package handlers

import (
	"bytes"
	"context"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/mimecast/dtail/internal/io/dlog"
	"github.com/mimecast/dtail/internal/io/fs"
	"github.com/mimecast/dtail/internal/io/line"
	"github.com/mimecast/dtail/internal/lcontext"
	"github.com/mimecast/dtail/internal/mapr/server"
	"github.com/mimecast/dtail/internal/omode"
	"github.com/mimecast/dtail/internal/regex"
)

type readCommand struct {
	server              readCommandServer
	mode                omode.Mode
	shutdownCoordinator *shutdownCoordinator
}

type readStrategy func(context.Context, lcontext.LContext, fs.FileReader, regex.Regex) error

type turboReadProcessor interface {
	ProcessLine(*bytes.Buffer, uint64, string) error
	Flush() error
	Close() error
}

func newReadCommand(server readCommandServer, mode omode.Mode) *readCommand {
	return &readCommand{
		server:              server,
		mode:                mode,
		shutdownCoordinator: newShutdownCoordinator(server),
	}
}

func (r *readCommand) Start(ctx context.Context, ltx lcontext.LContext,
	argc int, args []string, retries int) {

	re := regex.NewNoop()
	if argc >= 4 {
		deserializedRegex, err := regex.Deserialize(strings.Join(args[2:], " "))
		if err != nil {
			r.server.SendServerMessage(dlog.Server.Error(r.server.LogContext(),
				"Unable to parse command", err))
			return
		}
		re = deserializedRegex
	}
	if argc < 3 {
		r.server.SendServerMessage(dlog.Server.Warn(r.server.LogContext(),
			"Unable to parse command", args, argc))
		return
	}

	// In serverless mode, can also read data from pipe
	// e.g.: grep foo bar.log | dmap 'from STATS select ...'
	// Only read from pipe if no file argument is provided
	isPipe := r.isInputFromPipe() && (argc < 2 || args[1] == "" || args[1] == "-")

	if isPipe {
		dlog.Server.Debug("Reading data from stdin pipe")
		// Empty file path and globID "-" represents reading from the stdin pipe.
		r.read(ctx, ltx, "", "-", re)
		return
	}

	dlog.Server.Debug("Reading data from file(s)")
	r.readGlob(ctx, ltx, args[1], re, retries)
}

func (r *readCommand) readGlob(ctx context.Context, ltx lcontext.LContext,
	glob string, re regex.Regex, retries int) {

	retryInterval := r.server.ReadGlobRetryInterval()
	glob = filepath.Clean(glob)

	for retryCount := 0; retryCount < retries; retryCount++ {
		paths, err := filepath.Glob(glob)
		if err != nil {
			dlog.Server.Warn(r.server.LogContext(), glob, err)
			time.Sleep(retryInterval)
			continue
		}

		if numPaths := len(paths); numPaths == 0 {
			dlog.Server.Error(r.server.LogContext(), "No such file(s) to read", glob)
			r.server.SendServerMessage(dlog.Server.Warn(r.server.LogContext(),
				"Unable to read file(s), check server logs"))
			select {
			case <-ctx.Done():
				return
			default:
			}
			time.Sleep(retryInterval)
			continue
		}

		r.readFiles(ctx, ltx, paths, glob, re, retryInterval)
		return
	}

	r.server.SendServerMessage(dlog.Server.Warn(r.server.LogContext(),
		"Giving up to read file(s)"))
	return
}

func (r *readCommand) readFiles(ctx context.Context, ltx lcontext.LContext,
	paths []string, glob string, re regex.Regex, retryInterval time.Duration) {

	dlog.Server.Info(r.server.LogContext(), "Processing files", "count", len(paths), "glob", glob)

	// Track pending files for this batch
	totalPending := r.server.AddPendingFiles(int32(len(paths)))
	dlog.Server.Info(r.server.LogContext(), "Added pending files", "count", len(paths), "totalPending", totalPending)

	var wg sync.WaitGroup
	wg.Add(len(paths))
	for _, path := range paths {
		go r.readFileIfPermissions(ctx, ltx, &wg, path, glob, re)
	}
	wg.Wait()

	dlog.Server.Info(r.server.LogContext(), "All files processed", "count", len(paths))

