package compiler

import (
	"fmt"

	"git.sharkk.net/Sharkk/Mako/parser"
	"git.sharkk.net/Sharkk/Mako/types"
)

// Compile converts AST to bytecode
func Compile(program *parser.Program) *types.Bytecode {
	c := &compiler{
		constants:       []any{},
		instructions:    []types.Instruction{},
		scopes:          []scope{},
		currentFunction: nil,
	}

	// Start in global scope
	c.enterScope()

	// Add nil check for program
	if program == nil {
		c.exitScope()
		return &types.Bytecode{
			Constants:    c.constants,
			Instructions: c.instructions,
		}
	}

	// Process each statement safely
	for _, stmt := range program.Statements {
		// Skip nil statements
		if stmt == nil {
			continue
		}
		c.compileStatement(stmt)
	}

	c.exitScope()

	return &types.Bytecode{
		Constants:    c.constants,
		Instructions: c.instructions,
	}
}

type scope struct {
	variables map[string]bool
	upvalues  map[string]int
}

type compiler struct {
	constants       []any
	instructions    []types.Instruction
	scopes          []scope
	currentFunction *functionCompiler
}

type functionCompiler struct {
	constants    []any
	instructions []types.Instruction
	numParams    int
	upvalues     []upvalueInfo
}

type upvalueInfo struct {
	index        int  // Index in the upvalue list
	isLocal      bool // Whether this is a local variable or an upvalue from an outer scope
	capturedFrom int  // The scope level where this variable was captured from
}

func (c *compiler) enterScope() {
	c.scopes = append(c.scopes, scope{
		variables: make(map[string]bool),
		upvalues:  make(map[string]int),
	})
	c.emit(types.OpEnterScope, 0)
}

func (c *compiler) exitScope() {
	c.scopes = c.scopes[:len(c.scopes)-1]
	c.emit(types.OpExitScope, 0)
}

func (c *compiler) declareVariable(name string) {
	if len(c.scopes) > 0 {
		c.scopes[len(c.scopes)-1].variables[name] = true
	}
}

func (c *compiler) isLocalVariable(name string) bool {
	for i := len(c.scopes) - 1; i >= 0; i-- {
		if _, ok := c.scopes[i].variables[name]; ok {
			return true
		}
	}
	return false
}

func (c *compiler) compileStatement(stmt parser.Statement) {
	if stmt == nil {
		return
	}

	switch s := stmt.(type) {
	case *parser.VariableStatement:
		c.compileExpression(s.Value)
		nameIndex := c.addConstant(s.Name.Value)

		// Use SetGlobal for top-level variables to persist between REPL lines
		if len(c.scopes) <= 1 {
			c.emit(types.OpSetGlobal, nameIndex)
		} else {
			c.declareVariable(s.Name.Value)
			c.emit(types.OpSetLocal, nameIndex)
		}

	case *parser.IndexAssignmentStatement:
		c.compileExpression(s.Left)
		c.compileExpression(s.Index)
		c.compileExpression(s.Value)
		c.emit(types.OpSetIndex, 0)

	case *parser.EchoStatement:
		c.compileExpression(s.Value)
		c.emit(types.OpEcho, 0)

	case *parser.ReturnStatement:
		if s.Value != nil {
			c.compileExpression(s.Value)
		} else {
			nullIndex := c.addConstant(nil)
			c.emit(types.OpConstant, nullIndex)
		}
		c.emit(types.OpReturn, 0)

	case *parser.FunctionStatement:
		// Use the dedicated function for function statements
		c.compileFunctionDeclaration(s)

	// BlockStatement now should only be used for keyword blocks like if-then-else-end
	case *parser.BlockStatement:
		for _, blockStmt := range s.Statements {
			c.compileStatement(blockStmt)
		}

	case *parser.ExpressionStatement:
		c.compileExpression(s.Expression)
		// Pop the value since we're not using it
		c.emit(types.OpPop, 0)
	}
}

func (c *compiler) compileExpression(expr parser.Expression) {
	switch e := expr.(type) {
	case *parser.StringLiteral:
		constIndex := c.addConstant(e.Value)
		c.emit(types.OpConstant, constIndex)

	case *parser.NumberLiteral:
		constIndex := c.addConstant(e.Value)
		c.emit(types.OpConstant, constIndex)

	case *parser.BooleanLiteral:
		constIndex := c.addConstant(e.Value)
		c.emit(types.OpConstant, constIndex)

	case *parser.NilLiteral:
		constIndex := c.addConstant(nil)
		c.emit(types.OpConstant, constIndex)

	case *parser.Identifier:
		nameIndex := c.addConstant(e.Value)

