package tools

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

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

// NewReadFile creates a read_file tool that reads local files.
// Validates paths against cfg.AllowedPaths when non-empty.
func NewReadFile(cfg config.FileOpsCfg) Tool {
	return Tool{
		Def: Def{
			Name:        "read_file",
			Description: "Read the contents of a local file.",
			Parameters: []Param{
				{Name: "path", Type: "string", Description: "Absolute path to the file to read", Required: true},
			},
		},
		Exec: func(ctx context.Context, args map[string]any) Result {
			path := getString(args, "path")
			if path == "" {
				return Result{Err: fmt.Errorf("read_file: path is required")}
			}

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

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

			data, err := os.ReadFile(absPath)
			if err != nil {
				return Result{Err: fmt.Errorf("read_file: %w", err)}
			}

			// Limit output to 64 KB
			content := string(data)
			if len(content) > 64*1024 {
				content = content[:64*1024] + "\n... (truncated)"
			}

			return Result{Output: content}
		},
	}
}

func validatePath(absPath string, allowedPaths []string) error {
	if len(allowedPaths) == 0 {
		return nil
	}
	for _, allowed := range allowedPaths {
		a, err := filepath.Abs(allowed)
		if err != nil {
			continue
		}
		if strings.HasPrefix(absPath, a) {
			return nil
		}
	}
	return fmt.Errorf("path %q not under any allowed path", absPath)
}