	// In turbo mode, signal EOF once all pending file work is drained.
	// Active command count may still include side-effect commands (for example AUTHKEY),
	// so relying on "active == 1" can skip EOF signaling and lead to dropped output.
	if !r.server.TurboBoostDisabled() && !r.server.HasRegularAggregate() &&
		(r.mode == omode.CatClient || r.mode == omode.GrepClient || r.mode == omode.TailClient) {
		if r.server.IsTurboMode() && r.server.HasTurboEOF() {
			pending, active := r.server.PendingAndActive()
			shouldSignalEOF := pending == 0
			if !shouldSignalEOF {
				dlog.Server.Trace(r.server.LogContext(), "Skipping turbo EOF signal for non-final command",
					"pending", pending, "active", active)
				return
			}

			dlog.Server.Debug(r.server.LogContext(), "Turbo mode: flushing data before EOF signal")

			// Ensure all turbo data is flushed before signaling EOF.
			r.server.FlushTurboData()

			// Signal EOF by closing the channel, but only once.
			r.server.SignalTurboEOF()

			// Wait for an explicit reader acknowledgement instead of timing guesses.
			if !r.server.Serverless() {
				timeout := r.server.TurboEOFAckTimeout()
				if r.server.WaitForTurboEOFAck(timeout) {
					dlog.Server.Debug(r.server.LogContext(), "Turbo EOF acknowledged")
					// Allow transport buffers to flush after acknowledgement.
					time.Sleep(r.server.ShutdownTurboSerializeWait())
				} else {
					dlog.Server.Warn(
						r.server.LogContext(),
						"Timeout waiting for turbo EOF acknowledgement",
						"timeout", timeout,
						"remainingTurbo", r.server.TurboChannelLen(),
					)
				}
			}
		}
	}

	// In turbo mode with aggregate, we don't close the shared channel here
	// because it will be used across multiple invocations
	// The aggregate will handle channel closure when it's done
}

func (r *readCommand) readFileIfPermissions(ctx context.Context, ltx lcontext.LContext,
	wg *sync.WaitGroup, path, glob string, re regex.Regex) {

	defer wg.Done()
	defer func() {
		r.shutdownCoordinator.onFileProcessed(path)
	}()

	globID := r.makeGlobID(path, glob)
	if !r.server.CanReadFile(path) {
		dlog.Server.Error(r.server.LogContext(), "No permission to read file", path, globID)
		r.server.SendServerMessage(dlog.Server.Warn(r.server.LogContext(),
			"Unable to read file(s), check server logs"))
		return
	}
	r.read(ctx, ltx, path, globID, re)
}

func (r *readCommand) read(ctx context.Context, ltx lcontext.LContext,
	path, globID string, re regex.Regex) {

	dlog.Server.Info(r.server.LogContext(), "Start reading", path, globID)
	r.logRegexMode(re)

	var reader fs.FileReader
	var limiter chan struct{}

	switch r.mode {
	case omode.GrepClient, omode.CatClient:
		catFile := fs.NewCatFile(path, globID, r.server.ServerMessagesChannel(), r.server.MaxLineLength())
		reader = &catFile
		limiter = r.server.CatLimiter()
	case omode.TailClient:
		fallthrough
	default:
		tailFile := fs.NewTailFile(path, globID, r.server.ServerMessagesChannel(), r.server.MaxLineLength())
		reader = &tailFile
		limiter = r.server.TailLimiter()
	}

	defer func() {
		select {
		case <-limiter:
		default:
		}
	}()

	select {
	case limiter <- struct{}{}:
		dlog.Server.Debug(r.server.LogContext(), "Got limiter slot immediately", "path", path)
	case <-ctx.Done():
		dlog.Server.Debug(r.server.LogContext(), "Context cancelled while waiting for limiter", "path", path)
		return
	default:
		dlog.Server.Info(r.server.LogContext(), "Server limit hit, queueing file", "limiterLen", len(limiter), "path", path, "maxConcurrent", cap(limiter))
		select {
		case limiter <- struct{}{}:
			dlog.Server.Info(r.server.LogContext(), "Server limit OK now, processing file", "limiterLen", len(limiter), "path", path)
		case <-ctx.Done():
			dlog.Server.Debug(r.server.LogContext(), "Context cancelled while queued for limiter", "path", path)
			return
		}
	}

