// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

package lsp

import (
	"cmp"
	"io/fs"
	"net/url"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"time"

	"sourcedock.dev/petrbalvin/gasm-devkit/ast"
	"sourcedock.dev/petrbalvin/gasm-devkit/parser"
)

// workspaceIndex indexes the .s files under the workspace roots that the
// client has not opened.  Every workspace-scoped answer (definition,
// references, workspace symbols) reads it after the open documents, so a
// symbol resolves to and collects references from files the editor has never
// shown.  An open buffer always shadows its disk copy: the entry stays in the
// index but is skipped at query time, because the buffer may hold unsaved
// edits the disk has never seen.
//
// Freshness does not rest on the client's watched-file events alone: every
// query re-stats the indexed files and re-reads the ones whose stat identity
// changed.  Watched-file events remain necessary for files created after the
// build, which a stat of the known set cannot discover.  The index builds on
// first use, since the roots arrive with initialize.  The server serves one
// message at a time, so the index needs no lock.
type workspaceIndex struct {
	roots []string
	built bool
	files map[string]*workspaceFile // keyed by absolute path
}

// workspaceFile is one indexed on-disk file: its content, the parsed tree and
// the stat identity the freshness check compares.
type workspaceFile struct {
	text    string
	modTime time.Time
	size    int64
	file    *ast.File
}

// ensure builds the index on first use and refreshes it on every query
// afterwards: a stat per file, a re-read only for the ones that changed.
func (w *workspaceIndex) ensure() {
	if !w.built {
		w.built = true
		w.files = make(map[string]*workspaceFile)
		for _, root := range w.roots {
			w.walk(root)
		}
		return
	}
	for path := range w.files {
		w.load(path)
	}
}

// walk adds every .s file below root, skipping the directories the go tool
// itself ignores (hidden and underscore-prefixed names, testdata): the index
// covers the buildable surface, not the whole tree.
func (w *workspaceIndex) walk(root string) {
	filepath.WalkDir(root, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return nil // an unreadable entry never breaks the scan
		}
		if d.IsDir() {
			if path != root && skipDir(d.Name()) {
				return fs.SkipDir
			}
			return nil
		}
		if strings.HasSuffix(path, ".s") {
			w.load(path)
		}
		return nil
	})
}

// skipDir reports whether a directory is outside the buildable surface.
func skipDir(name string) bool {
	return name == "testdata" || strings.HasPrefix(name, ".") || strings.HasPrefix(name, "_")
}

// load reads one path into the index, or evicts it when it has disappeared.
// A file whose stat identity still matches is left untouched.
func (w *workspaceIndex) load(path string) {
	st, err := os.Stat(path)
	if err != nil || st.IsDir() {
		delete(w.files, path)
		return
	}
	if ef, ok := w.files[path]; ok && ef.size == st.Size() && ef.modTime.Equal(st.ModTime()) {
		return
	}
	text, err := os.ReadFile(path)
	if err != nil {
		delete(w.files, path)
		return
	}
	// Parsing is tolerant: a file with syntax errors still contributes its
	// usable declarations, exactly as an open buffer mid-edit does.
	body := string(text)
	f, _ := parser.Parse(path, body)
	w.files[path] = &workspaceFile{text: body, modTime: st.ModTime(), size: st.Size(), file: f}
}

// watched applies one client watched-file event: the named file is re-read
// (created or changed) or evicted (deleted).  Events for anything but .s
// files are ignored, and an event arriving before the first build no-ops:
// the build then reads the disk state that already includes it.
func (w *workspaceIndex) watched(path string, deleted bool) {
	if !w.built || !strings.HasSuffix(path, ".s") {
		return
	}
	if deleted {
		delete(w.files, path)
		return
	}
	w.load(path)
}

// scanUnit is one parseable source the workspace answers draw from: an open
// buffer or an indexed disk file.
type scanUnit struct {
	uri  string
	text string
	file *ast.File
}

// scanUnits returns every source the workspace answers cover, in URI order
// for deterministic results: the open documents, then the indexed disk files
// that no open buffer shadows.
func (s *Server) scanUnits() []scanUnit {
	open := make(map[string]bool, len(s.docs))
	for uri := range s.docs {
		open[uriPath(uri)] = true
	}
	units := make([]scanUnit, 0, len(s.docs))
	for _, of := range s.openASTs() {
		units = append(units, scanUnit{uri: of.uri, text: s.docs[of.uri], file: of.file})
	}
	s.ws.ensure()
	for path, ef := range s.ws.files {
		if ef.file == nil || open[path] {
			continue
		}
		units = append(units, scanUnit{uri: fileToURI(path), text: ef.text, file: ef.file})
	}
	slices.SortFunc(units, func(a, b scanUnit) int { return cmp.Compare(a.uri, b.uri) })
	return units
}

// fileToURI renders an absolute path as a file URI, percent-encoding the
// characters the URI rules reserve.
func fileToURI(path string) string {
	return (&url.URL{Scheme: "file", Path: path}).String()
}