package core

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

// Validate checks that cfg is coherent and all paths exist.
// Returns a human-readable error or nil.
func Validate(cfg *Config) error {
	if cfg.InputDir == "" || cfg.OutputDir == "" {
		return fmt.Errorf("source directory (-dir) and output directory (-out) are required")
	}

	if cfg.Width == 0 && cfg.Height == 0 {
		return fmt.Errorf("at least one of -width or -height must be specified")
	}

	if cfg.Width < 0 || cfg.Height < 0 {
		return fmt.Errorf("dimensions cannot be negative")
	}

	if cfg.Quality < 1 || cfg.Quality > 100 {
		return fmt.Errorf("quality must be between 1 and 100")
	}

	if cfg.Format != "" &&
		cfg.Format != "jpg" && cfg.Format != "jpeg" &&
		cfg.Format != "png" &&
		cfg.Format != "tif" && cfg.Format != "tiff" {
		return fmt.Errorf("unsupported output format: %s (options: jpg, png, tif)", cfg.Format)
	}

	absInput, err := filepath.Abs(cfg.InputDir)
	if err != nil {
		return fmt.Errorf("error resolving source path: %v", err)
	}

	absOutput, err := filepath.Abs(cfg.OutputDir)
	if err != nil {
		return fmt.Errorf("error resolving output path: %v", err)
	}

	if absInput == absOutput && cfg.Prefix == "" && cfg.Suffix == "" &&
		cfg.TSFile == "" && !cfg.B64Enabled {
		return fmt.Errorf(
			"input and output directories cannot be the same\n" +
				"  hint: use -prefix, -suffix, -b64 or -ts to avoid overwriting originals")
	}

	if _, err := os.Stat(cfg.InputDir); os.IsNotExist(err) {
		return fmt.Errorf("source directory does not exist: %s", cfg.InputDir)
	}

	if cfg.Workers < 1 {
		cfg.Workers = 1
	}

	for _, raw := range []string{cfg.Replace, cfg.ReplaceI, cfg.ReplaceP} {
		if raw == "" {
			continue
		}
		for _, pair := range strings.Split(raw, ",") {
			parts := strings.SplitN(pair, "/", 2)
			if len(parts) != 2 || parts[0] == "" {
				return fmt.Errorf("invalid replacement pair %q — expected: old/new", pair)
			}
		}
	}

	if cfg.FileFilter != "" {
		if _, err := filepath.Match(cfg.FileFilter, ""); err != nil {
			return fmt.Errorf("invalid -filter pattern %q: %v", cfg.FileFilter, err)
		}
	}

	if cfg.Lowercase && cfg.Uppercase {
		return fmt.Errorf("-lowercase and -uppercase are mutually exclusive")
	}

	if cfg.B64Enabled && cfg.TSFile != "" {
		return fmt.Errorf("-b64 and -ts are mutually exclusive")
	}

	return nil
}