package docgen

import (
	"fmt"
	"sort"
	"strings"
)

// Render produces the full Markdown page for a project, wrapped in generated
// markers. The output always carries the three level-2 audience headings that
// go-doc's reader keys off, so an imported page is immediately navigable.
func Render(p *Project) (string, error) {
	view := buildView(p)

	var b builder
	b.h1(p.Name)
	b.para(p.Summary)
	b.table(
		[]string{"", ""},
		[]row{
			{"Module", view.ModuleSummary},
			{"Endpoints", view.EndpointCount},
			{"Components", view.ComponentCount},
			{"Tests", view.TestSummary},
			{"Go lines", view.LineSummary},
		},
	)
	b.note("Everything between the generated markers is rewritten by every sync. " +
		"Notes written outside the markers are kept.")

	users(&b, view)
	operators(&b, view)
	developers(&b, view)

	return Wrap(p.Name, p.Signature, strings.TrimRight(b.String(), "\n")), nil
}

// ---------------------------------------------------------------------------
// Audience sections
// ---------------------------------------------------------------------------

func users(b *builder, v docView) {
	b.h2("For Users")

	b.h3("What this application does")
	b.para(v.Summary)

	if v.HasReadme {
		b.para(fmt.Sprintf(
			"The project ships its own README at `%s`, which is the long form of this page. "+
				"The three audience tabs split the same facts three ways so you only read the part "+
				"that concerns you.", v.Readme))
	} else {
		b.para("This project ships no README, so the summary above was derived from the source " +
			"tree. If that is wrong, write a README and re-run the sync.")
	}

	b.h3("Reading this in go-doc")
	b.para("Open the page and pick the tab that matches you:")
	b.bullets([]string{
		"**User** — you use the finished application. This section is all you need.",
		"**Operator** — you run it. Configuration, ports and deployment notes are under that tab.",
		"**Developer** — you integrate with it or change it. The API and layout tables are under that tab.",
	})
	b.para("The feedback panel stores a note per audience, tagged with your badge, so operators " +
		"and developers can see which audience raised it.")

	if len(v.Docs) > 0 {
		b.h3("Where the original documentation lives")
		b.para(fmt.Sprintf(
			"This project already carries %s. They stay in the project repository: this page "+
				"points at them instead of copying them, so there is always exactly one copy of "+
				"the truth.", plural(len(v.Docs), "Markdown document", "Markdown documents")))

		rows := make([]row, 0, len(v.Docs))
		for _, doc := range v.Docs {
			rows = append(rows, row{"`" + doc.Path + "`", fmt.Sprintf("%d bytes", doc.Bytes)})
		}
		b.table([]string{"Document", "Size"}, rows)
	}
}

func operators(b *builder, v docView) {
	b.rule()
	b.h2("For Operators")

	b.h3("Running it locally")
	if len(v.MakeTargets) > 0 {
		b.para(fmt.Sprintf("The root Makefile defines %s:",
			plural(len(v.MakeTargets), "target", "targets")))
		b.bullets(backtickEach(v.MakeTargets, "make "))
	} else {
		b.para("This project has no root Makefile, so the binary or container is run directly.")
	}

	if len(v.Compose) > 0 {
		b.h3("Local containers")
		b.para("The compose file defines these services:")

		rows := make([]row, 0, len(v.Compose))
		for _, service := range v.Compose {
			image := "built locally"
			if service.Image != "" {
				image = "`" + service.Image + "`"
			}
			ports := "internal only"
			if service.Ports != "" {
				ports = service.Ports
			}
			rows = append(rows, row{service.Name, image, ports})
		}
		b.table([]string{"Service", "Image", "Published ports"}, rows)
	}

	if v.Docker != nil {
		b.h3("Image")

		var sentence strings.Builder
		fmt.Fprintf(&sentence, "`%s` builds from", v.Docker.File)
		for i, base := range v.Docker.Bases {
			if i > 0 {
				sentence.WriteString(",")
			}
			fmt.Fprintf(&sentence, " `%s`", base)
		}
		if len(v.Docker.Stages) > 0 {
			fmt.Fprintf(&sentence, " in stages: %s", strings.Join(v.Docker.Stages, ", "))
		}
		if len(v.Docker.Exposed) > 0 {
			fmt.Fprintf(&sentence, " and exposes %s", strings.Join(v.Docker.Exposed, ", "))
		}
		sentence.WriteString(".")
		b.para(sentence.String())
	}

