// FlowGraph — in-memory model of a flow YAML.
//
// The YAML text is the canonical source of truth. The graph
// view derives a `FlowGraph` from the parsed YAML, and any
// edit in the graph view (drag a node, rename a step, add a
// connection) is re-emitted as YAML and pushed back into the
// shared text buffer. The graph never holds state the YAML
// can't represent — everything visible can be expressed in
// the YAML round-trip.
//
// Layout coordinates are the one piece that doesn't live in
// the YAML; those are stored in a sidecar file via
// [LayoutStore]. That keeps the YAML byte-identical to what
// `fai run` consumes.

import 'package:yaml/yaml.dart';

/// One flow, fully decoded from its YAML text.
class FlowGraph {
  /// Flow display name (`name:` at the top of the YAML).
  /// Optional — many example flows omit it and the file name
  /// serves as the identifier.
  final String? name;

  /// Declared inputs the operator supplies at run time.
  /// Each entry maps the input name to its declared shape.
  final Map<String, FlowInput> inputs;

  /// Ordered list of steps. Order matters for the linear
  /// engine; the graph view preserves it on save.
  final List<FlowStep> steps;

  /// Outputs the flow exposes — each value is an expression
  /// that references a step output or an input
  /// (`$step.field` / `$inputs.field`).
  final Map<String, String> outputs;

  /// Free-form comment block at the top of the file. Captured
  /// so the round-trip preserves human-authored context like
  /// example invocations or compliance notes. We can only
  /// preserve LEADING comments; mid-file comments are lost on
  /// graph -> YAML emission (acceptable trade-off — they're
  /// rare and the operator gets a warning if any are present).
  final String leadingComment;

  const FlowGraph({
    this.name,
    required this.inputs,
    required this.steps,
    required this.outputs,
    this.leadingComment = '',
  });

  /// Empty placeholder while a YAML buffer is still being
  /// loaded or has just been cleared.
  factory FlowGraph.empty() =>
      const FlowGraph(inputs: {}, steps: [], outputs: {});

  /// Parse [yamlText] into a [FlowGraph]. Returns `null` if
  /// the YAML can't be parsed at all (syntax error). For
  /// semantically invalid flows that still parse (missing
  /// step.id, etc.) the result is best-effort and any
  /// recovered structure is returned.
  static FlowGraph? tryParse(String yamlText) {
    try {
      return FlowGraph.fromYaml(yamlText);
    } catch (_) {
      return null;
    }
  }

  factory FlowGraph.fromYaml(String yamlText) {
    final leading = _captureLeadingComments(yamlText);
    final doc = loadYaml(yamlText);
    if (doc is! Map) {
      return FlowGraph(
        inputs: const {},
        steps: const [],
        outputs: const {},
        leadingComment: leading,
      );
    }
    final name = doc['name']?.toString();
    final inputs = _parseInputs(doc['inputs']);
    final steps = _parseSteps(doc['steps']);
    final outputs = _parseOutputs(doc['outputs']);
    return FlowGraph(
      name: name,
      inputs: inputs,
      steps: steps,
      outputs: outputs,
      leadingComment: leading,
    );
  }

  /// Emit a YAML representation. The output is intentionally
  /// stable and human-friendly: 2-space indent, double-quoted
  /// strings when needed, no flow-style maps. Designed to
  /// match the hand-authored examples shipped under
  /// `flows/` so the text view doesn't shock the operator
  /// after a graph edit.
  String toYaml() {
    final b = StringBuffer();
    if (leadingComment.isNotEmpty) {
      b.write(leadingComment);
      if (!leadingComment.endsWith('\n')) b.writeln();
      b.writeln();
    }
    if (name != null && name!.isNotEmpty) {
      b.writeln('name: ${_scalar(name!)}');
      b.writeln();
    }
    if (inputs.isNotEmpty) {
      b.writeln('inputs:');
      for (final entry in inputs.entries) {
        final v = entry.value;
        if (v.hasOnlyType) {
          b.writeln('  ${entry.key}: ${v.type}');
        } else {
          b.writeln('  ${entry.key}:');
          b.writeln('    type: ${v.type}');
          if (v.defaultValue != null) {
            b.writeln('    default: ${_scalar(v.defaultValue!)}');
          }
          if (v.hint != null) b.writeln('    hint: ${_scalar(v.hint!)}');
        }
      }
      b.writeln();
    }
    if (steps.isNotEmpty) {
      b.writeln('steps:');
      for (final s in steps) {
        b.writeln('  - id: ${s.id}');
        b.writeln('    use: ${s.use}');
        if (s.with_.isNotEmpty) {
          b.writeln('    with:');
          for (final entry in s.with_.entries) {
            b.writeln('      ${entry.key}: ${_scalar(entry.value.toString())}');
          }
        }
      }
      b.writeln();
    }
    if (outputs.isNotEmpty) {
      b.writeln('outputs:');
      for (final entry in outputs.entries) {
        b.writeln('  ${entry.key}: ${_scalar(entry.value)}');
      }
    }
    return b.toString();
  }

