import 'terminal_screen_patch.dart';
import 'terminal_screen_snapshot.dart';

/// Experiment-only state reducer for backend-authored screen snapshots and patches.
class TerminalScreenState {
  const TerminalScreenState({
    required this.sessionId,
    required this.screenVersion,
    required this.sourceSequence,
    required this.rows,
    required this.columns,
    required this.cursorRow,
    required this.cursorColumn,
    required this.cursorVisible,
    required this.activeBuffer,
    required this.primaryLines,
    required this.alternateLines,
  });

  final String sessionId;
  final int screenVersion;
  final int sourceSequence;
  final int rows;
  final int columns;
  final int cursorRow;
  final int cursorColumn;
  final bool cursorVisible;
  final String activeBuffer;
  final List<String> primaryLines;
  final List<String> alternateLines;

  factory TerminalScreenState.fromSnapshot(TerminalScreenSnapshot snapshot) {
    List<String> materialize(TerminalScreenBuffer? buffer) {
      final lines = List<String>.filled(snapshot.rows, '');
      final viewport = buffer?.viewport ?? const <TerminalScreenLine>[];
      for (final line in viewport) {
        if (line.index >= 0 && line.index < lines.length) {
          lines[line.index] = line.text;
        }
      }

      return lines;
    }

    return TerminalScreenState(
      sessionId: snapshot.sessionId,
      screenVersion: snapshot.screenVersion,
      sourceSequence: snapshot.sourceSequence,
      rows: snapshot.rows,
      columns: snapshot.columns,
      cursorRow: snapshot.cursorRow,
      cursorColumn: snapshot.cursorColumn,
      cursorVisible: snapshot.cursorVisible,
      activeBuffer: snapshot.activeBuffer,
      primaryLines: materialize(snapshot.primaryBuffer),
      alternateLines: materialize(snapshot.alternateBuffer),
    );
  }

  bool canApplyPatch(TerminalScreenPatch patch) {
    return sessionId == patch.sessionId &&
        screenVersion == patch.baseScreenVersion;
  }

  TerminalScreenState applyPatch(TerminalScreenPatch patch) {
    final nextPrimaryLines = List<String>.from(primaryLines, growable: false);
    final nextAlternateLines = List<String>.from(
      alternateLines,
      growable: false,
    );
    final targetLines = patch.activeBuffer == 'alternate'
        ? nextAlternateLines
        : nextPrimaryLines;
    for (final operation in patch.operations) {
      if (operation.type != 'replace_lines') {
        continue;
      }

      for (var index = 0; index < operation.lines.length; index += 1) {
        final row = operation.startRow + index;
        if (row >= 0 && row < targetLines.length) {
          targetLines[row] = operation.lines[index];
        }
      }
    }

    return TerminalScreenState(
      sessionId: sessionId,
      screenVersion: patch.screenVersion,
      sourceSequence: patch.sourceSequence,
      rows: patch.rows,
      columns: patch.columns,
      cursorRow: patch.cursorRow,
      cursorColumn: patch.cursorColumn,
      cursorVisible: patch.cursorVisible,
      activeBuffer: patch.activeBuffer,
      primaryLines: nextPrimaryLines,
      alternateLines: nextAlternateLines,
    );
  }

  String toDisplayText() {
    final lines = activeBuffer == 'alternate' ? alternateLines : primaryLines;
    return renderTerminalScreenText(
      lines: lines,
      cursorRow: cursorRow,
      cursorColumn: cursorColumn,
      cursorVisible: cursorVisible,
    );
  }

  String toReplaySequence() {
    final lines = activeBuffer == 'alternate' ? alternateLines : primaryLines;
    return buildTerminalScreenReplay(
      lines: lines,
      cursorRow: cursorRow,
      cursorColumn: cursorColumn,
      cursorVisible: cursorVisible,
    );
  }
}