// Copyright (c) 2026 Charles KWON OhJun (charleskwonohjun@gmail.com)
// All rights reserved.

// analyzer.go — Semantic analysis pass for Five AST.
//
// Runs AFTER parsing, BEFORE code generation.
// Checks:
//   1. Variable declaration: all LOCAL vars declared before use
//   2. Scope analysis: LOCAL vs PRIVATE vs PUBLIC vs FIELD
//   3. Undeclared variable warnings
//   4. Unused variable warnings
//   5. Function signature validation
//   6. Type hints (when available)

package analyzer

import (
	"five/compiler/ast"
	"five/compiler/token"
	"fmt"
	"strings"
)

// Diagnostic represents an analysis warning or error.
type Diagnostic struct {
	Pos      token.Position
	Message  string
	Severity Severity
}

type Severity int

const (
	SevError   Severity = iota // Must fix
	SevWarning                 // Should fix
	SevHint                    // Optional improvement
)

func (d Diagnostic) String() string {
	prefix := "HINT"
	switch d.Severity {
	case SevError:
		prefix = "ERROR"
	case SevWarning:
		prefix = "WARN"
	}
	return fmt.Sprintf("%s:%d:%d: %s: %s", d.Pos.File, d.Pos.Line, d.Pos.Col, prefix, d.Message)
}

// Scope tracks declared variables in a function.
type Scope struct {
	Name     string            // function name
	Declared map[string]VarInfo // upper(name) → info
	Used     map[string]bool   // upper(name) → was used
	Parent   *Scope            // outer scope (for blocks)
}

// VarInfo holds info about a declared variable.
type VarInfo struct {
	Name    string
	Pos     token.Position
	Kind    ast.VarScope // LOCAL, STATIC, FIELD, etc.
	IsParam bool
}

// Analyzer performs semantic analysis on a parsed AST file.
type Analyzer struct {
	file        *ast.File
	diagnostics []Diagnostic
	scope       *Scope
	funcNames   map[string]bool // declared function names
}

// Analyze runs semantic analysis and returns diagnostics.
func Analyze(file *ast.File) []Diagnostic {
	a := &Analyzer{
		file:      file,
		funcNames: make(map[string]bool),
	}

	// Phase 1: Collect all function names
	for _, d := range file.Decls {
		switch decl := d.(type) {
		case *ast.FuncDecl:
			a.funcNames[strings.ToUpper(decl.Name)] = true
		case *ast.ClassDecl:
			a.funcNames[strings.ToUpper(decl.Name)] = true
		}
	}

	// Phase 2: Analyze each function
	for _, d := range file.Decls {
		switch decl := d.(type) {
		case *ast.FuncDecl:
			a.analyzeFunc(decl)
		}
	}

	return a.diagnostics
}

func (a *Analyzer) analyzeFunc(fn *ast.FuncDecl) {
	a.scope = &Scope{
		Name:     fn.Name,
		Declared: make(map[string]VarInfo),
		Used:     make(map[string]bool),
	}

	// Register parameters as declared
	for _, p := range fn.Params {
		a.scope.Declared[strings.ToUpper(p.Name)] = VarInfo{
			Name:    p.Name,
			Pos:     p.NamePos,
			IsParam: true,
		}
	}

	// Register LOCAL/STATIC declarations
	for _, d := range fn.Decls {
		if vd, ok := d.(*ast.VarDecl); ok {
			for _, v := range vd.Vars {
				a.scope.Declared[strings.ToUpper(v.Name)] = VarInfo{
					Name: v.Name,
					Pos:  v.NamePos,
					Kind: vd.Scope,
				}
			}
		}
	}

	// Analyze body statements
	for _, stmt := range fn.Body {
		a.analyzeStmt(stmt)
	}

