using System.Globalization;
using System.Text.Json;

namespace MoShiro.Protocol;

public enum ParamType
{
    Int,
    Number,
    Bool,
    Enum,
}

/// <summary>
/// 参数定义：类型、默认值、上下限。节点与 Backend 使用同一套校验，禁止写没有上下限的参数。
/// </summary>
public abstract record ParamSpec(string Name, string Description, string? Unit)
{
    public abstract ParamType Type { get; }

    /// <summary>用于目录展示的默认值。</summary>
    public abstract JsonElement DefaultValue { get; }

    /// <summary>校验并规范化一个参数值；失败时返回错误说明。</summary>
    public abstract bool TryNormalize(JsonElement input, out JsonElement normalized, out string error);

    protected static JsonElement Of(long value) => JsonSerializer.SerializeToElement(value, ParamJson.Default.Int64);

    protected static JsonElement Of(double value) => JsonSerializer.SerializeToElement(value, ParamJson.Default.Double);

    protected static JsonElement Of(bool value) => JsonSerializer.SerializeToElement(value, ParamJson.Default.Boolean);

    protected static JsonElement Of(string value) => JsonSerializer.SerializeToElement(value, ParamJson.Default.String);
}

public sealed record IntParam(string Name, long Default, long Min, long Max, string? Unit = null, string Description = "")
    : ParamSpec(Name, Description, Unit)
{
    public override ParamType Type => ParamType.Int;

    public override JsonElement DefaultValue => Of(Default);

    public override bool TryNormalize(JsonElement input, out JsonElement normalized, out string error)
    {
        normalized = default;
        error = "";
        if (input.ValueKind != JsonValueKind.Number || !input.TryGetInt64(out long value))
        {
            error = "must be an integer";
            return false;
        }

        if (value < Min || value > Max)
        {
            error = $"must be between {Min.ToString(CultureInfo.InvariantCulture)} and {Max.ToString(CultureInfo.InvariantCulture)}";
            return false;
        }

        normalized = Of(value);
        return true;
    }
}

public sealed record NumberParam(string Name, double Default, double Min, double Max, string? Unit = null, string Description = "")
    : ParamSpec(Name, Description, Unit)
{
    public override ParamType Type => ParamType.Number;

    public override JsonElement DefaultValue => Of(Default);

    public override bool TryNormalize(JsonElement input, out JsonElement normalized, out string error)
    {
        normalized = default;
        error = "";
        if (input.ValueKind != JsonValueKind.Number || !input.TryGetDouble(out double value) || !double.IsFinite(value))
        {
            error = "must be a number";
            return false;
        }

        if (value < Min || value > Max)
        {
            error = $"must be between {Min.ToString(CultureInfo.InvariantCulture)} and {Max.ToString(CultureInfo.InvariantCulture)}";
            return false;
        }

        normalized = Of(value);
        return true;
    }
}

public sealed record BoolParam(string Name, bool Default, string Description = "")
    : ParamSpec(Name, Description, null)
{
    public override ParamType Type => ParamType.Bool;

    public override JsonElement DefaultValue => Of(Default);

    public override bool TryNormalize(JsonElement input, out JsonElement normalized, out string error)
    {
        normalized = default;
        error = "";
        if (input.ValueKind is not (JsonValueKind.True or JsonValueKind.False))
        {
            error = "must be a boolean";
            return false;
        }

        normalized = Of(input.GetBoolean());
        return true;
    }
}

public sealed record EnumParam(string Name, string Default, IReadOnlyList<string> Values, string Description = "")
    : ParamSpec(Name, Description, null)
{
    public override ParamType Type => ParamType.Enum;

    public override JsonElement DefaultValue => Of(Default);

    public override bool TryNormalize(JsonElement input, out JsonElement normalized, out string error)
    {
        normalized = default;
        error = "";
        string? value = input.ValueKind == JsonValueKind.String ? input.GetString() : null;
        if (value is null || !Values.Contains(value))
        {
            error = "must be one of: " + string.Join(", ", Values);
            return false;
        }

        normalized = Of(value);
        return true;
    }
}

/// <summary>参数声明的简写。</summary>
public static class P
{
    public static ParamSpec Int(string name, long @default, long min, long max, string? unit = null, string description = "") =>
        new IntParam(name, @default, min, max, unit, description);

    public static ParamSpec Number(string name, double @default, double min, double max, string? unit = null, string description = "") =>
        new NumberParam(name, @default, min, max, unit, description);

    public static ParamSpec Bool(string name, bool @default, string description = "") => new BoolParam(name, @default, description);

    public static ParamSpec Enum(string name, string @default, string[] values, string description = "") =>
        new EnumParam(name, @default, values, description);
}

[System.Text.Json.Serialization.JsonSerializable(typeof(long))]
[System.Text.Json.Serialization.JsonSerializable(typeof(double))]
[System.Text.Json.Serialization.JsonSerializable(typeof(bool))]
[System.Text.Json.Serialization.JsonSerializable(typeof(string))]
internal sealed partial class ParamJson : System.Text.Json.Serialization.JsonSerializerContext;

/// <summary>已经校验并补全了默认值的参数。</summary>
public sealed class ParamValues
{
    private readonly Dictionary<string, JsonElement> _values;

    public ParamValues(Dictionary<string, JsonElement> values)
    {
        _values = values;
    }

    public IReadOnlyDictionary<string, JsonElement> Values => _values;

    public long GetInt(string name) => _values[name].GetInt64();

    public double GetNumber(string name) => _values[name].GetDouble();

    public bool GetBool(string name) => _values[name].GetBoolean();

    public string GetString(string name) => _values[name].GetString()!;
}

public sealed record ParamResolution(ParamValues? Values, IReadOnlyDictionary<string, string> Errors)
{
    public bool IsValid => Errors.Count == 0;
}

public static class ParamResolver
{
    /// <summary>未知参数视为错误；缺失的参数取默认值。</summary>
    public static ParamResolution Resolve(IReadOnlyList<ParamSpec> specs, IReadOnlyDictionary<string, JsonElement>? input)
    {
        var errors = new Dictionary<string, string>();
        var values = new Dictionary<string, JsonElement>(specs.Count);
        foreach (ParamSpec spec in specs)
        {
            if (input is not null && input.TryGetValue(spec.Name, out JsonElement raw))
            {
                if (spec.TryNormalize(raw, out JsonElement normalized, out string error))
                {
                    values[spec.Name] = normalized;
                }
                else
                {
                    errors[spec.Name] = error;
                }
            }
            else
            {
                values[spec.Name] = spec.DefaultValue;
            }
        }

        if (input is not null)
        {
            foreach (string key in input.Keys)
            {
                if (!values.ContainsKey(key) && !errors.ContainsKey(key))
                {
                    errors[key] = "is not a parameter of this kind";
                }
            }
        }

        return new ParamResolution(errors.Count == 0 ? new ParamValues(values) : null, errors);
    }
}