// ingestion/internal/watcher/watcher.go
package watcher

import (
	"context"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"
	"strings"
	"time"
	"unicode"

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

// Config holds watcher configuration.
type Config struct {
	BrainDir string
	Interval time.Duration
	Pipeline pipeline.Config
}

// Start launches the watcher in a background goroutine.
// It returns immediately. The watcher stops when ctx is cancelled.
func Start(ctx context.Context, cfg Config) {
	go func() {
		ticker := time.NewTicker(cfg.Interval)
		defer ticker.Stop()
		for {
			select {
			case <-ctx.Done():
				return
			case <-ticker.C:
				date := time.Now().UTC().Format("2006-01-02")
				errs := processDir(ctx, cfg, date)
				for _, err := range errs {
					slog.Error("watcher: error processing file", "error", err)
				}
			}
		}
	}()
}

// processDir walks brain/raw/, processes each eligible file, returns any errors encountered.
func processDir(ctx context.Context, cfg Config, date string) []error {
	rawDir := filepath.Join(cfg.BrainDir, "raw")

	var errs []error
	err := filepath.WalkDir(rawDir, func(path string, d os.DirEntry, err error) error {
		if err != nil {
			return err
		}

		// Skip the root itself.
		if path == rawDir {
			return nil
		}

		// Skip processed/ and failed/ subdirectories entirely.
		if d.IsDir() {
			name := d.Name()
			if name == "processed" || name == "failed" {
				return filepath.SkipDir
			}
			return nil
		}

		// Only process supported extensions.
		ext := strings.ToLower(filepath.Ext(path))
		if ext != ".md" && ext != ".txt" && ext != ".pdf" {
			return nil
		}

		if err := processFile(ctx, cfg, path, date); err != nil {
			errs = append(errs, fmt.Errorf("process %s: %w", filepath.Base(path), err))
		}
		return nil
	})
	if err != nil {
		errs = append(errs, fmt.Errorf("walk raw dir: %w", err))
	}
	return errs
}

// processFile reads a file, calls pipeline.Run, moves it to processed/ or failed/.
func processFile(ctx context.Context, cfg Config, path, date string) error {
	filename := filepath.Base(path)
	source := deriveSource(filename)

	content, err := os.ReadFile(path)
	if err != nil {
		return fmt.Errorf("read file: %w", err)
	}

	_, runErr := pipeline.Run(ctx, cfg.Pipeline, cfg.BrainDir, string(content), source, false)
	if runErr != nil {
		// Move to failed/.
		failedDir := filepath.Join(cfg.BrainDir, "raw", "failed")
		if mkErr := os.MkdirAll(failedDir, 0o755); mkErr != nil {
			return fmt.Errorf("mkdir failed dir: %w", mkErr)
		}
		dest := filepath.Join(failedDir, filename)
		if mvErr := os.Rename(path, dest); mvErr != nil {
			return fmt.Errorf("move to failed: %w", mvErr)
		}

		slog.Warn("watcher: file failed, moved to failed/", "file", filename, "error", runErr)

		if logErr := appendWatcherLog(cfg.BrainDir, filename, runErr, date); logErr != nil {
			slog.Error("watcher: failed to write log entry", "error", logErr)
		}
		return runErr
	}

	// Move to processed/YYYY-MM-DD/.
	processedDir := filepath.Join(cfg.BrainDir, "raw", "processed", date)
	if err := os.MkdirAll(processedDir, 0o755); err != nil {
		return fmt.Errorf("mkdir processed dir: %w", err)
	}
	dest := filepath.Join(processedDir, filename)
	if err := os.Rename(path, dest); err != nil {
		return fmt.Errorf("move to processed: %w", err)
	}

	slog.Info("watcher: file processed", "file", filename, "source", source)
	return nil
}

// deriveSource turns a filename into a human-readable source name.
// "shape-up-book.md" → "Shape Up Book"
func deriveSource(filename string) string {
	// Strip extension.
	name := strings.TrimSuffix(filename, filepath.Ext(filename))
	// Split on hyphens.
	words := strings.Split(name, "-")
	// Title-case each word.
	for i, w := range words {
		if w == "" {
			continue
		}
		runes := []rune(w)
		runes[0] = unicode.ToUpper(runes[0])
		words[i] = string(runes)
	}
	return strings.Join(words, " ")
}

// appendWatcherLog appends a watcher error entry to brain/log.md.
func appendWatcherLog(brainDir, filename string, runErr error, date string) error {
	entry := fmt.Sprintf("## %s — watcher error\n\n- **File:** %s\n- **Error:** %s\n\n",
		date, filename, runErr.Error())

	logPath := filepath.Join(brainDir, "log.md")
	f, err := os.OpenFile(logPath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o644)
	if err != nil {
		return fmt.Errorf("open log: %w", err)
	}
	defer f.Close()

	if _, err = f.WriteString(entry); err != nil {
		return fmt.Errorf("write log: %w", err)
	}
	return nil
}