package manifest

import (
	"fmt"
	"os"
	"path/filepath"
	"slices"
	"sort"
	"strings"

	"github.com/BurntSushi/toml"
)

// ProjectName is the name of the manifest of a consuming repository. Which of
// the two manifests lies next to you tells you where you are, so the project
// one is never named like the suite one.
const ProjectName = ".conventions.toml"

// Component is one addressee of assembly inside a project: a region where every
// selected layer holds at once — one language, one set of tools, one kind of
// application (META-36).
//
// Lang and Stack are lists because a component may well take two stack layers
// at a time — sqlite and postgres in the schema topic hold together, being
// different tables of one service. Two languages never do: a line of code is
// written in one of them, which is what a component exists to separate.
type Component struct {
	Dir    string   `toml:"dir"`
	Lang   []string `toml:"lang,omitempty"`
	Stack  []string `toml:"stack,omitempty"`
	Topics []string `toml:"topics"`
}

// Project is a parsed .conventions.toml: where the copies are taken from and
// which components take what.
type Project struct {
	// Source is the reference to the suite. How the tool reaches it — a path
	// on disk, a git repository — is a matter of the reference itself.
	Source     string               `toml:"source"`
	Components map[string]Component `toml:"components"`

	// Path is where the manifest was read from.
	Path string `toml:"-"`
	// Root is the directory the manifest lies in; every path in it is relative
	// to that directory.
	Root string `toml:"-"`
	// Undecoded lists keys the tool does not know: a typo in a component name
	// or in a key would otherwise cost a whole subscription in silence.
	Undecoded []string `toml:"-"`
}

// LoadProject reads the project manifest from directory root.
func LoadProject(root string) (*Project, error) {
	path := filepath.Join(root, ProjectName)
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("reading the project manifest: %w", err)
	}

	var p Project
	meta, err := toml.Decode(string(data), &p)
	if err != nil {
		return nil, fmt.Errorf("parsing %s: %w", path, err)
	}
	p.Path = path
	p.Root = root
	for _, key := range meta.Undecoded() {
		p.Undecoded = append(p.Undecoded, key.String())
	}
	sort.Strings(p.Undecoded)
	return &p, nil
}

// Save writes the project manifest back to where it was read from.
func (p *Project) Save() error {
	return save(p.Path, p, p.Undecoded)
}

// Subscribe adds a topic to a component, keeping the list sorted so that the
// file does not churn on the order things were added in.
func (p *Project) Subscribe(name, topic string) {
	c := p.Components[name]
	c.Topics = append(c.Topics, topic)
	sort.Strings(c.Topics)
	p.Components[name] = c
}

// Unsubscribe drops a topic from a component. Nothing is kept behind: a
// subscription is a choice of the project, not a name anyone else may reuse.
func (p *Project) Unsubscribe(name, topic string) {
	c := p.Components[name]
	c.Topics = slices.DeleteFunc(c.Topics, func(t string) bool { return t == topic })
	p.Components[name] = c
}

// FindProject walks up from start looking for a project manifest, so that a
// command works from any subdirectory of a repository.
func FindProject(start string) (string, error) {
	return findUp(start, ProjectName)
}

// Names lists the components in an order stable between runs.
func (p *Project) Names() []string {
	names := make([]string, 0, len(p.Components))
	for name := range p.Components {
		names = append(names, name)
	}
	sort.Strings(names)
	return names
}

// Only picks the component a command works on. With a name given it is that
// one; without a name it is the single component of the project. A project of
// several components does not get one guessed for it — it gets the list.
func (p *Project) Only(name string) (string, Component, error) {
	if name != "" {
		c, ok := p.Components[name]
		if !ok {
			return "", Component{}, fmt.Errorf("the project declares no component %q; it declares: %s", name, joinNames(p.Names()))
		}
		return name, c, nil
	}
	switch len(p.Components) {
	case 0:
		return "", Component{}, fmt.Errorf("%s declares no component, and a copy is assembled for a component", p.Path)
	case 1:
		only := p.Names()[0]
		return only, p.Components[only], nil
	}
	return "", Component{}, fmt.Errorf("the project holds several components, and the command names none: pass --for with one of %s", joinNames(p.Names()))
}

// Subscribed reports whether a component takes a topic.
func (c Component) Subscribed(topic string) bool {
	return slices.Contains(c.Topics, topic)
}

func joinNames(names []string) string {
	return strings.Join(names, ", ")
}