using System;
using System.Collections.Generic;
using System.IO;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;
using ServiceStack.Extensions;
using ServiceStack.Text;

namespace ServiceStack.Script 
{
    
    /// <summary>
    /// Inverse of the #Script Language Template Syntax where each line is a statement
    /// i.e. in contrast to #Script's default where text contains embedded template expressions {{ ... }} 
    /// </summary>
    public sealed class ScriptCode : ScriptLanguage
    {
        private ScriptCode() {} // force usage of singleton

        public static readonly ScriptLanguage Language = new ScriptCode();
        
        public override string Name => "code";

        public override List<PageFragment> Parse(ScriptContext context, ReadOnlyMemory<char> body, ReadOnlyMemory<char> modifiers)
        {
            var quiet = false;
            
            if (!modifiers.IsEmpty)
            {
                quiet = modifiers.EqualsOrdinal("q") || modifiers.EqualsOrdinal("quiet") || modifiers.EqualsOrdinal("mute");
                if (!quiet)
                    throw new NotSupportedException($"Unknown modifier '{modifiers.ToString()}', expected 'code|q', 'code|quiet' or 'code|mute'");
            }
            
            var statements = context.ParseCodeStatements(body);
            
            return new List<PageFragment> {
                new PageJsBlockStatementFragment(new JsBlockStatement(statements)) {
                    Quiet = quiet,
                },
            };
        }

        public override async Task<bool> WritePageFragmentAsync(ScriptScopeContext scope, PageFragment fragment, CancellationToken token)
        {
            var page = scope.PageResult;
            if (fragment is PageJsBlockStatementFragment blockFragment)
            {
                var blockStatements = blockFragment.Block.Statements;
                if (blockFragment.Quiet && scope.OutputStream != Stream.Null)
                    scope = scope.ScopeWithStream(Stream.Null);
                
                await page.WriteStatementsAsync(scope, blockStatements, token).ConfigAwait();
                
                return true;
            }
            return false;
        }
        
        public override async Task<bool> WriteStatementAsync(ScriptScopeContext scope, JsStatement statement, CancellationToken token)
        {
            var page = scope.PageResult;
            if (statement is JsExpressionStatement exprStatement)
            {
                var value = exprStatement.Expression.Evaluate(scope);
                if (value != null && !ReferenceEquals(value, JsNull.Value) && value != StopExecution.Value && value != IgnoreResult.Value)
                {
                    var strValue = page.Format.EncodeValue(value);
                    if (!string.IsNullOrEmpty(strValue))
                    {
                        var bytes = strValue.ToUtf8Bytes();
                        await scope.OutputStream.WriteAsync(bytes, token).ConfigAwait();
                    }
                    await scope.OutputStream.WriteAsync(JsTokenUtils.NewLineUtf8, token).ConfigAwait();
                }
            }
            else if (statement is JsFilterExpressionStatement filterStatement)
            {
                await page.WritePageFragmentAsync(scope, filterStatement.FilterExpression, token).ConfigAwait();
                if (!page.Context.RemoveNewLineAfterFiltersNamed.Contains(filterStatement.FilterExpression.LastFilterName))
                {
                    await scope.OutputStream.WriteAsync(JsTokenUtils.NewLineUtf8, token).ConfigAwait();
                }
            }
            else if (statement is JsBlockStatement blockStatement)
            {
                await page.WriteStatementsAsync(scope, blockStatement.Statements, token).ConfigAwait();
            }
            else if (statement is JsPageBlockFragmentStatement pageFragmentStatement)
            {
                await page.WritePageFragmentAsync(scope, pageFragmentStatement.Block, token).ConfigAwait();
            }
            else return false;
            
            return true;
        }
    }

    public static class ScriptCodeUtils
    {
        [Obsolete("Use CodeSharpPage")]
        public static SharpPage CodeBlock(this ScriptContext context, string code) => context.CodeSharpPage(code);

