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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,112 @@ | ||
| import Foundation | ||
|
|
||
| /// A structure used to represent a template variable, and to resolve it in a given context. | ||
| final class KeyPath { | ||
| private var components = [String]() | ||
| private var current = "" | ||
| private var partialComponents = [String]() | ||
| private var subscriptLevel = 0 | ||
|
|
||
| let variable: String | ||
| let context: Context | ||
|
|
||
| // Split the keypath string and resolve references if possible | ||
| init(_ variable: String, in context: Context) { | ||
| self.variable = variable | ||
| self.context = context | ||
| } | ||
|
|
||
| func parse() throws -> [String] { | ||
| defer { | ||
| components = [] | ||
| current = "" | ||
| partialComponents = [] | ||
| subscriptLevel = 0 | ||
| } | ||
|
|
||
| for c in variable.characters { | ||
| switch c { | ||
| case "." where subscriptLevel == 0: | ||
| try foundSeparator() | ||
| case "[": | ||
| try openBracket() | ||
| case "]": | ||
| try closeBracket() | ||
| default: | ||
| try addCharacter(c) | ||
| } | ||
| } | ||
| try finish() | ||
|
|
||
| return components | ||
| } | ||
|
|
||
| private func foundSeparator() throws { | ||
| if !current.isEmpty { | ||
| partialComponents.append(current) | ||
| } | ||
|
|
||
| guard !partialComponents.isEmpty else { | ||
| throw TemplateSyntaxError("Unexpected '.' in variable '\(variable)'") | ||
| } | ||
|
|
||
| components += partialComponents | ||
| current = "" | ||
| partialComponents = [] | ||
| } | ||
|
|
||
| // when opening the first bracket, we must have a partial component | ||
| private func openBracket() throws { | ||
| guard !partialComponents.isEmpty || !current.isEmpty else { | ||
| throw TemplateSyntaxError("Unexpected '[' in variable '\(variable)'") | ||
| } | ||
|
|
||
| if subscriptLevel > 0 { | ||
| current.append("[") | ||
| } else if !current.isEmpty { | ||
| partialComponents.append(current) | ||
| current = "" | ||
| } | ||
|
|
||
| subscriptLevel += 1 | ||
| } | ||
|
|
||
| // for a closing bracket at root level, try to resolve the reference | ||
| private func closeBracket() throws { | ||
| guard subscriptLevel > 0 else { | ||
| throw TemplateSyntaxError("Unbalanced ']' in variable '\(variable)'") | ||
| } | ||
|
|
||
| if subscriptLevel > 1 { | ||
| current.append("]") | ||
| } else if !current.isEmpty, | ||
| let value = try Variable(current).resolve(context) { | ||
| partialComponents.append("\(value)") | ||
| current = "" | ||
| } else { | ||
| throw TemplateSyntaxError("Unable to resolve subscript '\(current)' in variable '\(variable)'") | ||
| } | ||
|
|
||
| subscriptLevel -= 1 | ||
| } | ||
|
|
||
| private func addCharacter(_ c: Character) throws { | ||
| guard partialComponents.isEmpty || subscriptLevel > 0 else { | ||
| throw TemplateSyntaxError("Unexpected character '\(c)' in variable '\(variable)'") | ||
| } | ||
|
|
||
| current.append(c) | ||
| } | ||
|
|
||
| private func finish() throws { | ||
| // check if we have a last piece | ||
| if !current.isEmpty { | ||
| partialComponents.append(current) | ||
| } | ||
| components += partialComponents | ||
|
|
||
| guard subscriptLevel == 0 else { | ||
| throw TemplateSyntaxError("Unbalanced subscript brackets in variable '\(variable)'") | ||
| } | ||
| } | ||
| } |
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