简单的字符串命名模板的写法

简单的字符串命名模板的写法，抄自微软的mvc.

test[testa] testa='123' test123

test[[testa]] testa='123' test[testa]

test [[[testa]]] testa='123' test [123]

/// copy from Microsoft.AspNetCore.Mvc.ApplicationModels
/// AttributeRouteModel.cs

public static string ReplaceTokens(string template, IDictionary<string, string> values)
{
var builder = new StringBuilder();
var state = TemplateParserState.Plaintext;

int? tokenStart = null;

// We'll run the loop one extra time with 'null' to detect the end of the string.
for (var i = 0; i <= template.Length; i++)
{
var c = i < template.Length ? (char?)template[i] : null;
switch (state)
{
case TemplateParserState.Plaintext:
if (c == '[')
{
state = TemplateParserState.SeenLeft;
break;
}
else if (c == ']')
{
state = TemplateParserState.SeenRight;
break;
}
else if (c == null)
{
// We're at the end of the string, nothing left to do.
break;
}
else
{
builder.Append(c);
break;
}
case TemplateParserState.SeenLeft:
if (c == '[')
{
// This is an escaped left-bracket
builder.Append(c);
state = TemplateParserState.Plaintext;
break;
}
else if (c == ']')
{
// This is zero-width parameter - not allowed.
var message =

"TokenReplacement_EmptyTokenNotAllowed";
throw new InvalidOperationException(message);
}
else if (c == null)
{
// This is a left-bracket at the end of the string.
var message = "TokenReplacement_UnclosedToken";
throw new InvalidOperationException(message);
}
else
{
tokenStart = i;
state = TemplateParserState.InsideToken;
break;
}
case TemplateParserState.SeenRight:
if (c == ']')
{
// This is an escaped right-bracket
builder.Append(c);
state = TemplateParserState.Plaintext;
break;
}
else if (c == null)
{
// This is an imbalanced right-bracket at the end of the string.
var message = "TokenReplacement_ImbalancedSquareBrackets";
throw new InvalidOperationException(message);
}
else
{
// This is an imbalanced right-bracket.
var message = "TokenReplacement_ImbalancedSquareBrackets";
throw new InvalidOperationException(message);
}
case TemplateParserState.InsideToken:
if (c == '[')
{
state = TemplateParserState.InsideToken | TemplateParserState.SeenLeft;
break;
}
else if (c == ']')
{
state = TemplateParserState.InsideToken | TemplateParserState.SeenRight;
break;
}
else if (c == null)
{
// This is an unclosed replacement token
var message = "TokenReplacement_UnclosedToken";
throw new InvalidOperationException(message);
}
else
{
// This is a just part of the parameter
break;
}
case TemplateParserState.InsideToken | TemplateParserState.SeenLeft:
if (c == '[')
{
// This is an escaped left-bracket
state = TemplateParserState.InsideToken;
break;
}
else
{
// Unescaped left-bracket is not allowed inside a token.
var message = "TokenReplacement_UnescapedBraceInToken";
throw new InvalidOperationException(message);
}
case TemplateParserState.InsideToken | TemplateParserState.SeenRight:
if (c == ']')
{
// This is an escaped right-bracket
state = TemplateParserState.InsideToken;
break;
}
else
{
// This is the end of a replacement token.
var token = template
.Substring(tokenStart.Value, i - tokenStart.Value - 1)
.Replace("[[", "[")
.Replace("]]", "]");

if (!values.TryGetValue(token, out var value))
{
// Value not found
var message = $"TokenReplacement_ReplacementValueNotFound{string.Join(", ", values.Keys.OrderBy(k => k, StringComparer.OrdinalIgnoreCase))}";
throw new InvalidOperationException(message);
}

builder.Append(value);

if (c == '[')
{
state = TemplateParserState.SeenLeft;
}
else if (c == ']')
{
state = TemplateParserState.SeenRight;
}
else if (c == null)
{
state = TemplateParserState.Plaintext;
}
else
{
builder.Append(c);
state = TemplateParserState.Plaintext;
}

tokenStart = null;
break;
}
}
}

return builder.ToString();
}

[Flags]
private enum TemplateParserState : uint
{
// default state - allow non-special characters to pass through to the
// buffer.
Plaintext = 0,

// We're inside a replacement token, may be combined with other states to detect
// a possible escaped bracket inside the token.
InsideToken = 1,

// We've seen a left brace, need to see the next character to find out if it's escaped
// or not.
SeenLeft = 2,

// We've seen a right brace, need to see the next character to find out if it's escaped
// or not.
SeenRight = 4,
}