package fejkdata

import (
	"fmt"
	"math"
	"sort"
	"strconv"
	"strings"
	"sync"
)

// table is a category whose rows come from a TSV beside it: the header names the
// columns, each row is one draw, and the format renders the drawn row. A column is a
// cell of the row a render pinned; a cell carrying tokens compiles to a string node.
type table struct {
	category       string
	path           string // the category's path from the data root, which a selector is written at
	file           string
	formatTemplate *template // fields are the column nodes
	header         []string
	col            map[string]int
	fields         map[string]node // column nodes, the format's fields
	pinnedRow      *tableRow
	cells          []string // rows × columns, flat
	cellTemplates  map[int]*template
	keyIndex       int // keyIndex through parentIndex are column indexes, -1 where the option is absent
	nameIndex      int
	weightIndex    int
	parentIndex    int
	cum            []float64 // cumulative weights, nil when uniform
	byKey          map[string]int
	parentT        *table
	children       map[string]*table
	once           sync.Once
	lookup         rowLookup
}

// rowLookup is what selection and linked draws look up, built on the first draw
// that needs it.
type rowLookup struct {
	byName       map[string][]int
	rowsByParent map[string][]int
	childCum     map[string][]float64 // cumulative weights per parent key, nil when uniform
}

func (*table) isNode() {}

// tableColumn is one column of a table, rendered as the cell of the row the render pinned.
type tableColumn struct {
	t *table
	i int
}

func (*tableColumn) isNode() {}

// tableRow is the row of a table the render pinned, rendered by the table's format.
type tableRow struct{ t *table }

func (*tableRow) isNode() {}

func (t *table) rowCount() int { return len(t.cells) / len(t.header) }

func (t *table) cell(row, col int) string { return t.cells[row*len(t.header)+col] }

// cellTemplate is what a cell renders: its compiled template where it carries tokens,
// else nil for its text.
func (t *table) cellTemplate(row, col int) *template { return t.cellTemplates[row*len(t.header)+col] }

// tableOptions are the keys a table object takes; every other key is refused.
var tableOptions = []string{"format", "key", "name", "parent", "rows", "weight"}

func isTableOption(name string) bool {
	for _, o := range tableOptions {
		if o == name {
			return true
		}
	}
	return false
}

// inSelector is what a key or name cell may not contain: the path grammar reserves
// brackets and braces, and a quote or a bar would make the selector no path and no
// token arm.
const inSelector = `[]{}"|`

// compileTable compiles a category object naming a rows file into a table.
func compileTable(m map[string]any, category string, files *categoryFiles) (*table, error) {
	o, err := readTableOptions(m)
	if err != nil {
		return nil, err
	}
	data, err := files.readRows(o.rows)
	if err != nil {
		return nil, err
	}
	t := &table{category: category, file: o.rows, keyIndex: -1, nameIndex: -1, weightIndex: -1, parentIndex: -1}
	if err := t.parseRows(data); err != nil {
		return nil, fmt.Errorf("%s: %w", o.rows, err)
	}
	if err := t.bindOptions(o); err != nil {
		return nil, err
	}
	if err := t.checkCells(); err != nil {
		return nil, fmt.Errorf("%s: %w", o.rows, err)
	}
	if err := t.compileRowFormat(o.format); err != nil {
		return nil, err
	}
	return t, nil
}

type tableOptionValues struct {
	format, keyColumn, nameColumn, parentColumn, rows, weightColumn string
}

func readTableOptions(m map[string]any) (tableOptionValues, error) {
	var o tableOptionValues
	for k := range m {
		if !isTableOption(k) {
			return o, fmt.Errorf("a table takes %s; %q is none of them", strings.Join(tableOptions, ", "), k)
		}
	}
	for k, into := range map[string]*string{"format": &o.format, "key": &o.keyColumn, "name": &o.nameColumn, "parent": &o.parentColumn, "rows": &o.rows, "weight": &o.weightColumn} {
		v, ok := m[k]
		if !ok {
			continue
		}
		s, isString := v.(string)
		if !isString {
			return o, fmt.Errorf("%s must be a string, got %T", k, v)
		}
		if k != "format" && s == "" {
			return o, fmt.Errorf("%s names a column, so it cannot be empty; drop it", k)
		}
		*into = s
	}
	if _, ok := m["format"]; !ok {
		return o, fmt.Errorf("template object missing string \"format\"")
	}
	if !strings.HasSuffix(o.rows, ".tsv") || strings.Contains(o.rows, "/") {
		return o, fmt.Errorf("rows names a .tsv file beside the category, not %q", o.rows)
	}
	if o.keyColumn != "" && o.keyColumn == o.nameColumn {
		return o, fmt.Errorf("name names the key column %q, which a selector already reads; drop it", o.nameColumn)
	}
	return o, nil
}

