// SPDX-License-Identifier: GPL-3.0-or-later

package cond

import (
	"errors"
	"fmt"
	"regexp"
	"regexp/syntax"
	"sort"
	"strings"

	"krino/internal/config"
	"krino/internal/norm"
	"krino/internal/sexp"
)

// maxDepth is the deepest a condition may nest; the top-level conditions
// are depth 1.
const maxDepth = 64

// Compile compiles a rule's (when ...) conditions, applying cost-based
// reordering. If it returns any diagnostic, the returned *Cond is nil: a
// caller that ignores errs and calls Eval/Explain on the result panics
// loudly, instead of silently treating a broken rule as "no conditions"
// (always true).
func Compile(file string, when []*sexp.Node, opt Options) (*Cond, []*config.Diag) {
	c, errs := compile(file, when, opt, true)
	if len(errs) > 0 {
		return nil, errs
	}
	return c, errs
}

// compile is Compile with cost reordering switchable, for the property
// test.
func compile(file string, when []*sexp.Node, opt Options, reorder bool) (*Cond, []*config.Diag) {
	c := &compiler{file: file, opt: opt, reorder: reorder, cond: &Cond{opt: opt}}
	var roots []*node
	for _, n := range when {
		if nd := c.compileNode(n, 1); nd != nil {
			roots = append(roots, nd)
		}
	}
	switch len(roots) {
	case 0:
		// no conditions: root stays nil, always true
	case 1:
		c.cond.root = roots[0]
	default:
		// several top-level conditions are an implicit and
		c.cond.root = c.combine(kAnd, "and", roots, when[0].Pos)
	}
	return c.cond, c.errs
}

// compiler holds the state of one Compile call.
type compiler struct {
	file    string
	opt     Options
	reorder bool
	cond    *Cond
	errs    []*config.Diag
}

// errorf records a diagnostic at n's position; a nil n means the file as a
// whole (unused here, kept for symmetry with config.diags).
func (c *compiler) errorf(n *sexp.Node, format string, args ...any) {
	var pos sexp.Pos
	if n != nil {
		pos = n.Pos
	}
	c.errs = append(c.errs, &config.Diag{File: c.file, Pos: pos, Msg: fmt.Sprintf(format, args...)})
}

// compileNode compiles one condition node at the given nesting depth (the
// top-level conditions are depth 1). It returns nil, having recorded at
// least one diagnostic, when n does not compile.
func (c *compiler) compileNode(n *sexp.Node, depth int) *node {
	if depth > maxDepth {
		c.errorf(n, "conditions nest deeper than %d levels", maxDepth)
		return nil
	}
	if n.Kind != sexp.List || n.Head() == "" {
		c.errorf(n, "a condition is a form like (type pdf), not %s", n.String())
		return nil
	}
	switch head := n.Head(); head {
	case "and":
		return c.compileCombiner(n, depth, kAnd, "and", "and needs at least one condition")
	case "or":
		return c.compileCombiner(n, depth, kOr, "or", "or needs at least one condition")
	case "not":
		return c.compileNot(n, depth)
	case "type":
		return c.compileType(n)
	case "name":
		return c.compileRegex(n, kName, "name")
	case "path":
		return c.compileRegex(n, kPath, "path")
	case "content":
		return c.compileContent(n)
	case "size":
		return c.compileSize(n)
	case "age":
		return c.compileAge(n)
	case "duplicate":
		return c.compileDuplicate(n)
	case "matched":
		return c.compileMatched(n)
	default:
		c.errorf(n, "unknown test (%s ...); tests are type, name, path, content, size, age, duplicate, matched, and, or, not", head)
		return nil
	}
}

// compileCombiner compiles (and ...) / (or ...): one or more child
// conditions, cost-summed and cost-sorted (via combine).
func (c *compiler) compileCombiner(n *sexp.Node, depth int, k kind, label, emptyMsg string) *node {
	args := n.Args()
	if len(args) == 0 {
		c.errorf(n, "%s", emptyMsg)
		return nil
	}
	children := make([]*node, 0, len(args))
	for _, a := range args {
		if ch := c.compileNode(a, depth+1); ch != nil {
			children = append(children, ch)
		}
	}
	return c.combine(k, label, children, n.Pos)
}

// combine builds an and/or node from already-compiled children: stable
// cost-sort when reordering, cost is the sum of the children's.
func (c *compiler) combine(k kind, label string, children []*node, pos sexp.Pos) *node {
	if len(children) == 0 {
		return nil
	}
	if c.reorder {
		sort.SliceStable(children, func(i, j int) bool { return children[i].cost < children[j].cost })
	}
	cost := 0
	for _, ch := range children {
		cost += ch.cost
	}
	return &node{kind: k, pos: pos, label: label, children: children, cost: cost}
}