        public static SharpPage CodeSharpPage(this ScriptContext context, string code) 
            => context.Pages.OneTimePage(code, context.PageFormats[0].Extension,p => p.ScriptLanguage = ScriptCode.Language);

        private static void AssertCode(this ScriptContext context)
        {
            if (!context.ScriptLanguages.Contains(ScriptCode.Language))
                throw new NotSupportedException($"ScriptCode.Language is not registered in {context.GetType().Name}.{nameof(context.ScriptLanguages)}");
        }

        private static PageResult GetCodePageResult(ScriptContext context, string code, Dictionary<string, object> args)
        {
            context.AssertCode();
            PageResult pageResult = null;
            try
            {
                var page = context.CodeSharpPage(code);
                pageResult = new PageResult(page);
                args.Each((x, y) => pageResult.Args[x] = y);
                return pageResult;
            }
            catch (Exception e)
            {
                if (ScriptContextUtils.ShouldRethrow(e))
                    throw;
                throw ScriptContextUtils.HandleException(e, pageResult ?? new PageResult(context.EmptyPage));
            }
        }

        public static string RenderCode(this ScriptContext context, string code, Dictionary<string, object> args=null)
        {
            var pageResult = GetCodePageResult(context, code, args);
            return pageResult.RenderScript();
        }

        public static async Task<string> RenderCodeAsync(this ScriptContext context, string code, Dictionary<string, object> args=null)
        {
            var pageResult = GetCodePageResult(context, code, args);
            return await pageResult.RenderScriptAsync().ConfigAwait();
        }

        public static JsBlockStatement ParseCode(this ScriptContext context, string code) =>
            context.ParseCode(code.AsMemory());

        public static JsBlockStatement ParseCode(this ScriptContext context, ReadOnlyMemory<char> code)
        {
            var statements = context.ParseCodeStatements(code);
            return new JsBlockStatement(statements);
        }

        public static string EnsureReturn(string code)
        {
            if (code == null)
                throw new ArgumentNullException(nameof(code));
            
            // if code doesn't contain a return, wrap and return the expression
            if (code.IndexOf(ScriptConstants.Return,StringComparison.Ordinal) == -1)
                code = ScriptConstants.Return + "(" + code + ")";
            return code;
        }

        public static T EvaluateCode<T>(this ScriptContext context, string code, Dictionary<string, object> args = null) =>
            context.EvaluateCode(code, args).ConvertTo<T>();
        
        public static object EvaluateCode(this ScriptContext context, string code, Dictionary<string, object> args=null)
        {
            var pageResult = GetCodePageResult(context, code, args);

            if (!pageResult.EvaluateResult(out var returnValue))
                throw new NotSupportedException(ScriptContextUtils.ErrorNoReturn);
            
            return ScriptLanguage.UnwrapValue(returnValue);
        }

        public static async Task<T> EvaluateCodeAsync<T>(this ScriptContext context, string code, Dictionary<string, object> args = null) =>
            (await context.EvaluateCodeAsync(code, args).ConfigAwait()).ConvertTo<T>();
        
        public static async Task<object> EvaluateCodeAsync(this ScriptContext context, string code, Dictionary<string, object> args=null)
        {
            var pageResult = GetCodePageResult(context, code, args);

            var ret = await pageResult.EvaluateResultAsync().ConfigAwait();
            if (!ret.Item1)
                throw new NotSupportedException(ScriptContextUtils.ErrorNoReturn);
            
            return ScriptLanguage.UnwrapValue(ret.Item2);
        }
        

        internal static JsStatement[] ParseCodeStatements(this ScriptContext context, ReadOnlyMemory<char> code)
        {
            var to = new List<JsStatement>();

            int startExpressionPos = -1;
            
            var cursorPos = 0;
            while (code.TryReadLine(out var line, ref cursorPos))
            {
                var lineLength = line.Length;
                line = line.TrimStart();
                var leftIndent = lineLength - line.Length;
                line = line.TrimEnd();
                var rightIndent = lineLength - leftIndent - line.Length;
                    
                if (line.IsEmpty)
                    continue;

                var firstChar = line.Span[0];

