using System.Net.Http.Headers;
using System.Text;
using System.Text.Json.Nodes;
using Microsoft.AspNetCore.WebUtilities;
using w4c_workflows.Models.Credentials;

namespace w4c_workflows.Services.Credentials;

/// <summary>
/// Applies a resolved credential to an outbound HTTP request according to its
/// type's injection strategy. Returns a human-readable error when the credential
/// cannot be injected (unknown type, missing field, unsupported strategy).
/// </summary>
public static class CredentialInjector
{
    public static string? Apply(CredentialData credential, CredentialTypeCatalog catalog, HttpRequestMessage request)
    {
        var type = catalog.Get(credential.Type);
        if (type == null)
            return $"unknown credential type '{credential.Type}'";

        var injection = type.Injection;
        return injection.Kind switch
        {
            CredentialInjectionKind.Basic => ApplyBasic(credential.Data, injection, request),
            CredentialInjectionKind.Bearer => ApplyBearer(credential.Data, injection, request),
            CredentialInjectionKind.Header => ApplyHeader(credential.Data, injection, request),
            CredentialInjectionKind.Query => ApplyQuery(credential.Data, injection, request),
            CredentialInjectionKind.None => null,
            _ => $"credential type '{credential.Type}' has an unsupported injection strategy '{injection.Kind}'",
        };
    }

    private static string? ApplyBasic(JsonObject data, CredentialInjection injection, HttpRequestMessage request)
    {
        var username = Read(data, injection.UsernameField);
        if (string.IsNullOrEmpty(username))
            return $"credential is missing '{injection.UsernameField}'";

        var password = Read(data, injection.PasswordField) ?? string.Empty;
        var token = Convert.ToBase64String(Encoding.UTF8.GetBytes($"{username}:{password}"));
        request.Headers.Authorization = new AuthenticationHeaderValue("Basic", token);
        return null;
    }

    private static string? ApplyBearer(JsonObject data, CredentialInjection injection, HttpRequestMessage request)
    {
        var token = Read(data, injection.TokenField);
        if (string.IsNullOrEmpty(token))
            return $"credential is missing '{injection.TokenField}'";

        request.Headers.Authorization = new AuthenticationHeaderValue(injection.Prefix, token);
        return null;
    }

    private static string? ApplyHeader(JsonObject data, CredentialInjection injection, HttpRequestMessage request)
    {
        var name = Read(data, injection.NameField);
        var value = Read(data, injection.ValueField);
        if (string.IsNullOrEmpty(name) || value == null)
            return "credential is missing its header name or value";

        request.Headers.TryAddWithoutValidation(name, value);
        return null;
    }

    private static string? ApplyQuery(JsonObject data, CredentialInjection injection, HttpRequestMessage request)
    {
        var name = Read(data, injection.NameField);
        var value = Read(data, injection.ValueField);
        if (string.IsNullOrEmpty(name) || value == null)
            return "credential is missing its query parameter name or value";
        if (request.RequestUri == null)
            return "cannot inject a query credential without a request URI";

        var query = QueryHelpers.AddQueryString(request.RequestUri.ToString(), name, value);
        request.RequestUri = new Uri(query);
        return null;
    }

    private static string? Read(JsonObject data, string? field)
        => field != null && data[field] is JsonValue value && value.TryGetValue<string>(out var text) ? text : null;
}