import 'package:flutter/material.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';

enum UnitType { text, amount, mass, volume, length, area }

class Unit {
  UnitType type = UnitType.text;

  Unit(this.type);

  factory Unit.fromId(int id) {
    switch (id) {
      case 1:
        return Unit(UnitType.amount);
      case 2:
        return Unit(UnitType.mass);
      case 3:
        return Unit(UnitType.volume);
      case 4:
        return Unit(UnitType.length);
      case 5:
        return Unit(UnitType.area);
      case 0:
      default:
        return Unit(UnitType.text);
    }
  }

  String name(BuildContext context) {
    final trans = AppLocalizations.of(context);

    if (type == UnitType.text) {
      return trans!.unitText;
    } else if (type == UnitType.amount) {
      return trans!.unitAmount;
    } else if (type == UnitType.mass) {
      return trans!.unitMass;
    } else if (type == UnitType.volume) {
      return trans!.unitVolume;
    } else if (type == UnitType.length) {
      return trans!.unitLength;
    } else if (type == UnitType.area) {
      return trans!.unitArea;
    }

    return trans!.unitText;
  }

  int get id {
    if (type == UnitType.text) {
      return 0;
    } else if (type == UnitType.amount) {
      return 1;
    } else if (type == UnitType.mass) {
      return 2;
    } else if (type == UnitType.volume) {
      return 3;
    } else if (type == UnitType.length) {
      return 4;
    } else if (type == UnitType.area) {
      return 5;
    }

    return 0;
  }

  static List<Unit> list() {
    return [
      Unit.fromId(0),
      Unit.fromId(1),
      Unit.fromId(2),
      Unit.fromId(3),
      Unit.fromId(4),
      Unit.fromId(5),
    ];
  }

  List<SubUnit> get subUnits {
    if (type == UnitType.text) {
      // NOTE: plain text does not need subunits
      return [];
    } else if (type == UnitType.amount) {
      // NOTE: amount does not need subunits
      return [];
    } else if (type == UnitType.mass) {
      // TODO: add subunits (with conversion)
      return [SubUnit.def('kg'), SubUnit.nth('g', 1 / 1000)];
    } else if (type == UnitType.volume) {
      // TODO: add subunits (with conversion)
      return [SubUnit.def('l')];
    } else if (type == UnitType.length) {
      // TODO: add subunits (with conversion)
      return [SubUnit.def('m')];
    } else if (type == UnitType.area) {
      // TODO: add subunits (with conversion)
      return [SubUnit.def('m²')];
    }

    return [];
  }

  int? get defaultSubUnit {
    if (type == UnitType.text) {
      // NOTE: plain text does not need subunits
      return null;
    } else if (type == UnitType.amount) {
      // NOTE: amount does not need subunits
      return null;
    } else if (type == UnitType.mass) {
      return 0;
    } else if (type == UnitType.volume) {
      return 0;
    } else if (type == UnitType.length) {
      return 0;
    } else if (type == UnitType.area) {
      return 0;
    }

    return null;
  }

  TextInputType get recommendedType {
    if (type == UnitType.text) {
      return TextInputType.text;
    } else {
      return TextInputType.number;
    }
  }
}

class SubUnit {
  final String name;
  // function to convert from default subunit to this subunit
  final String Function(String value) convertTo;
  // function to convert from this subunit to default subunit
  final String Function(String value) convertFrom;

  const SubUnit({
    required this.name,
    required this.convertTo,
    required this.convertFrom,
  });

  @override
  bool operator ==(Object other) {
    if (runtimeType != other.runtimeType) {
      return false;
    }

    return name.hashCode == other.hashCode;
  }

  @override
  int get hashCode {
    return name.hashCode;
  }

  factory SubUnit.def(String name) {
    return SubUnit(name: name, convertTo: (v) => v, convertFrom: (v) => v);
  }
  factory SubUnit.nth(String name, double fact) {
    return SubUnit(
        name: name,
        convertTo: (v) {
          try {
            final double number = double.parse(v);
            return (number * fact).toString();
          } catch (_) {
            return v;
          }
        },
        convertFrom: (v) {
          try {
            final double number = double.parse(v);
            return (number / fact).toString();
          } catch (_) {
            return v;
          }
        });
  }
}

class DynamicValueUnitInput extends StatefulWidget {
  final int initialUnit;
  final String initialValue;
  final Function(String)? onValueChange;
  final Function(int)? onUnitChange;

  const DynamicValueUnitInput(
      {super.key,
      required this.initialUnit,
      required this.initialValue,
      this.onValueChange,
      this.onUnitChange});