	b.h3("Configuration")
	if len(v.EnvVars) > 0 {
		b.para("Every environment variable found in the source or in a `.env` file:")

		rows := make([]row, 0, len(v.EnvVars))
		for _, env := range v.EnvVars {
			example := "—"
			if env.Example != "" {
				example = "`" + env.Example + "`"
			}
			source := "source"
			if env.FromEnv {
				source = ".env file"
			}
			rows = append(rows, row{"`" + env.Name + "`", example, source})
		}
		b.table([]string{"Variable", "Example", "Found in"}, rows)
	} else {
		b.para("No environment variables were found in the source or in a `.env` file.")
	}

	if len(v.Flags) > 0 {
		b.para("Command-line flags override the environment where both exist:")

		rows := make([]row, 0, len(v.Flags))
		for _, flag := range v.Flags {
			decl := "-" + flag.Name
			if flag.Default != "" {
				decl += "=" + flag.Default
			}
			def := "—"
			if flag.Default != "" {
				def = "`" + flag.Default + "`"
			}
			usage := "—"
			if flag.Usage != "" {
				usage = collapse(flag.Usage, 90)
			}
			rows = append(rows, row{"`" + decl + "`", def, usage})
		}
		b.table([]string{"Flag", "Default", "Purpose"}, rows)
	}

	b.h3("Network surface")
	if len(v.Ports) > 0 {
		quoted := make([]string, 0, len(v.Ports))
		for _, port := range v.Ports {
			quoted = append(quoted, "`"+port+"`")
		}
		b.para("Ports referenced across the project: " + strings.Join(quoted, ", ") + ".")
	} else {
		b.para("No explicit port declaration was found. Check the README and the compose file " +
			"before assuming a default.")
	}

	b.h3("Deployment artefacts")
	if len(v.HelmCharts) > 0 {
		b.para(fmt.Sprintf("Helm %s found:",
			plural(len(v.HelmCharts), "chart", "charts")))
		b.bullets(backtickEach(v.HelmCharts, ""))
	} else {
		b.para("No Helm chart was found, so deployment is expected to be plain Docker or a " +
			"managed platform.")
	}

	if len(v.OperatorDocs) > 0 {
		b.h3("Operations documentation that already exists")
		b.para("Read these in place rather than duplicating them here:")
		b.bullets(docBullets(v.OperatorDocs))
	}

	for _, note := range v.Notes {
		b.note(note)
	}
}

func developers(b *builder, v docView) {
	b.rule()
	b.h2("For Developers")

	b.h3("Module layout")
	if len(v.ModuleSummaries) > 0 {
		b.bullets(v.ModuleSummaries)
	} else {
		b.para("No go.mod in this tree: the project may be vendored, a workspace member, or " +
			"not Go at all.")
	}

	b.h3("HTTP API")
	if len(v.Routes) > 0 {
		b.para("Every route registration found in the source:")

		rows := make([]row, 0, len(v.Routes))
		for _, route := range v.Routes {
			method := "ANY"
			if route.Method != "" {
				method = "`" + route.Method + "`"
			}
			handler := "—"
			if route.Handler != "" {
				handler = "`" + route.Handler + "`"
			}
			rows = append(rows, row{method, "`" + route.Path + "`", handler})
		}
		b.table([]string{"Method", "Path", "Handler"}, rows)
	} else {
		b.para("No route registrations were detected, which is expected for a CLI, a library " +
			"or a worker.")
	}

	b.h3("Direct dependencies")
	if deps := v.DirectDeps(); len(deps) > 0 {
		items := make([]string, 0, len(deps))
		for _, dep := range deps {
			items = append(items, "`"+dep.Path+"` "+dep.Version)
		}
		b.bullets(items)
	} else {
		b.para("No third-party dependencies are declared.")
	}

	b.h3("Directory map")
	if len(v.Dirs) > 0 {
		rows := make([]row, 0, len(v.Dirs))
		for _, dir := range v.Dirs {
			rows = append(rows, row{
				"`" + dir.Name + "/`",
				fmt.Sprintf("%d", dir.Files),
				fmt.Sprintf("%d", dir.Lines),
				directoryPurpose(dir.Name),
			})
		}
		b.table([]string{"Directory", "Files", "Lines", "Likely purpose"}, rows)
	} else {
		b.para("No first-level directories were found.")
	}

	b.h3("Languages")
	if len(v.Languages) > 0 {
		items := make([]string, 0, len(v.Languages))
		for _, lang := range v.Languages {
			items = append(items, fmt.Sprintf("**%s** — %s, %d lines", lang.Name,
				plural(lang.Files, "file", "files"), lang.Lines))
		}
		b.bullets(items)
	} else {
		b.para("No source files were recognised.")
	}

	if len(v.DeveloperDocs) > 0 {
		b.h3("Developer documentation that already exists")
		b.bullets(docBullets(v.DeveloperDocs))
	}
}

