enhance: introduce template engine for commit templates (#704) (#719)

src/Models/CommitTemplate.cs

@@ -1,7 +1,4 @@
-using System;
+using System.Collections.Generic;
-using System.Collections.Generic;
-using System.Text;
-using System.Text.RegularExpressions;
 
 using CommunityToolkit.Mvvm.ComponentModel;
 
@@ -9,9 +6,6 @@ namespace SourceGit.Models
 {
     public partial class CommitTemplate : ObservableObject
     {
-        [GeneratedRegex(@"\$\{files(\:\d+)?\}")]
-        private static partial Regex REG_COMMIT_TEMPLATE_FILES();
-
         public string Name
         {
             get => _name;
@@ -26,55 +20,8 @@ namespace SourceGit.Models
 
         public string Apply(Branch branch, List<Change> changes)
         {
-            var content = _content
+            var te = new TemplateEngine();
-                .Replace("${files_num}", $"{changes.Count}")
+            return te.Eval(_content, branch, changes);
-                .Replace("${branch_name}", branch.Name);
-
-            var matches = REG_COMMIT_TEMPLATE_FILES().Matches(content);
-            if (matches.Count == 0)
-                return content;
-
-            var builder = new StringBuilder();
-            var last = 0;
-            for (int i = 0; i < matches.Count; i++)
-            {
-                var match = matches[i];
-                if (!match.Success)
-                    continue;
-
-                var start = match.Index;
-                if (start != last)
-                    builder.Append(content.Substring(last, start - last));
-
-                var countStr = match.Groups[1].Value;
-                var paths = new List<string>();
-                var more = string.Empty;
-                if (countStr is { Length: <= 1 })
-                {
-                    foreach (var c in changes)
-                        paths.Add(c.Path);
-                }
-                else
-                {
-                    var count = Math.Min(int.Parse(countStr.Substring(1)), changes.Count);
-                    for (int j = 0; j < count; j++)
-                        paths.Add(changes[j].Path);
-
-                    if (count < changes.Count)
-                        more = $" and {changes.Count - count} other files";
-                }
-
-                builder.Append(string.Join(", ", paths));
-                if (!string.IsNullOrEmpty(more))
-                    builder.Append(more);
-
-                last = start + match.Length;
-            }
-
-            if (last != content.Length - 1)
-                builder.Append(content.Substring(last));
-
-            return builder.ToString();
         }
 
         private string _name = string.Empty;

