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https://github.com/featurebasedb/featurebase.git
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528ebc93db
* Add meta-commands \set and \unset (for variables) * WIP: first pass at variable replacement * Use a mapReplacer instead of having Command implement replacer * remove circular reference with variables * remove the `replacer` interface; just have it be a struct * use a lexer for variable replacement
109 lines
2.8 KiB
Go
109 lines
2.8 KiB
Go
package cli
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import (
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"strings"
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"github.com/benhoyt/goawk/lexer"
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)
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// replacer can replace parts of a string based on some rules and the provided
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// map[string]string. For example, the Command can replace strings with values
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// in its `variables` map.
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type replacer struct {
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m map[string]string
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}
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func newReplacer(m map[string]string) *replacer {
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return &replacer{
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m: m,
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}
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}
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// replace replaces all instances of the string pattern `:key` with the value at
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// m[key]. For example we want something like this:
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//
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// GIVEN: `start :one,:'two', :"three" ::four ::`
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//
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// with map
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//
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// map[string]string{
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// "one": "repl1",
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// "three": "repl3",
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// }
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//
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// WANT: `start repl1,:'two', "repl3" ::four ::`
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func (r *replacer) replace(s string) string {
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// If no variables have been added to the map, there's no need to parse the
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// string for variable replacement.
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if len(r.m) == 0 {
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return s
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}
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line := []byte(s)
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lex := lexer.NewLexer(line)
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// finger contains the index into line at the start of non-variable text
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// that we want to include, as-is in the output.
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var finger int
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// sb builds the string which will be the final output.
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var sb strings.Builder
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for {
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pos, tok, _ := lex.Scan()
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switch tok {
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case lexer.COLON:
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// last is the last normal character position before the colon.
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last := pos.Column - 1
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// Get the next byte to see if the colon value is quoted, and if so,
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// whether its has single or double quotes.
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b := lex.PeekByte()
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// padding is the amount of padding we have to consider around the
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// variable name. If the variable is not quoted, it doesn't require
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// any padding. But if it has quotes, it needs 2 characters of
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// paddings to accomodate the quotes.
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padding := 0
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// quote holds the character to use to quote the final, replaced
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// output value. Because the lexer doesn't tell us how a certain
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// `string` token was quoted, we need to keep track of that here so
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// we can put them back.
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quote := ""
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switch b {
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case byte('\''): // single quote
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quote = `'`
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padding = 2
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case byte('"'): // double quote
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quote = `"`
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padding = 2
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}
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pos, tok, key := lex.Scan()
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switch tok {
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case lexer.NAME, lexer.STRING:
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// Write the normal text up to the variable replacement
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// position.
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sb.Write(line[finger:last])
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if v, ok := r.m[key]; ok {
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// Write replaced variable with the quotes it had.
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sb.WriteString(quote + v + quote)
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} else {
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// Since the variable was not found in the map, just write
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// back what was already there.
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sb.WriteString(":" + quote + key + quote)
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}
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// Reset finger to point to the next position after the
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// variable.
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finger = pos.Column + len(key) + padding - 1
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}
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case lexer.EOF:
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// Write the remainder of the string and return.
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sb.Write(line[finger:])
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return sb.String()
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}
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}
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}
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