fmt.Errorf("append_file: resulting file size (%d bytes) exceeds 10 MB limit", newTotal)}
			}

			// Create parent directories if they don't exist.
			dir := filepath.Dir(absPath)
			if err := os.MkdirAll(dir, 0755); err != nil {
				return tools.Result{Err: fmt.Errorf("append_file: cannot create directories: %w", err)}
			}

			f, err := os.OpenFile(absPath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
			if err != nil {
				return tools.Result{Err: fmt.Errorf("append_file: %w", err)}
			}
			defer f.Close()

			n, err := f.WriteString(content)
			if err != nil {
				return tools.Result{Err: fmt.Errorf("append_file: %w", err)}
			}

			finalSize := existingSize + int64(n)
			return tools.Result{Output: fmt.Sprintf("appended %d bytes to %s (total size: %d bytes)", n, absPath, finalSize)}
		},
	}
}