                // single-line comment
                if (firstChar == '*')
                {
                    if (line.EndsWith("*"))
                        continue;
                }
                // multi-line comment
                if (line.StartsWith("{{*"))
                {
                    var endPos = code.IndexOf("*}}", cursorPos - lineLength);
                    if (endPos == -1)
                        throw new SyntaxErrorException($"Unterminated multi-line comment, near {line.DebugLiteral()}");

                    cursorPos = endPos + 3; // "*}}".Length
                    continue;
                }

                // template block statement
                if (firstChar == '{' && line.Span.SafeCharEquals(1, '{') && line.Span.SafeCharEquals(2, '#'))
                {
                    var fromLineStart = code.ToLineStart(cursorPos, lineLength).AdvancePastWhitespace();
                    var literal = fromLineStart.Slice(3);

                    literal = literal.ParseTemplateScriptBlock(context, out var blockFragment);
                    blockFragment.OriginalText = fromLineStart.Slice(0, fromLineStart.Length - literal.Length);
                    to.Add(new JsPageBlockFragmentStatement(blockFragment));

                    cursorPos = code.Length - literal.Length;
                    continue;
                }
                
                // code block statement
                if (firstChar == '#') 
                {
                    var fromLineStart = code.ToLineStart(cursorPos, lineLength).AdvancePastWhitespace();
                    var literal = fromLineStart.Slice(1);

                    literal = literal.ParseCodeScriptBlock(context, out var blockFragment);
                    to.Add(new JsPageBlockFragmentStatement(blockFragment));
                    
                    blockFragment.OriginalText = fromLineStart.Slice(0, fromLineStart.Length - literal.Length);

                    cursorPos = code.Length - literal.Length;
                    continue;
                }

                const int delim = 2; // '}}'.length
                // multi-line expression
                if (startExpressionPos >= 0)
                {
                    // multi-line end
                    if (line.EndsWith("}}"))
                    {
                        if (code.Span.SafeCharEquals(startExpressionPos, '*'))
                        {
                            if (!line.EndsWith("*}}")) // not a closing block comment, continue
                                continue;
                            
                            // ignore multi-line comment
                        }
                        else
                        {
                            var CRLF = code.Span.SafeCharEquals(cursorPos - 2, '\r') ? 2 : 1;
                            var exprStr = code.Slice(startExpressionPos,  cursorPos - startExpressionPos - rightIndent - delim - CRLF).Trim();
                            var afterExpr = exprStr.Span.ParseExpression(out var expr, out var filters);
                        
                            to.AddExpression(exprStr, expr, filters);
                        }
                        
                        startExpressionPos = -1;
                    }
                    continue;
                }

                if (firstChar == '{' && line.Span.SafeCharEquals(1, '{'))
                {
                    // single-line {{ expr }}
                    if (line.EndsWith("}}"))
                    {
                        var exprStr = code.Slice(cursorPos - lineLength + leftIndent + delim);
                        exprStr = exprStr.Slice(0, exprStr.IndexOf("}}")).Trim();
                        var afterExpr = exprStr.Span.ParseExpression(out var expr, out var filters);
                        
                        to.AddExpression(exprStr, expr, filters);
                        continue;
                    }
                    
                    // multi-line start
                    var CRLF = code.Span.SafeCharEquals(cursorPos - 2, '\r') ? 2 : 1;
                    startExpressionPos = cursorPos - lineLength - CRLF + leftIndent + delim;
                    continue;
                }
                else
                {
                    // treat line as an expression statement
                    var afterExpr = line.Span.ParseExpression(out var expr, out var filters);
                    afterExpr = afterExpr.AdvancePastWhitespace();

                    if (!afterExpr.IsEmpty)
                        throw new SyntaxErrorException($"Unexpected syntax after expression: {afterExpr.ToString()}, near {line.DebugLiteral()}");
                    