		// Check if it's a local variable first
		if c.isLocalVariable(e.Value) {
			c.emit(types.OpGetLocal, nameIndex)
		} else {
			// Otherwise treat as global
			c.emit(types.OpGetGlobal, nameIndex)
		}

	case *parser.TableLiteral:
		c.emit(types.OpNewTable, 0)

		for key, value := range e.Pairs {
			c.emit(types.OpDup, 0)

			// Special handling for identifier keys in tables
			if ident, ok := key.(*parser.Identifier); ok {
				// Treat identifiers as string literals in table keys
				strIndex := c.addConstant(ident.Value)
				c.emit(types.OpConstant, strIndex)
			} else {
				// For other expressions, compile normally
				c.compileExpression(key)
			}

			c.compileExpression(value)
			c.emit(types.OpSetIndex, 0)
			c.emit(types.OpPop, 0)
		}

	case *parser.IndexExpression:
		c.compileExpression(e.Left)
		c.compileExpression(e.Index)
		c.emit(types.OpGetIndex, 0)

	case *parser.FunctionLiteral:
		c.compileFunctionLiteral(e)

	case *parser.CallExpression:
		// Compile the function expression first
		c.compileExpression(e.Function)

		// Then compile the arguments
		for _, arg := range e.Arguments {
			c.compileExpression(arg)
		}

		// Emit the call instruction with the number of arguments
		c.emit(types.OpCall, len(e.Arguments))

	// Arithmetic expressions
	case *parser.InfixExpression:
		switch e.Operator {
		case "and":
			// Compile left operand
			c.compileExpression(e.Left)

			// Duplicate to check condition
			c.emit(types.OpDup, 0)

			// Jump if false (short-circuit)
			jumpFalsePos := len(c.instructions)
			c.emit(types.OpJumpIfFalse, 0) // Will backpatch

			// Pop the duplicate since we'll replace it
			c.emit(types.OpPop, 0)

			// Compile right operand
			c.compileExpression(e.Right)

			// Jump target for short-circuit
			endPos := len(c.instructions)
			c.instructions[jumpFalsePos].Operand = endPos

		case "or":
			// Compile left operand
			c.compileExpression(e.Left)

			// Duplicate to check condition
			c.emit(types.OpDup, 0)

			// Need to check if it's truthy to short-circuit
			falseJumpPos := len(c.instructions)
			c.emit(types.OpJumpIfFalse, 0) // Jump to right eval if false

			// If truthy, jump to end
			trueJumpPos := len(c.instructions)
			c.emit(types.OpJump, 0) // Jump to end if true

			// Position for false case
			falsePos := len(c.instructions)
			c.instructions[falseJumpPos].Operand = falsePos

			// Pop the duplicate since we'll replace it
			c.emit(types.OpPop, 0)

			// Compile right operand
			c.compileExpression(e.Right)

			// End position
			endPos := len(c.instructions)
			c.instructions[trueJumpPos].Operand = endPos

		default:
			// Original infix expression compilation
			c.compileExpression(e.Left)
			c.compileExpression(e.Right)

			// Generate the appropriate operation
			switch e.Operator {
			case "+":
				c.emit(types.OpAdd, 0)
			case "-":
				c.emit(types.OpSubtract, 0)
			case "*":
				c.emit(types.OpMultiply, 0)
			case "/":
				c.emit(types.OpDivide, 0)
			case "==":
				c.emit(types.OpEqual, 0)
			case "!=":
				c.emit(types.OpNotEqual, 0)
			case "<":
				c.emit(types.OpLessThan, 0)
			case ">":
				c.emit(types.OpGreaterThan, 0)
			case "<=":
				c.emit(types.OpLessEqual, 0)
			case ">=":
				c.emit(types.OpGreaterEqual, 0)
			default:
				panic(fmt.Sprintf("Unknown infix operator: %s", e.Operator))
			}
		}

	case *parser.PrefixExpression:
		// Compile the operand
		c.compileExpression(e.Right)