// parseRows reads the TSV: the header line names the columns, each following line
// is a row of as many cells. Cells are substrings of data, so the file is held once.
func (t *table) parseRows(data string) error {
	data = strings.TrimSuffix(strings.TrimPrefix(data, "\xEF\xBB\xBF"), "\n")
	header, rest, _ := strings.Cut(data, "\n")
	header = strings.TrimSuffix(header, "\r")
	if header == "" {
		return fmt.Errorf("has no header line naming its columns")
	}
	t.header = strings.Split(header, "\t")
	t.col = make(map[string]int, len(t.header))
	t.fields = make(map[string]node, len(t.header))
	for i, name := range t.header {
		if err := checkName(name); err != nil {
			return fmt.Errorf("column %w", err)
		}
		if _, dup := t.col[name]; dup {
			return fmt.Errorf("column %q is named twice", name)
		}
		t.col[name] = i
		t.fields[name] = &tableColumn{t, i}
	}
	if header == data {
		return fmt.Errorf("has no rows below its header; a table is at least two rows")
	}
	m := len(t.header)
	t.cells = make([]string, 0, m*(strings.Count(rest, "\n")+1))
	for line := 2; ; line++ {
		row, more, found := strings.Cut(rest, "\n")
		row = strings.TrimSuffix(row, "\r")
		if err := t.appendRow(row, line); err != nil {
			return err
		}
		if !found {
			break
		}
		rest = more
	}
	if t.rowCount() < 2 {
		return fmt.Errorf("has one row, which is a template; write it as one")
	}
	return nil
}

// appendRow splits one line into as many cells as the header has columns.
func (t *table) appendRow(row string, line int) error {
	if row == "" {
		return fmt.Errorf("line %d is empty; every line below the header is a row", line)
	}
	m := len(t.header)
	for n := 0; n < m; n++ {
		cell, next, tab := strings.Cut(row, "\t")
		if !tab && n < m-1 || tab && n == m-1 {
			return fmt.Errorf("line %d has %s cells than the %d columns", line, map[bool]string{true: "more", false: "fewer"}[tab], m)
		}
		t.cells = append(t.cells, cell)
		row = next
	}
	return nil
}

// bindOptions resolves each option to its column and proves what it claims of the
// cells: a key is unique, a weight a positive number.
func (t *table) bindOptions(o tableOptionValues) error {
	for _, opt := range []struct {
		name, value string
		into        *int
	}{{"key", o.keyColumn, &t.keyIndex}, {"name", o.nameColumn, &t.nameIndex}, {"parent", o.parentColumn, &t.parentIndex}, {"weight", o.weightColumn, &t.weightIndex}} {
		if opt.value == "" {
			continue
		}
		i, ok := t.col[opt.value]
		if !ok {
			return fmt.Errorf("%s names no column %q of %s; the columns are %v", opt.name, opt.value, o.rows, t.header)
		}
		*opt.into = i
	}
	if t.nameIndex >= 0 && t.keyIndex < 0 && t.parentIndex < 0 {
		return fmt.Errorf("name selects a row as a key does, and lists the rows it matches by their keys, so it needs a key column, or a parent inside which each name is one row; add key")
	}
	if err := t.proveKeys(); err != nil {
		return err
	}
	if err := t.proveNamesInsideParent(); err != nil {
		return err
	}
	return t.sumWeights()
}

// proveNamesInsideParent proves a name without a key names one row inside its parent.
func (t *table) proveNamesInsideParent() error {
	if t.keyIndex >= 0 || t.nameIndex < 0 {
		return nil
	}
	inside := make(map[string]int, t.rowCount())
	for r := 0; r < t.rowCount(); r++ {
		k := t.cell(r, t.parentIndex) + "\t" + t.cell(r, t.nameIndex)
		if first, dup := inside[k]; dup {
			return fmt.Errorf("%s line %d: name %q repeats line %d inside %s %q; a name selects one row inside its parent; drop one, or add a key column", t.file, r+2, t.cell(r, t.nameIndex), first+2, t.header[t.parentIndex], t.cell(r, t.parentIndex))
		}
		inside[k] = r
	}
	return nil
}