                    to.AddExpression(line, expr, filters);
                }
            }

            return to.ToArray();
        }
        
        // #if ...
        //  ^
        public static ReadOnlyMemory<char> ParseCodeScriptBlock(this ReadOnlyMemory<char> literal, ScriptContext context, 
            out PageBlockFragment blockFragment)
        {
            literal = literal.ParseVarName(out var blockNameSpan);
            var endArgumentPos = literal.IndexOf('\n');
            var argument = literal.Slice(0, endArgumentPos).Trim();

            literal = literal.Slice(endArgumentPos + 1);

            var blockName = blockNameSpan.ToString();

            var language = context.ParseAsLanguage.TryGetValue(blockName, out var lang)
                ? lang
                : ScriptCode.Language;

            if (language.Name == ScriptVerbatim.Language.Name)
            {
                literal = literal.ParseCodeBody(blockNameSpan, out var body);
                body = body.ChopNewLine();

                blockFragment = language.ParseVerbatimBlock(blockName, argument, body);
                return literal;
            }

            literal = literal.ParseCodeBody(blockNameSpan, out var bodyText);
            var bodyFragments = language.Parse(context, bodyText);

            var elseBlocks = new List<PageElseBlock>();

            literal = literal.AdvancePastWhitespace();
            while (literal.StartsWith("else"))
            {
                literal = literal.ParseCodeElseBlock(blockNameSpan, out var elseArgument,  out var elseBody);
                    
                var elseBlock = new PageElseBlock(elseArgument, language.Parse(context, elseBody));
                elseBlocks.Add(elseBlock);

                literal = literal.AdvancePastWhitespace();
            }
            
            blockFragment = new PageBlockFragment(blockName, argument, bodyFragments, elseBlocks);

            return literal;
        }
        
        // cursorPos is after CRLF except at end where its at last char

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal static ReadOnlyMemory<char> FromStartToPreviousLine(this ReadOnlyMemory<char> literal, int cursorPos, int lineLength)
        {
            var ret = literal.Slice(0, cursorPos - lineLength);
            while (!ret.Span.SafeCharEquals(ret.Length - 1, '\n'))
            {
                ret = ret.Slice(0, ret.Length - 1);

                if (ret.Length == 0) // no previous line, so return empty string
                    return default;
            }
            
            return ret;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal static ReadOnlyMemory<char> ToLineStart(this ReadOnlyMemory<char> literal, int cursorPos, int lineLength)
        {
            var CLRF = literal.Span.SafeCharEquals(cursorPos - 2, '\r');
            var ret = literal.Slice(cursorPos - lineLength -
                 (cursorPos == literal.Length ? 0 : 1) -
                 (CLRF ? 1 : 0));
            
            return ret;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal static ReadOnlyMemory<char> ToLineStart(this ReadOnlyMemory<char> literal, int cursorPos, int lineLength, int statementPos)
        {
            var ret = literal.Slice(statementPos, cursorPos - statementPos - lineLength);
            while (!ret.Span.SafeCharEquals(ret.Length - 1, '\n'))
            {
                ret = ret.Slice(0, ret.Length - 1);

                if (ret.Length == 0) // no previous line, so return empty string
                    return default;
            }
            
            return ret;
        }

        //  #block arg\n  
        //              ^
        //  else
        //  /block
        internal static ReadOnlyMemory<char> ParseCodeBody(this ReadOnlyMemory<char> literal, ReadOnlyMemory<char> blockName, out ReadOnlyMemory<char> body)
        {
            var inStatements = 0;
            
            var cursorPos = 0;
            while (literal.TryReadLine(out var line, ref cursorPos))
            {
                var lineLength = line.Length;
                line = line.Trim();
                if (line.IsEmpty)
                    continue;

                var c = line.Span[0];

                if (c == '#')
                {
                    inStatements++;
                    continue;
                }