  @override
  State<StatefulWidget> createState() => _DynamicValueUnitInputState();
}

class _DynamicValueUnitInputState extends State<DynamicValueUnitInput> {
  Unit unit = Unit.fromId(0);
  bool enabled = true;
  TextEditingController controller = TextEditingController();
  SubUnit? sub;

  @override
  void initState() {
    super.initState();

    controller = TextEditingController(text: widget.initialValue);
    unit = Unit.fromId(widget.initialUnit);
  }

  @override
  Widget build(BuildContext context) {
    return Wrap(children: [
      // unit type picker
      Padding(
          padding: const EdgeInsets.all(8),
          child: DropdownMenu<int>(
            label: Text(AppLocalizations.of(context)!.selectUnitTypeLabel),
            enabled: enabled,
            initialSelection: unit.id,
            onSelected: (unit) {
              if (unit == null) {
                return;
              }

              final u = Unit.fromId(unit);
              SubUnit? s;
              if (u.defaultSubUnit != null) {
                s = u.subUnits[u.defaultSubUnit!];
              }
              // NOTE: we could run this here as well,
              // but at least to me it seems more natural without it
              // convertSubunit(s);

              if (widget.onUnitChange != null) {
                widget.onUnitChange!(unit);
              }

              setState(() {
                this.unit = u;
                sub = s;
              });
            },
            dropdownMenuEntries: Unit.list()
                .map((unit) => DropdownMenuEntry(
                    value: unit.id, label: unit.name(context)))
                .toList(),
          )),

      // (optional) subunit selector
      ...(unit.defaultSubUnit != null)
          ? [
              Padding(
                  padding: const EdgeInsets.all(8),
                  child: DropdownButtonFormField<SubUnit>(
                    hint: Text(AppLocalizations.of(context)!.selectUnitLabel),
                    decoration: InputDecoration(
                        label:
                            Text(AppLocalizations.of(context)!.selectUnitLabel),
                        border: const OutlineInputBorder()),
                    value: sub,
                    items: unit.subUnits
                        .map((sub) =>
                            DropdownMenuItem(value: sub, child: Text(sub.name)))
                        .toList(),
                    onChanged: (sub) {
                      // there is no way to select nothing
                      if (sub == null) {
                        return;
                      }

                      if (sub == this.sub) {
                        // no new subunit selected
                        return;
                      }

                      convertSubunit(sub);
                      setState(() {
                        this.sub = sub;
                      });
                    },
                  ))
            ]
          : [],

      // value input field
      Padding(
        padding: const EdgeInsets.all(8),
        child: TextField(
          controller: controller,
          keyboardType: unit.recommendedType,
          decoration: InputDecoration(
            labelText: AppLocalizations.of(context)!.inputUnitValueLabel,
            border: const OutlineInputBorder(),
          ),
          onChanged: (value) {
            final String intermediate =
                (sub != null) ? sub!.convertFrom(value) : value;

            if (widget.onValueChange != null) {
              widget.onValueChange!(intermediate);
            }
          },
        ),
      ),
    ]);
  }

  void convertSubunit(SubUnit? newest) {
    final String old2intermediate =
        (sub != null) ? sub!.convertFrom(value) : value;
    final String intermediate2new = (newest != null)
        ? newest.convertTo(old2intermediate)
        : old2intermediate;

    setState(() {
      value = intermediate2new;
    });
  }

  String get value {
    return controller.text;
  }

  set value(String txt) {
    controller.text = txt;
  }
}