66 lines
2.1 KiB
Go
66 lines
2.1 KiB
Go
// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
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// SPDX-License-Identifier: MIT
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// Package diagram renders Mermaid diagrams to SVG with an engine of its
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// own, built on the standard library alone. The flowchart grammar,
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// including the historical "graph" spelling, and the sequenceDiagram
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// grammar are covered; every other diagram type is refused with an error
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// naming it.
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//
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// The output is deterministic: the same source always renders
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// byte-identical SVG, because every layout decision falls back to the
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// order of appearance and never to map iteration.
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package diagram
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import (
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"fmt"
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"strings"
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)
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// Render renders the Mermaid diagram source to SVG. Statements are lines;
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// blank lines and lines opening with %% are comments. A diagram type the
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// engine does not carry is refused with an error naming the type, and a
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// statement the grammar does not know is refused with an error naming the
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// line.
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func Render(source []byte) ([]byte, error) {
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lines := statementLines(source)
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if len(lines) == 0 {
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return nil, fmt.Errorf("diagram: empty source")
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}
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header := strings.Fields(lines[0])
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switch strings.ToLower(header[0]) {
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case "flowchart", "graph":
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dir := "TB"
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if len(header) > 1 {
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dir = strings.ToUpper(header[1])
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if !flowDirections[dir] {
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return nil, fmt.Errorf("diagram: unknown flow direction %q", header[1])
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}
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}
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return renderFlowchart(lines[1:], dir)
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case "sequencediagram":
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auto := len(header) > 1 && strings.ToLower(header[1]) == "autonumber"
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return renderSequence(lines[1:], auto)
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default:
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return nil, fmt.Errorf("diagram: unsupported diagram type %q", header[0])
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}
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}
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var flowDirections = map[string]bool{
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"TB": true, "TD": true, "BT": true, "LR": true, "RL": true,
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}
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// statementLines splits the source into statements: one statement per
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// line, comments and blank lines dropped.
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func statementLines(source []byte) []string {
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var lines []string
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for raw := range strings.SplitSeq(string(source), "\n") {
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line := strings.TrimSpace(raw)
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if line == "" || strings.HasPrefix(line, "%%") {
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continue
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}
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lines = append(lines, line)
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}
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return lines
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}
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