// proveKeys proves every key names one row, and keeps the map a link is proved by.
func (t *table) proveKeys() error {
	if t.keyIndex < 0 {
		return nil
	}
	t.byKey = make(map[string]int, t.rowCount())
	for r := 0; r < t.rowCount(); r++ {
		k := t.cell(r, t.keyIndex)
		if k == "" {
			return fmt.Errorf("%s line %d: the key is empty", t.file, r+2)
		}
		if first, dup := t.byKey[k]; dup {
			return fmt.Errorf("%s line %d: key %q repeats line %d; a key selects one row", t.file, r+2, k, first+2)
		}
		t.byKey[k] = r
	}
	for r := 0; r < t.rowCount() && t.nameIndex >= 0; r++ {
		if n := t.cell(r, t.nameIndex); t.byKey[n] != r {
			if other, isKey := t.byKey[n]; isKey {
				return fmt.Errorf("%s line %d: name %q is the key of line %d, which a selector reads first, so the name could never select this row", t.file, r+2, n, other+2)
			}
		}
	}
	return nil
}

// sumWeights proves every weight is a positive number and builds the cumulative table.
func (t *table) sumWeights() error {
	if t.weightIndex < 0 {
		return nil
	}
	t.cum = make([]float64, t.rowCount())
	total := 0.0
	for r := range t.cum {
		w, err := strconv.ParseFloat(t.cell(r, t.weightIndex), 64)
		if err != nil || math.IsInf(w, 0) || math.IsNaN(w) || w <= 0 {
			return fmt.Errorf("%s line %d: weight %q is not a positive number", t.file, r+2, t.cell(r, t.weightIndex))
		}
		total += w
		t.cum[r] = total
	}
	if math.IsInf(total, 0) {
		return fmt.Errorf("%s: the weights sum past the largest number", t.file)
	}
	return nil
}

// checkCells compiles every cell carrying a token, and fences what a selector reads.
func (t *table) checkCells() error {
	for i, cell := range t.cells {
		row, col := i/len(t.header), i%len(t.header)
		if (col == t.keyIndex || col == t.nameIndex) && strings.ContainsAny(cell, inSelector) {
			return fmt.Errorf("line %d: %s %q contains %q, which a selector cannot spell", row+2, t.header[col], cell, cell[strings.IndexAny(cell, inSelector):][:1])
		}
		if strings.IndexByte(cell, '{') < 0 && strings.IndexByte(cell, '}') < 0 {
			continue
		}
		n, err := compileString(cell, cellSite{t, row})
		if err != nil {
			return fmt.Errorf("line %d, %s: %w", row+2, t.header[col], err)
		}
		if t.cellTemplates == nil {
			t.cellTemplates = map[int]*template{}
		}
		t.cellTemplates[i] = n
	}
	return nil
}

// compileRowFormat compiles the format a row renders through, over the columns as its
// fields.
func (t *table) compileRowFormat(format string) error {
	toks, err := parseFormat(format)
	if err != nil {
		return err
	}
	for _, tok := range toks {
		if tok.kind != fieldAlternation {
			continue
		}
		for _, name := range tok.names {
			a := splitArm(name, nil)
			if _, ok := t.col[a.key]; !ok && !isRef(a.key) && a.key != "" {
				return fmt.Errorf("format names no column %q of %s; the columns are %v", a.key, t.file, t.header)
			}
		}
	}
	if err := checkTokens(toks, t.fields); err != nil {
		return err
	}
	t.formatTemplate = &template{format: format, tokens: toks, fields: t.fields, repeat: 1, isRecord: true, table: t}
	t.pinnedRow = &tableRow{t}
	return nil
}

// setTablePaths gives every table the path a selector on it is written at, before a
// link or a draw can name one.
func setTablePaths(root map[string]node) {
	var walk func(dir string, children map[string]node)
	walk = func(dir string, children map[string]node) {
		for name, child := range children {
			switch n := child.(type) {
			case *folder:
				walk(join(dir, name), n.children)
			case *table:
				n.path = join(dir, name)
			}
		}
	}
	walk("", root)
}