// ---------------------------------------------------------------------------
// Markdown builder
// ---------------------------------------------------------------------------

// builder assembles Markdown with predictable spacing. Block elements ask for a
// separator instead of writing blank lines by hand, so every block is preceded
// by exactly one blank line no matter which branch produced it — the failure
// mode this replaces was headings glued to the paragraph above them.
type builder struct {
	out       strings.Builder
	lastBlank bool
}

func (b *builder) String() string { return b.out.String() }

// ensureBlank separates the next line from the previous one unless it already is.
func (b *builder) ensureBlank() {
	if b.out.Len() == 0 || b.lastBlank {
		return
	}
	b.out.WriteString("\n")
}

func (b *builder) line(text string) {
	b.out.WriteString(text)
	b.out.WriteString("\n")
	b.lastBlank = text == ""
}

func (b *builder) h1(text string) { b.ensureBlank(); b.line("# " + text) }

func (b *builder) h2(text string) { b.ensureBlank(); b.line("## " + text) }

func (b *builder) h3(text string) { b.ensureBlank(); b.line("### " + text) }

func (b *builder) para(text string) { b.ensureBlank(); b.line(text) }

func (b *builder) note(text string) { b.ensureBlank(); b.line("> " + text) }

// rule writes a horizontal rule, which always gets its own block.
func (b *builder) rule() { b.ensureBlank(); b.line("---") }

// bullets writes a tight list: the separator goes before the list, never between
// its items.
func (b *builder) bullets(items []string) {
	if len(items) == 0 {
		return
	}
	b.ensureBlank()
	for _, item := range items {
		b.line("- " + item)
	}
}

// row is one Markdown table row.
type row []string

// table writes a GitHub-flavoured table. Cell content is emitted verbatim: every
// caller has already added its own backticks, so the builder must not guess.
func (b *builder) table(headers []string, rows []row) {
	b.ensureBlank()

	cells := make([]string, len(headers))
	for i, header := range headers {
		cells[i] = header
	}
	b.line("| " + strings.Join(cells, " | ") + " |")

	separators := make([]string, len(headers))
	for i := range separators {
		separators[i] = "---"
	}
	b.line("| " + strings.Join(separators, " | ") + " |")

	for _, r := range rows {
		b.line("| " + strings.Join(r, " | ") + " |")
	}
}

// backtickEach renders values as a list of code-formatted bullet items.
func backtickEach(values []string, prefix string) []string {
	out := make([]string, 0, len(values))
	for _, value := range values {
		out = append(out, "`"+prefix+value+"`")
	}
	return out
}

// docBullets renders discovered documents as code-formatted bullets with their
// titles when they have one.
func docBullets(docs []DocFile) []string {
	out := make([]string, 0, len(docs))
	for _, doc := range docs {
		item := "`" + doc.Path + "`"
		if doc.Title != "" {
			item += " — " + doc.Title
		}
		out = append(out, item)
	}
	return out
}

// ---------------------------------------------------------------------------
// View model
// ---------------------------------------------------------------------------

// docView is the pre-computed, presentation-ready view of a project.
type docView struct {
	*Project

	ModuleSummary   string
	EndpointCount   string
	ComponentCount  string
	TestSummary     string
	LineSummary     string
	HasReadme       bool
	OperatorDocs    []DocFile
	DeveloperDocs   []DocFile
	ModuleSummaries []string
	Notes           []string
}