// compileNot compiles (not C): exactly one child condition.
func (c *compiler) compileNot(n *sexp.Node, depth int) *node {
	args := n.Args()
	if len(args) != 1 {
		c.errorf(n, "not takes exactly one condition")
		return nil
	}
	child := c.compileNode(args[0], depth+1)
	if child == nil {
		return nil
	}
	return &node{kind: kNot, pos: n.Pos, label: "not", children: []*node{child}, cost: child.cost}
}

// compileType compiles (type T...): symbols, lower-cased; a group name
// expands to its extensions, anything else is a literal (possibly
// multi-part) extension.
func (c *compiler) compileType(n *sexp.Node) *node {
	args := n.Args()
	if len(args) == 0 {
		c.errorf(n, "type needs at least one extension or group, like (type pdf)")
		return nil
	}
	var suffixes []string
	bad := false
	for _, a := range args {
		if a.Kind != sexp.Symbol {
			c.errorf(a, "type names are bare words: write (type pdf)")
			bad = true
			continue
		}
		lower := strings.ToLower(a.Text)
		if exts, ok := groups[lower]; ok {
			for _, e := range exts {
				suffixes = append(suffixes, "."+e)
			}
		} else {
			suffixes = append(suffixes, "."+lower)
		}
	}
	if bad {
		return nil
	}
	return &node{kind: kType, pos: n.Pos, label: argsLabel("type", args), cost: costCheap, suffixes: suffixes}
}

// compileRegex compiles (name "RE"...) / (path "RE"...).
func (c *compiler) compileRegex(n *sexp.Node, k kind, test string) *node {
	args := n.Args()
	if len(args) == 0 {
		c.errorf(n, "%s needs at least one regex in quotes", test)
		return nil
	}
	var patterns []pattern
	bad := false
	for _, a := range args {
		if a.Kind != sexp.String {
			c.quotedExampleErr(a, test, "regexes")
			bad = true
			continue
		}
		src := a.Text
		pat := src
		if c.opt.Fold {
			// E5: folding is applied to the regex source itself, not just
			// to the text it is matched against - so a fold that expands
			// one character into several changes the pattern's structure,
			// not just its literal characters: "ß+" (one letter, a
			// quantifier on it) becomes "ss+" (a quantifier on only the
			// second "s") once norm.Fold expands "ß" to "ss", and likewise
			// "æ" to "ae". A rule relying on repetition or anchoring
			// around such a letter needs to account for this.
			pat = norm.Fold(pat)
		}
		if c.opt.IgnoreCase {
			pat = "(?i)" + pat
		}
		re, err := regexp.Compile(pat)
		if err != nil {
			var se *syntax.Error
			if errors.As(err, &se) {
				c.errorf(a, "%s: bad regex %q: %s", test, src, se.Code)
			} else {
				c.errorf(a, "%s: bad regex %q: %s", test, src, err)
			}
			bad = true
			continue
		}
		patterns = append(patterns, pattern{re: re, src: src})
	}
	if bad {
		return nil
	}
	return &node{kind: k, pos: n.Pos, label: argsLabel(test, args), cost: costRegex, patterns: patterns}
}

// compileContent compiles (content "KW"...): each keyword is normalised;
// an empty result is an error.
func (c *compiler) compileContent(n *sexp.Node) *node {
	args := n.Args()
	if len(args) == 0 {
		c.errorf(n, "content needs at least one keyword in quotes")
		return nil
	}
	var keywords []keyword
	bad := false
	for _, a := range args {
		if a.Kind != sexp.String {
			c.quotedExampleErr(a, "content", "keywords")
			bad = true
			continue
		}
		normed := norm.Text(a.Text, c.opt.IgnoreCase, c.opt.Fold)
		if normed == "" {
			c.errorf(a, "content keyword is empty")
			bad = true
			continue
		}
		keywords = append(keywords, keyword{norm: normed, src: a.Text})
		c.cond.Keywords = append(c.cond.Keywords, Keyword{Opt: c.opt, Norm: normed})
	}
	if bad {
		return nil
	}
	c.cond.UsesContent = true
	return &node{kind: kContent, pos: n.Pos, label: argsLabel("content", args), cost: costContent, keywords: keywords}
}