		// Generate the appropriate operation
		switch e.Operator {
		case "-":
			c.emit(types.OpNegate, 0)
		case "not":
			c.emit(types.OpNot, 0)
		default:
			panic(fmt.Sprintf("Unknown prefix operator: %s", e.Operator))
		}

	case *parser.GroupedExpression:
		// Just compile the inner expression
		c.compileExpression(e.Expr)

	case *parser.IfExpression:
		// Compile condition
		c.compileExpression(e.Condition)

		// Emit jump-if-false with placeholder
		jumpNotTruePos := len(c.instructions)
		c.emit(types.OpJumpIfFalse, 0) // Will backpatch

		// Compile consequence (then block)
		if e.Consequence != nil {
			lastStmtIndex := len(e.Consequence.Statements) - 1
			for i, stmt := range e.Consequence.Statements {
				if i == lastStmtIndex {
					// For the last statement, we need to ensure it leaves a value
					if exprStmt, ok := stmt.(*parser.ExpressionStatement); ok {
						c.compileExpression(exprStmt.Expression)
					} else {
						c.compileStatement(stmt)
						// Push null if not an expression statement
						nullIndex := c.addConstant(nil)
						c.emit(types.OpConstant, nullIndex)
					}
				} else {
					c.compileStatement(stmt)
				}
			}

			// If no statements, push null
			if len(e.Consequence.Statements) == 0 {
				nullIndex := c.addConstant(nil)
				c.emit(types.OpConstant, nullIndex)
			}
		} else {
			// No consequence block, push null
			nullIndex := c.addConstant(nil)
			c.emit(types.OpConstant, nullIndex)
		}

		// Emit jump to skip else part
		jumpPos := len(c.instructions)
		c.emit(types.OpJump, 0) // Will backpatch

		// Backpatch jump-if-false to point to else
		afterConsequencePos := len(c.instructions)
		c.instructions[jumpNotTruePos].Operand = afterConsequencePos

		// Compile alternative (else block)
		if e.Alternative != nil {
			lastStmtIndex := len(e.Alternative.Statements) - 1
			for i, stmt := range e.Alternative.Statements {
				if i == lastStmtIndex {
					// For the last statement, we need to ensure it leaves a value
					if exprStmt, ok := stmt.(*parser.ExpressionStatement); ok {
						c.compileExpression(exprStmt.Expression)
					} else {
						c.compileStatement(stmt)
						// Push null if not an expression statement
						nullIndex := c.addConstant(nil)
						c.emit(types.OpConstant, nullIndex)
					}
				} else {
					c.compileStatement(stmt)
				}
			}

			// If no statements, push null
			if len(e.Alternative.Statements) == 0 {
				nullIndex := c.addConstant(nil)
				c.emit(types.OpConstant, nullIndex)
			}
		} else {
			// No else - push null
			nullIndex := c.addConstant(nil)
			c.emit(types.OpConstant, nullIndex)
		}

		// Backpatch jump to point after else
		afterAlternativePos := len(c.instructions)
		c.instructions[jumpPos].Operand = afterAlternativePos
	}
}

func (c *compiler) compileFunctionLiteral(fn *parser.FunctionLiteral) {
	// Save the current compiler state
	parentCompiler := c.currentFunction

	// Create a new function compiler
	fnCompiler := &functionCompiler{
		constants:    []any{},
		instructions: []types.Instruction{},
		numParams:    len(fn.Parameters),
		upvalues:     []upvalueInfo{},
	}

	c.currentFunction = fnCompiler

	// Enter a new scope for the function body
	c.enterScope()

	// Declare parameters as local variables
	for _, param := range fn.Parameters {
		c.declareVariable(param.Value)
		paramIndex := c.addConstant(param.Value)
		c.emit(types.OpSetLocal, paramIndex)
	}