	// Check if we should use the turbo boost optimizations
	// Enable turbo boost for cat/grep/tail modes, and now also for MapReduce operations
	// MapReduce now has a turbo mode implementation that bypasses channels
	dlog.Server.Debug(r.server.LogContext(), "Checking turbo mode", "turboBoostDisable", r.server.TurboBoostDisabled(),
		"mode", r.mode, "hasTurboAggregate", r.server.TurboAggregate() != nil, "hasAggregate", r.server.HasRegularAggregate())
	useTurboMode := false
	if !r.server.TurboBoostDisabled() {
		if r.server.TurboAggregate() != nil {
			// Keep turbo mode for MapReduce aggregate flow.
			useTurboMode = true
		} else if (r.mode == omode.CatClient || r.mode == omode.GrepClient || r.mode == omode.TailClient) && !r.server.HasRegularAggregate() {
			// Shared turbo direct-output flow is fragile under many concurrent commands.
			// Fall back to channel mode when session command concurrency is high.
			_, activeCommands := r.server.PendingAndActive()
			if activeCommands <= 1 {
				useTurboMode = true
			} else {
				dlog.Server.Info(r.server.LogContext(), "Skipping turbo mode for concurrent direct read commands",
					"mode", r.mode, "activeCommands", activeCommands)
			}
		}
	}

	if useTurboMode {
		dlog.Server.Info(r.server.LogContext(), "Using turbo mode for reading", path, "mode", r.mode, "hasTurboAggregate", r.server.TurboAggregate() != nil)
		r.readWithTurboProcessor(ctx, ltx, path, globID, re, reader)
		return
	}

	r.executeReadLoop(ctx, ltx, path, globID, re, reader, r.readViaChannels())
}

func (r *readCommand) readWithTurboProcessor(ctx context.Context, ltx lcontext.LContext,
	path, globID string, re regex.Regex, reader fs.FileReader) {

	dlog.Server.Info(r.server.LogContext(), "Using turbo channel-less implementation", path, globID)
	r.logRegexMode(re)

	r.ensureTurboModeEnabled()
	writer := r.makeTurboWriter()

	r.executeReadLoop(ctx, ltx, path, globID, re, reader, r.readViaTurboProcessor(path, globID, writer))
}

func (r *readCommand) executeReadLoop(ctx context.Context, ltx lcontext.LContext,
	path, globID string, re regex.Regex, reader fs.FileReader, strategy readStrategy) {

	for {
		if err := strategy(ctx, ltx, reader, re); err != nil {
			dlog.Server.Error(r.server.LogContext(), path, globID, err)
		}

		select {
		case <-ctx.Done():
			return
		default:
			if !reader.Retry() {
				return
			}
		}

		time.Sleep(r.server.ReadRetryInterval())
		dlog.Server.Info(path, globID, "Reading file again")
	}
}

func (r *readCommand) readViaChannels() readStrategy {
	return func(ctx context.Context, ltx lcontext.LContext, reader fs.FileReader, re regex.Regex) error {
		var linesCh chan *line.Line
		closeLines := false

		if r.server.HasRegularAggregate() {
			// For MapReduce operations, create a new channel that goes only to the aggregate.
			linesCh = make(chan *line.Line, r.server.AggregateLinesChannelBufferSize())
			r.server.RegisterAggregateLines(linesCh)
			closeLines = true
		} else {
			// For non-MapReduce operations, use the server's shared lines channel.
			linesCh = r.server.SharedLinesChannel()
		}

		err := reader.Start(ctx, ltx, linesCh, re)
		if closeLines {
			// Closing the aggregate line channel triggers flush.
			close(linesCh)
		}

		return err
	}
}

func (r *readCommand) readViaTurboProcessor(path, globID string, writer TurboWriter) readStrategy {
	return func(ctx context.Context, ltx lcontext.LContext, reader fs.FileReader, re regex.Regex) error {
		dlog.Server.Trace(r.server.LogContext(), path, globID, "readWithTurboProcessor -> starting read loop iteration")

		processor := r.makeTurboProcessor(path, globID, writer)

		dlog.Server.Trace(r.server.LogContext(), path, globID, "readWithTurboProcessor -> reader.StartWithPocessorOptimized -> about to start")
		startErr := reader.StartWithProcessorOptimized(ctx, ltx, processor, re)
		dlog.Server.Trace(r.server.LogContext(), path, globID, "readWithTurboProcessor -> reader.StartWithPocessorOptimized -> completed")

