using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;

using YesNt.Interpreter.Runtime;

namespace YesNt.Interpreter.Utilities;

/// <summary>
/// Provides high-performance template substitution for variables and stack parameters.
/// </summary>
internal static class TemplateProcessor
{
    /// <summary>
    /// Replaces all occurrences of ${variableName} with their current values.
    /// </summary>
    public static string ProcessVariables(string input, RuntimeInformation runtimeInfo)
    {
        if (string.IsNullOrEmpty(input))
        {
            return input;
        }

        int startIdx = input.IndexOf("${", StringComparison.Ordinal);
        if (startIdx == -1)
        {
            return input;
        }

        StringBuilder sb = new StringBuilder(input.Length);
        int lastIdx = 0;

        while (startIdx != -1)
        {
            _ = sb.Append(input, lastIdx, startIdx - lastIdx);
            int endIdx = input.IndexOf('}', startIdx + 2);
            if (endIdx == -1)
            {
                _ = sb.Append("${");
                lastIdx = startIdx + 2;
            }
            else
            {
                string varName = input[(startIdx + 2)..endIdx];
                if (runtimeInfo.Variables.TryGetValue(varName, out string value))
                {
                    _ = sb.Append(value);
                }
                else if (runtimeInfo.GlobalVariables.TryGetValue(varName, out value))
                {
                    _ = sb.Append(value);
                }
                else if (!runtimeInfo.IsSearching)
                {
                    runtimeInfo.Exit(ExitMessages.VariableNotFound(varName), true);
                    return input;
                }
                else
                {
                    _ = sb.Append("${");
                    _ = sb.Append(varName);
                    _ = sb.Append('}');
                }

                lastIdx = endIdx + 1;
            }

            startIdx = input.IndexOf("${", lastIdx, StringComparison.Ordinal);
        }

        _ = sb.Append(input, lastIdx, input.Length - lastIdx);
        return sb.ToString();
    }

    /// <summary>
    /// Replaces all occurrences of a placeholder (e.g., %in, %out) with values popped from a stack.
    /// </summary>
    public static string ProcessStackParameters(string input, string placeholder, Stack<string> stack, RuntimeInformation runtimeInfo, string emptyStackMessage)
    {
        if (string.IsNullOrEmpty(input))
        {
            return input;
        }

        int startIdx = input.IndexOf(placeholder, StringComparison.Ordinal);
        if (startIdx == -1)
        {
            return input;
        }

        StringBuilder sb = new StringBuilder(input.Length);
        int lastIdx = 0;
        int placeholderLen = placeholder.Length;

        while (startIdx != -1)
        {
            _ = sb.Append(input, lastIdx, startIdx - lastIdx);
            if (stack.Count == 0)
            {
                runtimeInfo.Exit(emptyStackMessage, true);
                return input;
            }
            _ = sb.Append(stack.Pop());
            lastIdx = startIdx + placeholderLen;
            startIdx = input.IndexOf(placeholder, lastIdx, StringComparison.Ordinal);
        }

        _ = sb.Append(input, lastIdx, input.Length - lastIdx);
        return sb.ToString();
    }

    /// <summary>
    /// Replaces all occurrences of a placeholder with a fixed value.
    /// </summary>
    public static string ProcessSimplePlaceholders(string input, string placeholder, string value)
    {
        return string.IsNullOrEmpty(input) ? input : input.Replace(placeholder, value, StringComparison.Ordinal);
    }

    /// <summary>
    /// Replaces all occurrences of a placeholder with values generated by a provider function.
    /// </summary>
    public static string ProcessDynamicPlaceholders(string input, string placeholder, Func<string> valueProvider)
    {
        if (string.IsNullOrEmpty(input))
        {
            return input;
        }

        int startIdx = input.IndexOf(placeholder, StringComparison.Ordinal);
        if (startIdx == -1)
        {
            return input;
        }

        StringBuilder sb = new StringBuilder(input.Length);
        int lastIdx = 0;
        int placeholderLen = placeholder.Length;

        while (startIdx != -1)
        {
            _ = sb.Append(input, lastIdx, startIdx - lastIdx);
            _ = sb.Append(valueProvider());
            lastIdx = startIdx + placeholderLen;
            startIdx = input.IndexOf(placeholder, lastIdx, StringComparison.Ordinal);
        }

        _ = sb.Append(input, lastIdx, input.Length - lastIdx);
        return sb.ToString();
    }

    /// <summary>
    /// Replaces all occurrences of arithmetic expressions with their results.
    /// </summary>
    public static string ProcessCalculations(string input, RuntimeInformation runtimeInfo, Regex calculationRegex)
    {
        if (string.IsNullOrEmpty(input))
        {
            return input;
        }

        MatchCollection matches = calculationRegex.Matches(input);
        if (matches.Count == 0)
        {
            return input;
        }

        StringBuilder sb = new StringBuilder(input.Length);
        int lastIdx = 0;

        for (int i = 0; i < matches.Count; i++)
        {
            Match match = matches[i];
            _ = sb.Append(input, lastIdx, match.Index - lastIdx);

            string res = Evaluator.Calculate(match.Value);
            if (res is null)
            {
                runtimeInfo.Exit(ExitMessages.InvalidOperation, true);
                return input;
            }
            _ = sb.Append(res);
            lastIdx = match.Index + match.Length;
        }

        _ = sb.Append(input, lastIdx, input.Length - lastIdx);
        return sb.ToString();
    }
}