  /// Derive the edges implied by `$step.field` /
  /// `$inputs.field` references found in step `with:` values
  /// and in outputs. The graph view paints one edge per
  /// reference.
  List<FlowEdge> get edges {
    final result = <FlowEdge>[];
    final stepIds = steps.map((s) => s.id).toSet();
    for (final step in steps) {
      for (final entry in step.with_.entries) {
        final value = entry.value;
        if (value is! String) continue;
        for (final ref in _scanRefs(value)) {
          if (ref.source == 'inputs' && inputs.containsKey(ref.field)) {
            result.add(
              FlowEdge(
                fromKind: EdgeEndpointKind.inputs,
                fromId: 'inputs',
                fromField: ref.field,
                toKind: EdgeEndpointKind.step,
                toId: step.id,
                toField: entry.key,
              ),
            );
          } else if (stepIds.contains(ref.source)) {
            result.add(
              FlowEdge(
                fromKind: EdgeEndpointKind.step,
                fromId: ref.source,
                fromField: ref.field,
                toKind: EdgeEndpointKind.step,
                toId: step.id,
                toField: entry.key,
              ),
            );
          }
        }
      }
    }
    for (final entry in outputs.entries) {
      for (final ref in _scanRefs(entry.value)) {
        if (ref.source == 'inputs' && inputs.containsKey(ref.field)) {
          result.add(
            FlowEdge(
              fromKind: EdgeEndpointKind.inputs,
              fromId: 'inputs',
              fromField: ref.field,
              toKind: EdgeEndpointKind.outputs,
              toId: 'outputs',
              toField: entry.key,
            ),
          );
        } else if (stepIds.contains(ref.source)) {
          result.add(
            FlowEdge(
              fromKind: EdgeEndpointKind.step,
              fromId: ref.source,
              fromField: ref.field,
              toKind: EdgeEndpointKind.outputs,
              toId: 'outputs',
              toField: entry.key,
            ),
          );
        }
      }
    }
    return result;
  }

  /// Immutable update — returns a new graph with one step
  /// replaced. Used by the properties panel + drag handlers.
  FlowGraph withStepUpdated(String stepId, FlowStep replacement) {
    final updated = [
      for (final s in steps)
        if (s.id == stepId) replacement else s,
    ];
    return FlowGraph(
      name: name,
      inputs: inputs,
      steps: updated,
      outputs: outputs,
      leadingComment: leadingComment,
    );
  }

  /// Append a fresh step at the end of the list.
  FlowGraph withStepAdded(FlowStep step) {
    return FlowGraph(
      name: name,
      inputs: inputs,
      steps: [...steps, step],
      outputs: outputs,
      leadingComment: leadingComment,
    );
  }

  /// Remove the step with [stepId]. Edges pointing to or
  /// from it become dangling references — the YAML still
  /// emits them; the engine will fail at run time with a
  /// clear "unknown ref" error. That's intentional: silently
  /// rewriting downstream `with:` values would surprise the
  /// operator.
  FlowGraph withStepRemoved(String stepId) {
    return FlowGraph(
      name: name,
      inputs: inputs,
      steps: steps.where((s) => s.id != stepId).toList(),
      outputs: outputs,
      leadingComment: leadingComment,
    );
  }

  // --- internals ---

  static Map<String, FlowInput> _parseInputs(dynamic node) {
    if (node is! Map) return const {};
    final result = <String, FlowInput>{};
    for (final entry in node.entries) {
      final key = entry.key.toString();
      final value = entry.value;
      if (value is String) {
        // shorthand: `name: text`
        result[key] = FlowInput(type: value);
      } else if (value is Map) {
        result[key] = FlowInput(
          type: value['type']?.toString() ?? 'text',
          defaultValue: value['default']?.toString(),
          hint: value['hint']?.toString(),
        );
      }
    }
    return result;
  }