		// Ensure we flush and close the processor before retry checks.
		dlog.Server.Trace(r.server.LogContext(), path, globID, "readWithTurboProcessor -> flushing processor")
		if flushErr := processor.Flush(); flushErr != nil {
			dlog.Server.Error(r.server.LogContext(), path, globID, "flush error", flushErr)
		}
		dlog.Server.Trace(r.server.LogContext(), path, globID, "readWithTurboProcessor -> closing processor")
		if closeErr := processor.Close(); closeErr != nil {
			dlog.Server.Error(r.server.LogContext(), path, globID, "close error", closeErr)
		}
		dlog.Server.Trace(r.server.LogContext(), path, globID, "readWithTurboProcessor -> processor closed")

		// Give time for data to be transmitted.
		// This is crucial for integration tests to ensure all data is sent
		// Skip this delay in serverless mode since data is written directly to stdout
		if !r.server.Serverless() {
			dlog.Server.Trace(r.server.LogContext(), path, globID, "readWithTurboProcessor -> waiting for data transmission")
			time.Sleep(r.server.TurboDataTransmissionDelay())
		}

		return startErr
	}
}

func (r *readCommand) ensureTurboModeEnabled() {
	// turboManager.enable() toggles mode and initializes shared channels.
	// Under high concurrency a goroutine can observe mode=true before channel
	// initialization is visible and create a writer with a nil turbo channel.
	// Require both mode and channel to be ready before proceeding.
	if r.server.IsTurboMode() && r.server.GetTurboChannel() != nil {
		return
	}
	r.server.EnableTurboMode()
	// Wake a potentially blocked reader goroutine so it can switch to turbo drain path.
	r.server.SendServerMessage(".turbo wake")
}

func (r *readCommand) makeTurboWriter() TurboWriter {
	// Create a writer instance per file to keep concurrent processing isolated.
	if r.server.Serverless() {
		return NewDirectTurboWriter(os.Stdout, r.server.Hostname(), r.server.PlainOutput(), r.server.Serverless())
	}

	return &TurboNetworkWriter{
		turboLines:     r.server.GetTurboChannel(),
		serverMessages: r.server.ServerMessagesChannel(),
		hostname:       r.server.Hostname(),
		plain:          r.server.PlainOutput(),
		serverless:     r.server.Serverless(),
	}
}

func (r *readCommand) makeTurboProcessor(path, globID string, writer TurboWriter) turboReadProcessor {
	if aggregate := r.server.TurboAggregate(); aggregate != nil {
		dlog.Server.Info(r.server.LogContext(), "Using turbo aggregate processor for MapReduce", path, globID)
		return server.NewTurboAggregateProcessor(aggregate, globID)
	}

	return NewDirectLineProcessor(writer, globID)
}

func (r *readCommand) logRegexMode(re regex.Regex) {
	if r.mode != omode.GrepClient {
		return
	}
	if re.IsLiteral() {
		dlog.Server.Info(r.server.LogContext(), "Using optimized literal string matching for pattern:", re.Pattern())
	} else {
		dlog.Server.Info(r.server.LogContext(), "Using regex matching for pattern:", re.Pattern())
	}
}

func (r *readCommand) makeGlobID(path, glob string) string {
	var idParts []string
	pathParts := strings.Split(path, "/")

	for i, globPart := range strings.Split(glob, "/") {
		if strings.Contains(globPart, "*") {
			idParts = append(idParts, pathParts[i])
		}
	}

	if len(idParts) > 0 {
		return strings.Join(idParts, "/")
	}
	if len(pathParts) > 0 {
		return pathParts[len(pathParts)-1]
	}

	r.server.SendServerMessage(dlog.Server.Warn("Empty file path given?", path, glob))
	return ""
}

func (r *readCommand) isInputFromPipe() bool {
	if !r.server.Serverless() {
		// Can read from pipe only in serverless mode.
		return false
	}
	fileInfo, _ := os.Stdin.Stat()
	return fileInfo.Mode()&os.ModeCharDevice == 0
}