                if (c == '/')
                {
                    if (inStatements == 0)
                    {
                        line.Slice(1).ParseVarName(out var name);
                        if (name.EqualsOrdinal(blockName))
                        {
                            body = literal.FromStartToPreviousLine(cursorPos, lineLength);
                            var ret = literal.Slice(cursorPos);
                            return ret;
                        }
                    }

                    inStatements--;
                }
                else if (line.StartsWith("else"))
                {
                    if (inStatements == 0)
                    {
                        body = literal.FromStartToPreviousLine(cursorPos, lineLength);
                        var ret = literal.ToLineStart(cursorPos, lineLength);
                        return ret;
                    }
                }
            }
            
            throw new SyntaxErrorException($"End block for '{blockName.ToString()}' not found.");
        }
        
        //  else if a=b  
        //  ^
        //  else
        //  ^
        //  /block
        internal static ReadOnlyMemory<char> ParseCodeElseBlock(this ReadOnlyMemory<char> literal, ReadOnlyMemory<char> blockName, 
            out ReadOnlyMemory<char> elseArgument, out ReadOnlyMemory<char> elseBody)
        {
            var inStatements = 0;
            var statementPos = -1;
            elseBody = default;
            elseArgument = default;
            
            var cursorPos = 0;
            while (literal.TryReadLine(out var line, ref cursorPos))
            {
                var lineLength = line.Length;
                line = line.Trim();
                if (line.IsEmpty)
                    continue;

                var c = line.Span[0];

                if (c == '#')
                {
                    inStatements++;
                }
                else if (c == '/')
                {
                    if (inStatements == 0)
                    {
                        line.Slice(1).ParseVarName(out var name);
                        if (name.EqualsOrdinal(blockName))
                        {
                            elseBody = literal.ToLineStart(cursorPos, lineLength, statementPos);
                            elseBody = elseBody.Trim();
                            var ret = literal.Slice(cursorPos);
                            return ret;
                        }
                    }

                    inStatements--;
                }
                else if (line.StartsWith("else"))
                {
                    if (inStatements == 0)
                    {
                        if (statementPos >= 0)
                        {
                            elseBody = literal.Slice(statementPos, (cursorPos - lineLength) - statementPos).Trim();
                            var ret = literal.Slice(cursorPos - lineLength);
                            return ret;
                        }

                        elseArgument = line.Slice(4).Trim();
                        statementPos = cursorPos;
                    }
                }
            }
            
            throw new SyntaxErrorException($"End 'else' statement not found.");
        }

        internal static ReadOnlySpan<char> ParseExpression(this ReadOnlySpan<char> literal, out JsToken expr, out List<JsCallExpression> filters)
        {
            literal = literal.ParseJsExpression(out expr, filterExpression: true);
            filters = null;


            literal = literal.AdvancePastWhitespace();
            if (literal.FirstCharEquals(ScriptTemplateUtils.FilterSep))
            {
                filters = new List<JsCallExpression>();
                literal = literal.AdvancePastPipeOperator();

                while (true)
                {
                    literal = literal.ParseJsCallExpression(out var filter, filterExpression: true);

                    filters.Add(filter);

                    literal = literal.AdvancePastWhitespace();

                    if (literal.IsNullOrEmpty())
                        return literal;

                    if (!literal.FirstCharEquals(ScriptTemplateUtils.FilterSep))
                        throw new SyntaxErrorException($"Expected filter separator '|' but was {literal.DebugFirstChar()}");

                    literal = literal.AdvancePastPipeOperator();
                }
            }
            else if (!literal.AdvancePastWhitespace().IsNullOrEmpty())
            {
                throw new SyntaxErrorException($"Unexpected syntax '{literal.ToString()}', Expected pipeline operator '|>'");
            }

            return literal;
        }
        

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void AddExpression(this List<JsStatement> ret, ReadOnlyMemory<char> originalText,
            JsToken expr, List<JsCallExpression> filters)
        {
            if (filters == null)
                ret.Add(new JsExpressionStatement(expr));
            else
                ret.Add(new JsFilterExpressionStatement(originalText, expr, filters));
        }        
    }
}