src/Models/TemplateEngine.cs

@@ -0,0 +1,410 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Text.RegularExpressions;
+
+namespace SourceGit.Models
+{
+    public class TemplateEngine
+    {
+        private class Context(Branch branch, IReadOnlyList<Change> changes)
+        {
+            public Branch branch = branch;
+            public IReadOnlyList<Change> changes = changes;
+        }
+
+        private class Text(string text)
+        {
+            public string text = text;
+        }
+
+        private class Variable(string name)
+        {
+            public string name = name;
+        }
+
+        private class SlicedVariable(string name, int count)
+        {
+            public string name = name;
+            public int count = count;
+        }
+
+        private class RegexVariable(string name, Regex regex, string replacement)
+        {
+            public string name = name;
+            public Regex regex = regex;
+            public string replacement = replacement;
+        }
+
+        private const char ESCAPE = '\\';
+        private const char VARIABLE_ANCHOR = '$';
+        private const char VARIABLE_START = '{';
+        private const char VARIABLE_END = '}';
+        private const char VARIABLE_SLICE = ':';
+        private const char VARIABLE_REGEX = '/';
+        private const char NEWLINE = '\n';
+        private const RegexOptions REGEX_OPTIONS = RegexOptions.Singleline | RegexOptions.IgnoreCase;
+
+        public string Eval(string text, Branch branch, IReadOnlyList<Change> changes)
+        {
+            Reset();
+
+            _chars = text.ToCharArray();
+            Parse();
+
+            var context = new Context(branch, changes);
+            var sb = new StringBuilder();
+            sb.EnsureCapacity(text.Length);
+            foreach (var token in _tokens)
+            {
+                switch (token)
+                {
+                    case Text text_token:
+                        sb.Append(text_token.text);
+                        break;
+                    case Variable var_token:
+                        sb.Append(EvalVariable(context, var_token));
+                        break;
+                    case SlicedVariable sliced_var:
+                        sb.Append(EvalVariable(context, sliced_var));
+                        break;
+                    case RegexVariable regex_var:
+                        sb.Append(EvalVariable(context, regex_var));
+                        break;
+                }
+            }
+
+            return sb.ToString();
+        }
+
+        private void Reset()
+        {
+            _pos = 0;
+            _chars = [];
+            _tokens.Clear();
+        }
+
+        private char? Next()
+        {
+            var c = Peek();
+            if (c is not null)
+            {
+                _pos++;
+            }
+            return c;
+        }
+
+        private char? Peek()
+        {
+            return (_pos >= _chars.Length) ? null : _chars[_pos];
+        }
+
+        private int? Integer()
+        {
+            var start = _pos;
+            while (Peek() is char c && c >= '0' && c <= '9')
+            {
+                _pos++;
+            }
+            if (start >= _pos)
+                return null;
+
+            var chars = new ReadOnlySpan<char>(_chars, start, _pos - start);
+            return int.Parse(chars);
+        }
+
+        private void Parse()
+        {
+            // text token start
+            var tok = _pos;
+            bool esc = false;
+            while (Next() is char c)
+            {
+                if (esc)
+                {
+                    esc = false;
+                    continue;
+                }
+                switch (c)
+                {
+                    case ESCAPE:
+                        // allow to escape only \ and $
+                        if (Peek() is char nc && (nc == ESCAPE || nc == VARIABLE_ANCHOR))
+                        {
+                            esc = true;
+                            FlushText(tok, _pos - 1);
+                            tok = _pos;
+                        }
+                        break;
+                    case VARIABLE_ANCHOR:
+                        // backup the position
+                        var bak = _pos;
+                        var variable = TryParseVariable();
+                        if (variable is null)
+                        {
+                            // no variable found, rollback
+                            _pos = bak;
+                        }
+                        else
+                        {
+                            // variable found, flush a text token
+                            FlushText(tok, bak - 1);
+                            _tokens.Add(variable);
+                            tok = _pos;
+                        }
+                        break;
+                }
+            }
+            // flush text token
+            FlushText(tok, _pos);
+        }
+
+        private void FlushText(int start, int end)
+        {
+            int len = end - start;
+            if (len <= 0)
+                return;
+            var text = new string(_chars, start, len);
+            _tokens.Add(new Text(text));
+        }
+
+        private object TryParseVariable()
+        {
+            if (Next() != VARIABLE_START)
+                return null;
+            int name_start = _pos;
+            while (Next() is char c)
+            {
+                // name character, continue advancing
+                if (IsNameChar(c))
+                    continue;
+
+                var name_end = _pos - 1;
+                // not a name character but name is empty, cancel
+                if (name_start >= name_end)
+                    return null;
+                var name = new string(_chars, name_start, name_end - name_start);
+
+                return c switch
+                {
+                    // variable
+                    VARIABLE_END => new Variable(name),
+                    // sliced variable
+                    VARIABLE_SLICE => TryParseSlicedVariable(name),
+                    // regex variable
+                    VARIABLE_REGEX => TryParseRegexVariable(name),
+                    _ => null,
+                };
+            }
+
+            return null;
+        }
+
+        private object TryParseSlicedVariable(string name)
+        {
+            int? n = Integer();
+            if (n is null)
+                return null;
+            if (Next() != VARIABLE_END)
