gno.land/r/moul/x/daily/toposortdemo/v0⧉

1// Package toposortdemo is a small gnoweb demo of the dependency ordering2// provided by the [p/moul/x/daily/toposort](/p/moul/x/daily/toposort/v0)3// library: it shows a build graph resolved into a safe install order, and a4// deliberately broken graph to show how a cycle is reported.5//6// It contains no ordering logic of its own — the graph, the sort and the cycle7// detection all come from the library. Stateless and read-only, so Render is8// fully deterministic.9package toposortdemo1011import (12	"strconv"13	"strings"1415	"gno.land/p/moul/x/daily/toposort/v0"16)1718// buildGraph is a small, realistic dependency graph: a realm on top of a couple19// of libraries, themselves on a shared core.20func buildGraph() *toposort.Graph {21	return toposort.FromPairs([][2]string{22		{"realm", "ui"},23		{"realm", "storage"},24		{"ui", "markdown"},25		{"storage", "avl"},26		{"markdown", "strings"},27		{"avl", "strings"},28	})29}3031// cyclicGraph is broken on purpose: auth and session need each other.32func cyclicGraph() *toposort.Graph {33	return toposort.FromPairs([][2]string{34		{"server", "auth"},35		{"auth", "session"},36		{"session", "auth"},37	})38}3940// Render renders the demo for gnoweb.41//42//	Render("")       / Render("/") -> the build graph, resolved43//	Render("/cycle")               -> the broken graph and its report44func Render(path string) string {45	var b strings.Builder46	b.WriteString("# Topological Sort\n\n")47	b.WriteString("Ordering a dependency graph so nothing is built before what it needs, ")48	b.WriteString("demoing the [`p/moul/x/daily/toposort`](/p/moul/x/daily/toposort/v0) library.\n\n")4950	if parseArg(path) == "cycle" {51		return b.String() + renderCycle()52	}5354	g := buildGraph()55	b.WriteString("## The graph\n\n```\n")56	b.WriteString(g.String())57	b.WriteString("```\n\n")5859	order, err := g.Sort()60	if err != nil {61		b.WriteString("_Unexpectedly cyclic._\n")62		return b.String()63	}64	b.WriteString("## Install order\n\n")65	for i, n := range order {66		b.WriteString(strconv.Itoa(i + 1))67		b.WriteString(". `")68		b.WriteString(n)69		b.WriteString("`\n")70	}71	b.WriteString("\nTies are broken lexicographically, so this ordering is the ")72	b.WriteString("*only* one the library will ever produce for this graph.\n\n")73	b.WriteString("> See [`/cycle`](/r/moul/x/daily/toposortdemo/v0:cycle) for what happens ")74	b.WriteString("when the graph is not a DAG.\n")75	return b.String()76}7778// renderCycle shows the failure mode.79func renderCycle() string {80	g := cyclicGraph()81	var b strings.Builder82	b.WriteString("## A graph with a cycle\n\n```\n")83	b.WriteString(g.String())84	b.WriteString("```\n\n")8586	order, err := g.Sort()87	if err == nil {88		b.WriteString("_Unexpectedly acyclic._\n")89		return b.String()90	}91	b.WriteString("`Sort` returns an error: **")92	b.WriteString(err.Error())93	b.WriteString("**\n\n")94	b.WriteString("Ordered before giving up: ")95	if len(order) == 0 {96		b.WriteString("_nothing_")97	} else {98		b.WriteString("`" + strings.Join(order, "`, `") + "`")99	}100	b.WriteString("\n\nStuck on the cycle: `")101	b.WriteString(strings.Join(g.CycleNodes(), "`, `"))102	b.WriteString("`\n\n> The nodes still stuck are named rather than silently dropped, ")103	b.WriteString("so a caller can report exactly which dependencies are tangled.\n")104	return b.String()105}106107// parseArg extracts the first path segment.108func parseArg(path string) string {109	s := strings.TrimSpace(path)110	s = strings.TrimPrefix(s, "/")111	if i := strings.IndexByte(s, '/'); i >= 0 {112		s = s[:i]113	}114	return s115}116