	// Check for unused variables
	for name, info := range a.scope.Declared {
		if !a.scope.Used[name] && !info.IsParam {
			// Skip common patterns: loop vars, error vars
			lower := strings.ToLower(info.Name)
			if lower == "i" || lower == "j" || lower == "k" || lower == "n" ||
				lower == "err" || lower == "_" {
				continue
			}
			a.hint(info.Pos, "unused variable '%s'", info.Name)
		}
	}
}

func (a *Analyzer) analyzeStmt(stmt ast.Stmt) {
	if stmt == nil {
		return
	}
	switch s := stmt.(type) {
	case *ast.ExprStmt:
		a.analyzeExpr(s.X)
	case *ast.ReturnStmt:
		if s.Value != nil {
			a.analyzeExpr(s.Value)
		}
		for _, v := range s.Values {
			a.analyzeExpr(v)
		}
	case *ast.IfStmt:
		a.analyzeExpr(s.Cond)
		for _, st := range s.Body {
			a.analyzeStmt(st)
		}
		for _, ei := range s.ElseIfs {
			a.analyzeExpr(ei.Cond)
			for _, st := range ei.Body {
				a.analyzeStmt(st)
			}
		}
		for _, st := range s.ElseBody {
			a.analyzeStmt(st)
		}
	case *ast.DoWhileStmt:
		a.analyzeExpr(s.Cond)
		for _, st := range s.Body {
			a.analyzeStmt(st)
		}
	case *ast.ForStmt:
		a.markUsed(s.Var)
		a.analyzeExpr(s.Start)
		a.analyzeExpr(s.To)
		if s.Step != nil {
			a.analyzeExpr(s.Step)
		}
		for _, st := range s.Body {
			a.analyzeStmt(st)
		}
	case *ast.ForEachStmt:
		a.markUsed(s.Var)
		a.analyzeExpr(s.Collection)
		for _, st := range s.Body {
			a.analyzeStmt(st)
		}
	case *ast.SwitchStmt:
		a.analyzeExpr(s.Expr)
		for _, c := range s.Cases {
			a.analyzeExpr(c.Value)
			for _, st := range c.Body {
				a.analyzeStmt(st)
			}
		}
		for _, st := range s.Otherwise {
			a.analyzeStmt(st)
		}
	case *ast.SeqStmt:
		for _, st := range s.Body {
			a.analyzeStmt(st)
		}
		for _, st := range s.RecoverBody {
			a.analyzeStmt(st)
		}
	case *ast.QOutStmt:
		for _, e := range s.Exprs {
			a.analyzeExpr(e)
		}
	case *ast.VarDecl:
		// Mid-function LOCAL — register
		for _, v := range s.Vars {
			a.scope.Declared[strings.ToUpper(v.Name)] = VarInfo{
				Name: v.Name,
				Pos:  v.NamePos,
				Kind: s.Scope,
			}
			if v.Init != nil {
				a.analyzeExpr(v.Init)
			}
		}
	case *ast.MultiAssignStmt:
		for _, name := range s.Targets {
			if name != "_" {
				a.markUsed(name)
			}
		}
		for _, v := range s.Values {
			a.analyzeExpr(v)
		}
	case *ast.DeferStmt:
		a.analyzeExpr(s.Call)
	case *ast.ChanSendStmt:
		a.analyzeExpr(s.Chan)
		a.analyzeExpr(s.Value)
	case *ast.WatchStmt:
		for _, c := range s.Cases {
			if c.RecvChan != nil {
				a.analyzeExpr(c.RecvChan)
			}
			if c.SendChan != nil {
				a.analyzeExpr(c.SendChan)
			}
			if c.SendVal != nil {
				a.analyzeExpr(c.SendVal)
			}
			if c.RecvVar != "" {
				a.markUsed(c.RecvVar)
			}
			for _, st := range c.Body {
				a.analyzeStmt(st)
			}
		}
		for _, st := range s.Otherwise {
			a.analyzeStmt(st)
		}
	case *ast.ParallelForStmt:
		a.markUsed(s.Var)
		a.analyzeExpr(s.Start)
		a.analyzeExpr(s.To)
		for _, st := range s.Body {
			a.analyzeStmt(st)
		}
	case *ast.TimeoutStmt:
		a.analyzeExpr(s.Duration)
		for _, st := range s.Body {
			a.analyzeStmt(st)
		}
	}
}

