using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using Newtonsoft.Json.Schema;
using StardewModdingAPI.Web.Framework;
using StardewModdingAPI.Web.Framework.Storage;
using StardewModdingAPI.Web.ViewModels.JsonValidator;

namespace StardewModdingAPI.Web.Controllers
{
    /// <summary>Provides a web UI for validating JSON schemas.</summary>
    internal class JsonValidatorController : Controller
    {
        /*********
        ** Fields
        *********/
        /// <summary>Provides access to raw data storage.</summary>
        private readonly IStorageProvider Storage;

        /// <summary>The supported JSON schemas (names indexed by ID).</summary>
        private readonly IDictionary<string, string> SchemaFormats = new Dictionary<string, string>
        {
            ["none"] = "None",
            ["manifest"] = "Manifest",
            ["content-patcher"] = "Content Patcher"
        };

        /// <summary>The schema ID to use if none was specified.</summary>
        private string DefaultSchemaID = "manifest";

        /// <summary>A token in an error message which indicates that the child errors should be displayed instead.</summary>
        private readonly string TransparentToken = "$transparent";


        /*********
        ** Public methods
        *********/
        /***
        ** Constructor
        ***/
        /// <summary>Construct an instance.</summary>
        /// <param name="storage">Provides access to raw data storage.</param>
        public JsonValidatorController(IStorageProvider storage)
        {
            this.Storage = storage;
        }

        /***
        ** Web UI
        ***/
        /// <summary>Render the schema validator UI.</summary>
        /// <param name="schemaName">The schema name with which to validate the JSON, or 'edit' to return to the edit screen.</param>
        /// <param name="id">The stored file ID.</param>
        [HttpGet]
        [Route("json")]
        [Route("json/{schemaName}")]
        [Route("json/{schemaName}/{id}")]
        public async Task<ViewResult> Index(string schemaName = null, string id = null)
        {
            schemaName = this.NormalizeSchemaName(schemaName);

            var result = new JsonValidatorModel(id, schemaName, this.SchemaFormats);
            if (string.IsNullOrWhiteSpace(id))
                return this.View("Index", result);

            // fetch raw JSON
            StoredFileInfo file = await this.Storage.GetAsync(id);
            if (string.IsNullOrWhiteSpace(file.Content))
                return this.View("Index", result.SetUploadError("The JSON file seems to be empty."));
            result.SetContent(file.Content, expiry: file.Expiry, uploadWarning: file.Warning);

            // skip parsing if we're going to the edit screen
            if (schemaName?.ToLower() == "edit")
                return this.View("Index", result);

            // parse JSON
            JToken parsed;
            try
            {
                parsed = JToken.Parse(file.Content, new JsonLoadSettings
                {
                    DuplicatePropertyNameHandling = DuplicatePropertyNameHandling.Error,
                    CommentHandling = CommentHandling.Load
                });
            }
            catch (JsonReaderException ex)
            {
                return this.View("Index", result.AddErrors(new JsonValidatorErrorModel(ex.LineNumber, ex.Path, ex.Message, ErrorType.None)));
            }

            // format JSON
            result.SetContent(parsed.ToString(Formatting.Indented), expiry: file.Expiry, uploadWarning: file.Warning);

            // skip if no schema selected
            if (schemaName == "none")
                return this.View("Index", result);

            // load schema
            JSchema schema;
            {
                FileInfo schemaFile = this.FindSchemaFile(schemaName);
                if (schemaFile == null)
                    return this.View("Index", result.SetParseError($"Invalid schema '{schemaName}'."));
                schema = JSchema.Parse(System.IO.File.ReadAllText(schemaFile.FullName));
            }

            // get format doc URL
            result.FormatUrl = this.GetExtensionField<string>(schema, "@documentationUrl");

            // validate JSON
            parsed.IsValid(schema, out IList<ValidationError> rawErrors);
            var errors = rawErrors
                .SelectMany(this.GetErrorModels)
                .ToArray();
            return this.View("Index", result.AddErrors(errors));
        }

        /***
        ** JSON
        ***/
        /// <summary>Save raw JSON data.</summary>
        [HttpPost, AllowLargePosts]
        [Route("json")]
        public async Task<ActionResult> PostAsync(JsonValidatorRequestModel request)
        {
            if (request == null)
                return this.View("Index", this.GetModel(null, null).SetUploadError("The request seems to be invalid."));

            // normalize schema name
            string schemaName = this.NormalizeSchemaName(request.SchemaName);

            // get raw text
            string input = request.Content;
            if (string.IsNullOrWhiteSpace(input))
                return this.View("Index", this.GetModel(null, schemaName).SetUploadError("The JSON file seems to be empty."));

            // upload file
            UploadResult result = await this.Storage.SaveAsync(input);
            if (!result.Succeeded)
                return this.View("Index", this.GetModel(result.ID, schemaName).SetUploadError(result.UploadError));

            // redirect to view
            return this.Redirect(this.Url.PlainAction("Index", "JsonValidator", new { schemaName = schemaName, id = result.ID }));
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Build a JSON validator model.</summary>
        /// <param name="pasteID">The stored file ID.</param>
        /// <param name="schemaName">The schema name with which the JSON was validated.</param>
        private JsonValidatorModel GetModel(string pasteID, string schemaName)
        {
            return new JsonValidatorModel(pasteID, schemaName, this.SchemaFormats);
        }