+                return null;
+
+            return new SlicedVariable(name, (int)n);
+        }
+
+        private object TryParseRegexVariable(string name)
+        {
+            var regex = ParseRegex();
+            if (regex == null)
+                return null;
+            var replacement = ParseReplacement();
+            if (replacement == null)
+                return null;
+
+            return new RegexVariable(name, regex, replacement);
+        }
+
+        private Regex ParseRegex()
+        {
+            var sb = new StringBuilder();
+            var tok = _pos;
+            var esc = false;
+            while (Next() is char c)
+            {
+                if (esc)
+                {
+                    esc = false;
+                    continue;
+                }
+                switch (c)
+                {
+                    case ESCAPE:
+                        // allow to escape only / as \ and { used frequently in regexes
+                        if (Peek() == VARIABLE_REGEX)
+                        {
+                            esc = true;
+                            sb.Append(_chars, tok, _pos - 1 - tok);
+                            tok = _pos;
+                        }
+                        break;
+                    case VARIABLE_REGEX:
+                        // goto is fine
+                        goto Loop_exit;
+                    case NEWLINE:
+                        // no newlines allowed
+                        return null;
+                }
+            }
+        Loop_exit:
+            sb.Append(_chars, tok, _pos - 1 - tok);
+
+            try
+            {
+                var pattern = sb.ToString();
+                if (pattern.Length == 0)
+                    return null;
+                var regex = new Regex(pattern, REGEX_OPTIONS);
+
+                return regex;
+            }
+            catch (RegexParseException)
+            {
+                return null;
+            }
+        }
+
+        private string ParseReplacement()
+        {
+            var sb = new StringBuilder();
+            var tok = _pos;
+            var esc = false;
+            while (Next() is char c)
+            {
+                if (esc)
+                {
+                    esc = false;
+                    continue;
+                }
+                switch (c)
+                {
+                    case ESCAPE:
+                        // allow to escape only }
+                        if (Peek() == VARIABLE_END)
+                        {
+                            esc = true;
+                            sb.Append(_chars, tok, _pos - 1 - tok);
+                            tok = _pos;
+                        }
+                        break;
+                    case VARIABLE_END:
+                        // goto is fine
+                        goto Loop_exit;
+                    case NEWLINE:
+                        // no newlines allowed
+                        return null;
+                }
+            }
+        Loop_exit:
+            sb.Append(_chars, tok, _pos - 1 - tok);
+
+            var replacement = sb.ToString();
+
+            return replacement;
+        }
+
+        private static bool IsNameChar(char c)
+        {
+            return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9');
+        }
+
+        // (?) notice or log if variable is not found
+        private static string EvalVariable(Context context, string name)
+        {
+            if (!s_variables.TryGetValue(name, out var getter))
+            {
+                return string.Empty;
+            }
+            return getter(context);
+        }
+
+        private static string EvalVariable(Context context, Variable variable)
+        {
+            return EvalVariable(context, variable.name);
+        }
+
+        private static string EvalVariable(Context context, SlicedVariable variable)
+        {
+            if (!s_slicedVariables.TryGetValue(variable.name, out var getter))
+            {
+                return string.Empty;
+            }
+            return getter(context, variable.count);
+        }
+
+        private static string EvalVariable(Context context, RegexVariable variable)
+        {
+            var str = EvalVariable(context, variable.name);
+            if (string.IsNullOrEmpty(str))
+                return str;
+            return variable.regex.Replace(str, variable.replacement);
+        }
+
+        private int _pos = 0;
+        private char[] _chars = [];
+        private readonly List<object> _tokens = [];
+
+        private delegate string VariableGetter(Context context);
+
+        private static readonly IReadOnlyDictionary<string, VariableGetter> s_variables = new Dictionary<string, VariableGetter>() {
+            // legacy variables
+            {"branch_name", GetBranchName},
+            {"files_num", GetFilesCount},
+            {"files", GetFiles},
+            //
+            {"BRANCH", GetBranchName},
+            {"FILES_COUNT", GetFilesCount},
+            {"FILES", GetFiles},
+        };
+
+        private static string GetBranchName(Context context)
+        {
+            return context.branch.Name;
+        }
+
+        private static string GetFilesCount(Context context)
+        {
+            return context.changes.Count.ToString();
+        }
+
+        private static string GetFiles(Context context)
+        {
+            var paths = new List<string>();
+            foreach (var c in context.changes)
+                paths.Add(c.Path);
+            return string.Join(", ", paths);
+        }
+
+        private delegate string VariableSliceGetter(Context context, int count);
+
+        private static readonly IReadOnlyDictionary<string, VariableSliceGetter> s_slicedVariables = new Dictionary<string, VariableSliceGetter>() {
+            // legacy variables
+            {"files", GetFilesSliced},
+            //
+            {"FILES", GetFilesSliced},
+        };
+
+        private static string GetFilesSliced(Context context, int count)
+        {
+            var sb = new StringBuilder();
+            var paths = new List<string>();
+            var max = Math.Min(count, context.changes.Count);
+            for (int i = 0; i < max; i++)
+                paths.Add(context.changes[i].Path);
+
+            sb.AppendJoin(", ", paths);
+            if (max < context.changes.Count)
+                sb.AppendFormat(" and {0} other files", context.changes.Count - max);
+
+            return sb.ToString();
+        }
+    }
+}