func (a *Analyzer) analyzeExpr(expr ast.Expr) {
	if expr == nil {
		return
	}
	switch e := expr.(type) {
	case *ast.IdentExpr:
		a.checkVarUsage(e.Name, e.NamePos)
	case *ast.BinaryExpr:
		a.analyzeExpr(e.Left)
		a.analyzeExpr(e.Right)
	case *ast.UnaryExpr:
		a.analyzeExpr(e.X)
	case *ast.PostfixExpr:
		a.analyzeExpr(e.X)
	case *ast.AssignExpr:
		a.analyzeExpr(e.Left)
		a.analyzeExpr(e.Right)
	case *ast.CallExpr:
		a.analyzeExpr(e.Func)
		for _, arg := range e.Args {
			a.analyzeExpr(arg)
		}
	case *ast.SendExpr:
		a.analyzeExpr(e.Object)
		for _, arg := range e.Args {
			a.analyzeExpr(arg)
		}
	case *ast.IndexExpr:
		a.analyzeExpr(e.X)
		a.analyzeExpr(e.Index)
	case *ast.SliceExpr:
		a.analyzeExpr(e.X)
		if e.Low != nil {
			a.analyzeExpr(e.Low)
		}
		if e.High != nil {
			a.analyzeExpr(e.High)
		}
	case *ast.DotExpr:
		a.analyzeExpr(e.X)
	case *ast.ArrayLitExpr:
		for _, item := range e.Items {
			a.analyzeExpr(item)
		}
	case *ast.HashLitExpr:
		for i := range e.Keys {
			a.analyzeExpr(e.Keys[i])
			a.analyzeExpr(e.Values[i])
		}
	case *ast.BlockExpr:
		a.analyzeExpr(e.Body)
	case *ast.AliasExpr:
		a.analyzeExpr(e.Alias)
		a.analyzeExpr(e.Field)
	case *ast.MacroExpr:
		a.analyzeExpr(e.Expr)
	case *ast.RefExpr:
		a.analyzeExpr(e.X)
	case *ast.NilSafeExpr:
		a.analyzeExpr(e.X)
		for _, arg := range e.Args {
			a.analyzeExpr(arg)
		}
	case *ast.ChanRecvExpr:
		a.analyzeExpr(e.Chan)
	case *ast.AsyncExpr:
		a.analyzeExpr(e.Call)
	case *ast.AwaitExpr:
		a.analyzeExpr(e.Future)
	}
}

// checkVarUsage verifies a variable is declared and marks it used.
func (a *Analyzer) checkVarUsage(name string, pos token.Position) {
	upper := strings.ToUpper(name)

	// Skip well-known RTL functions and constants
	if a.isKnownFunction(upper) || a.isBuiltinConstant(upper) {
		return
	}

	// Mark as used
	a.markUsed(name)

	// Check if declared in current scope
	if _, ok := a.scope.Declared[upper]; ok {
		return
	}

	// Check if it's an IMPORT package name
	for _, imp := range a.file.Imports {
		parts := strings.Split(imp.Path, "/")
		pkgName := parts[len(parts)-1]
		if strings.EqualFold(pkgName, name) || (imp.Alias != "" && imp.Alias == name) {
			return
		}
	}