  static List<FlowStep> _parseSteps(dynamic node) {
    if (node is! List) return const [];
    final result = <FlowStep>[];
    for (final item in node) {
      if (item is! Map) continue;
      final id = item['id']?.toString();
      final use = item['use']?.toString();
      if (id == null || use == null) continue;
      final with_ = <String, dynamic>{};
      final withNode = item['with'];
      if (withNode is Map) {
        for (final w in withNode.entries) {
          with_[w.key.toString()] = w.value;
        }
      }
      result.add(FlowStep(id: id, use: use, with_: with_));
    }
    return result;
  }

  static Map<String, String> _parseOutputs(dynamic node) {
    if (node is! Map) return const {};
    final result = <String, String>{};
    for (final entry in node.entries) {
      result[entry.key.toString()] = entry.value.toString();
    }
    return result;
  }

  static String _captureLeadingComments(String text) {
    final lines = text.split('\n');
    final buf = StringBuffer();
    for (final line in lines) {
      final trimmed = line.trimLeft();
      if (trimmed.isEmpty || trimmed.startsWith('#')) {
        buf.writeln(line);
      } else {
        break;
      }
    }
    return buf.toString();
  }

  /// Decide whether a value needs quoting in our emitter.
  /// Plain alphanumerics + simple tokens stay unquoted; the
  /// moment we see anything YAML could mis-interpret (colon,
  /// dash at start, quotes, multi-line) we double-quote with
  /// minimal escaping. Errs on the side of more quoting.
  static String _scalar(String v) {
    if (v.isEmpty) return '""';
    if (v.contains('\n')) {
      // Use literal block style for multi-line values; keeps
      // the prompt-heavy flows readable.
      final indented = v.split('\n').map((l) => '        $l').join('\n');
      return '|-\n$indented';
    }
    final needsQuote =
        v.contains(':') ||
        v.contains('#') ||
        v.startsWith('-') ||
        v.startsWith('?') ||
        v.startsWith('[') ||
        v.startsWith('{') ||
        v.startsWith('!') ||
        v.startsWith('&') ||
        v.startsWith('*') ||
        v.contains('"') ||
        v.trim() != v;
    if (!needsQuote) return v;
    final escaped = v.replaceAll(r'\', r'\\').replaceAll('"', r'\"');
    return '"$escaped"';
  }

  static Iterable<_Ref> _scanRefs(String value) sync* {
    // F∆I expression syntax: $<step_or_inputs>.<field>
    // Step IDs and field names match identifier rules:
    // [A-Za-z_][A-Za-z0-9_-]*. The hub also accepts
    // `${{ ... }}` but the canonical short form is what every
    // shipped example uses, so the graph view only mints the
    // short form on emit. Both are recognised on parse.
    final shortPattern = RegExp(
      r'\$([A-Za-z_][A-Za-z0-9_-]*)\.([A-Za-z_][A-Za-z0-9_-]*)',
    );
    for (final match in shortPattern.allMatches(value)) {
      yield _Ref(source: match.group(1)!, field: match.group(2)!);
    }
    final longPattern = RegExp(
      r'\$\{\{\s*([A-Za-z_][A-Za-z0-9_-]*)\.([A-Za-z_][A-Za-z0-9_-]*)\s*\}\}',
    );
    for (final match in longPattern.allMatches(value)) {
      yield _Ref(source: match.group(1)!, field: match.group(2)!);
    }
  }
}

class FlowInput {
  final String type;
  final String? defaultValue;
  final String? hint;
  const FlowInput({required this.type, this.defaultValue, this.hint});
  bool get hasOnlyType => defaultValue == null && hint == null;
}

class FlowStep {
  final String id;
  final String use;
  final Map<String, dynamic> with_;

  const FlowStep({required this.id, required this.use, this.with_ = const {}});

  /// True when the step is the built-in approval gate. The
  /// graph view styles these differently so the operator can
  /// see at a glance where the flow waits for a human.
  bool get isApproval => use.startsWith('system.approval@');

  FlowStep copyWith({String? id, String? use, Map<String, dynamic>? with_}) {
    return FlowStep(
      id: id ?? this.id,
      use: use ?? this.use,
      with_: with_ ?? this.with_,
    );
  }
}

enum EdgeEndpointKind { inputs, step, outputs }

/// One arrow on the graph. Identifies which step/field it
/// leaves from and which step/field it enters.
class FlowEdge {
  final EdgeEndpointKind fromKind;
  final String fromId;
  final String fromField;
  final EdgeEndpointKind toKind;
  final String toId;
  final String toField;

  const FlowEdge({
    required this.fromKind,
    required this.fromId,
    required this.fromField,
    required this.toKind,
    required this.toId,
    required this.toField,
  });
}

class _Ref {
  final String source;
  final String field;
  const _Ref({required this.source, required this.field});
}