// DirectDeps flattens the direct requirements of every module in the tree.
func (v docView) DirectDeps() []Dependency {
	var out []Dependency
	for _, m := range v.Modules {
		out = append(out, m.Direct...)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Path < out[j].Path })
	return out
}

func buildView(p *Project) docView {
	v := docView{Project: p}

	switch module := primaryModule(p); {
	case module == "":
		v.ModuleSummary = "no go.mod in this tree"
	default:
		parts := []string{module}
		for _, m := range p.Modules {
			if m.GoVersion != "" {
				parts = append(parts, "go "+m.GoVersion)
				break
			}
		}
		parts = append(parts, plural(p.Stats.GoFiles, "Go file", "Go files"))
		v.ModuleSummary = strings.Join(parts, " · ")
	}

	v.EndpointCount = plural(len(p.Routes), "endpoint", "endpoints")
	v.ComponentCount = plural(p.Stats.Components, "component directory", "component directories")
	v.LineSummary = plural(p.Stats.TotalLines, "line", "lines")
	v.HasReadme = p.Readme != ""

	if p.Stats.TestFuncs > 0 {
		v.TestSummary = fmt.Sprintf("%d in %s", p.Stats.TestFuncs,
			plural(p.Stats.TestFiles, "file", "files"))
	} else {
		v.TestSummary = "none detected"
	}

	// Route existing project docs under the audience that most likely owns them,
	// so the generated page points rather than duplicates.
	for _, doc := range p.Docs {
		lower := strings.ToLower(doc.Path)
		switch {
		case containsAny(lower, "operat", "runbook", "deploy", "infra", "install", "troubleshoot"):
			v.OperatorDocs = append(v.OperatorDocs, doc)
		case containsAny(lower, "architect", "develop", "api", "integration", "contract", "coding", "design"):
			v.DeveloperDocs = append(v.DeveloperDocs, doc)
		}
	}

	for _, m := range p.Modules {
		var summary strings.Builder
		summary.WriteString(m.File)
		if m.Path != "" {
			summary.WriteString(" — module " + m.Path)
		}
		if m.GoVersion != "" {
			summary.WriteString(", go " + m.GoVersion)
		}
		fmt.Fprintf(&summary, ", %d direct and %d indirect dependencies", len(m.Direct), m.Indirect)
		v.ModuleSummaries = append(v.ModuleSummaries, summary.String())
	}

	// Anything a reader should know before trusting the generated content.
	if !v.HasReadme {
		v.Notes = append(v.Notes,
			"This project ships no README, so the summary was derived from the tree layout. Add one and re-run the sync.")
	}
	if len(p.Modules) == 0 {
		v.Notes = append(v.Notes, "No go.mod was found, so this tree was analysed as plain source files.")
	}
	if p.Docker == nil {
		v.Notes = append(v.Notes, "No Dockerfile was found at any level.")
	}
	if len(p.Routes) == 0 && len(p.Modules) > 0 {
		v.Notes = append(v.Notes,
			"No HTTP route registrations were detected. If this is a server, the API table is incomplete — check for routes built dynamically.")
	}

	return v
}

func containsAny(haystack string, needles ...string) bool {
	for _, needle := range needles {
		if strings.Contains(haystack, needle) {
			return true
		}
	}
	return false
}

// directoryPurpose guesses what a top-level directory is for. It is a heuristic
// on names only, and it admits ignorance rather than inventing an answer.
func directoryPurpose(name string) string {
	switch strings.ToLower(name) {
	case "internal":
		return "unimportable application internals"
	case "pkg":
		return "public library packages"
	case "cmd", "bin", "main":
		return "binary entry points"
	case "api":
		return "HTTP handlers and routing"
	case "server":
		return "server entry point"
	case "services", "service":
		return "domain services"
	case "web", "ui", "frontend", "client":
		return "frontend assets"
	case "bdd", "e2e", "tests", "test", "features":
		return "tests"
	case "deploy", "deployment", "charts", "helm", "k8s", "kubernetes":
		return "deployment manifests"
	case "docker", "scripts", "script", "hack":
		return "operational tooling"
	case "docs", "documentation":
		return "project documentation"
	case "migrations":
		return "schema migrations"
	case "contracts", "openapi", "proto", "schemas":
		return "shared schemas or contracts"
	case "data":
		return "flat-file data"
	case "dist", "build", "out":
		return "build output"
	case "examples", "example":
		return "worked examples"
	case "auth":
		return "authentication"
	case "config":
		return "configuration loading"
	case "security":
		return "security controls"
	case "store", "storage":
		return "persistence layer"
	case "database":
		return "database access"
	case "models", "model", "schema":
		return "domain models"
	case "middleware":
		return "HTTP middleware"
	case "templates", "views":
		return "render templates"
	case "assets", "static":
		return "static assets"
	case "feedback", "comments":
		return "user feedback"
	default:
		return "unknown — inspect directly"
	}
}