// linkTables binds every table's parent to the table beside it, and proves the
// links: a parent has a key, every link cell is one, every parent row is linked
// to, no chain of parents closes, and no child is named like a parent's column.
// docs/decisions.md#a-parent-row-with-no-child-row-is-a-load-error
func linkTables(root map[string]node) error {
	var walk func(dir string, children map[string]node) error
	walk = func(dir string, children map[string]node) error {
		for _, name := range sortedNames(children) {
			path := join(dir, name)
			switch n := children[name].(type) {
			case *folder:
				if err := walk(path, n.children); err != nil {
					return err
				}
			case *table:
				if n.parentIndex < 0 {
					continue
				}
				if err := n.linkParent(path, children); err != nil {
					return fmt.Errorf("%s: %w", path, err)
				}
			}
		}
		return nil
	}
	return walk("", root)
}

func (t *table) linkParent(path string, siblings map[string]node) error {
	name := t.header[t.parentIndex]
	p, ok := siblings[name].(*table)
	switch {
	case siblings[name] == nil:
		return fmt.Errorf("parent %q names no table beside it", name)
	case !ok:
		return fmt.Errorf("parent %q is not a table; a link column reads a table's key", name)
	case p.keyIndex < 0:
		return fmt.Errorf("parent %q has no key column to link to", name)
	}
	var ancestors []*table
	for q, seen := p, map[*table]bool{t: true}; q != nil; q, _ = siblings[q.header[q.parentIndex]].(*table) {
		if seen[q] {
			return fmt.Errorf("parent cycle: %s reaches itself through its parents", q.category)
		}
		seen[q] = true
		ancestors = append(ancestors, q)
		if q.parentIndex < 0 {
			break
		}
	}
	for _, q := range ancestors {
		if _, clash := q.col[t.category]; clash {
			return fmt.Errorf("%q is named like a column of %q, its ancestor, so %s.%s could read either; rename one", t.category, q.category, q.category, t.category)
		}
	}
	linked := make(map[string]bool, p.rowCount())
	for r := 0; r < t.rowCount(); r++ {
		k := t.cell(r, t.parentIndex)
		if _, ok := p.byKey[k]; !ok {
			return fmt.Errorf("%s line %d: %s %q is no key of %s", t.file, r+2, name, k, p.file)
		}
		linked[k] = true
	}
	for r := 0; r < p.rowCount(); r++ {
		if k := p.cell(r, p.keyIndex); !linked[k] {
			return fmt.Errorf("%s links no row to %s %q; every %s row needs one, or drop line %d of %s", t.file, name, k, name, r+2, p.file)
		}
	}
	t.parentT = p
	if p.children == nil {
		p.children = map[string]*table{}
	}
	p.children[t.category] = t
	return nil
}

func (t *table) builtLookup() *rowLookup {
	t.once.Do(func() {
		if t.nameIndex >= 0 {
			t.lookup.byName = make(map[string][]int, t.rowCount())
			for r := 0; r < t.rowCount(); r++ {
				n := t.cell(r, t.nameIndex)
				t.lookup.byName[n] = append(t.lookup.byName[n], r)
			}
		}
		if t.parentIndex >= 0 {
			t.lookup.rowsByParent = map[string][]int{}
			for r := 0; r < t.rowCount(); r++ {
				k := t.cell(r, t.parentIndex)
				t.lookup.rowsByParent[k] = append(t.lookup.rowsByParent[k], r)
			}
			if t.cum != nil {
				t.lookup.childCum = make(map[string][]float64, len(t.lookup.rowsByParent))
				for k, rows := range t.lookup.rowsByParent {
					cum, total := make([]float64, len(rows)), 0.0
					for i, r := range rows {
						w, _ := strconv.ParseFloat(t.cell(r, t.weightIndex), 64) // sumWeights proved it
						total += w
						cum[i] = total
					}
					t.lookup.childCum[k] = cum
				}
			}
		}
	})
	return &t.lookup
}

// drawRow picks a row over the whole table. The session is concrete rather than the rng
// interface so that the walk that draws through it keeps its hold set off the heap.
func (t *table) drawRow(s *session) int {
	if t.cum == nil {
		return s.IntN(t.rowCount())
	}
	return pickCum(s, t.cum)
}

func pickCum(s *session, cum []float64) int {
	x := s.Float64() * cum[len(cum)-1]
	return min(sort.Search(len(cum), func(i int) bool { return cum[i] > x }), len(cum)-1) // x can round up to the total
}

