package claudewatcher

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

// Sink consumes batches of ingest-ready turns from the watcher. The
// production implementation builds wiki pages and calls pipeline.RunRaw
// against the brain. Tests substitute a counter.
//
// A Batch represents the turns ingested from one session file between
// two cursor checkpoints. Implementations must be idempotent — the
// watcher only advances the cursor on a nil return.
type Sink interface {
	Ingest(ctx context.Context, b Batch) error
}

// Batch is a per-file slice of turns plus identifying metadata.
type Batch struct {
	Host      string // origin host, e.g. "koala"
	FilePath  string // absolute path to the source .jsonl file
	SessionID string // first session_id seen in the batch
	ProjectID string // basename of the parent dir, e.g. "-home-mathias-dev"
	Turns     []Turn // never empty; caller filters Skip + scrubber matches
}

// Config drives one Watch loop. SessionsDir is the absolute path to the
// Claude Code projects directory (~/.claude/projects). Host is the
// label written into cursors and ingested page frontmatter. Interval
// is the poll cadence; a zero or negative value disables the loop.
//
// Sink is required. Cursors is optional — when nil the watcher
// re-reads from byte 0 on every tick (useful for first-run testing
// without a postgres dependency).
type Config struct {
	SessionsDir string
	Host        string
	Interval    time.Duration
	Sink        Sink
	Cursors     *CursorStore
	Logger      *slog.Logger
}

// Watch runs the polling loop until ctx is cancelled. Returns ctx.Err()
// on shutdown. Each tick walks SessionsDir for *.jsonl files, advances
// each file's cursor, and emits one Batch per file with new turns.
// Errors during a single file's parse or ingest are logged but do not
// abort the loop — a single bad file shouldn't block the others.
func Watch(ctx context.Context, cfg Config) error {
	if cfg.SessionsDir == "" {
		return fmt.Errorf("sessions dir is required")
	}
	if cfg.Sink == nil {
		return fmt.Errorf("sink is required")
	}
	if cfg.Interval <= 0 {
		return fmt.Errorf("interval must be positive")
	}
	if cfg.Host == "" {
		cfg.Host = "unknown"
	}
	if cfg.Logger == nil {
		cfg.Logger = slog.Default()
	}
	cfg.Logger.Info("claudewatcher: started",
		"sessions_dir", cfg.SessionsDir,
		"host", cfg.Host,
		"interval", cfg.Interval)

	ticker := time.NewTicker(cfg.Interval)
	defer ticker.Stop()
	// Run an immediate first sweep so first-launch users don't wait one
	// tick before anything happens.
	runTick(ctx, cfg)
	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-ticker.C:
			runTick(ctx, cfg)
		}
	}
}

// runTick is one polling pass. Exposed (lowercase) for tests via
// TickOnce.
func runTick(ctx context.Context, cfg Config) {
	files, err := listSessionFiles(cfg.SessionsDir)
	if err != nil {
		cfg.Logger.Warn("claudewatcher: list session files", "err", err)
		return
	}
	for _, f := range files {
		if ctx.Err() != nil {
			return
		}
		if err := processFile(ctx, cfg, f); err != nil {
			cfg.Logger.Warn("claudewatcher: file failed",
				"path", f, "err", err)
		}
	}
}

// TickOnce runs one sweep synchronously and returns. Used by tests +
// by ad-hoc CLI invocations.
func TickOnce(ctx context.Context, cfg Config) error {
	if cfg.SessionsDir == "" || cfg.Sink == nil {
		return fmt.Errorf("config invalid")
	}
	if cfg.Host == "" {
		cfg.Host = "unknown"
	}
	if cfg.Logger == nil {
		cfg.Logger = slog.Default()
	}
	runTick(ctx, cfg)
	return nil
}

func listSessionFiles(root string) ([]string, error) {
	var out []string
	err := filepath.WalkDir(root, func(path string, d os.DirEntry, walkErr error) error {
		if walkErr != nil {
			return walkErr
		}
		if d.IsDir() {
			return nil
		}
		if !strings.HasSuffix(path, ".jsonl") {
			return nil
		}
		out = append(out, path)
		return nil
	})
	if err != nil {
		return nil, fmt.Errorf("walk %s: %w", root, err)
	}
	return out, nil
}

func processFile(ctx context.Context, cfg Config, path string) error {
	startOffset := int64(0)
	if cfg.Cursors != nil {
		off, _, err := cfg.Cursors.GetOffset(ctx, cfg.Host, path)
		if err != nil {
			return fmt.Errorf("get cursor: %w", err)
		}
		startOffset = off
	}

	stat, err := os.Stat(path)
	if err != nil {
		return fmt.Errorf("stat: %w", err)
	}
	if stat.Size() <= startOffset {
		return nil // nothing new
	}

	f, err := os.Open(path)
	if err != nil {
		return fmt.Errorf("open: %w", err)
	}
	defer func() { _ = f.Close() }()
	if _, err := f.Seek(startOffset, 0); err != nil {
		return fmt.Errorf("seek: %w", err)
	}

	var keep []Turn
	var sessionID string
	var droppedScrub int
	endOffset, err := ParseStream(f, startOffset,
		func(format string, args ...any) {
			cfg.Logger.Warn(fmt.Sprintf("claudewatcher: parse: "+format, args...))
		},
		func(t Turn) error {
			if t.Skip || t.Content == "" {
				return nil
			}
			if rule := Scrub(t.Content); rule != "" {
				droppedScrub++
				cfg.Logger.Warn("claudewatcher: turn dropped by scrubber",
					"rule", rule, "path", path, "session_id", t.SessionID)
				return nil
			}
			if sessionID == "" {
				sessionID = t.SessionID
			}
			keep = append(keep, t)
			return nil
		})
	if err != nil {
		return fmt.Errorf("parse stream: %w", err)
	}

	if len(keep) == 0 {
		if cfg.Cursors != nil {
			if err := cfg.Cursors.SetOffset(ctx, cfg.Host, path, endOffset); err != nil {
				return fmt.Errorf("advance cursor (no-turns): %w", err)
			}
		}
		if droppedScrub > 0 {
			cfg.Logger.Info("claudewatcher: only scrubbed turns this tick",
				"path", path, "dropped", droppedScrub)
		}
		return nil
	}

	batch := Batch{
		Host:      cfg.Host,
		FilePath:  path,
		SessionID: sessionID,
		ProjectID: filepath.Base(filepath.Dir(path)),
		Turns:     keep,
	}
	if err := cfg.Sink.Ingest(ctx, batch); err != nil {
		return fmt.Errorf("sink ingest: %w", err)
	}
	if cfg.Cursors != nil {
		if err := cfg.Cursors.SetOffset(ctx, cfg.Host, path, endOffset); err != nil {
			return fmt.Errorf("advance cursor: %w", err)
		}
	}
	cfg.Logger.Info("claudewatcher: ingested batch",
		"path", path, "session_id", sessionID,
		"turns_kept", len(keep), "dropped_scrub", droppedScrub,
		"new_offset", endOffset)
	return nil
}