package tui

import (
	"errors"
	"fmt"
	"io"
	"os"
	"strings"

	tea "charm.land/bubbletea/v2"

	"gitgud.io/mike/mpv-manager/pkg/log"
)

const (
	// maxLogTailBytes caps how much is read from the end of the log file.
	maxLogTailBytes int64 = 256 << 10
	// maxLogTailLines caps how many trailing lines are shown in the viewer.
	maxLogTailLines = 500
)

// readLogTail returns up to maxLines trailing lines of the file at path,
// reading at most maxBytes from the end. truncated reports whether any
// content was cut.
func readLogTail(path string, maxBytes int64, maxLines int) (content string, truncated bool, err error) {
	file, err := os.Open(path)
	if err != nil {
		return "", false, err
	}
	defer file.Close()

	info, err := file.Stat()
	if err != nil {
		return "", false, err
	}
	if info.Size() > maxBytes {
		truncated = true
		if _, err := file.Seek(info.Size()-maxBytes, io.SeekStart); err != nil {
			return "", false, err
		}
	}
	data, err := io.ReadAll(io.LimitReader(file, maxBytes))
	if err != nil {
		return "", false, err
	}

	text := string(data)
	if truncated {
		// Drop the first, potentially partial, line.
		if idx := strings.IndexByte(text, '\n'); idx >= 0 {
			text = text[idx+1:]
		}
	}

	lines := strings.Split(strings.TrimRight(text, "\n"), "\n")
	if len(lines) > maxLines {
		lines = lines[len(lines)-maxLines:]
		truncated = true
	}
	return strings.Join(lines, "\n"), truncated, nil
}

// setupLogsView loads the tail of the mpv-manager log file into the viewport.
func (m *Model) setupLogsView() {
	m.logsStatusMsg = ""

	logPath := log.GetFilePath()
	if logPath == "" {
		m.logsStatusMsg = "Log file is not available (logger not initialized)."
		m.logsViewport.SetContent("")
		return
	}

	content, truncated, err := readLogTail(logPath, maxLogTailBytes, maxLogTailLines)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			m.logsStatusMsg = "No log file found at " + logPath
		} else {
			m.logsStatusMsg = "Failed to read log file: " + err.Error()
		}
		m.logsViewport.SetContent("")
		return
	}

	switch {
	case strings.TrimSpace(content) == "":
		m.logsStatusMsg = "Log file is empty: " + logPath
	case truncated:
		m.logsStatusMsg = fmt.Sprintf("Showing last %d lines of %s", maxLogTailLines, logPath)
	default:
		m.logsStatusMsg = logPath
	}
	m.logsViewport.SetContent(sanitizeTerminalText(content))
	m.logsViewport.GotoBottom()
}

// handleLogsViewerUpdate handles the logs viewer scroll state.
func (m *Model) handleLogsViewerUpdate(msg tea.Msg) (*Model, tea.Cmd) {
	if keyMsg, ok := msg.(tea.KeyPressMsg); ok {
		switch keyCode(keyMsg) {
		case tea.KeyEsc:
			m.resetToMainMenu()
			return m, nil
		case tea.KeyExtended:
			if runes := keyTextRunes(keyMsg); len(runes) == 1 && (runes[0] == 'r' || runes[0] == 'R') {
				m.setupLogsView()
				return m, nil
			}
		}
	}

	var cmd tea.Cmd
	m.logsViewport, cmd = m.logsViewport.Update(msg)
	return m, cmd
}

// logsViewerView renders the log tail viewer.
func (m Model) logsViewerView() string {
	var content strings.Builder

	content.WriteString(titleStyle.Render("📄 Logs"))
	content.WriteString("\n")
	content.WriteString(subtitleStyle.Render("═══════"))
	content.WriteString("\n\n")

	if m.logsStatusMsg != "" {
		content.WriteString(infoStyle.Render(m.logsStatusMsg))
		content.WriteString("\n\n")
	}

	content.WriteString(m.logsViewport.View())
	content.WriteString("\n")
	content.WriteString(infoStyle.Render("Press "))
	content.WriteString(subtitleStyle.Render("↑/↓"))
	content.WriteString(infoStyle.Render(" to scroll, "))
	content.WriteString(subtitleStyle.Render("R"))
	content.WriteString(infoStyle.Render(" to reload, "))
	content.WriteString(subtitleStyle.Render("Esc"))
	content.WriteString(infoStyle.Render(" to go back"))

	return content.String()
}