	// Not declared — warn (could be MEMVAR, FIELD, or typo)
	a.warn(pos, "undeclared variable '%s' (missing LOCAL?)", name)
}

func (a *Analyzer) markUsed(name string) {
	if a.scope != nil {
		a.scope.Used[strings.ToUpper(name)] = true
	}
}

func (a *Analyzer) isKnownFunction(name string) bool {
	// Check declared functions in this file
	if a.funcNames[name] {
		return true
	}
	// Common RTL functions
	rtl := map[string]bool{
		"LEN": true, "SUBSTR": true, "LEFT": true, "RIGHT": true,
		"UPPER": true, "LOWER": true, "TRIM": true, "LTRIM": true, "RTRIM": true,
		"STR": true, "VAL": true, "STRTRAN": true, "AT": true, "RAT": true,
		"SPACE": true, "REPLICATE": true, "PADR": true, "PADL": true, "PADC": true,
		"VALTYPE": true, "TYPE": true, "EMPTY": true, "HB_ISSTRING": true,
		"EVAL": true, "AEVAL": true, "ASCAN": true, "ASORT": true,
		"AADD": true, "ADEL": true, "AINS": true, "ASIZE": true, "ACOPY": true, "ACLONE": true,
		"ARRAY": true, "HASH": true, "HB_HASH": true,
		"DTOC": true, "CTOD": true, "DTOS": true, "DATE": true, "TIME": true, "YEAR": true, "MONTH": true, "DAY": true,
		"QOUT": true, "QQOUT": true, "OUTSTD": true, "ALERT": true,
		"INKEY": true, "LASTKEY": true, "CHR": true, "ASC": true,
		"FILE": true, "FOPEN": true, "FCLOSE": true, "FREAD": true, "FWRITE": true,
		"IIF": true, "IF": true, "STRZERO": true, "TRANSFORM": true,
		"FIELDNAME": true, "FIELDPUT": true, "FIELDGET": true, "FCOUNT": true,
		"ALIAS": true, "DBAPPEND": true, "DBDELETE": true, "DBSKIP": true,
		"DBGOTO": true, "DBGOTOP": true, "DBGOBOTTOM": true, "DBCOMMIT": true,
		"RECNO": true, "RECCOUNT": true, "EOF": true, "BOF": true, "FOUND": true,
		"CHANNEL": true, "CHSEND": true, "CHRECEIVE": true,
		"SLEEP": true, "HB_IDLEADD": true, "SECONDS": true,
		"ERRORBLOCK": true, "BREAK": true, "PCOUNT": true, "PROCNAME": true,
		"SETPOS": true, "ROW": true, "COL": true, "MAXROW": true, "MAXCOL": true,
		"ABS": true, "INT": true, "ROUND": true, "SQRT": true, "LOG": true, "EXP": true,
		"MAX": true, "MIN": true, "MOD": true,
		"SETCOLOR": true, "DISPBOX": true, "DISPBEGIN": true, "DISPEND": true,
		"HB_SYMBOL_UNUSED": true, "HB_DEFAULT": true, "HB_NTOS": true,
	}
	return rtl[name]
}

func (a *Analyzer) isBuiltinConstant(name string) bool {
	constants := map[string]bool{
		"NIL": true, "TRUE": true, "FALSE": true,
		"SELF": true, "SUPER": true,
		"K_ESC": true, "K_ENTER": true, "K_UP": true, "K_DOWN": true,
		"K_LEFT": true, "K_RIGHT": true, "K_PGUP": true, "K_PGDN": true,
	}
	return constants[name]
}

// --- Diagnostic helpers ---

func (a *Analyzer) diag(sev Severity, pos token.Position, format string, args ...interface{}) {
	a.diagnostics = append(a.diagnostics, Diagnostic{
		Pos:      pos,
		Message:  fmt.Sprintf(format, args...),
		Severity: sev,
	})
}

func (a *Analyzer) errorf(pos token.Position, format string, args ...interface{}) {
	a.diag(SevError, pos, format, args...)
}

func (a *Analyzer) warn(pos token.Position, format string, args ...interface{}) {
	a.diag(SevWarning, pos, format, args...)
}

func (a *Analyzer) hint(pos token.Position, format string, args ...interface{}) {
	a.diag(SevHint, pos, format, args...)
}