package suite

import (
	"slices"

	"git.vakhrushev.me/av/convy/internal/doc"
)

// Component is what a copy is assembled for: one language, one set of tools,
// one kind of application. Both axes may stay empty — a flat suite has no axes
// at all, and a component of it selects the base layer and nothing else.
//
// Each axis is a list because a component may take two stack layers at once:
// sqlite and postgres in the schema topic hold together, being different tables
// of one service. Two languages never hold together, and that the axis allows
// the list anyway is a matter of one shape for both rather than a licence.
type Component struct {
	Lang  []string
	Stack []string
}

// Assemble picks the layers of a topic a component takes, in the order they go
// into a copy: base, then language, then stack.
//
// A layer is chosen by the axis keys of its front matter rather than by where
// its file lies (META-38). A layer with no keys is the base one and travels
// always; a key the layer does not declare puts no demand on the component, so
// a language layer with no stack key fits any stack.
//
// This is the read-only half of assembly. The project commands write files out
// of the same selection, so the two must never come to differ — which is why
// the selection lives here rather than inside whichever command needs it.
func (s *Suite) Assemble(topic string, c Component) (taken, left []*doc.Document) {
	for _, d := range s.Layers(topic) {
		if fits(d, c) {
			taken = append(taken, d)
			continue
		}
		left = append(left, d)
	}
	return taken, left
}

// fits reports whether a component takes a layer.
func fits(d *doc.Document, c Component) bool {
	if d.Front.Lang != "" && !slices.Contains(c.Lang, d.Front.Lang) {
		return false
	}
	if d.Front.Stack != "" && !slices.Contains(c.Stack, d.Front.Stack) {
		return false
	}
	return true
}

// rank orders the layers of a topic the way a copy carries them. A layer on
// both axes comes last: it narrows the most.
func rank(d *doc.Document) int {
	switch {
	case d.Front.Lang == "" && d.Front.Stack == "":
		return 0
	case d.Front.Stack == "":
		return 1
	case d.Front.Lang == "":
		return 2
	}
	return 3
}

// Axis describes a layer in one word, for a report.
func Axis(d *doc.Document) string {
	switch {
	case d.Front.Lang != "" && d.Front.Stack != "":
		return "lang=" + d.Front.Lang + " stack=" + d.Front.Stack
	case d.Front.Lang != "":
		return "lang=" + d.Front.Lang
	case d.Front.Stack != "":
		return "stack=" + d.Front.Stack
	}
	return "base"
}