        /// <summary>Get a normalized schema name, or the <see cref="DefaultSchemaID"/> if blank.</summary>
        /// <param name="schemaName">The raw schema name to normalize.</param>
        private string NormalizeSchemaName(string schemaName)
        {
            schemaName = schemaName?.Trim().ToLower();
            return !string.IsNullOrWhiteSpace(schemaName)
                ? schemaName
                : this.DefaultSchemaID;
        }

        /// <summary>Get the schema file given its unique ID.</summary>
        /// <param name="id">The schema ID.</param>
        private FileInfo FindSchemaFile(string id)
        {
            // normalize ID
            id = id?.Trim().ToLower();
            if (string.IsNullOrWhiteSpace(id))
                return null;

            // get matching file
            DirectoryInfo schemaDir = new DirectoryInfo(Path.Combine(Directory.GetCurrentDirectory(), "wwwroot", "schemas"));
            foreach (FileInfo file in schemaDir.EnumerateFiles("*.json"))
            {
                if (file.Name.Equals($"{id}.json"))
                    return file;
            }

            return null;
        }

        /// <summary>Get view models representing a schema validation error and any child errors.</summary>
        /// <param name="error">The error to represent.</param>
        private IEnumerable<JsonValidatorErrorModel> GetErrorModels(ValidationError error)
        {
            // skip through transparent errors
            if (this.IsTransparentError(error))
            {
                foreach (var model in error.ChildErrors.SelectMany(this.GetErrorModels))
                    yield return model;
                yield break;
            }

            // get message
            string message = this.GetOverrideError(error);
            if (message == null || message == this.TransparentToken)
                message = this.FlattenErrorMessage(error);

            // build model
            yield return new JsonValidatorErrorModel(error.LineNumber, error.Path, message, error.ErrorType);
        }

        /// <summary>Get a flattened, human-readable message for a schema validation error and any child errors.</summary>
        /// <param name="error">The error to represent.</param>
        /// <param name="indent">The indentation level to apply for inner errors.</param>
        private string FlattenErrorMessage(ValidationError error, int indent = 0)
        {
            // get override
            string message = this.GetOverrideError(error);
            if (message != null && message != this.TransparentToken)
                return message;

            // skip through transparent errors
            if (this.IsTransparentError(error))
                error = error.ChildErrors[0];

            // get friendly representation of main error
            message = error.Message;
            switch (error.ErrorType)
            {
                case ErrorType.Const:
                    message = $"Invalid value. Found '{error.Value}', but expected '{error.Schema.Const}'.";
                    break;

                case ErrorType.Enum:
                    message = $"Invalid value. Found '{error.Value}', but expected one of '{string.Join("', '", error.Schema.Enum)}'.";
                    break;

                case ErrorType.Required:
                    message = $"Missing required fields: {string.Join(", ", (List<string>)error.Value)}.";
                    break;
            }

            // add inner errors
            foreach (ValidationError childError in error.ChildErrors)
                message += "\n" + "".PadLeft(indent * 2, ' ') + $"==> {childError.Path}: " + this.FlattenErrorMessage(childError, indent + 1);
            return message;
        }

        /// <summary>Get whether a validation error should be omitted in favor of its child errors in user-facing error messages.</summary>
        /// <param name="error">The error to check.</param>
        private bool IsTransparentError(ValidationError error)
        {
            if (!error.ChildErrors.Any())
                return false;

            string @override = this.GetOverrideError(error);
            return
                @override == this.TransparentToken
                || (error.ErrorType == ErrorType.Then && @override == null);
        }

        /// <summary>Get an override error from the JSON schema, if any.</summary>
        /// <param name="error">The schema validation error.</param>
        private string GetOverrideError(ValidationError error)
        {
            string GetRawOverrideError()
            {
                // get override errors
                IDictionary<string, string> errors = this.GetExtensionField<Dictionary<string, string>>(error.Schema, "@errorMessages");
                if (errors == null)
                    return null;
                errors = new Dictionary<string, string>(errors, StringComparer.InvariantCultureIgnoreCase);

                // match error by type and message
                foreach ((string target, string errorMessage) in errors)
                {
                    if (!target.Contains(":"))
                        continue;

                    string[] parts = target.Split(':', 2);
                    if (parts[0].Equals(error.ErrorType.ToString(), StringComparison.InvariantCultureIgnoreCase) && Regex.IsMatch(error.Message, parts[1]))
                        return errorMessage?.Trim();
                }

                // match by type
                return errors.TryGetValue(error.ErrorType.ToString(), out string message)
                    ? message?.Trim()
                    : null;
            }

            return GetRawOverrideError()
                ?.Replace("@value", this.FormatValue(error.Value));
        }

        /// <summary>Get an extension field from a JSON schema.</summary>
        /// <typeparam name="T">The field type.</typeparam>
        /// <param name="schema">The schema whose extension fields to search.</param>
        /// <param name="key">The case-insensitive field key.</param>
        private T GetExtensionField<T>(JSchema schema, string key)
        {
            if (schema.ExtensionData != null)
            {
                foreach ((string curKey, JToken value) in schema.ExtensionData)
                {
                    if (curKey.Equals(key, StringComparison.InvariantCultureIgnoreCase))
                        return value.ToObject<T>();
                }
            }

            return default;
        }

        /// <summary>Format a schema value for display.</summary>
        /// <param name="value">The value to format.</param>
        private string FormatValue(object value)
        {
            return value switch
            {
                List<string> list => string.Join(", ", list),
                _ => value?.ToString() ?? "null"
            };
        }
    }
}