	// Compile the function body
	for _, stmt := range fn.Body.Statements {
		c.compileStatement(stmt)
	}

	// Ensure the function always returns a value
	// If the last instruction is not a return, add one
	if len(fnCompiler.instructions) == 0 ||
		(len(fnCompiler.instructions) > 0 && fnCompiler.instructions[len(fnCompiler.instructions)-1].Opcode != types.OpReturn) {
		nullIndex := c.addConstant(nil)
		c.emit(types.OpConstant, nullIndex)
		c.emit(types.OpReturn, 0)
	}

	// Exit the function scope
	c.exitScope()

	// Restore the parent compiler
	c.currentFunction = parentCompiler

	// Extract upvalue information for closure creation
	upvalueIndexes := make([]int, len(fnCompiler.upvalues))
	for i, upvalue := range fnCompiler.upvalues {
		upvalueIndexes[i] = upvalue.index
	}

	// Create a Function object and add it to the constants
	function := types.NewFunction(
		fnCompiler.instructions,
		fnCompiler.numParams,
		fnCompiler.constants,
		upvalueIndexes,
	)

	functionIndex := c.addConstant(function)
	c.emit(types.OpFunction, functionIndex)
}

func (c *compiler) addConstant(value any) int {
	if c.currentFunction != nil {
		c.currentFunction.constants = append(c.currentFunction.constants, value)
		return len(c.currentFunction.constants) - 1
	}

	c.constants = append(c.constants, value)
	return len(c.constants) - 1
}

func (c *compiler) emit(op types.Opcode, operand int) {
	instruction := types.Instruction{
		Opcode:  op,
		Operand: operand,
	}

	if c.currentFunction != nil {
		c.currentFunction.instructions = append(c.currentFunction.instructions, instruction)
	} else {
		c.instructions = append(c.instructions, instruction)
	}
}

func (c *compiler) compileFunctionDeclaration(fn *parser.FunctionStatement) {
	// Save the current compiler state
	parentCompiler := c.currentFunction

	// Create a new function compiler
	fnCompiler := &functionCompiler{
		constants:    []any{},
		instructions: []types.Instruction{},
		numParams:    len(fn.Parameters),
		upvalues:     []upvalueInfo{},
	}

	c.currentFunction = fnCompiler

	// Enter a new scope for the function body
	c.enterScope()

	// Declare parameters as local variables
	for _, param := range fn.Parameters {
		c.declareVariable(param.Value)
		paramIndex := c.addConstant(param.Value)
		c.emit(types.OpSetLocal, paramIndex)
	}

	// Compile the function body
	for _, stmt := range fn.Body.Statements {
		c.compileStatement(stmt)
	}

	// Ensure the function always returns a value
	// If the last instruction is not a return, add one
	if len(fnCompiler.instructions) == 0 || fnCompiler.instructions[len(fnCompiler.instructions)-1].Opcode != types.OpReturn {
		nullIndex := c.addConstant(nil)
		c.emit(types.OpConstant, nullIndex)
		c.emit(types.OpReturn, 0)
	}

	// Exit the function scope
	c.exitScope()

	// Restore the parent compiler
	c.currentFunction = parentCompiler

	// Extract upvalue information for closure creation
	upvalueIndexes := make([]int, len(fnCompiler.upvalues))
	for i, upvalue := range fnCompiler.upvalues {
		upvalueIndexes[i] = upvalue.index
	}

	// Create a Function object and add it to the constants
	function := types.NewFunction(
		fnCompiler.instructions,
		fnCompiler.numParams,
		fnCompiler.constants,
		upvalueIndexes,
	)

	functionIndex := c.addConstant(function)
	c.emit(types.OpFunction, functionIndex)

	// Store the function in a global variable
	nameIndex := c.addConstant(fn.Name.Value)

	// Use SetGlobal for top-level variables to persist between REPL lines
	if len(c.scopes) <= 1 {
		c.emit(types.OpSetGlobal, nameIndex)
	} else {
		c.declareVariable(fn.Name.Value)
		c.emit(types.OpSetLocal, nameIndex)
	}
}