// compileSize compiles (size OP SIZE).
func (c *compiler) compileSize(n *sexp.Node) *node {
	args := n.Args()
	if len(args) != 2 || args[0].Kind != sexp.Symbol || args[1].Kind != sexp.Symbol {
		c.errorf(n, "size takes an operator and a size, like (size > 10M)")
		return nil
	}
	op := args[0].Text
	bad := false
	if !validOp(op) {
		c.errorf(args[0], "size operator is one of > >= < <= =, not %s", op)
		bad = true
	}
	val, err := config.ParseSize(args[1].Text)
	if err != nil {
		c.errorf(args[1], "size: %s", err)
		bad = true
	}
	if bad {
		return nil
	}
	return &node{kind: kSize, pos: n.Pos, label: argsLabel("size", args), cost: costCheap, op: op, sizeVal: val}
}

// compileAge compiles (age OP DURATION).
func (c *compiler) compileAge(n *sexp.Node) *node {
	args := n.Args()
	if len(args) != 2 || args[0].Kind != sexp.Symbol || args[1].Kind != sexp.Symbol {
		c.errorf(n, "age takes an operator and a duration, like (age > 30d)")
		return nil
	}
	op := args[0].Text
	bad := false
	if !validOp(op) {
		c.errorf(args[0], "age operator is one of > >= < <= =, not %s", op)
		bad = true
	}
	val, err := config.ParseDuration(args[1].Text)
	if err != nil {
		c.errorf(args[1], "age: %s", err)
		bad = true
	}
	if bad {
		return nil
	}
	return &node{kind: kAge, pos: n.Pos, label: argsLabel("age", args), cost: costCheap, op: op, ageVal: val}
}

// validOp reports whether op is one of the size/age comparison operators.
func validOp(op string) bool {
	switch op {
	case ">", ">=", "<", "<=", "=":
		return true
	}
	return false
}

// compileDuplicate compiles (duplicate "DIR"...): zero or more directories,
// stored raw for the engine to resolve. Every compiled test's list is
// appended to Cond.DupDirs, in order.
func (c *compiler) compileDuplicate(n *sexp.Node) *node {
	args := n.Args()
	dirs := make([]string, 0, len(args))
	bad := false
	for _, a := range args {
		if a.Kind != sexp.String {
			c.quotedExampleErr(a, "duplicate", "directories")
			bad = true
			continue
		}
		dirs = append(dirs, a.Text)
	}
	if bad {
		return nil
	}
	c.cond.DupDirs = append(c.cond.DupDirs, dirs)
	return &node{kind: kDuplicate, pos: n.Pos, label: argsLabel("duplicate", args), cost: costDuplicate, dirs: dirs}
}

// compileMatched compiles (matched): no arguments.
func (c *compiler) compileMatched(n *sexp.Node) *node {
	if len(n.Args()) != 0 {
		c.errorf(n, "matched takes nothing: write (matched)")
		return nil
	}
	return &node{kind: kMatched, pos: n.Pos, label: "matched", cost: costCheap}
}

// collectNameGroups walks n and its children — and and or included, not
// excluded — appending the capture-group count of every pattern of every
// kName node reachable without crossing a not, in compile order. B1: a
// name test under a not never supplies Result.Captures (eval.go's negated
// tracking takes captures only when !negated), so it must not count toward
// checkCaptures' "does some name test in this rule have enough groups"
// either - a rule combining a capturing name test with an unrelated
// (not (name ...)) must still pass.
func collectNameGroups(n *node, out *[]int) {
	if n == nil || n.kind == kNot {
		return
	}
	if n.kind == kName {
		for _, p := range n.patterns {
			*out = append(*out, p.re.NumSubexp())
		}
	}
	for _, ch := range n.children {
		collectNameGroups(ch, out)
	}
}

// quotedExampleErr records the shared "takes X in quotes: write (test
// "arg")" diagnostic used by name, path, content and duplicate.
func (c *compiler) quotedExampleErr(a *sexp.Node, test, noun string) {
	c.errorf(a, "%s takes %s in quotes: write (%s %s)", test, noun, test, sexp.Quote(a.Text))
}

// argsLabel renders a leaf test as written: the head followed by each
// argument, bare symbols verbatim, strings as their decoded text in double
// quotes without escaping.
func argsLabel(head string, args []*sexp.Node) string {
	var b strings.Builder
	b.WriteString(head)
	for _, a := range args {
		b.WriteByte(' ')
		if a.Kind == sexp.String {
			b.WriteByte('"')
			b.WriteString(a.Text)
			b.WriteByte('"')
		} else {
			b.WriteString(a.Text)
		}
	}
	return b.String()
}