// drawUnder picks a row among those linked to parent row pr.
func (t *table) drawUnder(s *session, pr int) int {
	lookup := t.builtLookup()
	k := t.parentT.cell(pr, t.parentT.keyIndex)
	rows := lookup.rowsByParent[k]
	if lookup.childCum == nil {
		return rows[s.IntN(len(rows))]
	}
	return rows[pickCum(s, lookup.childCum[k])]
}

// drawIn is the render's row of t: the one pinned in p, else one drawn inside the nearest
// pinned ancestor — its parent drawn inside that first where the ancestor is further up — or
// over the whole table, and pinned with its ancestors.
func (t *table) drawIn(s *session, p *pinSet) int {
	if r, ok := p.pinned(t); ok {
		return r
	}
	r := -1
	for a := t.parentT; a != nil && r < 0; a = a.parentT {
		if _, ok := p.pinned(a); !ok {
			continue
		}
		if t.parentT != a {
			t.parentT.drawIn(s, p)
		}
		pr, _ := p.pinned(t.parentT)
		r = t.drawUnder(s, pr)
	}
	if r < 0 {
		r = t.drawRow(s)
	}
	p.pin(t, r)
	return r
}

// descendant is the table named name among those linked to t, at any depth.
func (t *table) descendant(name string) *table {
	if c, ok := t.children[name]; ok {
		return c
	}
	for _, c := range t.children {
		if d := c.descendant(name); d != nil {
			return d
		}
	}
	return nil
}

// parentRow is the row of t's parent that row r links to.
func (t *table) parentRow(r int) int { return t.parentT.byKey[t.cell(r, t.parentIndex)] }

// under reports whether row r of t sits inside row pr of ancestor a.
func (t *table) under(r int, a *table, pr int) bool {
	for c, row := t, r; c.parentT != nil; c, row = c.parentT, c.parentRow(row) {
		if c.parentT == a {
			return c.parentRow(row) == pr
		}
	}
	return false
}

// find is the row a selector names: by key first, then by name, where a name
// naming several rows resolves inside the ancestors pinned.
func (t *table) find(sel string, pins *pinSet) (int, error) {
	if t.keyIndex < 0 && t.nameIndex < 0 {
		return 0, fmt.Errorf("%s has no key or name column to select a row by", t.path)
	}
	if r, ok := t.byKey[sel]; ok {
		return r, nil
	}
	rows := t.builtLookup().byName[sel]
	if len(rows) > 1 {
		rows = pins.inside(t, rows)
	}
	switch len(rows) {
	case 1:
		return rows[0], nil
	case 0:
		return 0, fmt.Errorf("no row of %s has key or name %q", t.path, sel)
	}
	return 0, t.ambiguous(sel, rows)
}

// ambiguous names each row a selector could have meant: a keyed table by its keys,
// and one told apart only by its parent by the path that selects it.
func (t *table) ambiguous(sel string, rows []int) error {
	spellings := make([]string, len(rows))
	for i, r := range rows {
		if t.keyIndex < 0 {
			spellings[i] = t.selectorSpelling(r)
		} else {
			spellings[i] = t.cell(r, t.keyIndex)
		}
	}
	listed := strings.Join(spellings, ", ")
	if t.keyIndex < 0 {
		return fmt.Errorf("%q names %d rows of %s; select it inside its %s, one of %s", sel, len(rows), t.path, t.parentT.path, listed)
	}
	inside := ""
	if t.parentT != nil {
		inside = fmt.Sprintf(", or select it inside its %s", t.parentT.path)
	}
	return fmt.Errorf("%q names %d rows of %s; select one by key, one of %s%s", sel, len(rows), t.path, listed, inside)
}

// selectorSpelling is how a path writes a selected row, for messages: by key, or
// by name inside its parent's row.
func (t *table) selectorSpelling(r int) string {
	switch {
	case t.keyIndex >= 0:
		return t.path + "[" + t.cell(r, t.keyIndex) + "]"
	case t.nameIndex >= 0:
		return t.parentT.selectorSpelling(t.parentRow(r)) + "." + t.category + "[" + t.cell(r, t.nameIndex) + "]"
	}
	return fmt.Sprintf("%s line %d", t.file, r+2)
}

// familyRoot is the table a chain of parents ends at.
func (t *table) familyRoot() *table {
	for t.parentT != nil {
		t = t.parentT
	}
	return t
}